Blumeria graminis f. sp. tritici (Bgt) is a globally important fungal wheat pathogen. Some wheat genotypes contain powdery mildew resistance (Pm) genes encoding immune receptors that recognize specific fungal-secreted effector proteins, defined as avirulence (Avr) factors. Identifying Avr factors is vital for understanding the mechanisms, functioning, and durability of wheat resistance. Here, we present AvrXpose, an approach to identify Avr genes in Bgt by generating gain-of-virulence mutants on Pm genes. We first identified six Bgt mutants with gain of virulence on Pm3b and Pm3c. They all had point mutations, deletions or insertions of transposable elements within the corresponding AvrPm3^b2/c2 gene or its promoter region. We further selected six mutants on Pm3a, aiming to identify the yet unknown AvrPm3^a3 recognized by Pm3a, in addition to the previously described AvrPm3^a2/f2. Surprisingly, Pm3a virulence in the obtained mutants was always accompanied by an additional gain of virulence on the unrelated tandem kinase resistance gene WTK4. No virulence toward 11 additional R genes tested was observed, indicating that the gain of virulence was specific for Pm3a and WTK4. Several independently obtained Pm3a-WTK4 mutants have mutations in Bgt-646, a gene encoding a putative, nonsecreted ankyrin repeat-containing protein. Gene expression analysis suggests that Bgt-646 regulates a subset of effector genes. We conclude that Bgt-646 is a common factor required for avirulence on both a specific nucleotide-binding leucine-rich repeat and a WTK immune receptor. Our findings suggest that, beyond effectors, another type of pathogen protein can control the race-specific interaction between powdery mildew and wheat.

Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Blumeria graminis f. sp。小麦( Bgt ) 是一种全球重要的小麦病原体。一些小麦基因型含有白粉病抗性（Pm）基因，编码免疫受体，识别特定的真菌分泌的效应蛋白，定义为无毒（Avr）因子。识别 Avr 因子对于了解小麦抗性的机制、功能和持久性至关重要。在这里，我们提出了 AvrXpose，一种通过在Pm基因上生成毒力增益突变体来识别Bgt中Avr基因的方法。我们首先鉴定了六种Bgt突变体，它们对Pm3b和Pm3c的毒力增强。它们在相应的AvrPm3 ^b2/c2基因或其启动子区域内均具有转座元件的点突变、缺失或插入。我们进一步选择了Pm3a上的 6 个突变体，旨在除了之前描述的 AvrPm3 ^a2/f2之外，还鉴定出 Pm3a 识别的未知 AvrPm3 ^a3。令人惊讶的是，所获得的突变体中的Pm3a毒力总是伴随着不相关的串联激酶抗性基因 WTK4 的毒力的额外增加。没有观察到对另外 11 个测试的R基因的毒力，表明毒力的增加是Pm3a和WTK4特异的。几个独立获得的Pm3a-WTK4突变体在Bgt-646中具有突变，Bgt-646 是编码推定的、非分泌的含有锚蛋白重复序列​​的蛋白质的基因。基因表达分析表明Bgt-646调节效应基因的子集。我们得出结论，Bgt-646是特定核苷酸结合富含亮氨酸重复序列和 WTK 免疫受体无毒所需的共同因素。我们的研究结果表明，除了效应子之外，另一种类型的病原体蛋白可以控制白粉病和小麦之间的种族特异性相互作用。

版权所有 © 2024 作者。这是一篇根据 CC BY-NC-ND 4.0 国际许可证分发的开放获取文章。