植物ABI5转录因子的研究进展

李鲁华,王忠妮,王文新,王怀玉,任明见,徐如宏*

植物ABI5转录因子的研究进展

李鲁华1,2,王忠妮3,王文新1,王怀玉1,任明见1,2,徐如宏1,2*

1. 贵州大学农学院, 贵州 贵阳 550025 2. 贵州大学国家小麦改良中心贵州分中心, 贵州 贵阳 550025 3. 贵州省农业科学院水稻研究所, 贵州 贵阳 550006

植物脱落酸不敏感蛋白5（Abscisic acid-insensitive 5, ABI5）为碱性亮氨酸拉链类型（Basic leucine zipper, bZIP）的转录因子，在ABA信号途径中起着重要作用。目前已经报道的ABI5功能研究主要是以模式植物拟南芥（）为研究对象，而在小麦（）、水稻（）等农作物中的研究报道极少。本文概述了植物中ABI5在种子发育、植物生长（特别是蔗糖信号途径和蛋白质泛素化过程）、花青素积累等生物学过程以及植物对干旱、低氮等逆境胁迫响应方面的最新研究进展，阐明在农作物中开展ABI5分子网络调控解析工作的重要性，以期为选育具有种子萌发可控（如抗穗发芽）、抗逆性强（如低氮）以及高产量等优良性状的作物品种提供理论基础，对作物分子育种具有指导意义。

ABI5转录因子; 研究进展

植物激素脱落酸（Abscisic acid, ABA）广泛参与植物生长发育的调控以及植物对逆境胁迫的响应过程。Finkelstein借助遗传学和分子生物学手段鉴定得到了一系列与ABA响应有关的组分如ABI1（Abscisic acid-insensitive 1）、ABI2、ABI3、ABI4、ABI5。其中，ABI5为碱性亮氨酸拉链（Basic leucine zipper, bZIP）类型的转录因子[1]。ABI5含有C1-C4 4个保守的结构域和1个bZIP结构域[2]（图1），其中bZIP结构域中含有分别与泛素化和苏素化有关的赖氨酸残基（分别为K344和K391），而C1-C4结构域中含有与磷酸化有关的丝氨酸残基（S42、S145和S439）和苏氨酸残基（T201）[3]。

图 1 ABI5保守结构域示意图

近年来研究发现，ABI5在种子休眠和萌发[4]、植物的生长发育[5]、植物对逆境胁迫的响应[6]、花青素的积累[7]以及26S蛋白酶体降解途径[8]等生物学过程起着重要的作用。本文对近年来ABI5的研究进展进行了梳理和归纳，以期为培育具有优良性状的农作物提供一定的思路。

1 ABI5与种子发育

ABA参与种子发育过程的调控，而在该生物学过程中ABI5起着重要的作用[1]。

1.1 通过对ABI5的转录调控

拟南芥中的研究发现，转录中介体（Mediator 25, MED25）和MADS-box转录因子AGL21（MADS-box transcription factor AGL21）能够结合到ABI5的启动子区域，分别负调控/正调控ABI5的表达进而参与种子发育过程的调控[9,10]；ABI5也能够直接结合到过氧化氢酶1（Catalase 1, CAT1）基因和SHB1（Short hypocotyl under blue 1, SHB1）基因的启动子区域，分别通过激活CAT1进而影响活性氧簇的动态平衡[11]和负调控SHB1[12]的表达进而调控ABI5下游信号组分的表达参与种子发育过程的调控。ABI5还能够直接靶向编码晚期胚胎丰富蛋白（Late embryogenesis abundant, LEA）的Em1和Em6基因并负调控两者的表达[13]；拟南芥核因子Y家族蛋白（Nuclear factor Y family protein, NF-YC9）能够直接与ABI5结合，进而使其结合并激活靶基因EM6的表达，实现对ABI5转录活性的正调控作用，从而参与种子萌发对ABA的响应[14]。小麦中的研究发现，ABI5基因的表达量随着小麦种子成熟度的增加而增加，表明其参与种子发育过程的调控[15]。

