SbHMA5 is a P1B-type Cu ATPase involved in Cu homeostasis by interacting with metallochaperones SbATX1 and SbFRN3

Copper (Cu) is required by prokaryotes and eukaryotes for fundamental life processes including photosynthesis, respiration and neurotransmission but excess Cu is toxic, causing severe problems ranging from weak plant growth to Wilson's disease in humans. Copper homeostasis was shown to be tightly regulated by P1B-type ATPase in yeast and other model organisms but the molecular mechanism by which sorghum plants maintain this delicate balance of Cu homeostasis remains poorly understood. We identified 31 orthologs of P1B-type metal transporters in Sorghum bicolor. From the identified sorghum orthologs of P1B-type ATPases, we complemented the yeast ∆ccc2 mutant with SbHMA5. We showed that SbHMA5 encodes a P1B- type Cu ATPase homologous to OsHMA5 and AtHMA5. The SbHMA5 transcript is detected in most sorghum tissues and induced by CuSO4 treatment. The protein is predominantly localized in the plasma membrane and physically interacts with Cu chaperones SbATX1 and SbFRN3. Our results suggest that SbHMA5 is an efflux carrier involved in Cu homeostasis required for sorghum growth and development.