PPR蛋白響應植物非生物脅迫的研究進展

李程，路凱，王才林，張亞東

PPR蛋白響應植物非生物脅迫的研究進展

李程，路凱，王才林，張亞東

江蘇省農業科學院糧食作物研究所/國家耐鹽堿水稻技術創新中心華東中心/江蘇省優質水稻工程技術研究中心/國家水稻改良中心南京分中心/江蘇省農業生物學重點實驗室，南京 210014

非生物脅迫是造成全球糧食減產的主要因素之一。研究植物逆境相關蛋白的功能及應答機制，對于提高作物抗逆性具有重要意義。三角狀五肽重復（PPR）蛋白屬于高等植物中最大的核編碼蛋白家族，因其包含高度特異性的PPR基序而得名。依據基序類型及其排列，PPR蛋白可分為P和PLS兩類，PLS類蛋白又可以根據其羧基末端的結構域進一步分為PLS、E、E+、DYW等亞類。PPR蛋白廣泛分布于陸生植物中，主要定位于葉綠體和線粒體，亦有少數定位于細胞核中。作為序列特異性RNA結合蛋白，PPR蛋白參與植物RNA加工的多個方面，包括RNA編輯、RNA剪接、RNA穩定和RNA翻譯。PPR蛋白在植物的整個生命進程中發揮多種重要作用，但對其在植物抗逆性中的作用機制還不清楚。本文在總結已有報道的非生物脅迫相關PPR蛋白定位和功能的基礎上，重點綜述了PPR蛋白參與調控植物非生物脅迫的作用機制（包括轉錄后調控和逆行信號），并對其進行討論。轉錄后調控與PPR蛋白參與RNA轉錄后的修飾作用有關，其一般被認為通過結合RNA并調節細胞器RNA代謝來調控逆境相關基因的表達，從而影響植物抗逆性。逆行信號方面，PPR蛋白的損傷導致線粒體或葉綠體功能受損，然后產生各類逆行信號（如ROS），進而調控相關基因表達，抵御逆境。然而，由于質體中的逆行信號會受到許多環境因素的影響，這些因素部分還未明確，導致PPR蛋白在逆行信號中的作用機制仍有很多問題有待闡明。此外，PPR蛋白存在一因多效性，部分蛋白在作用于抗逆性的同時，還會對植物的生長和生殖產生重要影響。最后，本文闡述了利用PPR蛋白作為RNA編輯工具的研究現狀，探討了目前PPR蛋白響應植物非生物脅迫方面尚待解決的問題及研究前景，提出了未來研究仍需關注的重點和難點，為深入研究PPR蛋白的功能和作物非生物脅迫抗性育種提供參考。

PPR蛋白；植物；非生物脅迫

隨著全球人口的不斷增長，糧食安全問題日益突出[1]。由于無法移動，氣候變化所帶來的干旱、高溫、土地鹽堿化和紫外線輻射等非生物逆境對農作物的生長、發育和結實造成了嚴重的不良影響，現已成為全球農業減產的重要因素[2]。因此，解析植物抗逆性機制，提高作物的非生物脅迫抗性對農業生產至關重要。

植物的抗逆反應是一個復雜的調控過程，包括從脅迫信號感知到調節基因表達，再到產生功能性蛋白質，最后到形態和生理生化代謝上的一系列調整[3]。脅迫應答蛋白質決定了植物對非生物脅迫的抗性[3]，近年來，大量與植物非生物脅迫響應相關的蛋白已被報道。由于細胞擴張驅動的生長與細胞壁的不斷重塑有關，當逆境發生時，植物體內的類受體激酶（receptor-like kinases，RLKs）先通過感應細胞壁的變化調節逆境脅迫下的細胞生長[4]。脅迫一旦被感應，刺激信號就會立即被第二信使（鈣離子、一氧化氮及不同類型的蛋白激酶等）傳遞和放大，以啟動復雜的特異性信號級聯反應。比如，鈣結合蛋白可以檢測到應激引起的細胞質鈣離子濃度變化，并將信號傳遞給相互作用的蛋白激酶或直接與之融合的激酶，如鈣依賴性蛋白激酶（calcium-dependent protein kinases，CDPKs），以進一步激活下游的應答過程[5]。值得一提的是，SNF1相關蛋白激酶（SnRKs）廣泛介導高等植物在各種脅迫下的脅迫信號，是細胞能量穩態的主要調節因子[6]。脅迫信號經過感應和轉導后會引起植物對脅迫的應答。其中，bHLH、ERF/AP2、MYB和WRKY等轉錄因子在非生物脅迫下可以快速反應，促進脅迫信號的轉導并調節相關基因的表達[7]。如，的轉錄水平在非生物脅迫下顯著提高，且能夠通過直接結合的啟動子來激活其表達，正向調節水稻的耐鹽性[8]。產生非生物脅迫后，末端作用蛋白可以在脅迫條件下保護蛋白質生物活性，進而恢復細胞穩態，減輕非生物脅迫對植物的損害，例如胚胎發育晚期豐富蛋白（late embryogenesis abundant proteins，LEA）、熱激蛋白（heat shock proteins，Hsps）和組成型光形態建成1（constitutively photomorphogenic 1，COP1）等均屬于此類[9-11]。隨著植物基因組學研究的不斷深入，越來越多新的蛋白不斷被報道和研究[12-15]。

三角狀五肽重復（pentatricopeptide repeat，PPR）蛋白因包含一種三角狀五肽重復結構域而得名，最早在擬南芥基因組測序分析中被發現[16]。PPR蛋白家族成員主要由細胞核基因編碼，并以多個氨基酸螺旋重復序列簡并串聯為特征，這些重復序列堆疊在一起形成可識別RNA的延伸表面[17]。對PPR蛋白功能的單獨或系統研究表明，PPR蛋白主要功能是與細胞器基因組轉錄產物特異RNA相結合，參與轉錄后修飾，以獲得成熟的轉錄本[18-22]。PPR家族對RNA的修飾主要分為以下4種類型，包括RNA編輯：PPR蛋白特異識別編輯位點上游的順式作用元件，并招募相關編輯因子共同起作用，將胞嘧啶（C）轉化為尿嘧啶（U）或者將U轉化為C，從而改變密碼子，進而影響氨基酸序列的構成[23-25]；RNA剪接：DNA轉錄后的前體RNA含有豐富的內含子，PPR蛋白從最初轉錄產物中去除順式和反式內含子，并將外顯子拼接成為成熟的RNA[26-28]；RNA穩定：PPR蛋白可以修飾mRNA前體的末端，阻礙RNA外切酶的活性，使其形成穩定的單順反子進行表達，以及結合在多順反子轉錄物中開放閱讀框（open reading frame，ORF）之間，處理產生的末端[29-31]；RNA翻譯：PPR蛋白能夠結合ORF的5′端特定非翻譯區（untranslated region，UTR），激活mRNA的翻譯調控[28, 32-33]。

本文收集了近年來與植物非生物脅迫響應相關PPR蛋白的信息，綜述了其對植物抗逆性的影響和作用機制，并就未來PPR蛋白在作物非生物脅迫抗性育種上的研究應用進行了展望。

