---

作 者 ：霍欢，孙蕾，田芳，陈华民，何晨阳

期 刊 ：植物病理学报 2012年 42卷 6期 页码：620-625

关键词：水稻白叶枯病菌；群体感应；DSF；hrp基因；调控；

Keywords:Xanthomonasoryzaepv.oryzae, quorumsensing, diffusiblesignalfactor, hrpgenes, regulation,

摘 要 ：为了阐明水稻白叶枯病菌(Xanthomonas oryzae pv. oryzae, Xoo)利用DSF信号群体感应(QS)系统对毒性表达进行调控的机理，本研究对编码QS的rpf基因进行了分子鉴定, 分析了Δrpf基因突变体在水稻叶组织中的种群量变化, 利用RT-qPCR方法定量测定了编码T3SS的hrp基因转录本以及rpf基因自身表达。结果表明，rpfF、rpfC和rpfG基因与几种主要植物病原黄单胞菌同源序列高度保守；RpfF是烯脂酰辅酶A水合酶家族成员之一，RpfC含有组氨酸磷酸激酶结构域(HisKA)和磷酸受体结构域(REC)，RpfG含有REC和HD-GYP结构域；Δrpf突变体在水稻叶组织中的种群量及其扩展能力均明显下降; hrp基因转录显著地受到QS调控；rpf基因表达与Xoo种群密度密切相关。因此，Xoo QS系统显著地调控了hrp基因的表达，在QS与T3SS表达之间存在一个信号通路。

Abstract:Bacterial virulence of Xanthomonas oryzae pv. oryzae (Xoo) was previously shown to be regulated by the diffusible signal factor (DSF)-mediated quorum sensing (QS). To further elucidate the regulatory mechanisms, structural features of QS-encoded rpf genes was identified through the bioinfomatic analysis, bacterial population of Δrpf mutants in the infacted leaf tissues of rice was detected, and transcription leavels of type Ⅲ secretion system (T3SS)-encoded hrp genes were measured via RT-qPCR assays in this study. The results showed that rpf genes were found to be highly conserved in plant-pathogenic Xanthomonas spp. RpfF was one of enoyl-CoA hydratase family members, RpfC was structurally featured in N-terminal histidine kinase domain and C-terminal receiver (REC) domain, while RpfG contained REC and HD-GYP domains. Significant decreases in bacterial population and spread in the rice leaf tissues of Δrpf mutants were observed compared with wild-type strain PXO99^A. Transcription of hrp genes was significantly regulated by QS. Expression of rpf genes was regulated by Rpf proteins and bacterial density-dependent. Therefore, it might be suggested that QS regulated T3SS expression via the DSF/c-di-GMP-mediated signaling pathway(s).

---