ANALYSIS OF A BACTERIAL PLANT NATRIURETIC PEPTIDE-LIKE GENE EXPRESSION UNDER DIFFERENT GROWTH CONDITIONS

GARAVAGLIA BS; FICARRA F; GOTTIG N; OTTADO J

Rosario

Congreso; IX Congreso de Microbiología General; 2013

Citrus canker, caused by Xanthomonas axonopodis pv. citri (Xac), is one of the most serious diseases affecting citrus production worldwide. Xac has a gene encoding a plant natriuretic peptide (PNP)-like protein (XacPNP) that shares significant sequence similarity and identical domain organization with PNPs and it is only found in this bacterium. PNPs are a class of peptide hormones implicated in the regulation of cell homeostasis. We demonstrated 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 living tissue. XacPNP has a role in plant cell homeostasis suggesting that this probably laterally acquired gene assists the pathogen in the manipulation of plant responses in order to create favorable conditions for its survival on the host. With the aim to study in vitro conditions that promote XacPNP expression, we cloned the XacPNP promoter region in the pPROBE-NT reporter plasmid that allows the quantification of gene expression by the measurement of the fluorescence emitted by the green fluorescence protein. This construction was transformed in Xac and different culture media were used to growth these bacteria to determine the basal gene expression level. We chose nutrient broth medium (NB) to analyze the effect of mannitol, fructose, sacarose and sorbitol as well as sodium, potassium, magnesium and ammonium salts. We observed that XacPNP expression was more induced in cultures supplemented with 0.5% sodium chloride. On the other hand, we tested XacPNP expression in a nutrient poor medium that simulates conditions in the apoplastic space and observed the highest expression levels compared with the other conditions. Furthermore, we prepared RNA isolated from Xac grown in NB and NB supplemented with 0.5% NaCl to verify XacPNP expression by qRT-PCR. Our results demonstrate that XacPNP is expressed under sodium chloride stress, consistent with a role in the regulation of cell homeostasis and also in apoplastic conditions, probably aiding the bacteria to colonize its plant host.