A Xanthomonas axonopodis pv. citri plant natriuretic peptide-like protein involved in pathogenicity

NATALIA GOTTIG; BETIANA S. GARAVAGLIA; LUCAS D. DAURELIO; ELENA G. ORELLANO; JORGELINA OTTADO

Rosario

Congreso; XLII Reunión Anual de SAIB (Sociedad Argentina de Investigación en Bioquímica y Biología Molecular); 2006

Xanthomonas axonopodis pv. citri (Xac) is the casual agent of citrus canker, which affects most commercial citrus cultivars resulting in significant losses worldwide. The Xac genome has been sequenced, although some conserved genes involved in plant-Xac interactions have been characterized, little is known about many Xac hypothetical genes. Xac has an hypothetical protein, only found in this bacteria (XacPNP), with sequence similarity to plant natriuretic peptides (PNPs), a class of peptide hormones implicated in the regulation of cell homeostasis. We observed an increase of XacPNP mRNA levels in a medium that mimics the intercellular space of leaves, suggesting a role for XacPNP in pathogenicity. To evaluate the participation of XacPNP in this process, we constructed a XacPNP deletion mutant. The lesions produced by this mutant were less rough and more necrotic than the lesions observed with Xac. Moreover, when we over-expressed XacPNP in Xac or in X. campestris pv. vesicatoria the resulting transgenic bacteria caused less necrotic lesions in their host plants than wild type bacteria. All these transgenic bacteria showed the same hypersensitive response in non-host plants. Our results suggest that XacPNP is involved in Xac pathogenicity interfering with plant tissue necrosis allowing a prolonged survival of plant cells and thus, maintaining the interaction with non-dead tissue.