Participation of Xanthomonas axonopodis pv. citri EPS in citrus canker and in non-host plants responses

DUNGER, G.; RELLING, V.; ORELLANO, E; JORGELINA OTTADO

Pinamar

Congreso; 10th Congress Panamerican Association for Biochemistry and Molecular Biology; 2005

Xanthomonas axonopodis pv. citri (Xac) causes citrus canker, a serious disease that results in important losses. The extracellular polysaccharide (EPS) produced by xanthomonads is termed xanthan and many roles have been suggested for the EPS in plant-pathogen interaction. A cluster of 12 genes are involved in the biosynthesis and secretion of xanthan, named gumB-gumM in X. campestris pv. campestris. We have characterized the participation of xanthan in the interaction with host and non-host plants. We isolated a region of the gum cluster of Xac and constructed mutants in the gumD gene, using a suicide vector transferred by biparental mating. For disease symptoms assays, bacterial suspensions were infiltrated into leaves of host plant orange (Citrus sinensis) and into leaves of non-host plants cotton, tomato and tobacco. No differences were observed in lesions and bacterial growth curves in wild type (WT) and mutant Xac inoculated host plant leaves. Also, epiphytic survival was investigated and no differences between inoculations with both strains were observed. The infiltration of WT and mutant Xac in non-host plants induced in both cases hypersensitive responses. The results suggest that xanthan may not be indispensable for Xac interactions with host and non-host plants.