Distinct domains of the AVRPM3 ^A2/F2 avirulence protein from wheat powdery mildew are involved in immune receptor recognition and putative effector function

Summary

• Recognition of the AVRPM3 ^A2/F2 avirulence protein from powdery mildew by the wheat PM3A/F immune receptor induces a hypersensitive response after co‐expression in Nicotiana benthamiana. The molecular determinants of this interaction and how they shape natural AvrPm3 ^a2/f2 allelic diversity are unknown.

• We sequenced the AvrPm3 ^a2/f2 gene in a worldwide collection of 272 mildew isolates. Using the natural polymorphisms of AvrPm3 ^a2/f2 as well as sequence information from related gene family members, we tested 85 single‐residue‐altered AVRPM3 ^A2/F2 variants with PM3A, PM3F and PM3 F ^{L 456P/Y458H} (modified for improved signaling) in Nicotiana benthamiana for effects on recognition.

• An intact AvrPm3 ^a2/f2 gene was found in all analyzed isolates and the protein variant recognized by PM3A/F occurred globally at high frequencies. Single‐residue alterations in AVRPM3 ^A2/F2 mostly disrupted, but occasionally enhanced, the recognition response by PM3A, PM3F and PM3 F ^{L 456P/Y458H}. Residues enhancing hypersensitive responses constituted a protein domain separate from both naturally occurring polymorphisms and positively selected residues of the gene family.

• These results demonstrate the utility of using gene family sequence diversity to screen residues for their role in recognition. This approach identified a putative interaction surface in AVRPM3 ^A2/F2 not polymorphic in natural alleles. We conclude that molecular mechanisms besides recognition drive AvrPm3 ^a2/f2 diversification.