Auxin steers root cell expansion via apoplastic pH regulation in Arabidopsis thaliana
Auxin steers root cell expansion via apoplastic pH regulation in Arabidopsis thaliana
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DOI：
10.1073/pnas.1613499114
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发表时间：
2017-06-13
影响因子：
11.1
通讯作者：
Busch, Wolfgang
中科院分区：
文献类型：
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作者：
Barbez, Elke;Duenser, Kai;Busch, Wolfgang
植物细胞嵌入细胞壁内，这提供了结构完整性，但也在空间上限制了细胞，因此必须进行修饰以允许细胞扩增。长期存在的酸性生长理论假设生长素触发质外体酸化，从而激活细胞壁疏松酶，使细胞在芽中扩展。有趣的是，这个模型仍然存在很大争议的根，因为生长素在植物发育中的复杂作用，以及在细胞分辨率的研究质外体pH值的技术限制。在这里，我们介绍8-羟基芘-1，3，6-三磺酸三钠盐（HPTS）作为一个合适的荧光pH值指示剂，用于评估质外体pH值，从而酸生长，在拟南芥根的细胞分辨率。使用HPTS，我们证明了细胞壁酸化触发细胞扩张，这与生长素信号的先前增加相关。生长素水平、感知或信号传导的降低消除了细胞外酸化和细胞扩张。这些发现共同表明，内源生长素控制质外体酸化和根细胞伸长的发生。相反，内源性或外源性生长素水平的增加诱导细胞外基质的短暂碱化，减少细胞伸长。受体样激酶FERONIA是这一生理过程所必需的，其在向重力反应期间影响细胞根的扩展。这些发现指出了一个复杂的，大概浓度依赖性的作用，生长素在质外体的pH值调节，指导根细胞扩张和向地性反应的速度。
Plant cells are embedded within cell walls, which provide structural integrity, but also spatially constrain cells, and must therefore be modified to allow cellular expansion. The long-standing acid growth theory postulates that auxin triggers apoplast acidification, thereby activating cell wall-loosening enzymes that enable cell expansion in shoots. Interestingly, this model remains heavily debated in roots, because of both the complex role of auxin in plant development as well as technical limitations in investigating apoplastic pH at cellular resolution. Here, we introduce 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) as a suitable fluorescent pH indicator for assessing apoplastic pH, and thus acid growth, at a cellular resolution in Arabidopsis thaliana roots. Using HPTS, we demonstrate that cell wall acidification triggers cellular expansion, which is correlated with a preceding increase of auxin signaling. Reduction in auxin levels, perception, or signaling abolishes both the extracellular acidification and cellular expansion. These findings jointly suggest that endogenous auxin controls apoplastic acidification and the onset of cellular elongation in roots. In contrast, an endogenous or exogenous increase in auxin levels induces a transient alkalinization of the extracellular matrix, reducing cellular elongation. The receptor-like kinase FERONIA is required for this physiological process, which affects cellular root expansion during the gravitropic response. These findings pinpoint a complex, presumably concentration-dependent role for auxin in apoplastic pH regulation, steering the rate of root cell expansion and gravitropic response.