安新艷 樓盼盼 郝娟


摘要TCPs是一類植物所特有的并普遍存在于植物中的轉錄因子家族。大多數 TCP蛋白具有保守的非典型螺旋-環-螺旋的結構域,研究表明,TCP轉錄因子與真核轉錄因子的bHLH類似,且該家族基因在植物體內發揮著重要作用,如植物生長發育、激素反應和逆境脅迫等。因而,TCP轉錄因子被越來越多的科研工作者所關注。迄今為止,科研工作者對TCP轉錄因子家族成員的生物學功能研究已經取得了重大進步??偨Y了TCP轉錄因子的研究進展,為植物的遺傳改良、次生代謝產物合成和生物學功能提供了參考。
關鍵詞TCP轉錄因子;結構特性;生長發育;生物學功能
中圖分類號Q943.2文獻標識碼A文章編號0517-6611(2020)15-0020-04
doi:10.3969/j.issn.0517-6611.2020.15.006
開放科學(資源服務)標識碼(OSID):
Research Progress on Plant TCP Transcription Factors
AN Xinyan, LOU Panpan, HAO Juan
(Hangzhou Normal University, Hangzhou, Zhejiang 310000)
AbstractCharacteristic of the TCPs is a kind of universal existence in the family of transcription factors in plants. Most TCP proteins have conservative atypical helixloophelix structure domain, studies show that TCP transcription factors is similar to the bHLH eukaryotic transcription factors, the family genes in plants play an important role in the body, such as plant growth and development, and adversity stress hormone responses. Therefore, TCP transcription factors are being paid more and more attention by more and more researchers. So far, researchers have made significant progress in the biological function research of TCP transcription factors family members. The latest research progress on TCP transcription factors was summarized, in order to provide reference for plant genetic improvement, synthesis of secondary metabolites and biological function.
Key wordsTCP transcription factors;Structural characteristics;Growth and development;Biological function
基金項目
浙江省新苗計劃項目“CrSLS參與UV-B調控長春花生物堿合成的功能分析”(2025C5151910177);國家自然科學基金項目“棉花TCP轉錄因子家族基因的表達模式分析”(Y201533081),“陸地棉纖維發育相關TCP轉錄因子的挖掘和功能研究”(31601343)。
作者簡介安新艷(1994—),女,河南焦作人,碩士研究生,研究方向:藥用植物生物堿合成。*通信作者,講師,博士,從事藥用植物次生代謝調控研究。
收稿日期2019-10-11;修回日期2019-12-05