此外，拟南芥SAG（A protein containing the midasin homologue 1 domain）[16]、萌发延迟基因1（Delay of Germination 1, DOG1）[17]、DELLA蛋白RGL2[4]以及转录因子AtMyb7[18]和RAV1[19]等都通过调控ABI5，进而参与ABA对种子萌发的调控。

1.2 通过对ABI5的稳定性调控

研究发现拟南芥BIN2（Brassinazole insensitive 2）[20]、SOS2类似的蛋白激酶5（SOS2-like protein kinase 5, PSK5）[21]和蛋白磷酸化2A相关蛋白（Protein phosphatase2A (PP2A)-associated protein, TAP46）[22]通过磷酸化作用稳定ABI5，维持种子中较高含量的ABI5水平从而抑制种子萌发。相反地，拟南芥光敏色素相关的丝氨酸/苏氨酸蛋白磷酸酶（Phytochrome associated serine/threonine protein phosphatase, FyPP）与SnRK2激酶拮抗作用调控ABI5的磷酸化，通过去磷酸化降低ABI5蛋白的稳定性，降低种子中ABI5的含量进而促进种子的萌发[23]。

拟南芥小泛素相关修饰物（Small ubiquitin-related modifier, SUMO）E3连接酶SIZ1通过SUMO修饰保护ABI5免受蛋白酶的降解，进而负调控ABA对种子萌发的调控[24]。相反，研究发现拟南芥CRWN（Crowded nuclei）蛋白家族通过调控ABI5的降解参与ABA控制的种子萌发，CRWN突变体对ABA超敏感并积累更高水平的ABI5蛋白[25]。此外，NO对ABI5蛋白153位半胱氨酸的S-亚硝基化有利于ABI5通过KEG（Keep on going）E3连接酶的生物学降解，从而促进种子的萌发。而ABI5蛋白153位半胱氨酸的突变能够引起NO失去对ABI5蛋白稳定性的调控，进而表现出抑制种子萌发的表型[26]。

综上可知，ABI5在种子发育过程中有着极其重要的作用，ABI5基因的表达水平及ABI5蛋白的稳定性直接影响种子的萌发和/或休眠等生物学过程。因此，在小麦、大豆、高粱等作物开展ABI5基因的研究是必要的，进而为种业技术的发展提供一定的理论基础。

2 ABI5与植物的生长

蔗糖具有类生长素信号分子的功能，在拟南芥生长发育过程中起着重要的调控作用[27]。研究发现，ABI5能够通过抑制生长素运输载体PIN1的积累引起根中生长素水平的降低，通过调节根中生长素的水平进而参与蔗糖介导的对根分生组织区的抑制过程[28]。过表达ABI5能够造成开花转变过程的延迟，染色质免疫沉淀发现ABI5通过结合到花发育基因FLC（Flowering locus c）的启动子元件参与植物的花发育过程，进一步研究发现蔗糖非发酵1型相关蛋白激酶2（Sucrose nonfermenting 1-related protein kinase2, SnRK2）介导的ABI5的磷酸化在该过程中起着重要的作用，SnRK2通过调控ABI5的磷酸化能够促进FLC基因的表达，进而实现拟南芥中ABA对开花转变过程的抑制作用[29]。

