Xu Qiang, Xu Xuewen, Shi Yang, Qi Xiaohua, Chen Xuehao
Department of horticulture, School of horticulture and plant protection, Yangzhou University, 48 east wenhui road, Yangzhou, Jiangsu, 225009, China.
BMC Genomics. 2017 Jan 5;18(1):21. doi: 10.1186/s12864-016-3438-z.
Powdery mildew (PM) is one of the most severe fungal diseases of cucurbits, but the molecular mechanisms underlying PM resistance in cucumber remain elusive. In this study, we developed a PM resistant segment substitution line SSL508-28 that carried a segment on chromosome five representing the Pm5.1 locus from PM resistant donor Jin5-508 using marker-assisted backcrossing of an elite PM susceptible cucumber inbred line D8.
Whole-genome resequencing of SSL508-28, Jin5-508 and D8 was performed to identify the exact boundaries of the breakpoints for this introgression because of the low density of available single sequence repeat markers. This led to the identification of a ~6.8 Mb substituted segment predicted to contain 856 genes. RNA-seq was used to study gene expression differences in PM treated (plants harvested 48 h after inoculation) and untreated (control) SSL508-28 and D8 lines. Exactly 1,248 and 1,325 differentially expressed genes (DEGs) were identified in SSL508-28 and D8, respectively. Of those, 88 DEGs were located in the ~6.8 Mb segment interval. Based on expression data and annotation, we identified 8 potential candidate genes that may participate in PM resistance afforded by Pm5.1, including two tandemly arrayed genes encoding receptor protein kinases, two transcription factors, two genes encoding remorin proteins, one gene encoding a P-type ATPase and one gene encoding a 70 kDa heat shock protein. The transcriptome data also revealed a complex regulatory network for Pm5.1-mediated PM resistance that may involve multiple signal regulators and transducers, cell wall modifications and the salicylic acid signaling pathway.
These findings shed light on the cucumber PM defense mechanisms mediated by Pm5.1 and provided valuable information for the fine mapping of Pm5.1 and breeding of cucumber with enhanced resistance to PM.
白粉病（PM）是葫芦科作物最严重的真菌病害之一，但黄瓜对白粉病抗性的分子机制仍不清楚。在本研究中，我们利用一个感白粉病的优良黄瓜自交系D8，通过标记辅助回交，培育出了一个白粉病抗性片段代换系SSL508-28，该代换系在5号染色体上携带了一个来自白粉病抗性供体津5-508的代表Pm5.1位点的片段。
由于可用的单序列重复标记密度较低，对SSL508-28、津5-508和D8进行了全基因组重测序，以确定该渗入片段断点的确切边界。这导致鉴定出一个约6.8 Mb的代换片段，预计包含856个基因。利用RNA测序研究了经白粉病处理（接种后48小时收获的植株）和未处理（对照）的SSL508-28和D8品系中的基因表达差异。在SSL508-28和D8中分别鉴定出1248个和1325个差异表达基因（DEG）。其中，88个DEG位于约6.8 Mb的片段区间内。基于表达数据和注释，我们鉴定出8个可能参与Pm5.1介导的白粉病抗性的潜在候选基因，包括两个串联排列的编码受体蛋白激酶的基因、两个转录因子、两个编码remorin蛋白的基因、一个编码P型ATP酶的基因和一个编码70 kDa热休克蛋白的基因。转录组数据还揭示了一个由Pm5.1介导的白粉病抗性的复杂调控网络，该网络可能涉及多个信号调节因子和转导因子、细胞壁修饰以及水杨酸信号通路。
这些发现揭示了由Pm5.1介导的黄瓜白粉病防御机制，并为Pm5.1的精细定位和培育对白粉病抗性增强的黄瓜提供了有价值的信息。
