Role of the HpaB-HpaA interaction in the secretion of HpaA by the type III secretion system of Xanthomonas axonopodis pv. citri
Miryam Marroquin-Quelopana1; Paola A. Cappelletti1; Cristiano B. Ferreira2; Julio C. F. de Oliveira2; Chuck S. Farah1
1 Departamento de Bioquímica, Instituto de Química, Universidade de São Paulo, São Paulo, SP.; 2 Departamento de Tecnologia, Universidade Estadual de São Paulo, Jaboticabal, SP.
We have previously identified an interaction between HpaA, HpaB and HrcV Xanthomonas axonopodis pv citri (Xac) proteins by in vivo and in vitro methods. All three proteins are coded by the Xac hrp locus responsible for the production of ca. 25 subunits of the type III secretion system (T3SS) that targets protein virulence factors to the plant host. Based on these results, we have proposed that HpaB directs HpaA to HrcV at the cytoplasmic face of the T3SS before subsequent secretion. In this study, we report the production of a Xac hpaB non-polar deletion mutant, using a suicide vector - mediated recombination protocol. In plant growth curves using the hpaB mutant strains inoculated on citrus host leaves have been initiated. HpaA secretion in the presence and absence of citrus leaf soluble extracts using the Xac wild-type, hpaB mutant and hpaB mutant strain containing a plasmid constituitively expressing wild-type hpaB showed that HpaA secretion is dependent on HpaB. Studies on HpaA function inside the plant cells are being initiated in order to better delineate the role of HpaA in Xac pathogenesis.
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