Regulation of plant development by known and unknown inter-cellular signaling molecules

本研究的目的是了解细胞间信号分子如何调节植物发育。本研究的重点是一个经典的植物激素细胞分裂素的生物合成，感知，信号转导和生物学作用；以及识别新的信号分子。在这个项目开始之前，我们确定了生物合成酶和细胞分裂素的受体，但是，详细的分析还没有完成。在本项目中，我们利用细胞分裂素生物合成异戊烯基转移酶和tRNA修饰异戊烯基转移酶的多个突变体，明确了细胞分裂素的生物合成途径。多重突变还揭示了内源性细胞分裂素的功能，包括一种新的功能，即形成层活性的调节。我们还破坏了所有细胞分裂素受体基因，这提供了细胞分裂素仅由cre1类组氨酸激酶感知的证据。我们探讨了细胞分裂素信号转导的详细机制，表明细胞分裂素调节双向磷接力信号传导。我们还筛选了新的细胞间信号分子。对于第一次筛选，我们过表达编码推定分泌小产物的基因，我们发现了一些引起有趣表型的基因。在这些基因中，我们研究了两个基因的作用，我们将其命名为EPF1和EPF2。EPF1调节气孔形态，EPF2调节表皮细胞密度。虽然EPF1和EPF2的作用时间不同，但它们被相同的一组蛋白质感知和转导，TMM受体样蛋白，er家族受体激酶和MAPKKK， YODA。我们将阐明其他候选信号分子的功能。

The aim of this study is to understand how inter-cellular signaling molecules regulate plant development. This study focused on biosynthesis, perception, signal transduction, and biological role of a classical plant hormone, cytokinin; and identification of new signaling molecules. Before the start of this project, we identified biosynthetic enzymes and a receptor of cytokinins, however, detailed analysis was yet to be done. In this project, we have clarified the biosynthetic routes of cytokinins, using multiple mutants of cytokinin biosynthetic isopentenyltransferases and tRNA modifying isopentenyltransferases. The multiple mutant also revealed the functions of endogenous cytokinins, including a novel function, regulation of cambial activity. We also disrupted all cytokinin receptor genes, which provided evidence that cytokinins are perceived exclusively by CRE1-class histidine kinases. We explored into detailed mechanisms of cytokinin signal transduction, showing that cytokinins regulate bidirectional phosphorelay signaling. We also screened for novel intercellular signaling molecules. For the first screening we overexpressed genes coding for putative secretory small products, and we found a number of genes that cause interesting phenotypes. Among those genes, we examined the roles of two genes, for which we named EPF1 and EPF2. EPF1 regulates the pattern of stomata, and EPF2 regulates epidermal cell density. Although the action-timings of EPF1 and EPF2 differ, they are perceived and transduced by the same set of proteins, TMM receptor-like protein, ER-family receptor kinases, and a MAPKKK, YODA. We will clarify the function of other candidate signaling-molecules.