A sorghum genome-wide association study (GWAS) identifies a WRKY transcription factor as a candidate gene underlying resistance to sugarcane aphid (Melanaphis sacchari) - A time course transcriptomic analysis of sorghum following SCA herbivory

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.

作物对昆虫害虫的抵抗性基于遗传编码的性状，这些性状往往在多样的种质资源中表现出变异性。在相对较近的一次事件中，一种主要的甘蔗蚜虫（SCA：Melanaphis sacchari）克隆已成为 grain sorghum（Sorghum bicolor）生产的重大农业害虫。为了揭示 SCAR（甘蔗蚜虫抗性）背后的候选基因，我们采用了一种正向遗传学方法，结合 Sorghum Association Panel（SAP）和 Bioenergy Association Panel（BAP）中的遗传多样性，进行全基因组关联研究，并采用已建立的 SCA 损伤评级。在染色体 9 上发现了统计学上显著的单一核苷酸多态性，位于 WRKY 转录因子 86（SbWRKY86）内。编码 SbWRKY86 的转录本先前已被识别为在 SCAR 抗性种质资源中上调，且在玉米中的同源基因在 Rhopalosiphum maidis 寄生后积累。SbWRKY86 转录本水平的分析显示，在额外的 SCAR 抗性高粱品系中存在升高。SbWRKY86 在烟草（Nicotiana benthamiana）和拟南芥（Arabidopsis）中的异源表达导致绿色桃蚜（Myzus persicae）种群增长减少。对表达 35S:SbWRKY86-YFP 的拟南芥品系进行比较 RNA-Seq 分析，发现与碳氮代谢和木栓质沉积相关的基因网络表达发生改变，这两者均为抗蚜虫的防御因素。为了测试植物反应的改变，使用 flagellin 表位诱导体 flg22 激活 35S:SbWRKY86 拟南芥品系，结果显示木栓质沉积显著增加。我们的研究结果指示，SbWRKY86 转录因子在异源和原位表达增加的情况下，与多种植物模型中蚜虫水平的降低相关。