拟南芥P1SA1/2调控PHOT1应答强蓝光抑制下胚轴向光弯曲机制分析

Blue light receptor PHOT1 and PHOT2 regulate hypocotyl phototropism induced by high blue light in functional redundancy. Given that the phenotype of rpt2 single mutant is similar with double mutant phot1 phot2 and rpt2 phot2, but rpt2 phot1 double mutant shows normal phototropic response, we infer that PHOT1 has dual opposite function with inducing and inhibiting hypocotyl phototropic response. However, the corresponding detailed mechanism of PHOT1-mediated inhibition remains to be elucidated. We have screened mutant p1sa1 and p1sa2 with normal phototropism from EMS mutagenesis of rpt2-2 and confirmed that P1SA1 and P1SA2 encode a protein kinase and a membrane protein respectively, and function in regulating PHOT1-mediated inhibition of phototropism. With multidisciplinary research technology, we will investigate the regulation mode and substrate of P1SA1 kinase, the physiological processes of P1SA1 and P1SA2 in regulating PHOT1-mediated inhibition and its regulating relationship with PHOT2. We will explore the relationship between P1SA1/P1SA2-mediated inhibition and the key components involved in phototropism induced by high blue light, and eventually elucidate the mechanism of P1SA1 and P1SA2 regulating PHOT1-mediated inhibition. This study will uncover the self-regulation mechanism of plant to reduce high light damage.

蓝光受体PHOT1在强蓝光诱导的下胚轴向光弯曲反应中具有促进和抑制双重作用，但其抑制机理研究仍很缺乏。前期研究表明，拟南芥rpt2，phot1phot2和rpt2phot2突变体皆缺失向光弯曲，而rpt2phot1突变体表现正常的向光反应，暗示在RPT2上游存在受PHOT1调节的抑制旁路。基于此，本项目以rpt2突变体为材料，诱变筛选向光弯曲恢复株，克隆到PHOT1下游信号组份蛋白激酶P1SA1和膜蛋白P1SA2。在此基础上，系统分析P1SA1/2调控PHOT1抑制的向光弯曲反应的遗传学基础，解析其调节模式；探讨P1SA1/2响应PHOT1抑制强光反应的生物学过程及其与PHOT2的相互调控；明确P1SA1/2与光诱导弯曲信号传递中关键组份的相互关系，回答PHOT1是如何应答强光进而差异启动促进和抑制这两个不同的生理过程，有望揭示植物应答强光避免伤害的自我调节机制。

蓝光受体PHOT1在强蓝光诱导的下胚轴向光弯曲反应中具有促进和抑制双重作用，但其抑制机理研究仍很缺乏。前期研究表明，拟南芥rpt2，phot1phot2和rpt2phot2突变体皆缺失向光弯曲，而rpt2 phot1突变体表现正常的向光反应，暗示在RPT2上游存在受PHOT1调节的抑制旁路。基于此，项目前期以rpt2突变体为材料，诱变筛选向光弯曲恢复株，克隆到PHOT1下游信号组份蛋白P1SA1和P1SA2。本项目研究拟南芥P1SA1与P1SA2调节强蓝光抑制黄化苗下胚轴向光弯曲的机制，发现：1.不同于rpt2-2突变体的表型，双突变体 rpt2-2 p1sa1-1和rpt2-2 p1sa2-1表型类似于rpt2-2 phot1表现向强蓝光弯曲，遗传分析显示P1SA1和P1SA2位于蓝光受体PHOT1下游调节强光抑制下胚轴向光弯曲反应；2. P1SA1促进强蓝光诱导的PHOT1降解可能受NPH3和RPT2共同调控；3. P1SA1与UBQ10的第五和第六个UBQ功能域互作招募UBQ10与PHOT1互助形成复合体，促进PHOT1降解，以解除PHOT1调节的强光抑制效应；4. JAC1与RPT2互作协同抑制PHOT2介导下胚轴弯曲反应增强强光抑制效应。项目提出并证实强蓝光诱导PHOT1的降解是解除强光抑制效应的主要途径，P1SA1通过和NPH3/RPT2互作招募UBQ10进而通过泛素化途径降解PHOT1。同时发现RPT2还可以与JAC1互作协同抑制PHOT2信号传递，该过程可能不依赖于PHOT1。该研究表明了随着蓝光强度的增强，PHOT1从正调节黄化苗下胚轴向光弯曲到抑制向光弯曲的转变以及解除PHOT1抑制的可能机制，寻找并证明了抑制PHOT2调节下胚轴向光弯曲的两个关键调节子RPT2和JAC1。上述研究结果初步揭示植物应答强光避免伤害的自我调节机制。