P-151 - Deciphering the dynamic regulation of effector genes in the beneficial root endophyte Serenpita indica during monocot colonization

Interactions between plants and beneficial root-endophytic fungi enhance plant performance by improving nutrient uptake, abiotic stress tolerance, and disease resistance. To successfully colonize plant roots, defend their niche against microbial competitors, and cooperate with other beneficial members of the microbiota, these fungi secrete effector proteins. However, the regulatory mechanisms governing effector gene expression, particularly in beneficial root endophytes, remain poorly understood. Here, we employed transcriptomic analysis and DNA Affinity Purification sequencing to identify effector genes and their transcriptional regulators in Serendipita indica. Our study revealed that effector gene expression is dynamically regulated in response to different host plants and microbial interaction partners. Using weighted gene co-expression network analysis, we identified two key S. indica transcriptional regulators orchestrating effector gene expression in monocot hosts. One regulator controls genes encoding several functionally characterized S. indica effectors, while the other regulates effectors involved in host cell wall hydrolysis during late-stage colonization. Notably, overexpression of the latter during early colonization impaired host colonization, underscoring the importance of precise temporal regulation of effector expression. These findings provide new insights into the complex regulatory networks that shape symbiotic interactions between plants and fungi.