Functional in planta analysis of a plasma membrane-associated brassinosteroid response pathway

油菜素内酯（BRs）是植物生长发育必需的激素。拟南芥中BR反应途径的普遍接受的“标准”模型包括质膜受体BRI1感知BR，其与辅助受体BAK1寡聚化，随后激活信号级联，最终导致BR反应基因的表达。我们最近发现了一种快速的、不依赖于基因表达的BR反应途径，它可以改变质膜电位（Em）和细胞壁的扩张，这两个过程都是细胞伸长生长之前的关键过程。该信号反应途径至少包括BRI1和质膜p型atp酶。然而，这一途径背后的分子机制尚不完全清楚。因此，利用质膜的Em和细胞壁的膨胀作为定量的细胞生理读数，我们旨在解决以下问题：(i)使BRI1激活质膜中p - atp酶的分子决定因素是什么；（ii）酪氨酸或丝氨酸/苏氨酸的磷酸化是否起作用；（iii）“标准”BR信号通路的其他元素和（iv）需要进一步的伸长生长促进物质？大多数拟议的实验将在活的植物细胞中进行，在定量水平上应用新的光谱显微镜技术。

Brassinosteroids (BRs) are essential hormones for plant growth and development. The generally accepted “standard” model of the BR response pathway in Arabidopsis includes the perception of BR by the plasma membrane receptor BRI1, its oligomerisation with the coreceptor BAK1 followed by the activation of a signalling cascade finally resulting in the expression of BR-responsive genes. We recently identified a fast, gene expressionindependent BR response pathway that modifies the plasma membrane potential (Em) and the expansion of the cell wall – both crucial processes preceding cell elongation growth. This signal-response pathway comprises at least BRI1 and the plasma membrane P-type ATPase. However, the molecular mechanisms underlying the pathway are not yet fully understood. Using the Em of the plasma membrane and the expansion of the cell wall as quantitative cell physiological readouts, we therefore aim to address the following questions: (i) what are the molecular determinants which enable BRI1 to activate the P-ATPases in the plasma membrane; (ii) does phosphorylation of tyrosines or serine/threonine play a role; (iii) are other elements of the “standard” BR signalling pathway and (iv) further elongation growth-promoting substances required? The majority of the proposed experiments will be carried in living plant cells at quantitative level applying novel spectro-microscopic technologies.