The Arabidopsis receptor kinase STRUBBELIG regulates the response to cellulose deficiency

Plant cells are encased in a semi-rigid cell wall of complex build. As a consequence, cell wall remodeling is essential for the control of growth and development as well as the regulation of abiotic and biotic stress responses. Plant cells actively sense physico-chemical changes in the cell wall and initiate corresponding cellular responses. However, the underlying cell wall monitoring mechanisms remain poorly understood. In Arabidopsis the atypical receptor kinase STRUBBELIG (SUB) mediates tissue morphogenesis. Here, we show that SUB-mediated signal transduction also regulates the cellular response to a reduction in the biosynthesis of cellulose, a central carbohydrate component of the cell wall. SUB signaling affects early increase of intracellular reactive oxygen species, stress gene induction as well as ectopic lignin and callose accumulation upon exogenous application of the cellulose biosynthesis inhibitor isoxaben. Moreover, our data reveal that SUB signaling is required for maintaining cell size and shape of root epidermal cells and the recovery of root growth after transient exposure to isoxaben. SUB is also required for root growth arrest in mutants with defective cellulose biosynthesis. Genetic data further indicate that SUB controls the isoxaben-induced cell wall stress response independently from other known receptor kinase genes mediating this response, such as THESEUS1 or MIK2. We propose that SUB functions in a least two distinct biological processes: the control of tissue morphogenesis and the response to cell wall damage. Taken together, our results reveal a novel signal transduction pathway that contributes to the molecular framework underlying cell wall integrity signaling.

植物细胞被结构复杂的半刚性细胞壁所包裹。因此，细胞壁重塑对于调控植物生长发育以及响应非生物与生物胁迫均至关重要。植物细胞可主动感知细胞壁的物理化学变化，并启动对应的细胞响应。然而，其潜在的细胞壁监测机制仍不甚明晰。在拟南芥中，非典型受体激酶STRUBBELIG（SUB）介导组织形态发生过程。本研究发现，SUB介导的信号转导同样可调控因细胞壁核心碳水化合物组分——纤维素合成受阻所引发的细胞响应。在外源施加纤维素合成抑制剂异恶草胺（isoxaben）后，SUB信号通路会影响细胞内活性氧的早期迸发、胁迫基因的诱导表达，以及异位木质素与胼胝质的积累。此外，本研究数据表明，SUB信号通路对于维持根表皮细胞的大小与形态，以及短暂暴露于异恶草胺（isoxaben）后根系生长的恢复均不可或缺。在纤维素合成存在缺陷的突变体中，SUB同样是根系生长停滞所必需的。遗传学数据进一步显示，SUB调控异恶草胺诱导的细胞壁胁迫响应的通路，与其他已知的介导该响应的受体激酶基因（如THESEUS1与MIK2）相互独立。我们提出，SUB至少参与两类截然不同的生物学过程：组织形态发生调控以及细胞壁损伤响应。综上，本研究结果揭示了一条全新的信号转导通路，为解析细胞壁完整性信号转导的分子机制补充了新的理论框架。