Maize cap1 encodes a novel SERCA-type calcium-ATPase with a calmodulin-binding domain

A cDNA (CAP1) isolated from maize roots shares sequence identity with genes encoding P-type Ca(2+)-ATPases and restores the growth phenotype of yeast mutants defective in Ca(2+)-pumps. CAP1 was transcribed and translated in the yeast mutant. Furthermore, the membrane-integrated product formed a Ca(2+)-dependent phosphorylated intermediate and supported Ca(2+) transport. Although CAP1 shares greater sequence identity with mammalian "endoplasmic reticulum-type" Ca(2+)-pumps, it differs from these genes by having features of calmodulin (CaM)-regulated Ca(2+)-pumps. CAP1 from yeast microsomes bound CaM, and the CAP1-dependent Ca(2+) transport in yeast was stimulated by CaM. Peptides from the C terminus of CAP1 bound CaM. Anti-CAP1 antibodies specifically recognized a maize microsomal polypeptide that also bound CaM. A similar polypeptide also formed a Ca(2+)-dependent phosphoenzyme. Our results suggest that cap1 encodes a novel form of CaM-regulated Ca(2+)-ATPase in maize. CAP1 appears to be encoded by one or two genes in maize. CAP1 RNA is induced only during early anoxia, indicating that the Ca(2+)-pump may play an important role in O(2)-deprived maize cells.