Deciphering the Role of Reshaped Fungal Microbiome in Cadmium Accumulation in Rice Grains

Rice cadmium (Cd) contamination is a serious threat to global food security and human health. Plant-associated microbiomes are known to affect Cd accumulation in plants. However, the response of the rice microbiome to Cd contamination and its role in modulating grain Cd accumulation remain poorly understood. In the present study, the responses of the rhizospheric fungi (RF) community and seed endophytic fungi (SEF) community to the soil physiochemical properties of rice from moderately (MC) and severely (SC1 and SC2) Cd-contaminated paddies were investigated. Moreover, the effects of soil physiochemical properties, RF community and SEF community on grain Cd accumulation were analyzed through correlation analysis. The results showed that the Cd concentration in rice grains from SC2 exceeded the food safety standard of China and was higher than that of SC1 and MC. The Cd concentration in rice grains was positively correlated with the soil-available Cd concentration, while being negatively correlated with the available nutrient elements and pH value of soil. In addition, it was found that the diversity of RF increased with the soil-available Cd concentration, while the diversity and richness of SEF decreased with the soil-available Cd concentration. Moreover, the RF community was influenced by soil physiochemical properties. The Spearman correlation analysis showed that the soil-available Cd was positively correlated with RF Sebacina, Clonostachys, Acremonium, Talaromyces and Fusarium, and most of them were related to grain Cd concentration, while unclassified SEF Pleosporales and Xylariales were associated with grain Cd concentration. These results suggested that Cd stress triggered a niche-specific response of the rice fungal microbiome. The fungi related to soil Cd availability and rice grain Cd accumulation may have a great potential application in food safety production in Cd-contaminated soil.