Isolation, Characterization and Immunolocalization of a Seed Dominant CaM from Finger Millet (Eleusine coracana L. Gartn.) for Studying Its Functional Role in Differential Accumulation of Calcium in Developing Grains

To understand the exceptional high grain calcium accumulation in finger millet grains, a calmodulin (CaM) gene that is strongly expressed during developing spikes of high grain calcium genotype was further characterized. Using 5′–3′ RACE, the full-length CaM open reading frame (ORF) was isolated and the deduced protein sequence showed the presence of four characteristic EF motifs. Phylogenetic analysis showed that the finger millet CaM (Eleusine coracana calmodulin [EcCaM]) was identical to the rice CaM 1-1. Southern hybridization showed the presence of at least four copies of CaM gene that might be located on different regions of the finger millet "AABB" genome. Immunodetection using monospecific polyclonal anti-EcCaM antibodies revealed that EcCaM is localized in the embryo and aleurone layer and accumulates in higher amounts in high grain calcium genotype compared to the low grain calcium genotype. Furthermore, in silico analysis showed that EcCaM interacts with aquaporin which indicates that calcium is probably delivered to developing spike via mass flow of water. These results indicate that higher expression of CaM might cause greater stimulation of the downstream calcium transport machinery operative in the aleurone layer leading to the higher calcium accumulation in the grains of high grain calcium genotype.