avr/pth13 Gene of Xanthomonas oryzae pv. oryzicola, a Novel Virulence Member of avrBs3/PthA Family, Strengthening Virulence of Xanthomonas oryzae pv. oryzae on Rice

An EcoRⅠ-BamHⅠ DNA, corresponding to the coding region NLS (nuclear localization signal) and AD (acidic transcriptional activation domain) of AvrXa3 of Xanthomonas oryzae pv. oryzae (Xoo), was used as a probe to screen the genomic library of Xanthomonas oryzae pv. oryzicola(Xooc). One avrBs3/PthA gene clone was obtained after positive clones of the library were digested by EcoRⅠ endoenzyme and proved by Southern blot. Sequencing subclone, pPth13, indicated that it contained a gene belonging to the avrBs3/PthA family of Xanthomonas pathogenic bacteria, and was nominated as avr/pth13 gene. As other AvrBs3/PthA, the putative protein of avr/pth13 gene possesses the same 5’- and 3’- terminals, one leucine zipper (LZ), three NLSs and one AD. However, the difference of the gene with other avrBs3/PthA family members was the repeat numbers of 34 amino acid unit coded by 102 bp repeat. The 102 bp unit was repeated 5.5 times in avr/pth13 gene. Blasting the sequence in GenBank database showed that avr/pth13 gene was the smallest in avrBs3/PthA family. (Alignment) of 12-13~(th) residues in 34 amino acid unit of Avr/Pth13 with those of other AvrBs3/PthA proteins demonstrated that at least three HD(His and Asp) residues in 12-13~(th) position of 34 amino acid unit might be necessary for avirulence or/and virulence. Pathogenicity tests of strain PXO99~(A )containing avr/pth13gene on near isogenic lines (NILs) of rice showed that avr/pth13 gene strengthened the virulence of Xoo on the tested NILs. All the above confirmed that avrBs3/PthA gene(s) existed in Xooc as that in Xoo, determining virulence in bacterial streak and blight diseases of rice.