Nucleotide-binding leucine-rich repeat (NLR) receptor is suggested as a component of nonhost resistance (NHR). However, the evolutionary process of how plants develop receptors for recognizing wide range of non-adapted pathogens is still elusive.
We observed that multiple RxLR effector families including 12 reported avirulence effectors of Phytophthora infestans are broadly conserved across the Phytophthora species. We cloned 69 effectors distributed into 8 families from 6 Phytophthora species, and confirmed that 60.87% (42/69) of the tested effectors are recognized by the corresponding Solanum NLR (R1, R2, R3a, R8, Rpi-amr1, Rpi-blb1, Rpi-blb2, Rpi-vnt1). Notably, all the tested Solanum NLRs, except for Rpi-blb2, were able to recognize homologous effectors of multiple Phytophthora species. Furthermore, we also confirmed that expression of R1, R8, and Rpi-amr1 conferred broad-spectrum resistance against multiple Phytophthora species in Nicotiana benthamiana.
Combined results suggest that conserved effector families of Phytophthora species allow Solanaceae plants to recognize wide-range of pathogens by using NLRs that originally reported to recognize P. infestans, thus contribute to NLR-mediated NHR. Moreover, considering that resistance genes against most of Phytophthora species, except for P. infestans, have never been identified, our homology-based approach would provide a powerful strategy to identify functional NLRs against multiple pathogens threatening crop production.