1 PPR蛋白的結構和種類

PPR蛋白的基本結構特征是在其氨基末端區域存在一個由35個氨基酸組成的重復序列基序——PPR基序[16]。因PPR基序具有高度特異性，根據基序類型及其排列，PPR蛋白可分為P和PLS兩類，P類蛋白僅含有35個氨基酸的典型P基序，而PLS類蛋白是由P-、L-和S-基序組成串聯重復的PLS三聯體[34]。PLS類蛋白大多具有高度保守的E、E+或DYW結構域的羧基末端延伸，因此，PLS類蛋白可以根據其羧基末端的結構域進一步分為PLS、E、E+和DYW亞類[35]。此外，有人根據第一個螺旋的差異將P基序分為P1和P2；根據第二個螺旋的不同將L基序分為L1（35個氨基酸）和L2（36個氨基酸）；同樣，S基序也可以分為S1（31個氨基酸）和S2（32個氨基酸）；還有一種SS基序，其同時存在與S1和P1基序重疊的序列[18]。目前，也有一些報道稱少數P類PPR蛋白的C末端包含額外的特征序列，如小MutS相關（small MutS-related，SMR）結構域，LAGLIDADG（His-Cys box and GIY-YIG，H-N-H）結構域和RNA識別結構域（RNA recognition motif，RRM）等（圖1）[36-39]。晶體結構解析發現，PPR蛋白的每個重復基序通常會形成一對穩定反向平行的α螺旋結構，多個串聯基序還可進一步螺旋化形成右手超螺旋結構，從而與相關蛋白發生互作[40-41]。

圖1 PPR蛋白家族主要分類

2 PPR蛋白分布和定位

PPR蛋白主要存在于真核生物中，且在陸生植物中數量最多，原核生物中的數量很少[35]。有研究表明，PPR蛋白在陸地植物中的多數量與其調控細胞器mRNA從C到U的轉錄后編輯功能有關[42]。然而，同樣是陸生植物，低等的苔蘚中僅有103個PPR基因，而在高等的被子植物（如在擬南芥和水稻）中，PPR基因卻多達400個以上，因此，推測PPR基因的數量隨著植物從低等到高等進化的過程中不斷增加和分化[43]。

大多數PPR蛋白的N末端具有定位信號序列[44]。在高等植物中，PPR蛋白多位于線粒體或葉綠體，也有極少數在細胞核中行使功能[45-46]。如，擬南芥MTL1蛋白定位于線粒體中，影響線粒體NADH脫氫酶亞基7（nad7）mRNA的翻譯；AtECB2定位于葉綠體的類囊體膜上，影響擬南芥葉綠體中多個基因轉錄本的編輯；細胞核定位的OsNPPR1參與了線粒體發育且影響水稻胚乳發育[47]。此外，還有少數PPR蛋白存在雙定位模式，如水稻OsPGL1蛋白（pale green leaf 1）同時定位于葉綠體和線粒體，其功能缺失會影響葉綠體和線粒體RNA編輯缺陷[48]，而擬南芥PNM1蛋白則同時定位于細胞核和線粒體，可能在線粒體和細胞核之間的基因表達調節中發揮作用[49]。因此，明確PPR蛋白的亞細胞定位將有助于揭示PPR蛋白的功能。

3 PPR蛋白對植物抗逆性的影響

葉綠體和線粒體是植物細胞中半自主性的細胞器，能夠感受逆境信號，在植物響應內外界環境變化的逆向信號傳導過程中發揮著重要的功能，因此，定位于葉綠體或線粒體中的PPR蛋白很可能與植物非生物脅迫有關。在擬南芥中，已有10個以上的PPR蛋白被證明對非生物脅迫有反應。如，在葉綠體中，PPR蛋白RARE1負責-C794位點的編輯，其與植物耐熱性有關，人工提高C794編輯的表達能夠增強擬南芥的耐熱性[50]；核編碼葉綠體PPR蛋白SVR7參與擬南芥抗氧化脅迫反應，其突變體積累更多活性氧（reactive oxygen species，ROS），并表現出較低的光氧化應激耐受性[51]；GUN1亦是一種葉綠體定位的PPR蛋白，突變體對蔗糖和脫落酸（ABA）高度敏感，同時，也表現出對去黃化過程中引起的光氧化應激更敏感的表型[52-55]，最新研究表明，GUN1是氧化細胞環境所必需的，通過依賴氧化還原的質體-核通訊參與了植物基礎耐熱性的獲得[56-57]。此外，擬南芥中還存在相當數量線粒體定位的PPR蛋白，如PPR40[58]、ABO5[59]、ABO8[60]、PGN[61]、AHG11[62]、SLG1[63]、SLO2[64]、PPR96[65]、POCO1[66]和LOI1/ MEF11[67]均參與多種非生物脅迫的響應（表1）。在細胞質-核雙定位的PPR蛋白中，SOAR1被證實是植物對非生物脅迫反應的一個正調節因子，與ABA信號傳遞和擬南芥對干旱、鹽和冷脅迫的耐受性有關[68]。此外，PPR蛋白GEND1和PPR2都與擬南芥的耐熱性有關，其突變體植株在高溫下表現出高度敏感表型，但這些蛋白的準確定位還未見報道[69-70]。

近年來，除了模式植物，在以水稻為代表的大田作物中，關于PPR蛋白參與非生物脅迫的研究也越來越多。Chen等[71]通過全基因組分析在水稻中共發現491個PPR基因，表達譜分析表明，大量PPR基因在非生物脅迫下被誘導，其中，鹽脅迫和干旱脅迫下分別有75和73個PPR基因表達上調，暗示這些PPR蛋白可能在水稻對非生物脅迫的反應中發揮作用。低溫脅迫下，2種定位于葉綠體的PPR蛋白OsV4和TCD10是水稻幼苗早期葉綠體發育所必需的[72-73]。同樣是定位于葉綠體的PPR蛋白WSL，其突變體在發育早期對ABA、鹽和糖的敏感性增強，H2O2積累量提高[74]。此外，2種定位于線粒體的PPR蛋白PPS1和OsNBL3也被證實與水稻非生物脅迫有關，其中，的抑制導致水稻對高鹽度和ABA的敏感性顯著增加[75]，而的抑制卻導致水稻對鹽脅迫的耐受性增加[76]。最近，Luo等[77]驗證了2個定位于線粒體的PPR蛋白PPR035和PPR406在耐旱中的功能，和突變體均對干旱和鹽脅迫表現出較強的耐受性，在提高水稻抗旱性方面具有很大的應用前景；LU等[78]在水稻中分別過表達和其同源基因，轉基因植株在幼苗生長階段的耐鹽性得到增強，表明SOAR1同源PPR蛋白可通過轉基因操作用于鹽脅迫條件下水稻的作物改良。Su等[79]在大豆基因組中鑒定出179個DYW亞群PPR基因，并發現在鹽脅迫和干旱脅迫下被誘導表達，其過表達轉基因植株對干旱脅迫的耐受性增強。

4 PPR蛋白參與植物非生物脅迫調控的作用機制

4.1 轉錄后途徑

PPR家族蛋白作為一類反式作用因子，主要參與RNA轉錄后的修飾，通過結合RNA并調節細胞器RNA代謝來調控基因的表達[42, 80-81]。一些與植物非生物脅迫響應相關的PPR蛋白已被證明在細胞器RNA轉錄后調控中發揮作用。擬南芥的突變會導致多個RNA編輯缺陷，在突變體中，ABA信號通路相關基因表達下調，進一步影響了許多與脅迫相關，特別是與干旱相關的基因表達，這與突變體的干旱敏感性增加一致[66]。另有研究表明，線粒體RNA編輯因子SLO2影響植物對ABA和非生物脅迫的敏感性，突變體中核編碼的非生物脅迫響應基因和線粒體復合物Ⅰ基因（）及替代呼吸途徑相關基因的表達增加，進一步支持了線粒體RNA編輯事件和應激反應兩者之間的聯系[64]。水稻的突變會導致水稻葉綠體轉錄本剪接的重大缺陷，突變體中，異常轉錄本積累及其產物減少，質體編碼聚合酶依賴的質體基因表達明顯下調，質體rRNAs和翻譯產物積累到非常低的水平，這表明翻譯效率的降低可能會影響突變體對非生物脅迫的反應[74]。最新研究發現，主要參與線粒體基因內含子4的剪接，其突變會導致線粒體的破壞和交替呼吸途徑的增加，從而產生類病變表型，增強水稻對鹽的抗性和耐受性[76]。Xiong等[82]研究表明水稻細胞質雄性不育系與其保持系之間的RNA編輯的差異是導致它們在環境脅迫下表現不同的原因之一，并證實了PPR基因介導的RNA編輯與水稻非生物脅迫耐受性的潛在關系。

