The OsNramp4 aluminum transporter is involved in cadmium accumulation in rice grains
Xiaohua Hao, Yifan Mo, Wenjin Ji, Xiao Yang, Zijing Xie, Dan Huang, Dongping Li, Lianfu Tian
Abstract
Cadmium (Cd) toxicity affects many crops. Members of the OsNramp (Natural resistance-associated macrophage protein) gene family play important roles in the transport of divalent or trivalent cations in rice (Oryza sativa L.). This study explored a possible involvement of OsNramp4 in Cd2+ transport in rice. We employed the CRISPR/cas9 technique to obtain rice OsNramp4 knockout lines. Using NMT (Non-invasive Micro-test Technology) system for real-time measurement, it was found that the net Cd2+ flux was significantly lower than that of wild-type. The yeast strain expressing OsNramp4 grew poorly under Cd2+ stress, and accumulated more Cd2+ than the control strain, which enhanced the sensitivity of yeast to Cd2+. OsNramp4 was membrane-localized and mainly expressed in roots, but after tillering, its expression shifted to the nodes and glumes. Furthermore, the loss-of-function OsNramp4 mutation lowered the root cell sap Cd2+ content, resulting in a significant decrease in Cd2+ content in shoot and Cd2+ accumulation in grains. We characterized the OsNramp4, an Al3+ transporter with the ability to alter the cellular distribution of Cd2+ in rice and to reduce Cd2+ content in the grain. Our study highlights the complexity of ion uptake and transport in plants.