此外，ABI5还参与植物子叶变绿[30]以及黑暗诱导叶片衰老[31]的生物学过程，但具体的作用机理仍有待于进一步的研究。

3 ABI5与逆境胁迫的响应

ABA与植物对逆境胁迫的响应过程紧密相关。对拟南芥突变体hls1（HOOKLESS1）进行研究，发现突变体中ABA介导的抗真菌侵染的现象消失，进一步研究发现HSL1介导的ABI5表达水平降低与该过程具有相关性[6]。低氮胁迫处理发现，拟南芥ABI5的表达水平受到显著诱导，上调表达超过100倍[32]。在棉花中共表达拟南芥ABI3/Viviparous1（命名为AtRAV2）和ABI5能够通过调节活性氧簇清除以及渗透调节marker基因的表达提高棉花对干旱胁迫的抗性[33]。此外，水稻[34]、水曲柳[35]等中的研究也发现ABI5与植物对逆境胁迫的响应有关。此外，ABI5还参与逆境胁迫下三酰基甘油（triacylglycerol, TAG）的积累。研究发现逆境胁迫条件下，拟南芥abi5中TAG合成途径的限速酶二酰基甘油转移酶（diacylglycerol acyltransferase 1, DGAT1）基因的表达水平以及TAG的积累量均降低；相反地，ABI5过表达转基因株系中DGAT1的表达水平以及TAG的积累量均升高[36]。ABI5参与植物对逆境胁迫响应的生物学过程，并在植物对逆境胁迫的响应过程中起着重要作用。

4 ABI5与花青素的积累

对拟南芥abi5-4进行研究，发现3%蔗糖处理使得突变体中花青素的积累量高于野生型[7]。对拟南芥丝氨酸/精氨酸丰富（serine/arginine-rich, SR）蛋白SR45的研究发现，3%蔗糖处理能够显著诱导sr45中花青素合成基因APL3（ADP-Glc pyrophosphorylase, large subunit）、CHS以及ABI5的表达[37]。此外，拟南芥中的研究发现外源蔗糖和葡萄糖处理能够诱导调控花青素合成途径的花色苷色素产生基因（Production of anthocyanin pigment, PAP）PAP1和PAP2的表达，而突变体abi5-1能够减弱该处理对PAP1和PAP2表达的诱导作用[38]，进而调节花青素的积累。可知，ABI5能够通过影响花青素合成相关基因的表达实现对花青素的生物学调控，但其作用机制仍需要进一步阐明。

5 ABI5与26S蛋白酶体降解途径

蛋白的泛素化过程在植物生长过程中具有广泛而重要的生物学功能，该过程一般由泛素激活酶（Ubiquitin-activating enzymes, E1）、泛素结合酶（Ubiquitin-conjugating enzymes, E2）和E3催化的级联反应完成[39]。26S蛋白酶体能够识别泛素化的蛋白，经过去泛素化酶（Deubiquitinating enzymes, DUBs）去泛素化后被26S蛋白酶体中的蛋白酶降解[40]。拟南芥中研究发现定位于细胞质和内膜系统的泛素化E3连接酶KOG能够通过泛素化作用抑制ABI5的积累水平[8]，进一步研究发现泛素化的ABI5通过26S蛋白酶体进行降解，从而实现KOG对ABI5蛋白表达水平的调控[3]。此外，Cullin4 E3复合体底物受体DWA1/DWA2（DWD hypersensitive to ABA1/2）和ABD1（ABA-hypersensitive DCAF1）也能够通过26S蛋白酶体途径调控细胞核中ABI5的水平[41]。总之，植物可以通过26S蛋白酶体降解途径实现对细胞核和细胞质中ABI5表达水平的调节，进而对ABA信号通路进行调控。

目前，对农作物中ABI5的功能报道较少，然而由于该蛋白是ABA信号途径中重要的转录因子，阐明农作物中ABI5的调控网络为最终应用于分子育种具有指导性的意义。

6 总结与展望

植物ABI5是ABA信号通路中重要的转录因子，参与种子发育、植物生长、花青素积累等生物学过程，并在植物对逆境胁迫如干旱、低氮等的响应方面起着重要的作用。目前拟南芥中ABI5的功能研究已有较多的报道，而对小麦、水稻等农作物中的研究报道极少。综上可知，ABI5在种子发育、植物生长（特别是蔗糖信号途径和蛋白质泛素化过程）、植物对逆境胁迫的响应以及花青素积累等生物学过程中起重要作用，在农作物中可以重点开展该蛋白在上述方面的研究。然而，农作物中ABI5具有的生物学功能是否与拟南芥中的功能相同？哪些蛋白（靶向或者非靶向）参与调控ABI5的生物学功能？ABI5又能够通过调控哪些蛋白实现上游信号的传递？在某一特定生物学过程中ABI5分子调控网络是如何协同的？等问题仍需要进行系统深入的研究和探讨。对小麦、水稻、玉米等重要农作物中ABI5进行深入的研究，有助于人们深入了解ABI5的分子调控网络，为培育具有抗穗发芽、抗逆性强、延缓衰老等优良性状的品种提供一定的理论基础。综上所述，在农作物中开展阐明ABI5分子调控网络的相关研究是必要可行的。

