Mercury-driven fungal endophytic community and the role of endophytes in rice grain mercury accumulation.

Rice, a staple food for over half of the global population, is an important dietary source of methylmercury (MeHg) due to its high accumulation capacity. Endophytes are known to impact host plants heavy metals (HMs) accumulation, conversely, HMs can alter host plants endophytics communities. However, the specifically addressing mercury-rice endophytic fungal system remains limited. In the present study, the fungal endophytic community of rice from Hg-contaminated and uncontaminated sites were investigated by Illumina sequencing, and its role on rice grains MeHg accumulation was evaluated through pot experiments. Results showed that soil Hg concentration significantly restructured rice fungal endophytic communities, and higher Hg concentration decreased the richness and diversity of fungal endophytes, and the effect differed with tissues and development stages. The endophytic community in grains was distinct from roots, stalks and leaves, enriching specific rare species while reducing others ubiquitous in the vegetative tissues. Pot experiments identified some specific endophytes that significantly modulated grain Hg accumulation. Two Epicoccum nigrum strains (DHJ7, FZT214) reduced grain MeHg by 44.67 % and 48.79 %, respectively (p < 0.05), whereas Phoma herbarum (CSJ51, CHJ4) increased grain MeHg or total mercury (THg) by 50.1 %-51.35 % and 77.39 %-81.81 %, respectively (p < 0.05). Furthermore, 62.5 % of the tested isolates (16) enhanced rice yield, while Mucor sp. DHJ19 and Ceratorhiza sp. CHJ27 improved production by 72.6 %-80.5 % compared to controls. These findings highlight promising fungal endophytes for mitigating grain Hg contamination and improving yield. Future work should elucidate the mechanisms governing the selective enrichment of grain endophytes to deepen understanding of plant-endophyte interactions.