水稻黄单胞菌avrBs3/PthA家族基因研究进展

 水稻黄单胞菌白叶枯致病变种（Xanthomonas oryzae pv.oryzae，Xoo）和稻生致病变种（X.oryzae pv.oryzicola，Xooc）分别引起水稻白叶枯病（bacterial blight，BB）和水稻细菌性条斑病（bacterial leaf streak，BLS），对中国和世界水稻产量造成较大损失。基因组学揭示，Xoo和Xooc不同小种中存在15～30个数量不等的avrBs3/PthA（avr/pth）家族基因。新近研究结果表明，avr/pth基因既是毒性基因，又是寄主植物先天免疫的抑制因子，还是与抗病基因（R）匹配的无毒基因。Xooc中虽然存在avr/pth基因，但因存在能够抑制avr/pth无毒基因功能的抑制因子，故而未在水稻中发现抗BLS的R基因。除结构上的共有特征外，avr/pth基因间的差异主要表现在102 bp重复单元在每个avr/pth基因中的重复数多少上。avr/pth基因的进化可能由简单进化为复杂，这可能是Xoo和Xooc致病性变异的主要原因。

Current Progress in the Research on avrBs3/PthA Family Genes of Xanthomonas oryzae

Xanthomonas oryzae pv. oryzae (Xoo) and Xanthomonas oryzae pv. oryzicola (Xooc) cause bacterial blight (BB) and bacterial leaf streak (BLS) in rice (Oryza sativa), which constrain rice production in China and the world. According to bioinformatics of Xoo and other recent reports, there are 15~30 avrBs3/PthA (avr/pth) genes in Xoo and Xooc. Recent research results suggest that avr/pth genes are not only involved in virulence when there are no corresponding R genes in rice, but also in suppressing plant immunity for hypersensitive response, and in avirulence when there are matching R genes in rice. Although avr/pth genes exist in Xooc, no R genes are present for BLS in rice. Members of avr/pth family genes are remarkably similar. However, the main differences are the number and apparent nature of near-identical 102-base-pair direct repeats in the central portion of the coding sequence. In this review, we postulated that the evolution of the avr/pth genes might occur from the simple to the complex. This might elucidate the pathogenicity differentiation of Xoo and Xooc in rice.