[1] Finkelstein RR, Lynch TJ. The Arabidopsis abscisic acid response gene ABI5 encodes a basic leucine zipper transcription factor[J]. Plant Cell, 2000,12(4):599-609

[2] Bensmihen S, Rippa S, Lambert G,. The homologous ABI5 and EEL transcription factors function antagonistically to fine-tune gene expression during late embryogenesis[J]. Plant Cell, 2002,14(6):1391-403

[3] Liu HX and Stone SL. Regulation of ABI5 turnover by reversible post-translational modifications[J]. Plant Signaling & Behavior, 2014,9:e27577

[4] Ibarra SE, Tognacca RS, Dave A,. Molecular mechanisms underlying the entrance in secondary dormancy of Arabidopsis seeds[J]. Plant Cell & Environment, 2016,39(1):213-221

[5] Yang X, Bai Y, Shang J,. The antagonistic regulation of abscisic acid-inhibited root growth by brassinosteroids is partially mediated via direct suppression of ABSCISIC ACID INSENSITIVE 5 expression by BRASSINAZOLE RESISTANT 1[J]. Plant Cell & Environment, 2016,39(9):1994-2003

[6] Liao CJ, Lai Z, Lee S,. Arabidopsis HOOKLESS1 regulates responses to pathogens and abscisic acid through interaction with MED18 and acetylation of WRKY33 and ABI5 chromatin[J]. Plant Cell, 2016,28(7):1662-1681

[7] Hoth S, Niedermeier M, Feuerstein A,. An ABA-responsive element in the AtSUC1 promoter is involved in the regulation of AtSUC1 expression[J]. Planta, 2010,232(4):911-923

[8] Liu HX, Stone SL. Cytoplasmic degradation of the Arabidopsis transcription factor ABSCISIC ACID INSENSITIVE 5 is mediated by the RING-type E3 ligase KEEP ON GOING[J]. The Journal of Biological Chemistry, 2013,288(28):20267-20279

[9] Chen R, Jiang H, Li L,The Arabidopsis mediator subunit MED25 differentially regulates jasmonate and abscisic acid signaling through interacting with the MYC2 and ABI5 transcription factors[J]. Plant Cell, 2012,24(7):2898-2916

[10] Yu LH, Wu J, Zhang ZS,. Arabidopsis MADS-box transcription factor AGL21 acts as environmental surveillance of seed germination by regulating ABI5 expression[J]. Molecular Plant, 2017,10(6):834-845

[11] Bi C, Ma Y, Wu Z,. Arabidopsis ABI5 plays a role in regulating ROS homeostasis by activating CATALASE 1 transcription in seed germination[J]. Plant Molecular Biology, 2017,94(1-2):197-213

[12] Cheng ZJ, Zhao XY, Shao XX,. Abscisic acid regulates early seed development in Arabidopsis by ABI5-mediated transcription of SHORT HYPOCOTYL UNDER BLUE1[J]. Plant Cell, 2014,26(3):1053-1068

[13] Tezuka K, Taji T, Hayashi T,. A novel abi5 allele reveals the importance of the conserved Ala in the C3 domain for regulation of downstream genes and salt tolerance during germination in Arabidopsis[J]. Plant Signaling & Behavior, 2013,8(3):e23455

[14] Bi C, Ma Y, Wang XF,. Overexpression of the transcription factor NF-YC9 confers abscisic acid hypersensitivity in Arabidopsis[J]. Plant Molecular Biology, 2017,95(4-5):425-439

