Abstract：
The soybean Rpp1 locus confers resistance to Phakopsora pachyrhizi, causal agent of rust, and resistance is usually dominant over susceptibility. However, dominance of Rpp1-mediated resistance is lost when a resistant genotype (Rpp1 or Rpp1b) is crossed with susceptible line TMG06_0011, and the mechanism of this dominant susceptibility (DS) is unknown. Sequencing the Rpp1 region reveals that the TMG06_0011 Rpp1 locus has a single nucleotide-binding site leucine-rich repeat (NBS-LRR) gene (DS-R), whereas resistant PI 594760B (Rpp1b) is similar to PI 200492 (Rpp1) and has three NBS-LRR resistance gene candidates. Evidence that DS-R is the cause of DS was reflected in virus-induced gene silencing of DS-R in Rpp1b/DS-R or Rpp1/DS-R heterozygous plants with resistance partially restored. In heterozygous Rpp1b/DS-R plants, expression of Rpp1b candidate genes was not significantly altered, indicating no effect of DS-R on transcription. Physical interaction of the DS-R protein with candidate Rpp1b resistance proteins was supported by yeast two-hybrid studies and in silico modeling. Thus, we conclude that suppression of resistance most likely does not occur at the transcript level, but instead probably at the protein level, possibly with Rpp1 function inhibited by binding to the DS-R protein. The DS-R gene was found in other soybean lines, with an estimated allele frequency of 6% in a diverse population, and also found in wild soybean (Glycine soja). The identification of a dominant susceptible NBS-LRR gene provides insight into the behavior of NBS-LRR proteins and serves as a reminder to breeders that the dominance of an R gene can be influenced by a susceptibility allele.
摘要：
大豆Rpp1基因座赋予对Phakopsorapachyrhizi的抗性，锈蚀的病原体，抗性通常比易感性占优势。然而,当抗性基因型（Rpp1或Rpp1b）与易感系TMG06_0011杂交时，Rpp1介导的抗性的优势丧失，并且这种显性易感性（DS）的机制尚不清楚。对Rpp1区进行测序表明，TMG06_0011Rpp1基因座具有单核苷酸结合位点富含亮氨酸的重复（NBS-LRR）基因（DS-R），而抗性PI594760B(Rpp1b)与PI200492(Rpp1)相似,并且具有三个NBS-LRR抗性候选基因。DS-R是DS原因的证据反映在Rpp1b/DS-R或Rpp1/DS-R杂合植物中病毒诱导的DS-R基因沉默中，抗性部分恢复。在杂合Rpp1b/DS-R植物中，Rpp1b候选基因的表达没有显著改变，表明DS-R对转录没有影响。酵母双杂交研究和计算机建模支持DS-R蛋白与候选Rpp1b抗性蛋白的物理相互作用。因此，我们得出结论，抑制抗性很可能不会发生在转录水平，但可能在蛋白质水平上，可能具有通过与DS-R蛋白结合而抑制的Rpp1功能。在其他大豆品系中发现了DS-R基因，在不同人群中估计等位基因频率为6%，也存在于野生大豆（甘氨酸大豆）中。显性易感NBS-LRR基因的鉴定提供了对NBS-LRR蛋白行为的了解，并提醒育种者R基因的优势可能受到易感性等位基因的影响。
