Dissecting immune response and pathogen suppression in citrus-Xanthomonas interactions.

ENRIQUE R.; SICILIANO F.; RIGANO L.; SENDÍN L.; VOJNOV A.A.; CASTAGNARO A.P.; MARANO M.R.

Mar del Plata, Buenos Aires

Congreso; XLIII Reunión Anual de la Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular; 2007

Sociedad Argentina de Investigaciones en Bioquímica y Biología Molecular (SAIB)

Xanthomonas axonopodis pv. citri (Xac) is responsible for the canker disease affecting citrus plants throughout the world. Many studies have implicated extracellular polysaccharides (EPS, i.e. xanthan) secreted by different species of Xanthomonas in pathogenicity and fitness. Recently, we have shown that xanthan plays an important role in the formation of biofilms and in bacterial survival on the leaf leading to canker development. However, other roles played by xanthan in disease development should not be ruled out. We have shown that xanthan from other Xanthomonas species is able to mediate suppression of plant defense response. We postulate that after invasion of host intercellular spaces sequestration of the Ca++ ions by xanthan prevents activation of defenses. Callus deposition and oxidative burst are triggered by xanthan defective mutant on lemon leaves, suggesting that xanthan play a key role in establishing compatibility through suppressing of PAMP recognition. We have established a Citrus limon–Xac assay and have used it to identify PAMP-mediated differential gene expression during Xac-citrus interaction. In order to study the function of these isolated genes we developed an RNAi transient assay to induce post-transcriptional gene silencing in lemon seedling. These results will be discussed.