Search

Eight putative avirulence genes in Xanthomonas campestris pv. campestris (Xcc) strain 8004 were characterized by Tn5gusA5 mutagenesis and gene expression analysis. The virulence test of mutants on Chinese radish showed that all mutants in individual avr genes except avrBs2 mutant were not significantly different from the wild type in virulence. The avrBs2 mutant showed reduced virulence and bacterial growth in planta. Gene expression analysis using β-glucuronidase as reporter indicated that avrBs1 . 1, avrBs1 avrXccB, avrXccC, avrXccE1 were regulated by hrpG, whereas avrXccA1, avrXccA2 and avrBs2 were not. RT-PCR analysis showed that all hrpG-regulated genes except avrBs1 were also regulated by hrpX. In addition, it was demonstrated that avrBs1 was responsible for elicitation of a type III dependent hypersensitive reaction (HR) on nonhost plant pepper ECW-10R, and wild type Xcc 8004 was unable to cause HR on pepper ECW-20R. [ABSTRACT FROM AUTHOR]

The expression of hrp genes in Xanthomonas is regulated by hrpG, an OmpR-type transcriptional activator, and can be induced by artificial mimic medium XVM2, but repressed in rich medium NYG. In this study, a rote-specific mutation of hrpG ha Xanthomonas campestris pv. campestris (Xcc) was generated by PCR-directed point mutagenesis and was characterized by in phenotype and transcriptional expression analyses. The results indicated that the E45K mutated hrpG rendered all the hrp genes expressing constitutively in the suppression medium NYG. Plant test showed that mutated hrpG enhanced the timing and intensity of hypersensitive reaction (HR) on the nonhost plant pepper, but did not affect the growth of Xcc in both culture medium and plants. The E45K mutation did not cause significant changes of production of exopolysaccharide, extracellular cellulase and amylase, but it inhibited the secretion of extracellular protean. This mutant 8004* is more suitable than the wild type for identifying hrp-dependent effectors in vitro and studying the transcriptional regulation genome-wide. [ABSTRACT FROM AUTHOR]