P-090 - Host Genetic Factors in S. indica-Mediated Plant Benefits

The mutualistic root endophyte Serendipita indica (order Sebacinales) promotes plant growth, development, and yield across a wide range of hosts, including Arabidopsis thaliana and barley. In addition to growth promotion, S. indica confers both local and systemic protection against pathogens such as the aggressive soil-borne fungus Bipolaris sorokiniana. While fungal effectors involved in this interaction have been well characterized, the role of host genetic factors in S. indica-mediated protection and growth promotion remains poorly understood. To address this, we performed weighted gene co-expression network analysis (WGCNA) on a previously generated RNA-seq dataset and identified several A. thaliana genes highly responsive to S. indica, including a well-characterized and a newly identified transcription factor. Functional analysis of corresponding T-DNA insertion lines revealed that both transcription factor mutants lost the growth promotion effect and displayed increased fungal colonization. In contrast, all tested mutants retained the pathogen protection phenotype, indicating that S. indica-mediated growth promotion and protection are genetically separable traits. These findings highlight the importance of host genetic factors and transcriptional regulation in mutualistic interactions, particularly for growth promotion, underscoring the need to further dissect their molecular functions in S. indica-mediated plant benefits.