| Bacterial blight caused by Xanthomonas oryzae pv. oryzae (Xoo) is one of most important bacterial diseases of rice worldwide. Understanding of molecular basis of interactions between rice and Xoo has been promoted by elucidating the roles of genes associated with pathogenesis. Nevertheless, the pathogenicity mechanisms of Xoo are complex, many aspects of virulence and avirulence mechanisms are still not understood. The whole genome sequence of Xoo has provided a very useful tool to study the pathogenicity/virulence mechanisms on genome-wide scale.GacAxoo, a response regulator of TCS and FleQxoo, a transcriptional regulator of flagellar gene cluster have been indentified in our previous study, which function as the regulators during the expression of virulence and motility of Xoo. To understand the regulatory roles and mechanisms of GacAxoo and FleQxoo on the genome scale, the transcriptional profiles ofâ–³gacAxoo,â–³fleQxoo and wildtype PXO99~A were revealed by DNA microarray analysis. Discovery of GacAxoo and FleQxoo regulons will provide important informations for interpretation of regulatory network of gene expression in Xoo.560 genes of Xoo were selected for the microarray fabrication including regulator genes, pathogenicity-related genes, specific genes of Xoo, genes of flagella gene cluster and conserved genes of bacteria according to the genome sequence of KACC10331. With the labeling of cDNA probes with Cy3 and/or Cy5, the transcriptional profiles of PXO99~A,â–³gaeAxoo andâ–³fleQxoo grown in nutrition-rich medium NBY and hrp-inducing medium XOM2 were analysed and compared.17 differentially-expressed genes of PXO99~A were observed in XOM2 compared with NBY. 10 of them are up-regulated while 7 down-regulated. Among the 10 up-regulated genes, 7 of them are hrp genes (hrpB, hrpB1, hrpB3, hrpD6, hrpF) and effector genes (hpal, hpaB), hpal gene is the most obviously up-regulated with an over expression of 13 folds. Thus, the results show that hrp genes of Xoo are significantly induced in XOM2.28 genes of AgacAxoo were found to be differentially expressed when grown in XOM2 compared with PXO99~A. 17 of them are up-regulated, while 12 down-regulated. Among 17 up-regulated genes, 7 of them encode hypothetical proteins and one is vieA gene. These genes may be suppressed by GacAxoo. Among 12 down-regulated genes, there are one gene for GGDEF family protein, one T3SS effector gene hpal, 4 genes of flagella gene cluster (flgC,fliC,fliO,cheA). GacAxoo regulate the expression of hpal and influence the motility through induction of some flagella genes. Furthermore, GacAxoo may influence the biosynthesis and degradation of c-di-GMP through negative or positive regulation of vieA and GGDEF family gene to modify the phenotypes of Xoo.16 differentially-expressed genes ofâ–³fleQxoo cultured in NBY were found in comparison to PXO99~A. 12 of them are up-regulated, while 4 down-regulated. Among 12 up-regulated genes, there are 4 genes encoding components of T2SS, one T2SS effector gene egl, 3 genes encoding extracellular enzyme (polygalacturonase, protease, cellulase S), 3 genes of flagella gene cluster, one GGDEF family gene and one O-antigen biosynthesis gene rbfC. These genes may be negatively regulated and suppressed by FleQXoo. Four down-regulated genes arefliE, hrpB4, one pectinesterase gene and one protease gene. RT-PCR analysis confirmed that fliE is obviously a gene positively-regulated by FleQxoo. Mostly importantly, RT-PCR assay shows that fleQxoo is highly expressed inâ–³fleQxoo, while expression offleQxoo is relatively low in PXO99~A. Therefore, results suggest that expression of fleQxoo may be self-suppressed.In summary, DNA microarray analysis was used to reveal the transcriptional profiles ofâ–³gacAxoo,â–³fleQxoo and PXO99~A, and GacAxoo and FleQxoo regulons and parts of differentially-expressed genes were identified from the pathogen. Further analysis of these informations will help us to interprete the molecular mechanisms of pathogenicity in Xoo. |
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