表1 參與調節植物非生物脅迫反應的部分PPR蛋白

4.2 逆行信號

一般來說，細胞器的發育和基因表達受核基因組調控，但來自葉綠體和線粒體的信號亦可“逆行”調控核基因的表達，這樣的調控信號被稱為“逆行信號”[83]。根據其功能含義，質體逆行信號被分為與質體發育相關的信號和與響應環境或代謝波動的操作微調有關的信號[84]。研究表明，PPR蛋白的損傷能夠導致線粒體或葉綠體功能受損，產生各類逆行信號（如ROS），從而調控抗逆相關基因表達[85]。最典型的例子是擬南芥PPR蛋白GENOMES UNCOUPLED 1（GUN1），被鑒定為葉綠體到細胞核逆行信號通路的中心整合因子[86]。GUN1的失活會在一定條件下抑制與光合作用相關的核基因（photosynthesis associated nuclear genes，）的表達，從而促進逆行信號傳導。突變體植株更容易受到葉綠體干擾因素的影響，包括光、質體翻譯抑制劑林可霉素（Linc）和類胡蘿卜素生物合成抑制劑去氟拉松（NF）處理[52-53]。一般來說，GUN1可能通過3條經典的逆行信號通路調控的表達：四吡咯生物合成途徑（tetrapyrrole biosynthesis pathway，TPB）、氧化還原反應和質體基因表達（plastid gene expression，PGE）[87]。最近，Wu等[88]提出一個新模型：當葉綠體發育過程中遭遇逆境時，GUN1通過與cpHSC70-1互作來增強質體的蛋白輸入，未及時轉運進葉綠體的前體蛋白在細胞質中過度積累，誘導細胞質中HSP90蛋白表達上調，進而維持表達。

除了cpHSC70-1伴侶外，還有許多其他假定的GUN1相互作用蛋白被陸續提出，包括葉綠體核糖體蛋白S1（plastid ribosomal protein S1，PRPS1）[89]、多細胞器RNA編輯因子（multiple organellar rna editing factor，MORF）[90]、核編碼RNA聚合酶（nuclear-encoded rna polymerase，NEP）[91]和各種四吡咯[92]等。研究表明，GUN1能夠在蛋白水平上控制葉綠體核糖體蛋白PRPS1的積累，并和參與葉綠體蛋白穩態的蛋白質相互作用，而PRPS1的功能是質體mRNA翻譯和耐熱性所必需的[89]。MORF蛋白家族是線粒體和葉綠體中RNA編輯體系的重要組成部分，幾乎所有位點的完全編輯都需要MORF蛋白[93]。最新研究表明，GUN1通過與MORF2發生物理相互作用，直接影響葉綠體RNA中多個位點的編輯效率，并調節核編碼的葉綠體RNA聚合酶的活性，特別是在逆行信號傳遞過程中[91, 94]。然而，過表達系只有在使用NF處理時才能看到表型，而使用Linc處理時卻無法看到表型，因此，突變對質體RNA編輯影響的潛在機制基礎和功能意義仍有待闡明[90]。這些相互作用支持GUN1可能作為一種支架蛋白，在各種生物環境中促進蛋白質復合物的形成的假設[95]。但是，由于葉綠體信號受到許多環境因素的影響，其中一些因素大多是未知的，難以控制的，導致不同實驗室對同一突變體得到的結果不同，因此，GUN1作為逆行通訊和細胞核信號通路的中心調節器的功能仍然有很多未解決的問題[86, 96]。部分觀點認為，GUN1能夠通過靶向細胞核中的多種轉錄因子，包括ABSCISIC ACID INSENSITIVE4（ABI4）、GOLDEN2-LIKE 1/2（GLK1/2）和ELONGATED HYPOCOTYL 5（HY5），將信息傳遞到細胞核[97-100]，這些核轉錄調控因子被認為是GUN1所涉及逆境信號中的一個重要的下游成分，它們的突變體在的解偶聯表達方面與突變體表現相似[101]。Veciana等[102-103]研究發現，BBX16作為GLK1的一個直接靶點，其在葉綠體損傷后通過GUN1/GLK1模塊被抑制，調節暴露在破壞性強光下的區域。總之，這些研究表明GUN1對于葉綠體RNA代謝和葉綠體-核逆行信號非常重要[104]。

近年來，亦有研究表明，其他PPR蛋白通過逆行信號調控植物抗逆性。如，擬南芥線粒體PPR蛋白LOI1參與呼吸鏈相關基因、和的RNA編輯，并調節類異戊二烯的生物合成，突變體對2種類異戊二烯合成抑制劑（真菌植物毒素洛伐他汀和除草劑氯馬松）的敏感性降低，從而引起胞質甲戊酸（cytosolic mevalonate，MVA）途徑和質體非甲戊酸（plastidal non-mevalonate，MEP）途徑的改變，已知此類途徑會影響防御基因的表達，以應對損傷，揭示了從線粒體到細胞質逆行信號的間接作用[105-106]；PPR蛋白PGN的失活會引起擬南芥線粒體編碼轉錄物差異表達，最顯著的是和表達水平的升高，它們在線粒體功能改變或抑制誘導的逆行信號傳導中發揮作用，突變體幼苗內源ABA和鹽脅迫下的ROS積累增加，因此，PGN可能通過轉錄編輯協調影響整體線粒體基因表達，從而有助于植物防御和維持細胞氧化還原平衡[61]；PPR蛋白AHG11和SLG1分別參與線粒體和的編輯，和是線粒體中電子傳遞鏈復合體Ⅰ的2個亞基，和的突變致使線粒體功能的部分損傷誘導氧化還原失衡，突變體植株表現出對干旱等非生物脅迫敏感性增強[62-63]；另有研究發現，ABA缺失抑制位點HAS2編碼參與線粒體RNA編輯的PPR蛋白LOI1/ MEF11，證明了ABA在線粒體逆行信號調節中起著重要作用[67]。

5 PPR蛋白的多效性

目前，鑒定到的很多PPR基因都具有一因多效性，通常在影響植物適應非生物脅迫的同時，對植物的生長和生殖也會產生重要影響。例如，水稻突變體在三葉期表現為白化表型和葉綠體異常，這種現象與葉綠素含量和葉綠體發育變化有關，且受溫度影響[72]；同樣，與低溫相關的PPR蛋白基因突變體亦表現出白化和葉綠體畸形[73]；擬南芥突變體不僅表現出光氧化應激耐受性降低，而且其幼期葉綠素含量也降低，呈現淡綠色表型[51]，這些PPR蛋白在葉綠體早期發育過程中起重要的作用，其功能的缺失會影響葉綠體的發育，從而影響葉片生長。此外，影響線粒體功能的PPR蛋白亦被證明具有一因多效性。例如，ABO8不僅和擬南芥對ABA的敏感性有關，還能夠通過ABA介導的線粒體ROS調控擬南芥根的分生組織活性[60]；突變體植株不僅根系變短，分生組織大小和細胞數量減少，還表現出對高溫的敏感性增強，功能分析表明，GEND1能夠結合并編輯線粒體mRNA，其突變會導致擬南芥細胞色素c水平降低[69]；的突變會使植株產生類病變表型（自發的細胞死亡反應和H2O2積累，對真菌和細菌病原體稻瘟病菌和水稻黃單胞菌的抗性增強），同時增強了水稻對鹽脅迫的耐受性[76]。POCO1被證明能夠影響擬南芥的開花時間，在長、短日照條件下，突變體均表現出早花表型，后續研究表明，POCO1還參與了擬南芥的抗旱，但二者之間的聯系還未見報道[107]。