TCP轉錄因子是一類高等植物所特有的轉錄家族,由TEOSINTE BRANCHED 1(TB1)、CYCLOIDEA(CYC)和PROLIFERATING CELL FACTORS(PCFs)這3個分離到的成員的首字母縮寫而得名。鑒于TCP轉錄家族有著重要且廣泛的調控作用,區分并說明TCP轉錄因子的作用機制對研究植物生物學功能具備重要的意義。隨著不同物種基因組測序的完成,越來越多的TCP轉錄因子家族被相繼挖掘和分析鑒定,如從番茄中分離到30個TCP轉錄因子[1],從西瓜中篩選出來27個TCP轉錄因子[2],從油菜中篩選到39個TCP轉錄因子[3],不同棉花品種中的TCP轉錄因子家族也隨基因組測序的完成相繼被分離鑒定出來并進行表達分析[4]。
許多報道表明TCP轉錄因子家族與植物成長發育的多個進程以及脅迫條件下的生存有關,因此TCP轉錄因子家族成員的功能研究受到科研工作者的普遍歡迎。筆者就植物TCP轉錄因子的最新研究進展進行介紹,并預測未來的研究方向。
1TCP轉錄因子的結構特點及分類
TCP轉錄因子家族參與植物生物學功能的多個進程,如植物分枝[5-6]、葉片發育[7]、激素途徑[8-9]、種子萌發[10]、晝夜節律[11]。而這些轉錄因子之所以具有這些功能特征主要是因為它們擁有被稱為TCP域的N末端非典型螺旋-環-螺旋(bHLH)結構域。但是,TCP 轉錄因子又與bHLH 轉錄因子幾乎沒有同源性,并和不同于bHLH 轉錄因子識別的DNA結構域結合[12]。 根據TCP蛋白保守結構域的序列同源性分析,可將TCP蛋白分為兩類,即I類和Ⅱ類[13]。I類在TCP結構域中缺失4個保守的氨基酸,Ⅱ類在TCP結構域中插入4個保守的氨基酸,例如谷氨酸-半胱氨酸-谷氨酸(ECE)[14]延伸或富含精氨酸的R結構域[15-16]。Ⅱ類成員可以根據TCP結構域中的序列差異進一步細分為CIN和CYC兩個分支[17]。CIN子代以Antirrhinum CINCINNATA(CIN)為代表[18],而CYC子代以CYC/TB1為代表[14]。
已知Ⅱ類TCP蛋白調節許多植物生長過程,最顯著的是植物發育(如枝葉分化[5]、腋生分生組織發育[9,19]、激素信號傳導[20]和脅迫[21]等)。例如,擬南芥中的AtBRC1[5]、水稻中的OsFC1[6]和郁金香中的TgTB1[22]參與腋芽的發育和分枝控制。另外,I類TCP成員參與植物子葉發育、生長和增殖[23-24]。如在擬南芥中,AtTCP15在雌蕊發育過程中調節內部遺傳物質復制以及細胞分裂素和生長素的刺激[8],AtTCP14和AtTCP15共同調節植物節間長度[7]和種子發芽[10],而AtTCP23參與植物開花節律和植物發育[25-26]。然而,由于它們結合的順式調控競爭位點相似,使得這兩類基因共同參與調控植物生長和發育[24,27]。
Liu等[28]利用系統發育分析表明TCP家族中的每個基因類別在其進化過程中均保守地分布在陸地植物中,并且Ⅱ類基因的CYC和CIN基因在陸地植物建立之初就出現了(圖1)。
2TCP轉錄因子的生物學功能
最初的報道顯示TCP轉錄因子家族與細胞增殖和植物生長的調控有關,此后又有許多研究表明TCP家族不同成員的詳細作用,這些研究揭示了TCPs參與調控了多個生物學功能的進程并以不同的機制來發揮作用。
2.1植物生長發育功能
據報道TCP轉錄因子普遍參與了植物生長發育的生物學進程。研究表明,TCP轉錄因子的Ⅱ類(CIN)成員主要參與葉片發育。之前的研究已經報道了包括TCP2、TCP3、TCP4、TCP10和TCP24在內的擬南芥TCP基因具有miR319結合位點。而miR319已經證實了對這些AtTCP轉錄物具有切割活性,TCP轉錄因子的Ⅱ類(CIN)成員起著抑制葉子中細胞增殖的作用。具有高水平的miR319或低水平的miR319結合位點的TCP蛋白可能會導致過量的細胞增殖,從而導致擬南芥、金魚草和番茄中的皺葉或單子葉植物(大米和蔓生的草皮)中的葉變大[29];AtTCP3間接調節邊界特異性基因CUC和LOB的表達[30];在番茄LA中,這類基因主要參與調節葉片的形成[31]。