Citrus canker. Modulation of the host homeostasis by a bacterial natriuretic peptide

GARAVAGLIA, B.; GOTTIG, N.; DAURELIO, L.D.; DUNGER, G.; GARÓFALO, C.; ZIMAROA, T.; THOMAS, L.; NDIMBAB, B.; GEHRING, C.; ORELLANO, E.G.; OTTADO, J.

Zaragoza, España

Congreso; XVIII Reunión de la Sociedad Española de Fisiología Vegetal (SEFV) XI Congreso Hispano-Luso de Fisiología Vegetal; 2009

Sociedad Española de Fisiología Vegetal

Citrus canker, caused by Xanthomonas axonopodis pv. citri (Xac), is one of the most serious diseases affecting citrus production worldwide. The pathogen enters host plant tissues through stomatal openings and wounds and then colonizes the apoplast causing the break of the epidermis due to cell hyperplasia. The infection is visualized as raised lesions on fruit, foliage and young stems. Severe disease can cause defoliation, dieback and fruit drop reducing production volume, increasing prices and causing high market losses [1]. Xac contains a gene encoding a plant natriuretic peptide (PNP), not present in any other bacteria. PNPs are a class of extracellular, systemically mobile molecules that elicit a number of plant responses important in homeostasis and growth. We expressed and purified XacPNP and demonstrated that the bacterial protein alters physiological responses including stomatal opening in plants. Although XacPNP is not expressed under standard nutrient rich culture conditions, it is strongly induced under conditions that mimic the nutrient poor intercellular apoplastic environment of leaves, as well as in infected tissue, suggesting that XacPNP transcription can respond to the host environment. To characterize the role of XacPNP during bacterial infection, we constructed a XacPNP deletion mutant. The lesions caused by this mutant were more necrotic than those observed with the wild-type, and bacterial cell death occurred earlier in the mutant. Moreover, when we expressed XacPNP in Xanthomonas axonopodis pv. vesicatoria, the transgenic bacteria caused less necrotic lesions in the host than the wild-type [2]. In addition, we further characterized XacPNP role in citrus leaves and observed a marked improvement of the photosynthetic process as well as no induction of pathogenesis related proteins. In conclusion, we present evidence that a plant-like bacterial PNP can enable a plant pathogen to modify host responses to create conditions favorable to its own survival. [1] Graham et al. (2004) Mol. Plant Pathol.5:1[2] Gottig, Garavaglia et al. (2008) Proc. Natl. Acad. Sci. USA.47:18631