6 展望

以往研究綜述大多針對PPR蛋白的起源、分類、定位，以及在植物生長發育中的功能。本文綜述了近年來PPR蛋白在植物非生物脅迫中的功能研究進展，并總結分析了PPR蛋白參與植物非生物脅迫調控的分子機制，以期為作物非生物脅迫分子育種提供參考。盡管已經鑒定出多種植物PPR蛋白，但與數目眾多的PPR成員相比，還有很多發揮重要功能的PPR蛋白未被研究，它們是否和植物非生物脅迫抗性有關？此外，由于PPR蛋白基因普遍存在的一因多效性，當利用PPR蛋白改良作物抗逆性時，需要注意其對作物其他生理功能的影響，這也是應用PPR蛋白育種時的重點和難點之一。

因為PPR蛋白在植物線粒體和葉綠體中負責C-to-U和U-to-C的RNA編輯，已有研究將其作為RNA編輯工具來利用[25]。如，Oldenkott等[108]通過表達來自腎葉白頭翁（）的含有單個DYW結構域的PPR蛋白，在大腸桿菌中構建了C-to-U RNA編輯；Ichinose等[25]成功開發了一種基于DYW:KP蛋白的U-to-C RNA編輯因子，該因子在細菌和人類細胞中起作用。在臨床治療中，相比于現在流行的以CRISPR-Cas9為代表的DNA編輯而言，RNA編輯更靈活、更安全，因為RNA編輯其通常只在特定的細胞類型中或在特定的時間表達，預期脫靶導致的編輯副作用更少，而且由于基因組序列不受影響，錯誤的RNA編輯也不會影響胎兒發育，停止治療后，突變的RNA會迅速降解[109]。這些研究為未來的基因治療和作物改良提供了參考。

近年來，雖然PPR蛋白的研究取得了重要的進展，但關于PPR蛋白參與植物非生物脅迫響應中的分子機制還不十分清楚，需要進一步深入探究。首先，PPR蛋白在調節植物非生物脅迫過程中是否存在時空性和組織特異性？其次，PPR蛋白之間如何相互作用或與其他蛋白相互作用以實現其最終功能，這些相互作用又是如何在細胞器RNA轉錄后加工中影響PPR活性的？第三，PPR蛋白是如何特異識別并與RNA結合的？最后，PPR蛋白在陸生植物核-細胞質相互作用的逆行信號調控網絡中的具體角色是什么？也許大量的進化分析和更多其他PPR蛋白的功能鑒定，以及對共表達PPR基因的進一步分析將揭示這些問題的答案。然而，為了更詳細地闡明PPR蛋白在植物非生物脅迫抗性中的具體機制，有必要對PPR蛋白的RNA靶點進行鑒定，并對蛋白質-RNA復合物的晶體結構進行分析，同時，還應加強對MORF等直接影響PPR蛋白作用的相互作用蛋白給予關注。這些研究將有助于更好地闡明PPR蛋白在植物非生物脅迫下的調控網絡和特異性，有助于了解植物細胞器RNA加工的細節，從而為作物育種改良提供支撐。值得期待的是，人工PPR蛋白可以被定制并在體內結合特定的內源性RNA，這為開發用于分子設計育種的RNA結合蛋白（RNA binding protein，RBPs）提供了廣闊的研究前景[110]。

[1] Gong Z Z, Xiong L M, Shi H Z, Yang S H, Herrera- Estrella L R, Xu G H, Chao D Y, Li J R, Wang P Y, Qin F,LI J, DING Y L, SHI Y T, WANG Y, YANG Y Q, GUO Y, ZHU J K. Plant abiotic stress response and nutrient use efficiency, Science China Life Sciences, 2020, 63(5): 635-674.

[2] Chang Y N, Zhu C, Jiang J, Zhang H M, Zhu J K, Duan C G. Epigenetic regulation in plant abiotic stress responses. Journal of integrative plant biology, 2020, 62(5): 563-580.

[3] 陳柯岐, 鄧星光, 林宏輝, 植物響應非生物脅迫的分子機制, 生物學雜志, 2021, 38(6): 1-8.

Chen K Q, Deng X G, Lin H H. Molecular mechanisms of plant in response to abiotic stress, Journal of Biology, 2021, 38(6): 1-8. (in Chinese)

[4] Zhang H, Zhao Y, Zhu J K. Thriving under stress: how plants balance growth and the stress response, Developmental Cell, 2020, 55(5): 529-543.

[5] YUAN F, YANG H M, XUE Y, KONG D D, YE R, LI C J, ZHANG J Y, THEPRUNGSIRIKUL L, SHRIFT T, KRICHILSKY B, JOHNSON D M, SWIFT G B, HE Y K, SIEDOW J N, PEI Z M. OSCA1 mediates osmotic-stress-evoked Ca2+increases vital for osmosensing in. Nature, 2014, 514(7552): 367-371.

[6] JAMSHEER K M, JINDAL S, LAXMI A. Evolution of TOR-SnRK dynamics in green plants and its integration with phytohormone signaling networks. Journal of Experimental Botany, 2019, 70(8): 2239-2259.

[7] YOON Y, SEO D H, SHIN H, KIM H J, KIM C M, JANG G. The role of stress-responsive transcription factors in modulating abiotic stress tolerance in plants. Agronomy, 2020, 10(6): 788.

[8] ZHANG M X, ZHAO R R, WANG H T, REN S L, SHI L Y, HUANG S Z, WEI Z Q, GUO B Y, JIN J Y, ZHONG Y, CHEN M J, JIANG W Z, WU T, DU X L. OsWRKY28 positively regulates salinity tolerance by directly activating OsDREB1B expression in rice. Plant Cell Reports, 2023, 42(2): 223-234.

[9] Haq S u, Khan A, Ali M, Khattak A M, Gai W X, Zhang H X, Wei A M, Gong Z H. Heat shock proteins: dynamic biomolecules to counter plant biotic and abiotic stresses. International journal of molecular sciences, 2019, 20(21): 5321.

[10] Kim J Y, Jang I C, Seo H S. COP1 controls abiotic stress responses by modulating AtSIZ1 function through its E3 ubiquitin ligase activity. Frontiers in plant science, 2016, 7: 1182.

[11] LIANG Y, KANG K, GAN L, NING S B, XIONG J Y, SONG S Y, XI L Z, LAI S Y, YIN Y T, GU J W, XIANG J, LI S S, WANG B S, LI M T. Drought‐responsive genes, late embryogenesis abundant group3 (LEA 3) and vicinal oxygen chelate, function in lipid accumulation inandmainly via enhancing photosynthetic efficiency and reducing ROS. Plant Biotechnology Journal, 2019, 17(11): 2123-2142.

[12] YE Y Y, DING Y F, JIANG Q, WANG F J, SUN J W, ZHU C. The role of receptor-like protein kinases (RLKs) in abiotic stress response in plants. Plant cell reports, 2017, 36(2): 235-242.

[13] HAN G L, LU C X, GUO J R, QIAO Z Q, SUI N, QIU N W, WANG B S. C2H2zinc finger proteins: master regulators of abiotic stress responses in plants. Frontiers in plant science, 2020, 11: 115.

[14] Yu Z Y, Wang X, Zhang L S. Structural and functional dynamics of dehydrins: a plant protector protein under abiotic stress. International Journal of Molecular Sciences, 2018, 19(11): 3420.

