Functional Characterization of Two Putative DAHP Synthases of AroG1 and AroG2 and Their Links With Type III Secretion System in .

Type three secretion system (T3SS) is essential for to cause disease in host plants and we previously screened AroG1 as a candidate with impact on the T3SS expression. Here, we focused on two putative DAHP synthases of AroG1 and AroG2, which control the first step of the shikimate pathway, a common route for biosynthesis of aromatic amino acids (AAA), to characterize their functional roles and possible links with virulence in . Deletion of or , but not , significantly impaired the T3SS expression both and , and the impact of AroG1 on T3SS was mediated with a well-characterized PrhA signaling cascade. Virulence of the or mutants was completely diminished or significantly impaired in tomato and tobacco plants, but not the mutants. The mutants failed to grow in limited medium, but grew slowly . This significantly impaired growth was also observed in the mutants both and limited medium, but not in mutants. Complementary significantly restored the impaired or diminished bacterial growth, T3SS expression and virulence. Supplementary AAA or shikimic acid, an important intermediate of the shikimate pathway, significantly restored diminished growth in limited medium. The promoter activity assay showed that expression of and was greatly increased to 10-20-folder higher levels with deletion of the other. All these results demonstrated that both AroG1 and AroG2 are involved in the shikimate pathway and cooperatively essential for AAA biosynthesis in . The AroG1 plays a major role on bacterial growth, T3SS expression and pathogenicity, while the AroG2 is capable to partially carry out the function of AroG1 in the absence of AroG1.