必需调控系统PhoPQ快速起源及与细菌有丝分裂的调控关系

phoP-phoQ分别编码反应调节蛋白和组氨酸激酶，是调控细菌致病因子表达的关键双组分信号转导系统。前期研究发现：在水稻黄单胞菌（Xoo）中，phoP-phoQ是非必需基因。而在极近缘的野油菜黄单胞菌（Xcc）中，phoP-phoQ是必需基因，突变后细胞分裂异常、致死，表明phoP-phoQ及其调控功能发生了快速分化。为解析该进化现象的分子机制，项目拟利用比较转录组学和分子遗传分析方法，在Xcc和Xoo中筛选、鉴定与转录因子PhoP发生直接相互作用的顺式调控元件，对比PhoP-PhoQ调控元的差异。在此基础上，通过异源表达、蛋白磷酸化和突变分析等方法，探索在PhoP-PhoQ调控功能的快速分化过程中，转录因子-顺式调控元件重联接（rewiring）和在细菌有丝分裂中的调控机制，阐明在Xcc中，phoP-phoQ进化为必需基因的原因。研究将为新调控基因的起源和病原细菌的快速进化提供分子基础。

The two-component signal transduction system PhoP-PhoQ is a critical regulatory mechanism in controlling expression of bacterial virulence factors. Among them, phoP encodes a cytoplasmic response regulator whereas phoQ encodes a membrane-bound histidine kinase. Previous investigations have revealed that phoP-phoQ genes are highly conserved between two close-relative phytopathogenic bacteria: Xanthomonas oryzae pv. oryzae (Xoo) and X. campestris pv. campestris (Xcc). However, in Xoo, phoP-phoQ are mutatable and non-essential genes, wherease in Xcc, phoP-phoQ are bona fide essential genes that cause lethal phenotype and abnomality of cellular mitosis after being mutated. These results suggested that an accelerated evolution taken place for phoP-phoQ in Xanthomonas.In order to deciphering the molecular basis of phoP-phoQ evolution, the present project will employ genetic and comparative transcriptomic methods to identify the consensus sequences which are the cis-regulatory elements of transcription factor PhoP. Based on this result, the differences between regulons of PhoP of Xcc and Xoo will be compared. By identifying the downstream essential gene that is specifically modulated by PhoP of Xcc, the project will reveal the fundamental role of rewiring between transcription factor and cis-regulatory elements during the accelarated evolution of essential genes. The results of this project will have broad interest for understanding the origin of novel regulatory genes and evolution of bacterial pathogens.