I am very interested in plant bacterial pathogenesis and the mechanisms by which they utilize host resources for their own growth and survival. Genome sequence and resources for many plant pathogenic bacteria are now available like- Xanthomonas, Pseudomonas, Ralstonia including many of their model plant host system such as rice, Arabidopsis. I want to identify both host and pathogen factors that promote and suppress pathogenesis.

a) Role of cell-cell signaling in Xanthomonas virulence

Several plant pathogenic bacteria make extracellular signaling molecules in a density dependent manner to co-ordinate regulation of virulence factor synthesis. The phenomena called as quorum sensing (Fig. 1) is an important trait in the pathogenesis of many plant pathogenic bacteria like .Xanthomonas, Pseudomonas.

Xanthomonas makes an extracellular fatty acid like signaling molecule called as Diffusible Signaling Molecule (DSF), which appears to differ in structure as well as mode of action in regulating virulence functions across closely related Xanthomonas. We will use both forward and reverse genetics approach to identify role of DSF like signaling molecules in Xanhomonas like- Rice pathogen.s= Xanthomonas oryzae pv. oryzae, Xanthomonas oryzae pv. oryzaecola., crucifer pathogen= Xanthomonas campestris pv. campestris (Xcc) and the tomato pathogen=Xanthomonas campestris pv. vesicatoria (XCV).

B) Role of di-Cylcic GMP as intracellular signaling molecule in plant pathogens


Recent advances in plant-pathogen interaction as elucidated the role of cyclic di-GMP as an intracellular signaling molecule which couples extracellular quorum sensing signal and is involved in variety of process like-Biofilm formation, motility, quorum sensing and regulation of virulence gene expression (Fig. 2). Three protein domains-HD-GYP, GGDEF and EAL have been implicated in the synthesis and degradation of di-Cyclic GMP (Fig. 3). Genome analysis indicates that various Xanthomonas have proteins with potential di-Cyclic GMP modulating activity.

Interestingly several two component signal transduction systems have the di-cyclic GMP modulating domains, role of these in virulence and adaptation inside the plant will give us understanding of how pathogens couples different extracellular signals with physiological adaptation to different environment (Fig. 3).

c)Biology of Xanthomonas citri

Xanthomonas citri is an important member of the Xanthomonas group of plant pathogen. It causes an economically important disease called as Citrus Canker. In India, it causes severe economic loss in the citrus production. Very little information is known about the biology of this pathogen, its interaction with host plant. Large genetic variation and lack of well defined resistance citrus plants makes it a challenging pathosystem to work with. We will explore the biology of this pathogen by molecular genetics studies which will elucidate new virulence functions in this pathogen.