Boyce Thompson Institute for Plant Research, Ithaca, NY, 14853, USA.
Plant Pathology and Plant-Microbe Biology Section, School of Integrative Plant Science, Cornell University, Ithaca, NY, 14853, USA.
Plant J. 2020 Aug;103(4):1433-1445. doi: 10.1111/tpj.14810. Epub 2020 Jun 3.
The Ptr1 (Pseudomonas tomato race 1) locus in Solanum lycopersicoides confers resistance to strains of Pseudomonas syringae pv. tomato expressing AvrRpt2 and Ralstonia pseudosolanacearum expressing RipBN. Here we describe the identification and phylogenetic analysis of the Ptr1 gene. A single recombinant among 585 F2 plants segregating for the Ptr1 locus was discovered that narrowed the Ptr1 candidates to eight nucleotide-binding leucine-rich repeat protein (NLR)-encoding genes. From analysis of the gene models in the S. lycopersicoides genome sequence and RNA-Seq data, two of the eight genes emerged as the strongest candidates for Ptr1. One of these two candidates was found to encode Ptr1 based on its ability to mediate recognition of AvrRpt2 and RipBN when it was transiently expressed with these effectors in leaves of Nicotiana glutinosa. The ortholog of Ptr1 in tomato and in Solanum pennellii is a pseudogene. However, a functional Ptr1 ortholog exists in Nicotiana benthamiana and potato, and both mediate recognition of AvrRpt2 and RipBN. In apple and Arabidopsis, recognition of AvrRpt2 is mediated by the Mr5 and RPS2 proteins, respectively. Phylogenetic analysis places Ptr1 in a distinct clade compared with Mr5 and RPS2, and it therefore appears to have arisen by convergent evolution for recognition of AvrRpt2.
Ptr1（番茄假单胞菌 1 型）基因在番茄野生近缘种中的作用，赋予其对表达 AvrRpt2 的丁香假单胞菌 pv. tomato 菌株和表达 RipBN 的茄属假单胞菌的抗性。本研究描述了 Ptr1 基因的鉴定和系统发育分析。在分离鉴定 585 株 F2 代植物的 Ptr1 基因时，发现了一个单一的重组体，将 Ptr1 候选基因缩小到 8 个核苷酸结合亮氨酸重复蛋白（NLR）编码基因。通过对 S. lycopersicoides 基因组序列和 RNA-Seq 数据中基因模型的分析，这 8 个基因中的两个基因被认为是 Ptr1 的最强候选基因。其中一个候选基因被发现可以编码 Ptr1，因为它能够在 Nicotiana glutinosa 的叶片中瞬时表达这些效应子时，介导对 AvrRpt2 和 RipBN 的识别。番茄和 Solanum pennellii 中的 Ptr1 同源基因是一个假基因。然而，在 Nicotiana benthamiana 和马铃薯中存在功能正常的 Ptr1 同源基因，并且都能介导对 AvrRpt2 和 RipBN 的识别。在苹果和拟南芥中，AvrRpt2 的识别分别由 Mr5 和 RPS2 蛋白介导。系统发育分析将 Ptr1 置于与 Mr5 和 RPS2 不同的分支，因此它似乎是为了识别 AvrRpt2 而通过趋同进化产生的。
