The TIR-Type NLR Protein Is Involved in the Regulation of Phelipanche aegyptiaca Resistance in Cucumis melo

Phelipanche aegyptiaca is an obligate holoparasite that causes serious negative effects on crop growth and productivity, effective control of which is difficult due to its unique biological characteristics. In this study, we performed a comparative transcriptome analysis of resistant and susceptible Cucumis melo cultivars (KR1326 and K1237) inoculated with P. aegyptiaca. CmNLR (encodes a TIR-type NLR protein, consistently highly expressed in KR1326 roots) and CmNLRh (homologous gene of CmNLR) were cloned and overexpressed in K1237 roots to verify whether the TIR-type NLR protein can enhance C. melo resistance to P. aegyptiaca. The variations in enzymes related to active oxygen metabolism were further detected in transformed roots. The results showed that (1) some differentially expressed genes (DEGs) were enriched in pathways associated with active oxygen scavenging; (2) several DEGs encoded transcription factors, calcium channel proteins, and receptor-like proteins were upregulated and expressed in KR1326 roots; (3) the complete CmNLR and CmNLRh proteins prevented P. aegyptiaca from connecting to the vascular system of C. melo roots; and (4) stronger active oxygen burst and scavenging capacity were detected in transformed roots. We herein demonstrated that the TIR-type NLR protein confers C. melo resistance to P. aegyptiaca. The results provided clues for finding a new direction for host resistance against parasitic plants and shed new light on the cultivation of resistant varieties to control P. aegyptiaca.