摘要
Alternaria leaf spot in apple(Malus x domestica),caused by the fungal pathogen Alternaria alternata f.sp.mali(also called A.mali),is a devastating disease resulting in substantial economic losses.We previously established that the resistance(R)protein MdRNL2,containing a coiled-coil,nucleotide-binding,and leucine-rich repeat(CC R-NB-LRR)domain,interacts with another CC R-NB-LRR protein,MdRNL6,to form a MdRNL2–MdRNL6 complex that confers resistance to A.mali.Here,to investigate the function of the MdRNL2–MdRNL6 complex,we identified two novel pathogenesis-related(PR)proteins,MdPR10-1 and MdPR10-2,that interact with MdRNL2.Yeast two-hybrid(Y2H)assays and bimolecular fluorescence complementation(BiFC)assays confirmed that MdPR10-1 and MdPR10-2 interact with MdRNL2 and MdRNL6 at the leucine-rich repeat domain.Transient expression assays demonstrated that accumulation of MdPR10-1 and MdPR10-2 enhanced the resistance of apple to four strains of A.mali that we tested:ALT1,GBYB2,BXSB5,and BXSB7.In vitro antifungal activity assays demonstrated that both the proteins contribute to Alternaria leaf spot resistance by inhibiting fungal growth.Our data provide evidence for a novel regulatory mechanism in which MdRNL2 and MdRNL6 interact with MdPR10-1 and MdPR10-2 to inhibit fungal growth,thereby contributing to Alternaria leaf spot resistance in apple.The identification of these two novel PR proteins will facilitate breeding for fungal disease resistance in apple.
