Rice and Magnaporthe oryzae constitutes an ideal pathosystem for studying host-pathogen interaction in cereals crops. There are two alternative hypotheses, viz. Arms race and Trench warfare, which explain the co-evolutionary dynamics of hosts and pathogens which are under continuous confrontation. Arms race proposes that both R- and Avr- genes of host and pathogen, respectively, undergo positive selection. Alternatively, trench warfare suggests that either R- or Avr- gene in the pathosystem is under balanced selection intending to stabilize the genetic advantage gained over the opposition. Here, we made an attempt to test the above-stated hypotheses in rice-M. oryzae pathosystem at loci of three R-Avr gene pairs, Piz-t-AvrPiz-t, Pi54-AvrPi54 and Pita-AvrPita using allele mining approach. Allele mining is an efficient way to capture allelic variants existing in the population and to study the selective forces imposed on the variants during evolution. Results of nucleotide diversity, neutrality statistics and phylogenetic analyses reveal that Piz-t, Pi54 and AvrPita are diversified and under positive selection at their corresponding loci, while their counterparts, AvrPiz-t, AvrPi54 and Pita are conserved and under balancing selection, in nature. These results imply that rice-M. oryzae populations are engaged in a trench warfare at least at the three R/Avr loci studied. It is a maiden attempt to study the co-evolution of three R-Avr gene pairs in this pathosystem. Knowledge gained from this study will help in understanding the evolutionary dynamics of host-pathogen interaction in a better way and will also aid in developing new durable blast resistant rice varieties in future.

中文翻译：

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水稻-稻瘟病菌病原体系统中宿主抗性和病原体无毒力基因之间的共同进化相互作用。

水稻和稻瘟病菌是研究谷物作物中宿主与病原体相互作用的理想病理系统。有两个备选假设，即。军备竞赛和海沟战，这说明了在持续对抗下的宿主和病原体的共同进化动力学。军备竞赛建议宿主和病原体的R-和Avr-基因分别经历阳性选择。另外，战trench表明病态系统中的R-基因或Avr-基因处于平衡选择之下，目的是稳定相对于对手获得的遗传优势。在这里，我们尝试检验水稻-M中的上述假设。使用等位基因挖掘方法，在三个R-Avr基因对的基因座上的水稻稻瘟病系统，Piz-t-AvrPiz-t，Pi54-AvrPi54和Pita-AvrPita。等位基因挖掘是捕获种群中存在的等位基因变异并研究进化过程中施加在变异上的选择力的有效方法。核苷酸多样性，中性统计和系统发育分析的结果表明，Piz-t，Pi54和AvrPita在其相应的基因座处是多样化的且处于阳性选择之下，而其对应的AvrPiz-t，AvrPi54和Pita却是保守的且处于平衡选择之下。这些结果暗示米-M。至少在所研究的三个R / Avr基因座处，稻米种群参与了海战。这是研究该病原系统中三个R-Avr基因对共同进化的首次尝试。