Function of NOT9B and the CCR4-NOT complex in phytochrome A dependent light signalling

光敏色素（Phytochromes，phys）是植物中的红色/远红色光感受器，在植物生长和发育对环境变化的适应中起着关键作用。在大多数植物中，光敏色素以小基因家族为代表。PhyA和PhyB是种子植物中主要的光敏色素，参与种子萌发、去黄化、诱导开花和对遮荫的反应等生长发育的调控。PhyB是红光的主要受体，而phyA是感知远红光和极低强度光所必需的。当被光激活时，光敏色素从细胞质转移到细胞核并调节基因表达。光敏色素下游有两条研究充分的抑制光反应的信号通路。光敏色素相互作用因子（PIF）是bHLH转录因子的一个亚组，负调节光信号。与此同时，PHYA-105（COP 1/SPA）E3泛素连接酶复合物的组成性光形态发生1/供应商靶向光信号传导的正调节因子，用于蛋白酶体降解。光激活的光敏色素抑制PIFs和COP 1/SPA，从而诱导响应light.To确定新的信号转导途径下游的光敏色素是潜在的独立的PIFs和COP 1/SPA，我们进行了酵母双杂交筛选蛋白质与光激活的phyA相互作用。在这个屏幕中，我们发现了NOT 9 B，它是CCR 4-NOT复合物的一个组成部分。CCR 4-NOT复合物在酵母、果蝇和哺乳动物中被充分表征，并在RNA代谢和基因表达调控的不同方面发挥作用。然而，对CCR 4-NOT在植物中的功能知之甚少。我们表明，NOT 9 B是一个负调控phyA介导的光反应，我们建议，NOT 9 B与CCR 4-NOT抑制光信号。初步数据显示，光激活的phyA结合N 0 T9 B，从而从CCR 4-N 0 T置换N 0 T9 B，以减轻phyA依赖性光信号传导的抑制。在拟议的项目中，我们希望进一步研究phyA调控CCR 4-NOT的分子机制，并了解CCR 4-NOT如何调节光控基因的表达。

Phytochromes (phys) are red/far-red photoreceptors in plants that play a critical role in adaptation of growth and development to changes in the environment. In most plants, phytochromes are represented by small gene families. PhyA and phyB are the main phytochromes in seed plants involved in regulation of growth and development, including seed germination, de-etiolation, induction of flowering, and responses to canopy shade. PhyB is the primary receptor for red light, while phyA is required for sensing far-red light and light of very low intensity.When activated by light, phytochromes translocate from the cytosol into the nucleus and regulate gene expression. There are two well-investigated signalling pathways downstream of phytochromes that inhibit light responses. The PHYTOCHROME INTERACTING FACTORs (PIFs), a subgroup of the bHLH transcription factors, negatively regulate light signalling. In parallel, the CONSTITUTIVELY PHOTOMORPHOGENIC 1/SUPPRESSOR OF PHYA-105 (COP1/SPA) E3 ubiquitin ligase complex targets positive regulators of light signalling for degradation by the proteasome. Light-activated phytochromes inhibit both PIFs and COP1/SPA and thereby induce responses to light.To identify novel signalling pathways downstream of phytochromes that are potentially independent of PIFs and COP1/SPA, we performed a yeast two hybrid screen for proteins that interact with light-activated phyA. In this screen we found NOT9B, a component of the CCR4-NOT complex. The CCR4-NOT complex is comparably well characterised in yeast, Drosophila, and mammals and plays a role in different aspects of RNA metabolism and regulation of gene expression. However, much less is known about the function of CCR4-NOT in plants. We show that NOT9B is a negative regulator of phyA-mediated light responses and we propose that NOT9B associated with CCR4-NOT represses light signalling. Preliminary data show that light-activated phyA binds NOT9B and thereby displaces NOT9B from CCR4-NOT to relieve repression of phyA-dependent light signalling. In the proposed project we want to further investigate the molecular mechanisms underlying regulation of CCR4-NOT by phyA and understand how CCR4-NOT modulates expression of light-controlled genes.