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.

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.

Auxin,one of the first identified and most widely studied phytohormones,has been and will re-main a hot topic in plant biology.After more than a century of passionate exploration,the mys-teries of its synthesis,transport,signaling,and metabolism have largely been unlocked.Due to the rapid development of new technologies,new methods,and new genetic materials,the study of auxin has entered the fast lane over the past 30 years.Here,we highlight advances in understanding auxin signaling,including auxin perception,rapid auxin responses,TRANSPORT INHIBITOR RESPONSE 1 and AUXIN SIGNALING F-boxes (TIR1/AFBs)-mediated transcriptional and non-transcriptional branches,and the epi-genetic regulation of auxin signaling.We also focus on feedback inhibition mechanisms that prevent the over-amplification of auxin signals.In addition,we cover the TRANSMEMBRANE KINASE-mediated non-canonical signaling,which converges with TIR1/AFBs-mediated transcriptional regulation to coordinate plant growth and development.The identification of additional auxin signaling components and their regulation will continue to open new avenues of research in this field,leading to an increasingly deeper,more comprehensive understanding of how auxin signals are interpreted at the cellular level to regulate plant growth and development.

Callus induction, which results in fate transition in plant cells, is considered as the first and key step for plant regeneration. This process can be stimulated in different tissues by a callus-inducing medium (CIM), which contains a high concentration of phyto-hormone auxin. Although a few key regulators for callus induction have been identified, the multiple aspects of the regulatory mechanism driven by high levels of auxin still need further investigation. Here, we find that high auxin induces callus through a H3K36 histone methylation-dependent mechanism, which requires the methyltransferase SET DOMAIN GROUP 8 (SDG8). During callus induction, the in-creased auxin accumulates SDG8 expression through a TIR1/AFBs-based transcriptional regu-lation. SDG8 then deposits H3K36me3 modifications on the loci of callus-related genes, including a master regulator WOX5 and the cell proliferation-related genes, such as CYCB1.1. This epigenetic regulation in turn is required for the transcriptional activation of these genes during callus formation. These findings suggest that the massive transcriptional reprogram-ming for cell fate transition by auxin during callus formation requires epigenetic modifications including SDG8-mediated histone H3K36 methylation. Our re-sults provide insight into the coordination between auxin signaling and epigenetic regulation during fundamental processes in plant development.