Strigolactone analog GR24 modulates hyphal growth, mitochondrial activity, and superoxide accumulation in the ectomycorrhizal fungus Rhizopogon roseolus

Abstract Plant hormone strigolactone (SL) is an important rhizosphere signal that mediate communication between plants and diverse soil organisms. However, the role of SL in ectomycorrhizal (ECM) fungi remains largely unexplored, despite ECM fungi representing a major group of plant symbiotic fungi. To address this knowledge gap, we examined the effects of widely used SL analog GR24 with different stereoisomers and concentrations on several ECM fungal species. Deeper investigation on cellular and transcriptional response to GR24 was conducted on Rhizopogon roseolus . The evaluated parameters include fungal growth and branching, mitochondrial activity, superoxide accumulation, Ca 2+ signaling, and gene expression. Our findings reveal that ECM fungal responses to GR24 depend on fungal species, as well as GR24 stereoisomers and concentration. Further analysis on R. roseolus suggested that GR24 enhanced mitochondrial activity and increased mitochondria-associated superoxide accumulation. Based on pharmacological approach, the response of R. roseolus to GR24 required extracellular Ca 2+ influx. Consistent with these morphological and cellular responses, GR24 induce transcriptional response in genes related to cell-wall biosynthesis, mitochondrial respiratory chain, superoxide detoxification, and Ca 2+ signaling. Together, these findings provide novel insight into SL responsiveness in ECM fungi by integrating morphological, cellular, and transcriptional analyses.