Cracking the wall: the fungal cell wall assembly protein ECM33 is a promising molecular target in powdery mildew fungi

Abstract

Cucurbit powdery mildew, predominantly caused by Podosphaera xanthii, poses a major threat to global cucurbit production due to the pathogen’s rapid adaptability and resistance to conventional fungicides. This growing challenge highlights the urgent need for alternative, sustainable disease management strategies. As the primary interface between the fungus, host plant, and environment, the fungal cell wall emerges as a strategic target for development of innovative control approaches. This study focuses on ECM33, a glycophosphatidylinositol (GPI)-anchored protein believed to play a role in cell wall architecture and integrity, although its specific biochemical function remains undefined. In silico structural modeling revealed that PxECM33 resembles leucine-rich repeat proteins and contains potential carbohydrate-binding motifs. Recombinant PxECM33 exhibited binding affinity for chitin, β-glucans, and mannans, the main glycosidic components of the P. xanthii cell wall, supporting these structural predictions. Molecular docking analyses uncovered distinct ligand-specific interactions with these carbohydrates, further implicating PxECM33 in cell wall dynamics. Silencing PxECM33 via RNA interference significantly impaired fungal growth and caused pronounced cell wall disorganization. Notably, dual silencing with the melon immune receptor gene CmCERK1 mitigated these defects, suggesting that PxECM33 may function in masking immunogenic oligosaccharides to evade host detection. Furthermore, spray-induced gene silencing (SIGS) targeting PxECM33 effectively reduced disease symptoms in melon plants, highlighting its potential as a sustainable and nontoxic biocontrol strategy. Given the high-sequence conservation of ECM33 among ascomycete fungi, these findings support its candidacy as a broad-spectrum molecular target for managing powdery mildew in cucurbits and potentially other crops.

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