MSB2-activated pheromone pathway regulates fungal plasma membrane integrity in response to herbicide adjuvant

Glyphosate-based herbicides (GBHs) are used worldwide for weed management. However, GBHs pose a threat to soil fungal community, although fungi can degrade and use glyphosate as a nutrient source. How fungi respond to GBHs remains enigmatic. Here, we found that, not as in plants, the commercial GBH Roundup does not target the 5-enolpyruvyl-shikimate-3-phosphate synthase in the soil-derived fungus Trichoderma guizhouense, whereas it impairs fungal growth. We demonstrate that the herbicide adjuvant Triton CG-110 is more toxic to fungal cells than pure glyphosate. It limits nitrogen uptake, which induces the expression of proteinase YPS1 to catalyze the shedding of the MSB2 extracellular domain from the plasma membrane, leading to the activation of the MAPK TMK1 pheromone pathway. The downstream B2H2-type transcription factor STE12 directly regulates ergosterol biosynthesis, affecting membrane fluidity and stability. To our knowledge, this is the first evidence that the pheromone pathway is implicated in ergosterol biosynthesis and plasma membrane integrity.