8 January 2026
Unnati Sonawala - Molecular Plant-Microbe Interactions, 2026
Picture a molecular masquerade with effectors wearing vastly different sequence “costumes” but sharing a similar underlying structural “skeleton” and plant immune receptors having to tell them apart. This is the challenge facing wheat’s PM3 immune receptors as they navigate detection of effector proteins from the powdery mildew pathogen Blumeria graminis f. sp. tritici (Bgt). One of the world’s most important crops at close to 800 million metric tonnes produced annually, wheat suffers 21.5% losses to pathogens and pests, with powdery mildew as a major contributor (FAO 2025; Savary et al. 2019). Understanding Bgt’s molecular dialogue with the wheat immune system is therefore critical.
The Bgt genome encodes over 800 candidate effectors, 70% or more of which are predicted to adopt a conserved RNase-like fold structure (Cao et al. 2023). A family of these effectors with an RNase-like fold present a dual paradox when it comes to their interaction with the wheat immune system. On the one hand, the wheat Pm3 gene comprises an allelic series of at least 17 functional variants sharing over 97% amino acid identity, yet they display exquisite specificity for recognizing the sequence-diverse AVRPM3 effectors (Bhullar et al. 2009; Bourras et al. 2019). How do these nearly identical immune receptors achieve such discrimination? Furthermore, since these sequence-diverse effectors share an RNase-like structural scaffold, what determines the specificity of their recognition by a PM3 allelic variant?
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