拟南芥P2SA4整合强蓝光和糖信号调节下胚轴向光弯曲的机制分析

Blue light receptor PHOT1 and PHOT2 regulate high blue light (HBL)-induced hypocotyl phototropism in Arabidopsis, and this signaling pathway involves NPH3, RPT2, PKSs and depends on the variation of intracellular Ca2+. Cryptochromes regulate phototropins-mediated phototropism maybe through inducing the expression of RPT2, suppressing the expression of ABCB19 and reduction in the gibberellic acid (GA). GA and sugar antagonistically mediate degradation of DELLAs to release PIFs and regulate gene expression. We previously identified P2SA4 (PHOT2 Signaling Associated 4), a WD40 transcription factor located in nuclear, specifically regulated HBL-induced hypocotyl phototropism and auxin asymmetric distribution in the hypocotyl, and the process was dependent on sugar supply. However, most of the functions and mechanisms of P2SA4 are still unknown, such as how P2SA4 is activated, what is its role on lateral auxin distribution, how P2SA4 integrate blue light and sugar signaling to modulate its activity? In this study, we will study the mode of P2SA4 activated by HBL and sugar signaling and the expression of its target genes. We will explore the relationship between P2SA4 and NPH3, RPT2, PKSs, P2SA1, COP1 and HY5 which mediate phototropism or involved CRYs mediated- photomorphogenesis under HBL. The role of target genes regulated by P2SA4 in regulating intracellular Ca2+ changes and lateral auxin distribution will be analyzed, thus to elucidate the mechanism of P2SA4 integrating of blue light and sugar signaling in regulating hypocotyl phototropism, and provide clue for understanding the crosstalk of PHOTs and CRYs in controlling HBL-induced hypocotyl phototropism.

蓝光受体向光素PHOT1和PHOT2调节强蓝光诱导的拟南芥下胚轴向光弯曲，该信号通路涉及NPH3、RPT2和PKSs蛋白及胞内钙的变化调控。我们前期筛选到一个WD40类转录因子P2SA4，定位于细胞核，响应强蓝光和糖信号调节生长素在下胚轴中的侧向梯度形成和下胚轴向光弯曲反应。然而P2SA4的激活模式、其整合强蓝光与糖信号的机制以及影响生长素侧向梯度形成的机理并不清楚。本项目拟通过解析P2SA4应答强蓝光和糖信号的激活机制及对下游靶基因表达的调控模式，分析其与蓝光激活隐花色素CRYs信号通路的调控关系；研究P2SA4靶基因与NPH3、RTP2、COP1和HY5等光信号通路中关键组份之间关系；鉴定P2SA4靶基因在强蓝光诱导胞内Ca2+ 变化和生长素侧向运输中的功能。该研究将揭示P2SA4整合强蓝光和糖信号调控下胚轴弯曲的机制，明确CRYs在PHOTs调节强蓝光诱导下胚轴向光弯曲中的贡献机制。

蓝光受体向光素phot1和phot2以功能冗余的方式调节拟南芥下胚轴向强蓝光弯曲反应，限制了对phot2调节拟南芥强蓝光反应机制的研究。课题前期通过EMS诱变phot1突变体，获得一个响应强蓝光调节拟南芥下胚轴向光弯曲的WD40类转录因子P2SA4。本项目研究P2SA4应答强蓝光调节拟南芥下胚轴向光弯曲的机制，发现：1.P2SA4特异调节拟南芥向强蓝光弯曲反应，该过程受蔗糖影响；2.P2SA4分别与CRY1和E3泛素连接酶LRB2互作，通过26S蛋白酶体途径促进CRY1降解，解除CRY1对拟南芥向强蓝光弯曲的抑制；3.外源GA、eBL和IAA能够恢复p2sa4突变体和CRY1过表达植株向强蓝光弯曲，揭示P2SA4促进CRY1降解进而解除CRY1对激素信号的抑制。4.蔗糖拮抗P2SA4行为，通过稳定CRY1和RGA进而抑制拟南芥向强蓝光弯曲。项目证明了P2SA4响应强蓝光通过促进CRY1降解，解除CRY1对GA、eBL和IAA信号抑制，促进拟南芥下胚轴向强蓝光弯曲。此外，解析了JAC1与RPT2协同抑制phot2调节植物向强蓝光弯曲的机制，明确了雷蒙德氏棉和亚洲棉响应强蓝光差异调节向光弯曲的机制，阐述了RPT2调节phot1介导强蓝光下叶绿体聚光运动的机制。