OsHMA7 mediates copper transport into the chloroplast to maintain photosynthetic efficiency and alleviate oxidative stress

The chloroplast is a major sink for copper (Cu), which plays a crucial role in photosynthesis and oxidative stress protection in this organelle. The molecular mechanisms controlling Cu homeostasis in the chloroplast in rice remain unclear. Here, we identify OsHMA7, a P1B-type ATPase, as a chloroplast envelope-localized Cu transporter necessary for transporting Cu into the chloroplast. Temporal expression analysis revealed that OsHMA7 is expressed in both roots and leaves, with diurnal rhythmicity in the latter. Subcellular fractionation and confocal microscopy confirmed its exclusive localization to the leaf chloroplast envelope membrane and likely in plastids of roots. Heterologous expression in yeast demonstrated the Cu-transport activity of OsHMA7. Knockout of OsHMA7 by CRISPR/Cas9 significantly decreased the concentration of Cu in chloroplasts, resulting in large decreases in the abundance of the Cu-containing proteins plastocyanin and Cu/Zn-superoxide dismutase 2. Consequently, photosynthetic electron transfer efficiency and photosynthesis rate were reduced and the production of reactive oxygen species was increased. oshma7 mutants displayed severe growth impairments, with a 76-78% decrease in the tiller number and an 81-96% reduction in grain yield. Our findings establish OsHMA7 as an important Cu transporter in chloroplasts in rice, directly linking Cu homeostasis to photosynthetic efficiency and crop productivity.