[15] Robles P, Quesada V. Unveiling the functions of plastid ribosomal proteins in plant development and abiotic stress tolerance. Plant Physiology and Biochemistry, 2022, 189: 35-45.

[16] Small I D, Peeters N. The PPR motif-a TPR-related motif prevalent in plant organellar proteins. Trends in biochemical sciences, 2000, 25(2): 45-47.

[17] Rovira A G, Smith A G. PPR proteins-orchestrators of organelle RNA metabolism. Physiologia plantarum, 2019, 166(1): 451-459.

[18] CHENG S F, GUTMANN B, ZHONG X A, YE Y T, FISHER M F, BAI F Q, CASTLEDEN I, SONG Y E, SONG B, HUANG J Y, LIU X, XU X, LIM B L, BOND C S, YIU S M, SMALL I. Redefining the structural motifs that determine RNA binding and RNA editing by pentatricopeptide repeat proteins in land plants. The Plant Journal, 2016, 85(4): 532-547.

[19] Khrouchtchova A, Monde R A, Barkan A. A short PPR protein required for the splicing of specific group Ⅱ introns in angiosperm chloroplasts. Rna, 2012, 18(6): 1197-1209.

[20] Meierhoff K, Felder S, Nakamura T, Bechtold N, Schuster G. HCF152, anRNA binding pentatricopeptide repeat protein involved in the processing of chloroplast psbB-psbT-psbH-petB-petD RNAs. The Plant Cell, 2003, 15(6): 1480-1495.

[21] Yamazaki H, Tasaka M, Shikanai T. PPR motifs of the nucleus-encoded factor, PGR3, function in the selective and distinct steps of chloroplast gene expression in. The Plant Journal,2004, 38(1): 152-163.

[22] Li X L, Sun M D, Liu S J, Teng Q A, Li S H, Jiang Y S. Functions of PPR proteins in plant growth and development. International Journal of Molecular Sciences, 2021, 22(20): 11274.

[23] ANDRéS-COLáS N, ZHU Q A, TAKENAKA M, DE RYBEL B, WEIJERS D, VAN DER STRAETEN D. Multiple PPR protein interactions are involved in the RNA editing system inmitochondria and plastids. Proceedings of the National Academy of Sciences of the United States of America, 2017, 114(33): 8883-8888.

[24] GUILLAUMOT D, LOPEZ-OBANDO M, BAUDRY K, AVON A, RIGAILL G, FALCON DE LONGEVIALLE A, BROCHE B, TAKENAKA M, BERTHOMé R, DE JAEGER G, DELANNOY E, LURIN C. Two interacting PPR proteins are majorediting factors in plastid and mitochondria. Proceedings of the National Academy of Sciences of the United States of America, 2017, 114(33): 8877-8882.

[25] ICHINOSE M, KAWABATA M, AKAIWA Y, SHIMAJIRI Y, NAKAMURA I, TAMAI T, NAKAMURA T, YAGI Y, GUTMANN B. U-to-C RNA editing by synthetic PPR-DYW proteins in bacteria and human culture cells. Communications Biology, 2022, 5(1): 968.

[26] CHEN X Z, FENG F, QI W W, XU L M, YAO D S, WANG Q SONG R T. Dek35 encodes a PPR protein that affects cis-splicing of mitochondrial nad4 intron 1 and seed development in maize. Molecular Plant, 2017, 10(3): 427-441.

[27] SUN F, ZHANG X Y, SHEN Y, WANG H C, LIU R, WANG X M, GAO D H, YANG Y Z, LIU Y W, TAN B C. The pentatricopeptide repeat protein EMPTY PERICARP8 is required for the splicing of three mitochondrial introns and seed development in maize. The Plant Journal, 2018, 95(5): 919-932.

[28] LEGEN J, RUF S, KROOP X, WANG G W, BARKAN A, BOCK R, SCHMITZ-LINNEWEBER C. Stabilization and translation of synthetic operon-derived mRNA s in chloroplasts by sequences representing PPR protein-binding sites. The Plant Journal, 2018, 94(1): 8-21.

[29] ZHANG Y F, SUZUKI M, SUN F, TAN B C. The mitochondrion- targeted PENTATRICOPEPTIDE REPEAT78 protein is required for nad5 mature mRNA stability and seed development in maize. Molecular Plant, 2017, 10(10): 1321-1333.

[30] WANG C D, AUBé F, PLANCHARD N, QUADRADO M, DARGEL- GRAFFIN C, NOGUé F, MIREAU H. The pentatricopeptide repeat protein MTSF2 stabilizes a nad1 precursor transcript and defines the 3? end of its 5?-half intron. Nucleic Acids Research, 2017, 45(10): 6119-6134.

[31] LEE K, HAN J H, PARK Y I, COLAS DES FRANCS-SMALL C, SMALL I, KANG H. The mitochondrial pentatricopeptide repeat protein PPR19 is involved in the stabilization of NADH dehydrogenase 1 transcripts and is crucial for mitochondrial function anddevelopment. New Phytologist, 2017, 215(1): 202-216.

[32] HA?LI N, PLANCHARD N, ARNAL N, QUADRADO M, VRIELYNCK N, DAHAN J, FRANCS-SMALL C C D, MIREAU H. The MTL1 pentatricopeptide repeat protein is required for both translation and splicing of the mitochondrial NADH DEHYDROGENASE SUBUNIT7 mRNA in. Plant Physiology, 2016, 170(1): 354-366.

[33] ZOSCHKE R, WATKINS K P, MIRANDA R G, BARKAN A. The PPR-SMR protein PPR53 enhances the stability and translation of specific chloroplast RNA s in maize. The Plant Journal, 2016, 85(5): 594-606.

[34] LURIN C, ANDREéS C, AUBOURG S, BELLAOUI M, BITTON F, BRUYE?RE C, CABOCHE M, DEBAST C, GUALBERTO J, HOFFMANN B. Genome-wide analysis ofpentatricopeptide repeat proteins reveals their essential role in organelle biogenesis. The Plant Cell, 2004, 16(8): 2089-2103.

[35] 李景芳, 王寶祥, 劉艷, 劉金波, 陳庭木, 孫志廣, 楊波, 邢運高, 遲銘, 徐波. PPR蛋白在水稻生長發育中的功能研究進展. 植物遺傳資源學報, 2022, 23(2): 358-367.

LI J F, WANG B X, LIU Y, LIU J B, CHEN T M, SUN Z G, YANG B, XING Y G, CHI M, XU B. Progress of research in functions of PPR proteins in growth and development of rice. Journal of Plant Genetic Resources, 2022, 23(2): 358-367. (in Chinese)

[36] ZHANG Y, LU C. The enigmatic roles of PPR-SMR proteins in plants. Advanced Science, 2019, 6(13): 1900361.

[37] ZHANG J H, GUO Y P, FANG Q, ZHU Y L, ZHANG Y, LIU X J, LIN Y J, BARKAN A, ZHOU F. The PPR-SMR protein ATP4 is required for editing the chloroplastmRNA in rice and maize. Plant Physiology, 2020, 184(4): 2011-2021.

[38] LONGEVIALLE A F D, HENDRICKSON L, TAYLOR N L, DELANNOY E, LURIN C, BADGER M, MILLAR A H, SMALL I. The pentatricopeptide repeat genewith two LAGLIDADG motifs is required for the cis-splicing of plastidintron 2 in. The Plant Journal, 2008,56(1): 157-168.

[39] SCHMITZ-LINNEWEBER C, WILLIAMS-CARRIER R E, WILLIAMS- VOELKER P M, KROEGER T S, VICHAS A, BARKAN A. A pentatricopeptide repeat protein facilitates the trans-splicing of the maize chloroplastpre-mRNA. The Plant Cell, 2006, 18(10): 2650-2663.

