AvrBs3-like genes and TAL Effectors Specific to Race Structure in Xanthomonas axonopodis pv. glycines

Abstract

The avrBs3-like genes designated avrXg3 and avrXg2 cloning from representative strains of Xanthomonas axonopodis pv. glycines (Xag), a causal agent of bacterial pustule disease were harbored by race 1 (new strain SP4); and race 2 (recent strain 12-2) respectively, whereas avrXg1 (reported by Athinuwat et al., 2009) was uniquely detected in race 3 (recent strain KU-P-SW005) that characterized based on their ability to confer virulence toward soybean cultivars. Most of the new strains collected in this study (169 strains) belonged to race 2 (62.72%), the highly virulence strain group. Structural analysis of transcription activator-like effector (TALe) genes determined to particular races was shown that these race strains including race 1 strain SP4, race 2 strain 12-2, and race 3 strain KU-P-SW005 carried TAL effectors of 6 (tal1a, tal1b, tal1c, tal2a, tal2b, and tal3), 6 (same as strain SP4), and 5 (same as strain SP4 but tal1c absent) tale gene members that guided by 15-23, 15-23, and 15-20 repeat variable diresidues (RVDs) respectively. The individual mutants of each tal genes (17-tal derivatives) revealed that only tal2b in each race strains (XagSP4/tal2b, Xag12-2/ tal2b, XagKU-P-SW005/tal2b) exhibited a positive regulator of similar defense-related phenotype on soybean cultivars of Xag/avrBs3-race typing group, suggesting R genes mediated specifically recognition of directly tal2b induction. Phylogenetic construction and hybridization analysis demonstrated high potential in rapid genotyping of many Xag-race strains using primers and DNA probes designed from either specific avrBs3 or tale-like genes characterized. Genetic mapping and RT-PCR evidence showed that soybean GmLOB1 resistance genes mediated recognition of Xag12-2/tal2b-expressing strain (highly virulent strain) to give disease development on resistance cultivar, Williams82. The tal2b and non-TALe type of type III effectors that may establish a co-opted activity targeting host R genes other than GmLOB1 should be experimentally-further analyzed. This is the first description of TALes indicating their translocation through the Xag-T3SS which the work reports two new avrBs3-like genes and seventeen tale- like genes characterized from soybean-3 pathogenic Xag race strains.