组蛋白去甲基化酶JMJ16调控植物叶片衰老分子机制研究

Currently, it has been shown that a histone methyltransferase involves in leaf senescence regulation through affecting important senescence regulating gene expression, indicating that histone modifications play important role during senescence. It is possible that histone demethylase(s) may also regulates histone methylation status of senescence regulating locus, but remains to be identified. Recently, we have found that the JmjC domain-containing protein, JMJ16, possess H3K4 demethylase activity, and the jmj16 mutation causes early leaf senescence, which could be rescued by the expression of JMJ16. We also found that the expression level of leaf senescence positive regulators, WRKY53, was up-regulated in jmj16, whereas mutation in WRKY53 only could partially rescue early sencesce phenotype of jmj16, indicating that JMJ16 regulates senescence through WRKY53-dependent and -independent pathways. Moreover, it has been shown that JMJ16 is a SUMO substrate. Research will characterize JMJ16-direct target genes and its function, and determine if the JMJ16 is regulated by SUMO modification. The proposed experiments will dissect mechanisms by which the histone demethylase, JMJ16, controls the histone methylation state of senescence locus chromatin to regulate leaf senescence. The project will provide comprehensive insight into processes by which histone methylation/demethylation and SUMOylation regulate leaf senescence in plants and provide foundational resources for research that dissects epigenetic regulation of development.

最近研究发现组蛋白甲基转移酶调控重要叶片衰老调节子组蛋白修饰及叶片衰老，说明组蛋白修饰变化对叶片衰老起重要作用，但组蛋白去甲基化酶调控衰老的分子机制尚不清楚。在前期工作中发现，JMJ16具有H3K4组蛋白去甲基化酶活性，其突变体具有叶片早衰表型，互补后表型得到恢复。叶片衰老正调节因子WRKY53的基因表达水平在jmj16突变体中增高，而WRKY53的突变部分恢复jmj16早衰表型，说明除了WRKY53外，JMJ16还通过其它因子调控叶片衰老。此外，前人的研究发现JMJ16可能是SUMO底物。本课题拟鉴定出JMJ16的重要靶基因及其功能，并探索JMJ16是否受SUMO化修饰调控，从而深入解析JMJ16调控叶片衰老相关重要靶基因表达的表观遗传学分子机制。本课题将拓展人们对植物叶片衰老过程中组蛋白甲基化修饰和SUMO化修饰功能的认识。

伴随着叶片年龄的增长，大量叶片衰老相关基因会被诱导表达。研究发现很多叶片衰老相关基因的诱导表达与H3K4me3水平增高正相关，但其分子调控机制尚不清楚。本研究发现一个拟南芥JmjC功能域包含蛋白JMJ16是H3K4组蛋白去甲基化酶，并通过其酶活性负调控叶片衰老。全基因组分析发现JMJ16直接结合大量叶片衰老相关基因，并降低这些基因的H3K4me3和转录水平。遗传学分析发现JMJ16至少通过两个叶片衰老正调节因子WRKY53和SAG201负调控叶片衰老。在衰老前，JMJ16 与WRKY53 和 SAG201结合，并降低H3K4me3水平，从而抑制WRKY53 和 SAG201 的提前转录。衰老起始时，JMJ16蛋白水平急剧降低，导致WRKY53 和 SAG201 的H3K4me3水平增高，从而诱导WRKY53 和 SAG201的基因表达。综上所述，JMJ16在不同叶片年龄时期蛋白水平的变化是控制叶片衰老相关基因诱导表达时期的重要分子机制。