[40] YIN P, LI Q X, YAN C Y, LIU Y, LIU J J, YU F, WANG Z, LONG J F, HE J H, WANG H W, WANG J W, ZHU J K, SHI Y G, YAN N. Structural basis for the modular recognition of single-stranded RNA by PPR proteins. Nature, 2013, 504(7478): 168-171.

[41] YAN J, ZHANG Q, YIN P. RNA editing machinery in plant organelles. Science China Life Sciences, 2018, 61(2): 162-169.

[42] BARKAN A, SMALL I. Pentatricopeptide repeat proteins in plants. Annual Review of Plant Biology, 2014, 65: 415-442.

[43] FUJII S, SMALL I. The evolution of RNA editing and pentatricopeptide repeat genes. New Phytologist, 2011, 191(1): 37-47.

[44] 王婉珍, 任育軍, 繆穎. PPR蛋白在植物生長發育中的作用. 熱帶亞熱帶植物學報, 2019, 27(2): 225-234.

WANG W Z, REN Y J, MIAO Y. Roles of PPR proteins in plant growth and development. Journal of Tropical and Subtropical Botany, 2019, 27(2): 225-234. (in Chinese)

[45] COLCOMBET J, LOPEZ-OBANDO M, HEURTEVIN L, BERNARD C, MARTIN K, BERTHOMé R, LURIN C. Systematic study of subcellular localization ofPPR proteins confirms a massive targeting to organelles. RNA Biology, 2013, 10(9): 1557-1575.

[46] HAMMANI K, TAKENAKA M, MIRANDA R A. Barkan, A PPR protein in the PLS subfamily stabilizes the 5′-end of processed rpl16 mRNAs in maize chloroplasts. Nucleic Acids Research, 2016, 44(9): 4278-4288.

[47] HAO Y Y, WANG Y L, WU M M, ZHU X P, TENG X, SUN Y L, ZHU J P, ZHANG Y Y, JING R N, LEI J, LI J F, BAO X H, WANG C M, WANG Y H, WAN J M. The nuclear-localized PPR protein OsNPPR1 is important for mitochondrial function and endosperm development in rice. Journal of Experimental Botany, 2019, 70(18): 4705-4720.

[48] XIAO H J, XU Y H, NI C Z, ZHANG Q N, ZHONG F Y, HUANG J S, ZHU Y G, HU J. A rice dual-localized pentatricopeptide repeat protein is involved in organellar RNA editing together with OsMORFs. Journal of Experimental Botany, 2018, 69(12): 2923-2936.

[49] HAMMANI K, GOBERT A, HLEIBIEH K, CHOULIER L, SMALL I, GIEGé P. Andual-localized pentatricopeptide repeat protein interacts with nuclear proteins involved in gene expression regulation. The Plant Cell, 2011, 23(2): 730-740.

[50] HUANG C, LIU D, LI Z A, MOLLOY D P, LUO Z F, SU Y, LI H O, LIU Q, WANG R Z, XIAO L T. The PPR protein RARE1-mediated editing of chloroplast accD transcripts is required for fatty acid biosynthesis and heat tolerance in. Plant Communications, 2023, 4(1): 100461.

[51] LV H X, HUANG C, GUO G Q, YANG Z N. Roles of the nuclear-encoded chloroplast SMR domain-containing PPR protein SVR7 in photosynthesis and oxidative stress tolerance in. Journal of Plant Biology, 2014, 57(5): 291-301.

[52] MOCHIZUKI N, SUSEK R, CHORY J. An intracellular signal transduction pathway between the chloroplast and nucleus is involved in de-etiolation. Plant Physiology, 1996, 112(4): 1465-1469.

[53] WU G Z, CHALVIN C, HOELSCHER M, MEYER E H, WU X N, BOCK R. Control of retrograde signaling by rapid turnover of GENOMES UNCOUPLED1, Plant Physiology, 2018, 176(3): 2472-2495.

[54] COTTAGE A, MOTT E K, KEMPSTER J A, GRAY J C. Theplastid-signalling mutant() shows altered sensitivity to sucrose and abscisic acid and alterations in early seedling development. Journal of Experimental Botany, 2010, 61(13): 3773-3786.

[55] GUO J G, ZHOU Y P, LI J A, SUN Y J, SHANGGUAN Y, ZHU Z N, HU Y J, LI T, HU Y H, ROCHAIX J D, MIAO Y C, SUN X W. COE 1 and GUN1 regulate the adaptation of plants to high light stress. Biochemical and biophysical research communications, 2020, 521(1): 184-189.

[56] LASORELLA C, FORTUNATO S, DIPIERRO N, JERAN N, TADINI L, VITA F, PESARESI P, PINTO M C D E. Chloroplast-localized GUN1 contributes to the acquisition of basal thermotolerance in. Frontiers in Plant Science, 2022, 13: 1058831.

[57] FORTUNATO S, LASORELLA C, TADINI L, JERAN N, VITA F, PESARESI P, PINTO M C D E. GUN1 involvement in the redox changes occurring during biogenic retrograde signaling. Plant Science, 2022, 320: 111265.

[58] ZSIGMOND L, RIGóG, SZARKA A, SZEKELY G, OTVOS K, DARULA Z, MEDZIHRADSZKY K F, KONCZ C, KONCZ Z, SZABADOS L.PPR40 connects abiotic stress responses to mitochondrial electron transport. Plant Physiology, 2008, 146(4): 1721-1737.

[59] LIU Y, HE J N, CHEN Z Z, REN X Z, HONG X H, GONG Z Z., encoding a pentatricopeptide repeat protein required for cis-splicing of mitochondrialintron 3, is involved in the abscisic acid response in. The Plant Journal, 2010, 63(5): 749-765.

[60] YANG L, ZHANG J, HE J N, QIN Y Y, HUA D P, DUAN Y, CHEN Z Z, GONG Z Z. ABA-mediated ROS in mitochondria regulate root meristem activity by controlling PLETHORA expression in. PLoS Genetics, 2014, 10(12): e1004791.

[61] LALUK K, ABUQAMAR S, MENGISTE T. Themitochondria-localized pentatricopeptide repeat protein PGN functions in defense against necrotrophic fungi and abiotic stress tolerance. Plant Physiology, 2011, 156(4): 2053-2068.

[62] MURAYAMA M, HAYASHI S, NISHIMURA N, ISHIDE M, KOBAYASHI K, YAGI Y, ASAMI T, NAKAMURA T, SHINOZAKI K, HIRAYAMA T. Isolation of, a weak ABA hypersensitive mutant defective in nad4 RNA editing. Journal of Experimental Botany, 2012, 63(14): 5301-5310.

[63] YUAN H, LIU D. Functional disruption of the pentatricopeptide protein SLG1 affects mitochondrial RNA editing, plant development, and responses to abiotic stresses in. The Plant Journal, 2012, 70(3): 432-444.

[64] ZHU Q, DUGARDEYN J, ZHANG C Y, MüHLENBOCK P, EASTMOND P J, VALCKE R, CONINCK B DE, ?DEN S, KARAMPELIAS M, CAMMUE B P. TheRNA editing factor SLO2, which affects the mitochondrial electron transport chain, participates in multiple stress and hormone responses. Molecular Plant, 2014, 7(2): 290-310.

[65] LIU J M, ZHAO J Y, LU P P, CHEN M, GUO C H, XU Z S, MA Y Z. The E-subgroup pentatricopeptide repeat protein family inand confirmation of the responsiveness PPR96 to abiotic stresses. Frontiers in Plant Science, 2016, 7: 1825.

