A sorghum genome-wide association study (GWAS) identifies a WRKY transcription factor as a candidate gene underlying resistance to sugarcane aphid (Melanaphis sacchari) - Heterologous expression of SbWRKY86 in Arabidopsis

Crop plant resistance to insect pests is based on genetically encoded traits which often display variability across diverse germplasm. In a comparatively recent event, a predominant sugarcane aphid (SCA: Melanaphis sacchari) clone has become a significant agronomic pest for grain sorghum (Sorghum bicolor) production. In an effort to uncover candidate genes underlying SCA resistance, we used a forward genetics approach combining the genetic diversity present in the Sorghum Association Panel (SAP) and the Bioenergy Association Panel (BAP) for a Genome Wide Association Study, employing an established SCA damage rating. Statistically significant single nucleotide polymorphisms were found on Chromosome 9 within the WRKY transcription factor 86 (SbWRKY86). Transcripts encoding SbWRKY86 were previously identified as upregulated in SCA-resistant germplasm and the syntenic ortholog in maize accumulates following Rhopalosiphum maidis infestation. Analyses of SbWRKY86 transcript levels displayed elevated levels in additional SCA resistant sorghum lines. Heterologous expression of SbWRKY86 in both tobacco (Nicotiana benthamiana) and Arabidopsis resulted in reduced population growth of green peach aphid (Myzus persicae). Comparative RNA-Seq analyses of Arabidopsis lines expressing 35S:SbWRKY86-YFP identified changes in expression for a small network of genes associated with carbon-nitrogen metabolism and callose deposition, both contributing factors to defense against aphids. As a test of altered plant responses, 35S:SbWRKY86 Arabidopsis lines were activated using the flagellin epitope elicitor, flg22, and displayed significantly increased callose deposition. Our findings indicate that both heterologous and increased native expression of the transcription factor SbWRKY86 is associated with reduced aphid levels in diverse plant models.

作物对害虫的抗性基于遗传编码的特性，这些特性在多样化的种质资源中往往表现出变异性。在相对近期的事件中，一种主要的甘蔗蚜虫（SCA：Melanaphis sacchari）克隆已成为玉米高粱（Sorghum bicolor）生产的重要农业害虫。为了揭示SCA抗性的候选基因，我们采用了一种正向遗传学方法，结合了高粱协会面板（SAP）和生物能源协会面板（BAP）中存在的遗传多样性，进行了全基因组关联研究，并采用了已建立的SCA损伤评级。在染色体9上发现了具有统计学意义的单核苷酸多态性，位于WRKY转录因子86（SbWRKY86）内部。编码SbWRKY86的转录本先前已被确认为在SCA抗性种质资源中上调，而在玉米中的同源基因在Rhopalosiphum maidis感染后积累。对SbWRKY86转录本水平的分析显示，在额外的SCA抗性高粱品种中存在升高的水平。在烟草（Nicotiana benthamiana）和拟南芥（Arabidopsis）中异源表达SbWRKY86导致绿色桃蚜（Myzus persicae）种群增长减少。对表达35S:SbWRKY86-YFP的拟南芥系进行RNA-Seq比较分析，发现与碳氮代谢和木聚糖沉积相关的基因网络表达发生变化，这两者均为抗蚜虫的防御因素。为了测试植物响应的改变，通过flagellin表位诱导体flg22激活了35S:SbWRKY86拟南芥系，并显示出显著增加的木聚糖沉积。我们的研究结果表明，在多种植物模型中，SbWRKY86转录因子的异源表达和原生表达的提高与蚜虫水平的降低相关。