Host transcriptional and microbiome metatranscriptomic changes in soybean plants carrying the insect-pathogenic fungus Beauveria bassiana as an endophyte

Abstract

Entomopathogenic fungi, such as Beauveria bassiana, have been naturally isolated from various plant species and have also been introduced as endophytes to enhance plant health and resilience. These fungal endophytes are often associated with improved plant defense against insect pest herbivory. This study aimed to assess the endophytic capacity of B. bassiana ARSEF 2860 in soybean plants and to investigate the associated changes in gene expression and leaf microbiome activity one-week post-inoculation. The results showed that B. bassiana successfully colonized the leaves, stems, and roots of soybean plants and induced gene expression changes in both the host leaves and their associated microbiome. In the soybean leaves, the fungal endophyte down-regulated genes related to responses to far-red light and the abscisic acid pathway, while up-regulating genes involved in photosynthesis, lipid and carbohydrate biosynthesis, and stress response. Additionally, plant inoculation with B. bassiana was associated with a reduction in total microbiome transcript abundance. This shift was characterized by a relative decrease in reads mapping to potentially pathogenic bacteria, alongside a relative increase in transcripts from bacteria commonly associated with beneficial functions. Total fungal reads were also lower in B. bassiana-colonized plants compared to control samples, with plant-pathogenic fungal reads being reduced. These findings highlight the role of entomopathogenic fungal endophytes to promote plant growth by potentially enhancing photosynthesis and strengthening plant defense mechanisms. The shift in the microbial activity highlights the capacity of endophytes to modulate plant-associated microbiota towards communities that may enhance health and resilience.