The specificity between pathotypes of Pyricularia oryzae and genera of gramineous plants is governed by gene-for-gene interactions. Here, we show that avirulence genes involved in this host specificity have undergone different modes of functional losses dependent on or affected by genomic compartments harboring them. The avirulence of an Eleusine pathotype on wheat is controlled by five genes, including PWT3, which played a key role in the evolution of the Triticum pathotype (the wheat blast fungus). We cloned another gene using an association of its presence or absence with pathotypes and designated it as PWT6. PWT6 was widely distributed in a lineage composed of Eleusine and Eragrostis isolates but was completely absent in a lineage composed of Lolium and Triticum isolates. On the other hand, PWT3 homologs were present in all isolates, and their loss of function in Triticum isolates was caused by insertions of transposable elements or nucleotide substitutions. Analyses of whole-genome sequences of representative isolates revealed that these two genes were located in different genomic compartments; PWT6 was located in a repeat-rich region, while PWT3 was located in a repeat-poor region. These results suggest that the course of differentiation of the pathotypes in P. oryzae appears to be illustrated as processes of functional losses of avirulence genes but that modes of the losses are affected by genomic compartments in which they reside.

Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Pyricularia oryzae 的致病型与禾本科植物属之间的特异性受基因间相互作用的控制。在这里，我们表明参与这种宿主特异性的无毒基因经历了不同的功能丧失模式，这些模式依赖于包含它们的基因组区室或受其影响。Eleusine致病型对小麦的无毒力由五个基因控制，包括PWT3，其在小麦致病型（小麦稻瘟病菌）的进化中起关键作用。我们利用其存在与否与病理类型的关联克隆了另一个基因，并将其命名为PWT6。PWT6广泛分布在由Eleusine和画眉草分离株，但在由黑麦属和小麦分离株组成的谱系中完全不存在。另一方面，PWT3同源物存在于所有分离株中，它们在小麦分离株中的功能丧失是由插入转座元件或核苷酸取代引起的。对代表性分离株的全基因组序列的分析表明，这两个基因位于不同的基因组区室；PWT6位于重复序列丰富区域，而PWT3位于重复序列贫乏区域。这些结果表明，稻瘟病菌病原的分化过程 似乎被说明为无毒基因功能丧失的过程，但丧失的模式受到它们所在的基因组区室的影响。

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