[66] H. EMAMI, A. KUMAR, F. KEMPKEN. Transcriptomic analysis of poco1, a mitochondrial pentatricopeptide repeat protein mutant in. BMC Plant Biology, 2020, 20(1): 1-21.

[67] SECHET J, ROUX C, PLESSIS A, EFFROY D, FREY A, PERREAU F, BINIEK C, KRIEGER-LISZKAY A, MACHEREL D, NORTH H M. The ABA-deficiency suppressor locus HAS2 encodes the PPR protein LOI1/MEF11 involved in mitochondrial RNA editing. Molecular Plant, 2015, 8(4): 644-656.

[68] JIANG S C, MEI C, LIANG S, YU Y T, LU K, WU Z, WANG X F, ZHANG D P. Crucial roles of the pentatricopeptide repeat protein SOAR1 inresponse to drought, salt and cold stresses. Plant Molecular Biology, 2015, 88(4): 369-385.

[69] GUO Z F, WANG X Y, HU Z B, WU C Y, SHEN Z G. The pentatricopeptide repeat protein GEND1 is required for root development and high temperature tolerance in. Biochemical and Biophysical Research Communications, 2021, 578: 63-69.

[70] PARK Y J, LEE H J, KWAK K J, LEE K, HONG S W, KANG H. MicroRNA400-guided cleavage of pentatricopeptide repeat protein mRNAs rendersmore susceptible to pathogenic bacteria and fungi. Plant and Cell Physiology, 2014, 55(9): 1660-1668.

[71] CHEN G L, ZOU Y, HU J H, DING Y. Genome-wide analysis of the rice PPR gene family and their expression profiles under different stress treatments. BMC Genomics, 2018, 19(1): 720.

[72] GONG X D, SU Q Q, LIN D Z, JIANG Q, XU J L, ZHANG J H, TENG S, DONG Y J. The riceencoding a novel pentatricopeptide repeat protein is required for chloroplast development during the early leaf stage under cold stress. Journal of Integrative Plant Biology, 2014, 56(4): 400-410.

[73] WU L L, WU J, LIU Y X, GONG X D, XU J L, LIN D Z, DONG Y J. The rice pentatricopeptide repeat geneis needed for chloroplast development under cold stress. Rice, 2016, 9(1): 67.

[74] TAN J J, TAN Z H, WU F Q, SHENG P K, HENG Y Q, WANG X H, REN Y L, WANG J L, GUO X P, ZHANG X, CHENG Z J, JIANG L, LIU X M, WANG H Y, WAN J M. A novel chloroplast-localized pentatricopeptide repeat protein involved in splicing affects chloroplast development and abiotic stress response in rice. Molecular Plant, 2014, 7(8): 1329-1349.

[75] XIAO H J, LIU Z J, ZOU X, XU Y H, PENG L L, HU J, LIN H H. Silencing of rice PPR geneexhibited enhanced sensibility to abiotic stress and remarkable accumulation of ROS. Journal of Plant Physiology, 2021, 258-259: 153361.

[76] QIU T C, ZHAO X S, FENG H J, QI L L, YANG J, PENG Y L, ZHAO W S. OsNBL3, a mitochondrion-localized pentatricopeptide repeat protein, is involved in splicingintron 4 and its disruption causes lesion mimic phenotype with enhanced resistance to biotic and abiotic stresses. Plant Biotechnology Journal, 2021, 19(11): 2277-2290.

[77] LUO Z, XIONG J, XIA H, WANG L, HOU G H, LI Z Y, LI J, ZHOU H L, LI T F, LUO L J. Pentatricopeptide repeat gene-mediated mitochondrial rna editing impacts on rice drought tolerance. Frontiers in Plant Science, 2022, 13: 926285.

[78] LU K, LI C, GUAN J, LIANG W H, CHEN T, ZHAO Q Y, ZHU Z, YAO S, HE L, WEI X D, ZHAO L, ZHOU L H, ZHAO C F, WANG C L, ZHANG Y D. The PPR-Domain Protein SOAR1 Regulates Salt Tolerance in Rice. Rice, 2022, 15: 1-16.

[79] SU H G, LI B, SONG X Y, MA J, CHEN J, ZHOU Y B, CHEN M, MIN D H, XU Z S, MA Y Z. Genome-wide analysis of the DYW subgroup PPR gene family and identification ofresponses to drought stress. International Journal of Molecular Sciences, 2019, 20(22): 5667.

[80] SCHMITZ-LINNEWEBER C, SMALL I. Pentatricopeptide repeat proteins: a socket set for organelle gene expression. Trends in plant science, 2008, 13(12): 663-670.

[81] PRIKRYL J, ROJAS M, SCHUSTER G, BARKAN A. Mechanism of RNA stabilization and translational activation by a pentatricopeptide repeat protein. Proceedings of the National Academy of Sciences of the United State of America, 2011, 108(1): 415-420.

[82] XIONG J, TAO T, LUO Z, YAN S G, LIU Y, YU X Q, LIU G L, XIA H, LUO L J. RNA editing responses to oxidative stress between a wild abortive type male-sterile line and its maintainer line. Frontiers in Plant Science, 2017, 8: 2023.

[83] RICHTER A S, N?GELE T, GRIMM B, KAUFMANN K, SCHRODA M, LEISTER D, KLEINE T. Retrograde signaling in plants: A critical review focusing on the GUN pathway and beyond. Plant Communications, 2023, 4(1): 20.

[84] POGSON B J, WOO N S, F?RSTER B, SMALL I D. Plastid signalling to the nucleus and beyond, Trends in Plant Science, 2008, 13(11): 602-609.

[85] LEE K, KANG H. Roles of organellar RNA-binding proteins in plant growth, development, and abiotic stress responses. International Journal of Molecular Sciences, 2020, 21(12): 4548.

[86] PESARESI P, KIM C. Current understanding of GUN1: a key mediator involved in biogenic retrograde signaling. Plant Cell Reports, 2019, 38(7): 819-823.

[87] HERNáNDEZ-VERDEJA T, STRAND ?. Retrograde signals navigate the path to chloroplast development. Plant Physiology, 2018, 176(2): 967-976.

[88] WU G Z, MEYER E H, RICHTER A S, SCHUSTER M, LING Q, SCH?TTLER M A, WALTHER D, ZOSCHKE R, GRIMM B, JARVIS R P. Control of retrograde signalling by protein import and cytosolic folding stress. Nature Plants, 2019, 5(5): 525-538.

[89] TADINI L, PESARESI P, KLEINE T, ROSSI F, GULJAMOW A, SOMMER F, MüHLHAUS T, SCHRODA M, MASIERO S, PRIBIL M. GUN1 controls accumulation of the plastid ribosomal protein S1 at the protein level and interacts with proteins involved in plastid protein homeostasis. Plant Physiology, 2016, 170(3): 1817-1830.

[90] ZHAO X B, HUANG J Y, CHORY J. GUN1 interacts with MORF2 to regulate plastid RNA editing during retrograde signaling. Proceedings of the National Academy of Sciences of the United State of America, 2019, 116(20): 10162-10167.

[91] TADINI L, PERACCHIO C, TROTTA A, COLOMBO M, MANCINI I, JERAN N, COSTA A, FAORO F, MARSONI M, VANNINI C. GUN1 influences the accumulation of NEP-dependent transcripts and chloroplast protein import incotyledons upon perturbation of chloroplast protein homeostasis. The Plant Journal, 2020, 101(5): 1198-1220.

[92] SHIMIZU T, KACPRZAK S M, MOCHIZUKI N, NAGATANI A, WATANABE S, SHIMADA T, TANAKA K, HAYASHI Y, ARAI M, LEISTER D. The retrograde signaling protein GUN1 regulates tetrapyrrole biosynthesis. Proceedings of the National Academy of Sciences of the United State of America, 2019, 116(49): 24900-24906.

