Identification of an avirulence gene island in Pyriculazia chromosomes and analyses of its transposition and disorganization

通过研究稻瘟病菌在稻瘟病菌中的功能和分布，探讨了稻瘟病菌无毒基因Avr1-CO39在稻瘟病菌进化分化中的意义。用rDNA构建的树状图绘制AVR1-CO39的存在/不存在时，其分布与稻瘟病菌的系统发育完全平行。AVR1-CO39同源物仅存在于稻瘟病菌中，表明AVR1-CO39存在于稻瘟病菌进化的早期阶段。转化试验表明，所有克隆的同源物都具有无毒基因的功能，表明选择保持了它们的功能。然而，水稻分离物(对水稻有毒力的分离物)在稻瘟病菌中，AVR1-CO39的携带者是例外的。所有的水稻分离物都在Avr1-CO39基因座经历了两种已知重排中的一种，即G型和J型。这些类型与MGR586和Maggy确定的日本水稻分离物的两个主要谱系一致。这些结果表明，在水稻专化亚群进化的早期阶段，AVR1-CO39基因已经丢失。有趣的是，其相应的抗性基因Pi-CO39(T)在水稻中并不广泛分布，而与PITA对应的无毒基因AVR-PITA的同源基因不仅在稻瘟病菌中广泛分布，而且在稻瘟病菌和稻瘟病菌中也广泛分布。有趣的是，含有同源物的染色体在不同的菌株之间是不同的。对这些同系物侧翼区域的分析表明，转座元件插入到它们的侧翼区域使它们具有迁移性。

The significance of AVR1-CO39, an avirulence gene of the blast fungus corresponding to Pi-CO39(t) in rice cultivars, during the evolution and differentiation of the blast fungus was evaluated by studying its function and distribution in Pyricularia spp. When the presence/absence of AVR1-CO39 was plotted on a dendrogram constructed from rDNA sequences, a perfect parallelism was observed between its distribution and the phylogeny of Pyricularia isolates. AVR1-CO39 homologs were exclusively present in one species, P.oryzae, suggesting that AVR1-CO39 appeared during the early stage of evolution of P.oryzae. Transformation assays showed that all the cloned homologs tested are functional as an avirulence gene, indicating that selection has maintained their function. Nevertheless, Oryza isolates (isolates virulent on Oryza spp.) in P. oryzae were exceptionally non-carriers of AVR1-CO39. All Oryza isolates suffered from one of the two types of known rearrangements at the Avr1-CO39 locus, i.e., G type and J type. These types were congruous to the two major lineages of Oryza isolates from Japan determined by MGR586 and MAGGY. These results indicate that AVR1-CO39 was lost during the early stage of evolution of the Oryza-specific subgroup of P.oryzae. Interestingly, its corresponding resistance gene, Pi-CO39(t) is not widely distributed in Oryza spp.Homologs of AVR-Pita, an avirulence gene corresponding to Pita, were widely distributed not only in P.oryzae, but also in P.grisea and P.spp. Interestingly, the chromosomes with the homologs were different from isolates to isolates. Analyses of flanking regions of these homologs suggested that the insertion of transposable elements into their flanking regions gave them mobility.