H3K9组蛋白去甲基化酶JMJ27调控旱胁迫响应的分子机制研究

It has been shown that activation of drought stress-responsive gene expression is corelated with the reduced H3K9me2 level, but how H3K9me2 and its modifying enzymes regulate drought stress response remains unknown. Recently, we have found that the JmjC domain-containing protein, JMJ27, possess H3K9 demethylase activity, and positively regulates drought stress response through its activity. Moreover, we have also found that the JMJ27 interacts with two known proteins, drought stress positive regulator CAT3 and drought stress negative regulator RPN1a. The jmj27 mutant exhibits drought sensitive and impaired stomatal closure phenotype, and this phenotype is similar to that of cat3 loss-of-function mutant, inferring that JMJ27 and CAT3 may cooperatively regulate drought stress response. Drought stress did not affect the expression level of JMJ27, but promoted accumulation of JMJ27. It has been shown that ABA down-regulates expression level of RPN1a, a 26S proteasome subunit, and rpn1a loss-of-function mutants exhibt drought tolerant phenotype, which is opposite to that of jmj27, infering that drought stress regulates JMJ27 protein stability may through RPN1a-dependent pathways. Research will determine drought stress response-related JMJ27-direct target genes, dissect mechanisms by which the JMJ27 and its interacting partners control drought stress response. The project will provide comprehensive insight into processes by which H3K9 methylation regulates drough stress response in plants.

研究表明旱胁迫响应基因的表达与H3K9me2水平下降相关，但目前尚不清楚H3K9me2修饰及其修饰酶调控旱胁迫响应的分子机理。在前期工作中发现JMJ27具有H3K9组蛋白去甲基化酶活性，并通过其活性正调控旱胁迫响应。此外，JMJ27与已知的旱胁迫正调节因子CAT3和旱胁迫负调节因子RPN1a互作。jmj27具有旱胁迫敏感和气孔关闭不敏感等表型，此表型与cat3表型类似，暗示JMJ27可能与CAT3协同调控旱胁迫响应。旱胁迫不影响JMJ27的转录水平，但诱导其蛋白积累。据报道ABA抑制26S蛋白酶体亚基RPN1a的表达水平，且rpn1a突变体具有与jmj27相反的旱胁迫相关表型，暗示旱胁迫可能通过RPN1a调控JMJ27的蛋白稳定性。本课题拟鉴定出JMJ27的重要靶基因、JMJ27及其互作蛋白调控植物抗旱反应的机理。本课题将拓展人们对植物旱胁迫响应过程中H3K9组蛋白甲基化修饰功能的认识。

组蛋白H3K9me2修饰主要富集在异染色质区域，促进转座子及其他重复序列的沉默。有趣的是H3K9me2修饰还富集在基因区域，且干旱胁迫响应基因的诱导表达与H3K9me2修饰水平降低相关，但H3K9me2修饰调控干旱胁迫响应的分子机理尚不清楚。.我们发现一个JmjC功能域包含蛋白JMJ27的突变体具有旱敏感表型。进一步研究发现JMJ27具有组蛋白H3K9去甲基化酶活性，并通过其酶活性正调控植物干旱胁迫响应。利用RNA-seq分析，鉴定出JMJ27调控靶基因GOLS2和RD20（两个旱胁迫响应的正调节因子）。遗传学分析表明JMJ27部分通过GOLS2和RD20调节干旱胁迫响应。我们还利用蛋白组学等手段鉴定出26S蛋白酶体的一个亚基RPN1a与JMJ27互作，并负调控JMJ27积累。在正常条件下，JMJ27与GOLS2和RD20基因组结合，并通过降低这些基因的H3K9me2水平，抑制这些基因的沉默。而在干旱胁迫条件下，RPN1a蛋白水平下降，导致JMJ27在GOLS2和RD20基因位点的丰度增高，从而增强了这些基因的转录激活。