Cloning and expression analysis of Phytoplasma protein translocation genes

Genes encoding SecA and SecY proteins, essential components of the Sec prot ein translocation system, were cloned from onion yellows phytoplasma, an un culturable plant pathogenic bacterium. The secA gene consists of 2,505 nucl eotides encoding an 835 amino acid protein (95.7 kDa) and shows the highest similarity with SecA of Bacillus subtilis. Anti-SecA rabbit antibody was p repared from a purified partial SecA protein, with a histidine tag expresse d in Escherichia coli. Western blot analysis con. firmed that SecA protein (approximately 96 kDa) is produced in phytoplasma-infected plants. Immunohi stochemical thin sections observed by optical microscopy showed that SecA i s characteristically present in plant phloem tissues infected with phytopla sma. The secY gene consists of 1,239 nucleotides encoding a 413 amino acid protein (45.9 kDa) and shows the highest similarity with SecY of B. subtili s. These results suggest the presence of a functional Sec system in phytopl asmas. Because phytoplasmas are endocellular bacteria lacking cell walls, t his system might secrete bacterial proteins directly into the host cytoplas m. This study is what we believe to be the first report of the sequence and expression analysis of phytoplasma genes encoding membrane proteins with a predicted function.