[93] TAKENAKA M, ZEHRMANN A, VERBITSKIY D, KUGELMANN M, H?RTEL B, BRENNICKE A. Multiple organellar RNA editing factor (MORF) family proteins are required for RNA editing in mitochondria and plastids of plants. Proceedings of the National Academy of Sciences of the United State of America, 2012, 109(13): 5104-5109.

[94] JIA Y B, TIAN H Y, ZHANG S, DING Z J, MA C L. GUN1- interacting proteins open the door for retrograde signaling. Trends in Plant Science, 2019, 24(10): 884-887.

[95] COLOMBO M, TADINI L, PERACCHIO C, FERRARI R, PESARESI P. GUN1, a jack-of-all-trades in chloroplast protein homeostasis and signaling. Frontiers in Plant Science, 2016, 7(257): 1427.

[96] BRUNKARD J O, BURCH-SMITH T M. Ties that bind: the integration of plastid signalling pathways in plant cell metabolism. Essays in Biochemistry, 2018, 62(1): 95-107.

[97] SUN X W, FENG P Q, XU X M, GUO H L, MA J F, CHI W, LIN R C, LU C M, ZHANG L X. A chloroplast envelope-bound PHD transcription factor mediates chloroplast signals to the nucleus. Nature Communications, 2011, 2: 477.

[98] PAGE M T, KACPRZAK S M, MOCHIZUKI N, OKAMOTO H, SMITH A G, TERRY M J. Seedlings lacking the PTM protein do not show amutant phenotype. Plant Physiology, 2017, 174(1): 21-26.

[99] KINDGREN P, NOREN L, LOPEZ J D D B, SHAIKHALI J, STRAND ?. Interplay between Heat Shock Protein 90 and HY5 controlsexpression in response to the GUN5 plastid signal. Molecular Plant, 2012, 5(4): 901-913.

[100] KAKIZAKI T, MATSUMURA H, NAKAYAMA K, CHE F S, TERAUCHI R, INABA T. Coordination of plastid protein import and nuclear gene expression by plastid-to-nucleus retrograde signaling. Plant Physiology, 2009, 151(2): 1339-1353.

[101] KOUSSEVITZKY S, NOTT A, MOCKLER T C, HONG F X, SACHETTO-MARTINS G, SURPIN M, LIM J, MITTLER R, CHORY J. Signals from chloroplasts converge to regulate nuclear gene expression. Science, 2007, 316(5825): 715-719.

[102] MARTIN G, LEIVAR P, LUDEVID D, TEPPERMAN J M, QUAIL P H, MONTE E. Phytochrome and retrograde signalling pathways converge to antagonistically regulate a light-induced transcriptional network. Nature Communications, 2016, 7: 11431.

[103] VECIANA N, MARTíN G, LEIVAR P, MONTE E. BBX16 mediates the repression of seedling photomorphogenesis downstream of the GUN1/GLK1 module during retrograde signalling. New Phytologist, 2022, 234(1): 93-106.

[104] WU G Z, BOCK R. GUN control in retrograde signaling: how GENOMES UNCOUPLED proteins adjust nuclear gene expression to plastid biogenesis. The Plant Cell, 2021, 33(3): 457-474.

[105] KOBAYASHI K, SUZUKI M, TANG J, NAGATA N, OHYAMA K, SEKI H, KIUCHI R, KANEKO Y, NAKAZAWA M, MATSUI M. Lovastatin insensitive 1, a novel pentatricopeptide repeat protein, is a potential regulatory factor of isoprenoid biosynthesis in. Plant and Cell Physiology, 2007, 48(2): 322-331.

[106] TANG J W, KOBAYASHI K, SUZUKI M, MATSUMOTO S, MURANAKA T. The mitochondrial PPR protein LOVASTATIN INSENSITIVE 1 plays regulatory roles in cytosolic and plastidial isoprenoid biosynthesis through RNA editing. The Plant Journal, 2010, 61(3): 456-466.

[107] EMAMI H, KEMPKEN F. PRECOCIOUS1 (POCO1), a mitochondrial pentatricopeptide repeat protein affects flowering time in. The Plant Journal, 2019, 100(2): 265-278.

[108] OLDENKOTT B, YANG Y, LESCH E, KNOOP V, SCHALLENBERG- RüDINGER M. Plant-type pentatricopeptide repeat proteins with a DYW domain drive C-to-U RNA editing in.Communications Biology, 2019, 2: 85.

[109] NAKAMURA T. Understanding RNA editing and its use in gene editing. Gene and Genome Editing, 2022(3/4): 100021.

[110] MCDERMOTT J J, WATKINS K P, WILLIAMS-CARRIER R, BARKAN A. Ribonucleoprotein capture by in vivo expression of a designer pentatricopeptide repeat protein in. The Plant Cell, 2019, 31(8): 1723-1733.

Research progress of PPR protein in plant abiotic stress response

LI Cheng, LU Kai, WANG CaiLin, ZHANG YaDong

Institute of Food Crops, Jiangsu Academy of Agricultural Sciences/East China Branch of National Center of Technology Innovation for Saline-Alkali Tolerant Rice/Jiangsu High Quality Rice R&D Center/Nanjing Branch of China National Center for Rice Improvement/Key laboratory of Jiangsu Province for Agrobiology, Nanjing 210014

Abiotic stress is one of the main factors causing global grain yield reduction. It is of great significance to study the function and response mechanisms of plant stress-related proteins to improve crop stress resistance. Pentatricopeptide repeat (PPR) proteins, belong to the largest family of nuclear coding proteins in higher plants and are named because they contain highly specific PPR motifs. Depending on motif type and arrangement, PPR proteins can be classified as P and PLS, and PLS proteins can be further classified as PLS, E, E+, DYW, and other subclasses based on their carboxyl-terminal domains. PPR proteins are widely distributed in terrestrial plants, mainly in chloroplasts and mitochondria, and a few in the nucleus. As sequence-specific RNA binding proteins, PPR proteins are involved in multiple aspects of plant RNA processing, including RNA editing, splicing, stabilization, and translation. PPR protein plays a variety of important roles in the whole life process of plants, but the mechanism of its action in plant stress resistance is not well understood. Based on the localization and function of PPR proteins related to abiotic stress reported, the mechanism of PPR proteins involved in regulation of abiotic stress, including post-transcriptional regulation and retrograde signaling, was reviewed and discussed in this paper. Post-transcriptional regulation is related to the role of PPR proteins in the modification of RNA after transcription. It is generally believed that PPR affects stress resistance in plants by regulating the expression of stress-related genes via binding RNA and by regulating the metabolism of organelle RNA. In terms of retrograde signaling, damage to PPR proteins can lead to impaired mitochondrial or chloroplast function, and then produce various retrograde signals (such as ROS), thereby regulating the expression of related genes and resisting adversity. However, since plastid signaling is affected by many environmental factors, some of which are still unclear, the mechanism of the PPR protein in retrograde signaling remains to be clarified. In addition, PPR proteins are pleiotropic and some have important effects on plant growth and reproduction while acting on stress resistance. Finally, this paper further analyzed the current research status of PPR protein as an RNA editing tool, discussed the remaining problems and research prospects of PPR protein in the direction of abiotic stress, and pointed out the key points and difficulties that need to be paid attention to in future research, to provide references for further research on PPR protein and crop abiotic stress resistance breeding.

PPR protein; plant; abiotic stress

10.3864/j.issn.0578-1752.2023.24.001

2023-05-25；

2023-07-24

江蘇省種業振興揭榜掛帥項目（JBGS[2021]001）

李程，E-mail：cli1024shine@163.com。通信作者張亞東，E-mail：zhangyd@jaas.ac.cn

（責任編輯 李莉）