Cloning and characterization of a novel avirulence gene (arp3) from Xanthomonas oryzae pv. oryzae.

A novel avirulence gene was cloned from Xanthomonas oryzae pv. oryzae strain PX0339, which is the standard representative of the Philippines race 9a. The full-length gene spans 2118 bp and encodes a protein of 705 amino acids. BLAST search in NCBI indicated that the gene belongs to avrBs3 gene family, and designated arp3 (AvrBs3-related protein 3, arp3). The central region of the arp3 contains only 5.5 copies of 102bp repeats, the smallest copy number of repeats found in avrBs3 gene family by now. Together with the repeats is heptad repeats, resembling leucine zippers. Three functional nuclear localization signals and an acidic activation domain are also found in the C-terminal region. However, the arp3 lacks of two segments in its N-terminal region, which is unique in avrBs3 gene family. Southern blotting data showed that the arp3 is present as a single-copy in genomic DNA of PX0339 and locus in plasmid clone. The arp3 could be expressed in vitro in Escherichia coli BL21 and a 128kDa fusion protein was detected by Western analysis.