Auxin‐mediated Aux/IAA‐ARF‐HB signaling cascade regulates secondary xylem development in Populus

First author: Changzheng Xu; Affiliations: Southwest University (西南大学): Chongqing, China

Corresponding author: Keming Luo

Wood development is strictly regulated by various phytohormones and auxin plays a central regulatory role in this process. However, it remains obscure how the auxin signaling is transducted in developing secondary xylem during wood formation in tree species. Here, we identified an Aux/INDOLE‐3‐ACETIC ACID 9 (IAA9)‐AUXIN RESPONSE FACTOR 5 (ARF5) module in Populus tomentosa as a key mediator of auxin signaling to control early developing xylem development. PtoIAA9, a canonical Aux/IAA gene, is predominantly expressed in vascular cambium and developing secondary xylem and induced by exogenous auxin. Overexpression of PtoIAA9m encoding a stabilized IAA9 protein significantly represses secondary xylem development in transgenic poplar. We further showed that PtoIAA9 interacts with PtoARF5 homologs via the C‐ erminal III/IV domains. The truncated PtoARF5.1 protein without the III/IV domains rescued the PtoIAA9m‐ esulting defective phenotypes. Expression analysis showed that the PtoIAA9‐PtoARF5 module regulated the expression of genes associated with secondary vascular development in PtoIAA9m‐ and PtoARF5.1‐overexpressing plants. Furthermore, PtoARF5.1 could bind to the promoters of two Class III homeodomain‐leucine zipper (HD‐IP III) genes PtoHB7 and PtoHB8 to modulate secondary xylem formation. Taken together, our results suggest that the Aux/IAA9‐ARF5 module is required for auxin signaling to regulate wood formation via orchestrating the expression of HD‐IP III transcription factors in poplar.

木材的发育受到多个激素的调控，而生长素在其中扮演着一个非常重要的作用。然而，林木的木材形成过程中生长素在发育的次生木质部中的信号转导还不是很清楚。本文中，作者在毛白杨中鉴定到了一个IAA9-ARF5模块作为生长素信号转导的核心调控子，控制木质部的早期发育。PtoIAA9属于典型的Aux/IAA基因，主要在维管形成层和发育中的木质部中表达，并且受到外源生长素处理的诱导。过表达PtoIAA9m基因编码一个稳定的IAA9蛋白显著抑制转基因杨树中的次生木质部的发育。进一步的试验显示PtoIAA9与PtoARF5同源蛋白通过C末端III/IV结构域发生互作。将III/IV结构域截掉了的PtoARF5.1蛋白能够拯救PtoIAA9m所导致的缺陷表型。表达分析显示PtoIAA9‐PtoARF5模块在PtoIAA9m和PtoARF5.1过表达植株中调控参与次生维管发育相关基因的表达。此外，PtoARF5.1能够结合到两个HD‐IP III基因PtoHB7和PtoHB8的启动子区，进而调控次生木质部的形成。综上，本文的研究揭示了杨树中，Aux/IAA9‐ARF5模块通过HD‐IP III转录因子作用于调控木材形成的生长素信号转导。

通讯：罗克明 (http://smkxxy.swu.edu.cn/viscms/smkxxyidex/jiaoshou3736/20151008/242191.html)

个人简介：1995–1999年，西南师范大学生命科学学院，学士；1999–2004年，西南农业大学与美国康涅狄格大学联合培养，博士；2001–2003年，美国康涅狄格大学植物系，访问学者；2007–2008年，美国密歇根理工大学生物技术中心，博士后。

研究方向：以杨树、拟南芥为模式植物，研究植物在干旱、盐碱、高光等逆境下适应性生长的分子机制和维管组织次生生长发育的遗传调控机理，筛选和培育具有重要经济价值和生态价值的林木新品种。

doi: https://doi.org/10.1111/nph.15658

Journal: New Phytologist

First Published: 24 December, 2018