An endophytic fungus interacts with the defensin-like protein OsCAL1 to regulate cadmium allocation in rice.

Defensin-like proteins are conserved in multicellular organisms and contribute to innate immune responses against fungal pathogens. In rice, defensins play a novel role in regulating cadmium (Cd) efflux from the cytosol. However, whether the antifungal activity of defensins correlates with Cd-efflux function remains unknown. In this study, we isolated an endophytic Fusarium , designed Fo 10, by a comparative microbiome analysis of rice plants grown in a paddy contaminated with Cd. Fo 10 is tolerant to high levels of Cd, but is sensitive to the defensin-like protein OsCAL1, which mediates Cd efflux to the apoplast. We found that Fo 10 symbiosis in rice is regulated by OsCAL1 dynamics, and Fo 10 coordinates multiple plant processes, including Cd uptake, vacuolar sequestration, efflux to the environment, and formation of Fe plaques in the rhizosphere. These processes are dependent on the salicylic acid signaling pathway to keep Cd levels low in the cytosol of rice cells and to decrease Cd levels in rice grains without any yield penalty. Fo 10 also plays a role in Cd tolerance in the poaceous crop maize and wheat, but has no observed effects in the eudicot plants Arabidopsis and tomato. Taken together, these findings provide insights into the mechanistic basis underlying how a fungal endophyte and host plant interact to control Cd accumulation in host plants by adapting defense responses to promote the establishment of a symbiosis that permits adaptation to high-Cd environments. This study identifies an endophytic Fusarium Fo 10 that interacts reciprocally with the defensin-like protein OsCAL1 to reduce cytosolic Cd levels in rice. Fo10 modulates iron plaque formation, vacuolar Cd sequestration, and rhizosphere Cd efflux likely by activating SA signaling pathway. [ABSTRACT FROM AUTHOR]