除此之外,還有研究表明幾個CIN同源基因在細胞增殖中起到明顯作用[32];另外還有一些CYC家族成員參與調節枝條分化,如豌豆TCP轉錄因子PsBRC1作用于Strigolactones的下游以抑制芽的生長和控制枝條的分枝[32];有些基因在花的生長發育過程中起著重要作用[33-34]??傊@些結果表明CIN和CYC兩類基因主要參與植物發育,此外,雖然I類成員也參與調節植物的發育,但與Ⅱ類成員的作用相反。其中最顯著的功能是葉片發育的調節:I類成員促進細胞增殖,而Ⅱ類(CIN)成員則負調控此過程[35-36]。除此之外,I類成員還可以在許多其他發育功能過程中發揮作用。如擬南芥中的AtTCP14和AtTCP15基因在節間、葉片和花組織的細胞增殖中起作用,并影響節間長度和葉片形狀[7];菊花CmTCP14基因調節器官大小[37],蝴蝶蘭PePCF10基因影響胚珠發育[3];陸地棉GhTCP14基因參與植物生長素介導的棉纖維發育[38]。
2.2非生物脅迫功能
Mukhopadhyay等[39]證實了過表達OsTCP19可以誘導一些反應通路如JA、ABA、IAA、CK和ET通路,并能促進脂肪滴合成、降低水分損失和減少氧離子,進而提高轉基因株系的甘露醇處理和高鹽的耐受力。
Guan等[40]、Almeida等[41]研究表明,使用一個雜化酵母(Y1H)系統,可以確定5個TCP轉錄因子,使OSPCF2、OSCPP5、AtTCP20這3個轉錄因子去結合OsNHX1啟動子。研究發現這些轉錄因子編碼的基因在OsNHX1作用下可以參與調節不同的非生物脅迫反應,并證實OsPCF2調節參與鹽脅迫。
通過使用硝酸鹽增強劑篩選酵母單雜交系統中擬南芥轉錄因子的文庫,鑒定了轉錄因子基因TEOSINTE BRANCHED1 / CYCLOIDEA / PROLIFERATING的細胞因子1-20(TCP20)。TCP20屬于古老植物特有的基因家族,可調控芽、花和胚的發育。該植物具有結合100多個受硝酸鹽調節的基因能力,從而參與了硝酸鹽信號傳導。根據TCP20插入突變體的分析表明,它們在均質硝酸鹽培養基上具有正常的初生和側根生長,但在分裂根中的異質培養基上,其優先側根生長(根覓食)受到損害。即使銨鹽均勻地存在于培養基中,突變體仍優先抑制側根生長,這表明TCP20對硝酸鹽的刺激具有一定的響應。比較TCP20突變體與NLP7突變體,發現TCP20突變體在根生長的局部控制方面有缺陷,但在根覓食反應中沒有缺陷,這表明TCP20功能獨立于NLP7功能且與NLP7功能不同。進一步的分析表明,無論局部硝酸鹽濃度如何,TCP20突變體均缺乏對根生長的系統控制??傊?,TCP20在介導擬南芥根硝酸鹽覓食的系統信號傳導途徑中起著關鍵作用[42]。
2.3生物脅迫功能
研究表明,在植物免疫中TCP基因有著顯著的作用。如擬南芥中的一些TCP基因,如Ⅱ類(CIN)成員中的AtTCP13和I類成員中的AtTCP14,15,19和21是作為病原體的效應目標[43]。在對旱稻(O.sativa)報道中,Ⅱ類(CIN)成員中的OsTCP21參與病原體防御[44]。在對西紅柿(S.lycopersicum)報道中,AtTCP14-2(AtTCP14的直系同源物)有助于增強對辣椒疫霉菌的免疫力[45]。同時,許多Ⅱ類TCP基因已被證明是植原體效應[46]。如在擬南芥中,SAP11作用在Ⅱ類不穩定的不同成員中,因此導致嚴重的葉起皺和茉莉酸水平下調[44,46]。最近,一些Ⅱ類(CYC)成員也被證明是SAP11效應子(如小麥藍矮植原體效應子SWP1[47-48])。研究表明TCP13、TCP14和TCP19 這3種免疫互作因子是2種病原體效應物的直接靶標[49]。進一步的功能研究也表明了tcp13、tcp14和tcp19單突變體對2種不同的無毒性Hyalop-eronosporaarabidopsidis(Hpa)分離株(Emwa1和Emoy2)更敏感,因此這3種TCP轉錄因子中的每一種都是完整免疫系統功能所必需的;此外,TCP15突變體對毒性Hpa分離株Noco2的抗病性在增強[50]。
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