生长素是调控果实发育成熟的重要植物激素之一.在生长素介导的信号转导机制中,ARF和Aux/IAA扮演重要的角色.ARF与生长素响应基因启动子区域内的生长素响应元件结合,促进或抑制基因的表达.Aux/IAA通过结构域Ⅲ和Ⅳ与ARF特异性结合,从而调节生长素早期应答基因的转录功能.研究表明,ARF因子参与调控果实形态发育、硬度和糖分积累等,Aux/IAA因子在授粉、果实形态发育等方面作用明显.此外ARF和Aux/IAA之间相互或与自身发生的互作以调控下游基因表达是植物体响应生长素信号的主要机制.介绍了ARF和Aux/IAA的结构特征、在不同植物中的分布状况以及与果实发育成熟的关系,同时讨论了ARF和Aux/IAA互作的研究现状,旨为进一步阐明生长素调控果实发育成熟的机制提供参考.

由多亚基组成的中介体复合物(Mediator complex)是真核生物转录调控中不可或缺的纽带,它的核心功能就是将基因特异的转录因子和基于RNA聚合酶II的转录机器相连接,形成转录预起始复合物(Pre-initiation complex,PIC),从而实现特定转录信号的传递.Mediator 25(MED25)是植物中介体复合物的一个多功能亚基,参与调控植物生长发育和抗逆境胁迫等多种复杂的生理过程.MED25可以和多种转录激活子(如MYCs、AP2/ERFs及ARFs等)、转录抑制子(如JAZs和Aux/IAAs等)以及其它中介体亚基(如MED13和MEDl6等)在蛋白水平上直接互作,调控植物激素茉莉酸(JA)、脱落酸(ABA)、生长素(Auxin)和乙烯(Ethvlene)等信号途径以响应各种生物和非生物胁迫.近年来对MED25的靶标分离及功能鉴定已经成为一个热点话题.本文系统介绍了MED25在各激素信号途径转导中的调控作用机制,对深入讨论植物如何启动特定激素信号途径进而调控特定生理过程的分子机制提供新的研究思路.

Microtubule reorientation is a long-standing observation that has been implicated in regulating the inhibitory effect of ethylene on axial elongation of plant cells.However,the signaling mechanism underlying ethylene-induced microtubule reorientation has remained elusive.Here,we reveal,by live confocal imaging and kinetic root elongation assays,that the time courses of ethylene-induced microtubule reorientation and root elongation inhibition are highly correlated,and that microtubule reorientation is required for the full responsiveness of root elongation to ethylene treatment.Our genetic analysis demonstrated that the effect of ethylene on microtubule orientation and root elongation is mainly transduced through the canonical linear ethylene signaling pathway.By using pharmacological and genetic analyses,we demonstrate further that the TIR1/AFBs-Aux/IAAs-ARFs auxin signaling pathway,but not the ABP1-ROP6-RIC1 auxin signaling branch,is essential for ethylene-induced microtubule reorientation and root elongation inhibition.Together,these findings offer evidence for the functional significance and elucidate the signaling mechanism for ethylene-induced microtubule reorientation in fast root elongation inhibition in Arabidopsis.

依赖于受体TIR1以及下游Aux/IAAs-ARFs介导的信号通路是目前研究最为深入的生长素信号转导途径.徐通达课题组最新研究发现,高浓度生长素能够诱导质膜定位的TMK1激酶发生剪切,导致其羧基(C-)端部分转入细胞核并磷酸化修饰细胞核内的非经典IAA32/34,后者通过与生长素响应转录因子ARFs互作,调控下游基因表达,从而解析了生长素通过TMK1-IAA32/34-ARFs通路调控植物顶端弯钩内外侧差异性生长的分子机制.该研究发现了一条新的生长素TMK1-IAA32/34-ARFs信号途径,此信号通路独立于经典生长素受体TIR1介导的生长素信号转导通路.

In Arabidopsis thaliana,canonical auxin-dependent gene regulation is mediated by 23 transcription factors from the AUXIN RESPONSE FACTOR(ARF)family that interact with auxin/indole acetic acid repressors(Aux/IAAs),which themselves form co-receptor complexes with one of six TRANSPORT INHIBITOR1/AUXIN-SIGNALLlNG F-BOX(TIR1/AFB)proteins.Different combinations of co-receptors drive specific sensing outputs,allowing auxin to control a myriad of processes.ARF6 and ARF8 are positive regulators of adventitious root initiation upstream of jasmonate,but the exact auxin co-receptor complexes control-ling the transcriptional activity of these proteins has remained unknown.Here,using loss-of-function mu-tants we show that three Aux/IAA genes,IAA6,IAA9,and IAA 17,act additively in the control of adventitious root(AR)initiation.These three IAA proteins interact with ARF6 and/or ARF8 and likely repress their activity in AR development.We show that TIR1 and AFB2 are positive regulators of AR formation and TIR1 plays a dual role in the control of jasmonic acid(JA)biosynthesis and conjugation,as several JA biosynthesis genes are up-regulated in the tir1-1 mutant.These results lead us to propose that in the presence of auxin,TIR1 and AFB2 form specific sensing complexes with IAA6,IAA9,and/or IAA 17 to modulate JA homeostasis and control AR initiation.

植物激素生长素参与调控植物生长发育的各个过程,包括胚胎发育、器官发生和向性运动等.植物通过协调生长素的合成代谢、极性运输以及信号转导来实现对不同生长发育过程的精准调控.生长素的功能依赖于其信号被感知后经由信号转导通路转换为下游复杂多样的反应.经典的生长素信号转导通路阐明了细胞核内从SCFTIR1/AFB受体到Aux/IAA蛋白的泛素化降解最终通过ARF转录因子调控基因转录的完整生长素响应过程.该核内信号通路揭示了生长素转录调控生长发育的诸多分子机制,但植物生长发育调控过程中仍有许多生长素响应过程无法通过该经典信号通路解析.重点阐述生长素非经典信号通路的调控机制及其对植物生长发育的重要作用,并讨论和展望生长素非经典信号通路研究目前所面临的挑战以及研究前景.