Interplay between Cell Wall and Auxin Mediates the Control of Differential Cell Elongation during Apical Hook Development

First author: Bibek Aryal; Affiliations: Beijing Forestry University (北京林业大学): Beijing, China

Corresponding author: Rishikesh P. Bhalerao

Differential growth plays a crucial role during morphogenesis. In plants, development occurs within mechanically connected tissues, and local differences in cell expansion lead to deformations at the organ level, such as buckling or bending. During early seedling development, bending of hypocotyl by differential cell elongation results in apical hook structure that protects the shoot apical meristem from being damaged during emergence from the soil. Plant hormones participate in apical hook development, but not how they mechanistically drive differential growth. Here, we present evidence of interplay between hormonal signals and cell wall in auxin-mediated differential cell elongation using apical hook development as an experimental model. Using genetic and cell biological approaches, we show that xyloglucan (a major primary cell wall component) mediates asymmetric mechanical properties of epidermal cells required for hook development. The xxt1 xxt2 mutant, deficient in xyloglucan, displays severe defects in differential cell elongation and hook development. Analysis of xxt1 xxt2 mutant reveals a link between cell wall and transcriptional control of auxin transporters PINFORMEDs (PINs) and AUX1 crucial for establishing the auxin response maxima required for preferential repression of elongation of the cells on the inner side of the hook. Genetic evidence identifies auxin response factor ARF2 as a negative regulator acting downstream of xyloglucan-dependent control of hook development and transcriptional control of polar auxin transport. Our results reveal a crucial feedback process between the cell wall and transcriptional control of polar auxin transport, underlying auxin-dependent control of differential cell elongation in plants.

差异生长在形态建成中扮演至关重要的作用。在植物中，邻近组织的发育以及细胞扩张的局部差异导致了器官层面上的形变，比如说屈曲或弯曲。在幼苗早期发育过程中，下胚轴的弯曲是由顶钩（apical hook）结构中细胞伸长的差异所导致的，从而保护茎尖分生组织免受土壤出芽时可能遭受的损害。植物激素参与顶钩发育，但其如何驱动差异生长还不清楚。本文中，作者利用顶钩发育作为一个试验模型，揭示了在生长素介导的差异细胞伸长过程中，植物激素信号和细胞壁之间的互作。利用遗传学和细胞生物学方法，作者显示细胞壁一个主要组成组分木葡聚糖（xyloglucan）介导上皮细胞的不对称机械特性，该过程对于顶钩的发育是必需的。木葡聚糖存在缺陷的xxt1 xxt2双突植株在差异细胞伸长和顶钩发育过程中均存在缺陷。对于xxt1 xxt2双突植株的分析显示在细胞壁与生长素转运蛋白PINs和AUX1的转录调控之间存在的关联对于建立生长素响应最大值点至关重要，而这对于顶钩内侧细胞伸长的抑制是必需的。遗传学证据鉴定了生长素响应基因ARF2作为一个负调控因子，在木葡聚糖依赖性的顶钩发育调控以及极性生长素转运转录调控的下游发挥作用。本文的研究揭示了一个植物中细胞壁和极性生长素转运转录调控之间的反馈过程，作用于生长素依赖性的差异细胞伸长调控。

通讯：Rishikesh P. Bhalerao (http://icmb.bjfu.edu.cn/rcdw/yjzPIgw/284873.html)

个人简介：1993年，于默奥大学，博士；1994-1996年，德国马克斯-普朗克植物育种研究所，博士后；1997年，瑞典农业大学，博士后。

研究方向：植物周期性生长发育的调控机制：1）多年生木本植物如何感应外界环境的变化：杨树如何感应短日照，并调节其生长和发育的分子基础；2）探究植物细胞伸长的调节机制：草本植物拟南芥细胞延伸和细胞壁重塑的关键调节因子；3）多年生植物生长停止和休眠的分子基础：短日照诱导的生长停止和休眠的分子机制。

doi: https://doi.org/10.1016/j.cub.2020.02.055

Journal: Current Biology

Published date: March 19, 2020

p.s. 植物顶钩发育相关研究链接：

Plant Cell：水杨酸抑制拟南芥顶钩形成的分子机制

Developmental Cell：植物幼苗出土前后顶钩发育状态转变的分子调控机制

Nature：TMK1介导的生长素信号调控植物的顶勾发育