Microarray/Mutation Studies to Identify New Virulence Genes in Erwinia Chrysanthemi

University Of California-Riverside, Riverside CA

Investigators

Abstract

Substantial empirical evidence indicates that pathogenic bacteria express virulence genes at high levels only when they infect a host. Indeed, it is likely that pathogens that can exist in various alternative ecological niches express unique gene sets in all of them. Using microarray and in vivo expression technique (IVET), the gene expression pattern of a plant pathogenic bacterium, Erwinia chrysanthemi, grown in its leaf host as compared to growth in laboratory culture medium was studied. These results have offered powerful insights into new pathogen genes that are important for virulence. In particular, a substantial number of class III virulence genes were upregulated in planta. The class III genes do not appear to be directly involved in damaging the host, as is the case with class I and II virulence genes, but are probably important in adapting the pathogen to survive and grow in the host environment. Mutations in several of the plant upregulated E. chrysanthemi genes were constructed. Mutations in a putative class I virulence gene encoding a previously unidentified peptide synthase, and two novel class III virulence genes, all greatly reduced virulence of the bacteria on host African violet leaves. The objectives of this project are to: (i) continue screening of host upregulated genes by IVET; (ii) perform systematic mutation and virulence assays of host upregulated genes obtained from IVET and previous microarray assays; and (iii) identify virulence genes regulated by the pathogenicity gene cluster hrp of E. chrysanthemi by functional cloning in E. coli cells carrying the cloned E. chrysanthemi hrp gene cluster. These cross-complementary approaches are expected to identify new genes important for bacterial virulence on plant hosts.