Identification and Functional Analysis of the Ph-2 Gene Conferring Resistance to Late Blight (Phytophthora infestans) in Tomato

Late blight is a destructive disease affecting tomato production. The identification and characterization of resistance (R) genes are critical for the breeding of late blight-resistant cultivars. The incompletely dominant gene <i>Ph-2</i> confers resistance against the race T₁ of <i>Phytophthora infestans</i> in tomatoes. Herein, we identified <i>Solyc10g085460</i> (<i>RGA1</i>) as a candidate gene for <i>Ph-2</i> through the analysis of sequences and post-inoculation expression levels of genes located within the fine mapping interval. The <i>RGA1</i> was subsequently validated to be a <i>Ph-2</i> gene through targeted knockout and complementation analyses. It encodes a CC-NBS-LRR disease resistance protein, and transient expression assays conducted in the leaves of <i>Nicotiana benthamiana</i> indicate that <i>Ph-2</i> is predominantly localized within the nucleus. In comparison to its susceptible allele (<i>ph-2</i>), the transient expression of <i>Ph-2</i> can elicit hypersensitive responses (HR) in <i>N. benthamiana</i>, and subsequent investigations indicate that the structural integrity of the <i>Ph-2</i> protein is likely a requirement for inducing HR in this species. Furthermore, ethylene and salicylic acid hormonal signaling pathways may mediate the transmission of the <i>Ph-2</i> resistance signal, with <i>PR1</i>- and HR-related genes potentially involved in the <i>Ph-2</i>-mediated resistance. Our results could provide a theoretical foundation for the molecular breeding of tomato varieties resistant to late blight and offer valuable insights into elucidating the interaction mechanism between tomatoes and <i>P. infestans</i>.