Micro-area and transcriptome analysis revealed the mechanism of manganese inhibits the accumulation and upward transport of cadmium in the first node of rice

• Foliar-spraying EDTA-Mn obtained the maximum reduction of 66.7 % in Cd content of grain. • The central stem node (enlarged vascular bundles and diffuse vascular bundles) of the first node was the key tissues for transportation between Cd and Mn. • Spraying Mn regulated the expression of OsACA3, OsYSL8, OsYSL12, OsZIP1 genes in the first node to inhibit the upward transportation of Cd. It was proved that manganese (Mn) inhibits the accumulation of cadmium (Cd) in rice, and Mn and Cd share multiple transporter proteins, but the interaction mechanism between Mn and Cd in rice is still unclear. This study confirmed that Mn decreased the Cd content of grain (Cd grain ) through field and pot experiments. Moreover, the foliar spraying of EDTA-Mn with the Mn level of 0.135 g L -1 obtained the best inhibitory effect (66.7 %) on Cd grain . Cd grain was significantly positively correlated with Cd in the first node (N1) which showed the greatest decrease(0.19 mg kg -1 ) compared with that of the other parts after Mn spraying. It was observed by LA-ICP-MS that Mn significantly decreased the density both of Cd and Zn in N1, and the reduction of Cd in the central stem bundle was higher than that in the peripheral sheath bundle. The SEM-EDS results also verified that the proportion of Cd and Zn in N1 decreased with the increase of Mn proportion. Therefore, N1 is the key part of the interaction between Cd and Mn. Transcriptome data supported that the spraying of Mn upregulated the expression of OsACA3 , downregulated the expressions of metal transporter genes in N1, which may inhibit the upward transport of Cd by downregulate genes such as OsYSL8, OsABCG39, OsPT8, NAT2, NAT6, OsYSL12 , and OsZIP1 . This study identified the optimal practical form and application concentration of Mn, and improved the molecular regulation mechanism of spraying Mn to inhibit Cd grain , which provided an important research basis for the application of spraying Mn in rice safety production.