Beijing Key Laboratory of Growth and Developmental Regulation for Protected Vegetable Crops, Department of Vegetable Science, China Agricultural University, Beijing, 100193, China.
Joint Laboratory for International Cooperation in Crop Molecular Breeding, Ministry of Education of the People's Republic of China, Beijing, 100193, China.
Plant J. 2021 Mar;105(6):1630-1644. doi: 10.1111/tpj.15138. Epub 2021 Jan 16.
Bacterial spot, which is caused by several Xanthomonas species, is an economically important disease in tomato (Solanum lycopersicum). Great efforts have been made for the identification of resistant sources and the genetic analysis of resistance. However, the development of resistant commercial varieties is slow due to the existence of multiple species of the pathogen and a poor understanding of the resistance mechanism in tomato. The current study revealed that the Rx4 gene encodes a nucleotide-binding leucine-rich repeat protein in the wild tomato species Solanum pimpinellifolium and specifically recognizes and confers a hypersensitive response (HR) to Xanthomonas euvesicatoria pv. perforans race T3 expressing the AvrXv3 avirulence protein. Complementation of the Rx4 gene in the susceptible tomato line Ohio 88119 using a transgenic approach resulted in HR, whereas knockout of the gene through CRISPR/Cas9 editing in resistant lines Hawaii 7981 and PI 128216 led to non-HR to race T3. Transcription of Rx4 was not induced by the presence of race T3. Furthermore, the Rx4 protein did not show physical interaction with AvrXv3 but interacted with SGT1-1 and RAR1. Virus-induced gene silencing of SGT1-1 and RAR1 in the resistant line PI128216 suppressed the HR to race T3. Taken together, our study confirms Rx4 is the gene conferring the HR to bacterial spot race T3 and reveals the potential roles of SGT1-1 and RAR1 as signals in the Rx4-mediated HR. This discovery represents a step forward in our understanding of the mechanism of resistance to bacterial spot in tomato and may have important implications for understanding plant-bacterial interactions.
细菌性斑点病是由几种黄单胞菌引起的，是番茄（Solanum lycopersicum）上一种重要的经济病害。人们已经做出了巨大的努力来鉴定抗性来源和分析抗性的遗传基础。然而，由于病原体存在多个物种以及对番茄抗性机制的了解不足，抗性商业品种的开发进展缓慢。本研究表明，Rx4 基因在野生番茄种 Solanum pimpinellifolium 中编码一个核苷酸结合亮氨酸丰富重复蛋白，该基因特异性识别并赋予对表达 AvrXv3 无毒蛋白的 Xanthomonas euvesicatoria pv. perforans 致病变种 T3 的感病反应（HR）。通过转基因方法在感病番茄品系 Ohio 88119 中补充 Rx4 基因导致 HR，而通过 CRISPR/Cas9 编辑在抗性品系 Hawaii 7981 和 PI 128216 中敲除该基因则导致对致病变种 T3 不发生 HR。Rx4 的转录不受致病变种 T3 的诱导。此外，Rx4 蛋白与 AvrXv3 没有表现出物理相互作用，但与 SGT1-1 和 RAR1 相互作用。在抗性品系 PI128216 中，病毒诱导的 SGT1-1 和 RAR1 基因沉默抑制了对致病变种 T3 的 HR。总之，我们的研究证实 Rx4 是赋予番茄对细菌性斑点病致病变种 T3 感病反应的基因，并揭示了 SGT1-1 和 RAR1 作为 Rx4 介导的 HR 信号的潜在作用。这一发现代表着我们对番茄细菌性斑点病抗性机制理解的一个进步，可能对理解植物与细菌的相互作用具有重要意义。
