中文摘要：

[目的]水稻黄单胞水稻致病变种（Xanthomonas oryzae pv.oryzae,简称Xoo）侵染引起水稻白叶枯病,在侵染过程中Xoo可产生胞外多糖（EPS）、胞外酶、黏附因子、T3SS以及其产生的效应因子等毒性因子。细菌第二信使环鸟苷二磷酸（c-di-GMP）的水平在Xoo毒性调控中发挥了重要的作用,而PXO02944是包含REC、GGDEF和EAL结构域的蛋白,是c-di-GMP信号蛋白家族的成员,研究旨在阐明水稻白叶枯病菌的环鸟苷二磷酸信号蛋白家族成员PXO02944的基因结构和功能。[方法]根据PXO02944基因序列信息,以PXO99A基因组DNA为模板,设计引物扩增PXO02944基因全长,将其GGDEF结构域和EAL结构域分别与已经报道的保守的GGDEF结构域或EAL结构域蛋白进行氨基酸序列比对分析;分别扩增PXO02944左右臂片段,将其与目的载体pK18mobsacB载体连接,得到质粒pK2944,将pK2944与pMD-GmR载体回收获得的GmR基因片段进行连接,获得重组质粒pK2944-GmR,用于构建基因突变体。将PXO02944全长基因克隆到载体pHM1上,获得重组质粒pHM1-2944并转化到ΔPXO02944中,即获得互补菌株ΔPXO02944：：C。对野生型菌株、突变体和互补菌株进行表型测定,分析PXO02944基因缺失突变对Xoo致病性和EPS产生、生物膜形成、胞外酶活性和鞭毛运动性的影响,并通过qRT-PCR方法测定EPS合成基因和毒性相关基因的表达。[结果]用特异性引物进行PCR扩增,成功地从野生型菌株PXO99A中克隆了PXO02944;生物信息学分析发现,PXO02944蛋白具有磷酸化信号接收的REC输入结构域和GGDEF、EAL输出结构域,但GGDEF和EAL结构域保守序列发生了突变。与野生型菌株PXO99A相比,虽然PXO02944突变体胞外纤维素酶和木聚糖酶活性、鞭毛运动性都无明显变化,但其对水稻的致病性、EPS产生和生物膜形成能力显著增强,T3SS调控基因hrpG和EPS合成基因gumG的转录水平也明显升高。[结论]应答调控因子PXO02944负调控了水稻

英文摘要：

[Objective]Xanthomonas oryzae pv. oryzae（Xoo） is the causing pathogen of bacterial blight of rice. Xoo can use extracellular polysaccharide（EPS） and enzymes, T3SS and its effectors for sucessful infection of rice. It has been shown that cyclic di-GMP signaling plays an important role in regulation of virulence in Xoo. PXO_02944, the GGDEF, EAL and REC domain containing protein, belongs to c-di-GMP signaling protein family. The objective of this study is to demonstrate the structure and function of the PXO_02944 in regulation of virulence expression of Xoo. [Method] Based on the sequences of PXO_02944, the specific primers were designed to amplify the full length of gene using the genomic DNA of the wildtype strain PXO99A as the template. In silico analysis of the GGDEF and EAL domains of PXO_02944 with the conserved ones from other bacteria were done. Then the upstream and downstream fragments of PXO_02944 were amplified, and ligated to vector pK18mobsacB to get the plasmid pK2944. Then a Gm resistance gene（GmR） was inserted into pK2944 resulting in plasmid pK2944-GmR to construct the gene deletion mutation by marker exchange. The full length of PXO_02944 was cloned and ligated into the vector pHM1, and the plasmid was electroporated into ΔPXO_02944 to get the complementory strain. The virulence, EPS production, enzymatic activities, biofilm formation and motility of ΔPXO_02944 were tested compared with PXO99A, ΔPXO_02944 and complemented strain. And the expression of EPS production and virulence related genes were analyzed.[Result]Bioinformatic analysis indicated that PXO_02944 was a response regulator of two-component regulatory system（TCS）, which contained the REC input domain and the GGDEF and EAL output domains. In the mutant, PXO_02944 was deleted by replacing of the GmR. The mutation in PXO_02944 led to significant increases in bacterial virulence on rice, EPS production, biofilm formation, hrpG and gumG gene transcripts compared to PXO99A. Interestingly, no changes in activities of cell