The Effect of Rhizophagus intraradices on Cadmium Uptake and OsNRAMP5 Gene Expression in Rice

The molecular mechanism of arbuscular mycorrhizal fungi (AMF) in reducing cadmium (Cd) accumulation in plants remains unclear. In this respect, the effects of Rhizophagus intraradices (Ri) inoculation under Cd stress on rice growth, the uptake of Cd along with other elements, and the expression of Cd transport genes, including OsNRAMP1/5, were studied using wild-type (WT) and osnramp5 mutant rice. The results showed that Ri inoculation did not affect rice growth. The uptake of Cd of the osnramp5 mutant was much lower than the WT, as 27.6%, 17.5%, and 39.9% of Cd were noted in the grains, shoots, and roots, respectively. For the WT, Cd alone significantly promoted the OsNRAMP5 expression in shoots, but Ri inoculation significantly suppressed OsNRAMP5 expression and significantly reduced its grain and shoot Cd by 44.4% and 62.3%, respectively, compared to the Cd alone treatment. In contrast, for the osnramp5 mutant, Ri inoculation did not influence OsNRAMP5 expression or the grain and shoot Cd. Furthermore, the expression of other Cd transporters (OsIRT1, OsZIP3/7, OsCAX1a) in both varieties were not changed under the treatments. In conclusion, Ri inoculating significantly reduced Cd uptake by rice, with the molecular mechanism by negative regulation of expression of the OsNRAMP5 gene.