[15] 孙晓燕.ABI5基因在不同休眠特性小麦中的鉴定和表达特异性研究[D].呼和浩特:内蒙古农业大学,2016:3-4

[16] Chen C, Wu C, Miao J,. Arabidopsis SAG protein containing the MDN1 domain participates in seed germination and seedling development by negatively regulating ABI3 and ABI5[J]. Journal of Experimental Botany, 2014,65(1):35-45

[17] Dekkers BJ, He H, Hanson J,. The Arabidopsis DELAY OF GERMINATION 1 gene affects ABSCISIC ACID INSENSITIVE 5 (ABI5) expression and genetically interacts with ABI3 during Arabidopsis seed development[J]. Plant Journal, 2016,85(4):451-465

[18] Kim JH, Hyun WY, Nguyen HN,. AtMyb7, a subgroup 4 R2R3 Myb, negatively regulates ABA-induced inhibition of seed germination by blocking the expression of the bZIP transcription factor ABI5[J]. Plant Cell & Environment, 2014,38(3):559-571

[19] Feng CZ, Chen Y, Wang C,. Arabidopsis RAV1 transcription factor, phosphorylated by SnRK2 kinases, regulates the expression of ABI3, ABI4, and ABI5 during seed germination and early seedling development[J]. Plant Journal, 2014,80(4):654-668

[20] Hu Y, Yu D. BRASSINOSTEROID INSENSITIVE2 interacts with ABSCISIC ACID INSENSITIVE5 to mediate the antagonism of brassinosteroids to abscisic acid during seed germination in Arabidopsis[J]. Plant Cell, 2014,26(11):4394-4408

[21] Zhou X, Hao H, Zhang Y,. SOS2-LIKE PROTEIN KINASE5, an SNF1-RELATED PROTEIN KINASE3-type protein kinase, is important for abscisic acid responses in Arabidopsis through phosphorylation of ABSCISIC ACID-INSENSITIVE5[J]. Plant Physiology, 2015,168(2):659-676

[22] Hu R, Zhu Y, Shen G,. TAP46 plays a positive role in the ABSCISIC ACID INSENSITIVE5-regulated gene expression in Arabidopsis[J]. Plant Physiology, 2014,164(2):721-734

[23] Dai M, Xue Q, Mccray T,. The PP6 phosphatase regulates ABI5 phosphorylation and abscisic acid signaling in Arabidopsis[J]. Plant Cell, 2013,25(2):517-534

[24] Miura K, Lee J, Jin JB,. Sumoylation of ABI5 by the Arabidopsis SUMO E3 ligase SIZ1 negatively regulates abscisic acid signaling[J]. Proceedings of the National Academy of Sciences of the United States of America, 2009,106(13):5418-5423

[25] Zhao W, Guan C, Feng J,. The Arabidopsis CROWDED NUCLEI genes regulate seed germination by modulating degradation of ABI5 protein[J]. Journal of Integrative Plant Biology, 2015,58(7):669-678

[26] Albertos P, Romero-Puertas MC, Tatematsu K,. S-nitrosylation triggers ABI5 degradation to promote seed germination and seedling growth[J]. Nature Communications, 2015,6:8669

[27] Karve A, Xia X, Moore B. Arabidopsis Hexokinase-Like1 and Hexokinase1 form a critical node in mediating plant glucose and ethylene responses[J]. Plant Physiology, 2012,158:1965-1975

[28] Yuan T, Xu H, Zhang K,. Glucose inhibits root meristem growth via ABA INSENSITIVE 5, which represses PIN1 accumulation and auxin activity in Arabidopsis[J]. Plant Cell & Environment, 2014,37(6):1338-1350

[29] Wang Y, Li L, Ye T,. The inhibitory effect of ABA on floral transition is mediated by ABI5 in Arabidopsis[J]. Journal of Expereimental Botany, 2013,64(2):675-684

[30] Guan C, Wang X, Feng J,. Cytokinin antagonizes abscisic acid-mediated inhibition of cotyledon greening by promoting the degradation of abscisic acid insensitive5 protein in Arabidopsis[J]. Plant Physiology, 2014,164(3):1515-1526

