The Histological, Effectoromic, and Transcriptomic Analyses of Solanum pinnatisectum Reveal an Upregulation of Multiple NBS-LRR Genes Suppressing Phytophthora infestans Infection

Utilization of disease resistance components from wild potatoes is a promising and sustainable approach to control Phytophthora blight. Here, we combined avirulence (Avr) genes screen with RNA-seq analysis to discover the potential mechanism of resistance in Mexican wild potato species, Solanum pinnatisectum. Histological characterization displayed that hyphal expansion was significantly restricted in epidermal cells and mesophyll cell death was predominant, indicating that a typical defense response was initiated in S. pinnatisectum. Inoculation of S. pinnatisectum with diverse Phytophthora infestans isolates showed distinct resistance patterns, suggesting that S. pinnatisectum has complex genetic resistance to most of the prevalent races of P. infestans in northwestern China. Further analysis by Avr gene screens and comparative transcriptomic profiling revealed the presence and upregulation of multiple plant NBS-LRR genes corresponding to biotic stresses. Six NBS-LRR alleles of R1, R2, R3a, R3b, R4, and Rpi-smira2 were detected, and over 60% of the 112 detected NLR proteins were significantly induced in S. pinnatisectum. On the contrary, despite the expression of the Rpi-blb1, Rpi-vnt1, and Rpi-smira1 alleles, fewer NLR proteins were expressed in susceptible Solanum cardophyllum. Thus, the enriched NLR genes in S. pinnatisectum make it an ideal genetic resource for the discovery and deployment of resistance genes for potato breeding.