A single-amino acid substitution in the sixth leucine-rich repeat of barley MLA6 and MLA13 alleviates dependence on RAR1 for disease resistance signaling
A single-amino acid substitution in the sixth leucine-rich repeat of barley MLA6 and MLA13 alleviates dependence on RAR1 for disease resistance signaling
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DOI：
10.1111/j.1365-313x.2004.02032.x
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发表时间：
2004-04-01
期刊：
影响因子：
7.2
通讯作者：
Wise, RP
中科院分区：
文献类型：
--
作者：
Halterman, DA;Wise, RP
大麦与白粉病菌Blumeria graminis f.大麦白粉病抗性基因座（Bgh）是由指定为抗白粉病基因座（Ml）的宿主抗性基因和同源病原体无毒力基因的独特组合决定的。这些相互作用既依赖于又不依赖于Rar 1（Mla 12抗性所需）和Sgt 1（skp 1的G-2等位基因的抑制因子），这是不同植物抗病途径所需的差异。我们已经分离出两个新的功能性Mla等位基因，Rar 1独立的Mla 7和Rar 1依赖的Mla 10，以及Mla旁系同源物，Mla 6 -2和Mla 13 -2。利用Mla编码的蛋白质之间的固有多样性，我们确定了在RAR 1依赖性MLA 6、MLA 10、MLA 12和MLA 13中唯一保守的两个氨基酸，它们在RAR 1非依赖性MLA 1和MLA 7中的相应位置不同。二维和三维建模将这些残基放置在第六个富含亮氨酸的重复序列（LRR）结构域的预测表面上，其位置与假设用于确定耐药特异性的β折叠内的位置不同。这些残基的定点诱变表明RAR 1的独立性需要在位置721处存在天冬氨酸，因为将该残基突变为结构相似但不带电荷的天冬酰胺并不改变RAR 1的依赖性。这些结果表明，第六个MLA LRR中的单个氨基酸取代可以改变宿主信号传导，但不会改变对B的抗性特异性。禾本科植物
Interactions between barley and the powdery mildew pathogen, Blumeria graminis f. sp. hordei, (Bgh) are determined by unique combinations of host resistance genes, designated Mildew-resistance locus (Ml), and cognate pathogen avirulence genes. These interactions occur both dependent and independent of Rar1 (required for Mla12 resistance) and Sgt1 (Suppressor of G-two allele of skp1), which are differentially required for diverse plant disease-resistance pathways. We have isolated two new functional Mla alleles, Rar1-independent Mla7 and Rar1-dependent Mla10, as well as the Mla paralogs, Mla6-2 and Mla13-2. Utilizing the inherent diversity amongst Mla-encoded proteins, we identified the only two amino acids exclusively conserved in RAR1-dependent MLA6, MLA10, MLA12, and MLA13 that differ at the corresponding position in RAR1-independent MLA1 and MLA7. Two- and three-dimensional modeling places these residues on a predicted surface of the sixth leucine-rich repeat (LRR) domain at positions distinct from those within the beta-sheets hypothesized to determine resistance specificity. Site-directed mutagenesis of these residues indicates that RAR1 independence requires the presence of an aspartate at position 721, as mutation of this residue to a structurally similar, but uncharged, asparagine did not alter RAR1 dependence. These results demonstrate that a single-amino acid substitution in the sixth MLA LRR can alter host signaling but not resistance specificity to B. graminis.