SUMO蛋白酶ASP1调控光形态建成的分子机制研究

Photomorphogenesis is one of the important plant developmental processes in response to changing light environment. Currently, it has been shown that SUMO modification involves in the regulation of photomorphogenesis, but the complex regulatory mechanisms remains to be elucidated. We have found that SUMO E3 ligase, SIZ1, mediated SUMO modification of COP1 enhances its E3 Ubiquitin ligase activity. We also found that mutations in a SUMO protease, ASP1, cause long-hypocotyl phenotype under blue and far-red light, but short-hypocotyl phenotype under red light, and this phenotype is similar to that of COP1 overexpressing seedlings. Biochemical and genetic evidences indicate that ASP1 regulates photomorphogenesis through its SUMO protease activity. cop1-4 partially suppresses long-hypocotyl phenotype of asp1, inferring that ASP1 regulates photomorphogenesis may through COP1-dependent and –independent pathways. We found that FHY1, a PHYA signaling regulator, is a potential SUMO substrate. Moreover, current research has found that HFR1, a positive regulator of photomorphogenesis, is a SUMO substrate, but whether the modification involves in the regulation of photomorphogenesis remains to be characterized. Research will determine if SUMO modification of FHY1 and HFR1 regulates photomorphogenesis, and analyze if ASP1 mediates deSUMOylation of COP1, FHY1 and/or HFR1. The proposed experiments will characterize molecular mechanisms by which ASP1 regulates photomorphogenesis. The project will provide comprehensive insight into processes by which SUMOylation and deSUMOylation regulate photomorphogenesis.

光形态建成是植物发育过程中响应光信号的重要生物学过程。最近的研究结果表明SUMO化修饰参与此过程，但有待进一步深入研究其复杂的分子调控网络。我们发现SUMO E3连接酶SIZ1介导的COP1的SUMO化修饰增强其泛素E3连接酶活性。我们还发现一个SUMO蛋白酶的功能缺失突变体asp1在蓝光和远红光下具有长下胚轴表型，在红光下具有微弱的短下胚轴表型，此表型与COP1过表达幼苗的表型类似。cop1-4部分抑制asp1的长下胚轴表型，暗示ASP1可能通过COP1依赖和不依赖途径调控光形态建成。前人报道和我们的前期工作表明HFR1和FHY1是可能的SUMO底物。本课题拟鉴定FHY1和HFR1的SUMO化修饰是否调控光形态建成，并探索ASP1是否介导COP1、FHY1及HFR1的去SUMO化修饰，从而深入解析ASP1调控光形态建成的分子机制。本课题将拓展人们对光形态建成中SUMO化修饰功能的认识。

植物通过远红光受体phytochrome A（phyA）感知远红光信号。转运蛋白FAR-RED ELONGATED HYPOCOTYL 1（FHY1) 与受光激活的phyA互作，介导phyA进入细胞核，传递远红光信号。远红光信号转导过强或缺失对植物正常生长发育都是不利的。因此，植物需要精细调控phyA起始的远红光信号转导。远红光诱导FHY1蛋白降解，但具体分子机制目前并不清楚。.我们研究发现FHY1是一个SUMO底物，且第32位和103位赖氨酸是FHY1主要的SUMO化修饰位点。远红光诱导FHY1 的SUMO化修饰，从而促进FHY1蛋白降解。进一步研究发现，远红光条件下，SUMO蛋白酶ASP1与FHY1互作，介导FHY1的去SUMO化修饰。与此结果相符，远红光条件下，asp1-1突变体背景下，FHY1 的SUMO化修饰水平提高，FHY1蛋白降解更快，导致phyA进核速率变缓，主要的光形态建成促进因子HY5蛋白积累减少，导致asp1-1突变体表现出对远红光不敏感的长下胚轴表型。此外，远红光抑制ASP1转录，促进ASP1蛋白降解。综上所述，远红光诱导的FHY1 的SUMO化修饰和ASP1介导的FHY1的去SUMO化修饰，精细调控远红光信号转导。