[31] Su M, Huang G, Zhang Q,. The LEA protein, ABR, is regulated by ABI5 and involved in dark-induced leaf senescence in Arabidopsis thaliana[J]. Plant Scince, 2016,247:93-103

[32] Yang X, Yang YN, Xue LJ,. Rice ABI5-Like1 regulates abscisis acid and auxin responses by affecting the expression of ABRE-containing genes[J]. Plant Physiology, 2011,156(3):1397-1409

[33] Mittal A, Gampala SS, Ritchie GL,Related to ABA-Insensitive3(ABI3)/Viviparous1 and AtABI5 transcription factor coexpression in cotton enhances drought stress adaptation[J]. Plant Biotechnology Journal, 2014,12(5):578-589

[34] Yang Y, Yu X, Song L,. ABI4 activates DGAT1 expression in Arabidopsis seedlings during nitrogen deficiency[J]. Plant Physiology, 2011,156(2):873-883

[35] 孙爽,赵兴堂,梁楠松,等.水曲柳FmABI5基因非生物胁迫及信号诱导的表达模式分析[J].植物研究,2017,37(3):453-460

[36] Kong Y, Chen S, Yang Y,. ABA-insensitive (ABI) 4 and ABI5 synergistically regulate DGAT1 expression in Arabidopsis seedlings under stress[J]. FEBS Letters, 2013,587(18):3076-3082

[37] Carvalho RF, Carvalho SD, Duque P. The plant-specific SR45 protein negatively regulates glucose and ABA signaling during early seedling development in Arabidopsis[J]. Plant Physiology, 2010,154(2):772-783

[38] Luo QJ, Mittal A, Jia F, et al. An autoregulatory feedback loop involving PAP1 and TAS4 in response to sugars in Arabidopsis[J]. Plant Molecular Biology, 2012,80(1):117-129

[39] Vierstra RD. The expanding universe of ubiquitin and ubiquitin-like modifiers[J]. Plant Physiology, 2012,160(1):2-14

[40] Isono E, Nagel MK. Deubiquitylating enzymes and their emerging role in plant biology[J]. Frontier in Plant Science, 2014,5:56

[41] Seo KI, Lee JH, Nezames CD,. ABD1 is an Arabidopsis DCAF substrate receptor for CUL4-DDB1-based E3 ligases that acts as a negative regulator of abscisic acid signaling[J]. Plant Cell, 2014,26(2):695-711

Research Advances of Plant ABI5 Transcription Factors

LI Lu-hua1,2, WANG Zhong-ni3, WANG Wen-xin1, WANG Huai-yu1, REN Ming-jian1,2, XU Ru-hong1,2*

1.550025,2.550025,3.550006,

Plant abscisic acid insensitive 5 (ABI5) protein is transcription factors of basic leucine zipper (bZIP) type and plays an important role in ABA signaling pathway. Currently, the functional research of ABI5 in plant mainly focused on, while few studies have been reported on crops such as wheat () and rice (). In this paper, we summarized the advanced researches of ABI5 in biological process such as seed development, plant growth (especially the sucrose signaling pathway and protein ubiquitination process), anthocyanin accumulation and in stress responses such as drought and low nitrogen, and elucidated the importance of carrying out the molecular regulation research of ABI5 in crops, which would provide theoretical basis for crop varieties with excellent traits, such as controllable seed germination (e.g. preharvest sprouting resistance), strong stress resistance (e.g. low nitrogen) and high yield, and has instructive significance of molecular breeding in crops.

ABI5 transcription factors; research advance

Q7

A

1000-2324(2019)04-0537-05

2018-08-22

2018-10-10

贵州省科技计划项目(黔科合基础[2019]1073号);国家自然科学基金项目(31660390); 贵州省农业成果转化计划项目(黔科合成果(2016)4022号);贵州大学引进人才科研项目(贵大人基合字2017(49号))

李鲁华(1985-),男,博士,讲师,主要从事作物遗传育种工作. E-mail:luhua_li@163.com

Author for correspondence. E-mail:xrhgz@163.com