Poster: Plant Pathogen/Symbiont Interactions

Abs # 747: Characterization of early chlorosis factor (ecf) from the bacterial pathogen Xanthomonas

Presenter:	Posada, Jessica M.
Authors	Posada, Jessica M. (A)   Morales, Christina Q. (A)   Franklin, Darleen  (A)   Whalen, Maureen C. (A)
Affiliations:	(A): San Francisco State University

Xanthomonas axonopodis pv. vesicatoria (Xav) is the casual agent for bacterial spot disease in tomato. A gene in Xav named early chlorosis factor (ecf) triggers one of the early disease symptoms, chlorosis. Our goal is to understand the molecular mechanisms of chlorosis induction. Since ecf is not similar to any known gene, the DNA flanking ecf was shotgun-cloned and sequenced. ABC transporter components, outer membrane proteins (OMP), and L-sorbosone dehydrogenase were identified in the flanking DNA. The correlation, if any, of these functions with induction of chlorosis is not clear. To predict the function of ecf, several secondary prediction programs were utilized to analyze the 688 amino acid ORF in ecf. We found that ecf contains seven transmembrane regions and is similar on a 3D-structural level to colicin Ia, a toxic pore-forming protein from E.coli. Mutagenesis and subcellular localization will verify these results. The chlorosis function of ecf requires the type III translocation system. We therefore addressed the possibility that the ecf gene product is translocated into the host cell cytoplasm by analyzing host responses to Agrobacterium-mediated in planta transient expression. It appears that the ecf gene product does not directly function in the host cell or cannot function alone to induce chlorosis. Studies are underway to learn under what conditions ecf is expressed and about possible indirect mechanisms of ecf-mediated chlorosis induction.