Abstract：
FLAGELLIN SENSING 2 (FLS2) encodes a pattern recognition receptor that perceives bacterial flagellin. While putative FLS2 orthologs are broadly conserved in plants, their functional characterization remains limited. Here, we report the identification of orthologs in cucumber (Cucumis sativus) and melon (C. melo), named CsFLS2 and CmFLS2, respectively. Homology searching identified CsFLS2, and virus-induced gene silencing (VIGS) demonstrated that CsFLS2 is required for flg22-triggered ROS generation. Interestingly, genome re-sequencing of melon cv. Lennon and subsequent genomic PCR revealed that Lennon has two CmFLS2 haplotypes, haplotype I encoding full-length CmFLS2 and haplotype II encoding a truncated form. We show that VIGS-mediated knockdown of CmFLS2 haplotype I resulted in a significant reduction in both flg22-triggered ROS generation and immunity to a bacterial pathogen in melon cv. Lennon. Remarkably, genomic PCR of CmFLS2 revealed that 68% of tested commercial melon cultivars possess only CmFLS2 haplotype II: these cultivars thus lack functional CmFLS2. To explore evolutionary aspects of CmFLS2 haplotype II occurrence, we genotyped the CmFLS2 locus in 142 melon accessions by genomic PCR and analyzed 437 released sequences. The results suggest that CmFLS2 haplotype II is derived from C. melo subsp. melo. Furthermore, we suggest that the proportion of CmFLS2 haplotype II increased among the improved melo group compared with the primitive melo group. Collectively, these findings suggest that the deleted FLS2 locus generated in the primitive melo subspecies expanded after domestication, resulting in the spread of commercial melon cultivars defective in flagellin recognition, which is critical for bacterial immunity.
摘要：
FLAGELLINSensing2(FLS2)编码感知细菌鞭毛蛋白的模式识别受体。虽然推定的FLS2直向同源物在植物中广泛保守，它们的功能特征仍然有限。这里,我们报告了黄瓜（Cucumissativus）和甜瓜（C.melo),分别命名为CsFLS2和CmFLS2。同源性搜索鉴定了CsFLS2,并且病毒诱导的基因沉默(VIGS)证明CsFLS2是flg22触发的ROS产生所必需的。有趣的是,甜瓜简历的基因组重测序。Lennon和随后的基因组PCR显示Lennon具有两个CmFLS2单倍型，编码全长CmFLS2的单倍型I和编码截短形式的单倍型II。我们表明，VIGS介导的CmFLS2单倍型I敲低导致甜瓜cv中flg22触发的ROS产生和对细菌病原体的免疫力显着降低。列侬值得注意的是,CmFLS2的基因组PCR显示，68％的测试商业甜瓜品种仅具有CmFLS2单倍型II：因此，这些品种缺乏功能性CmFLS2。探索CmFLS2单倍型II发生的进化方面，我们通过基因组PCR对142个甜瓜品种的CmFLS2基因座进行了基因分型，并分析了437个释放序列。结果表明，CmFLS2单倍型II来自C.melo亚种。梅洛.此外，我们建议与原始melo组相比，改良melo组的CmFLS2单倍型II的比例增加。总的来说，这些发现表明，在原始melo亚种中产生的缺失的FLS2基因座在驯化后扩展，导致鞭毛蛋白识别缺陷的商业甜瓜品种的传播，这对细菌免疫至关重要。
