Zinc supply influences the root-specific traits with the expression of root architecture modulating genes in millets

This study analyzed the root phenotypic, seed yield, biochemical, and molecular changes of seven millets under differential Zn supply. Seven types of millets, such as foxtail millet, finger millet, kodo millet, little millet, pearl millet, proso millet, and barnyard millet were grown under diverse concentrations of Zn (0.05 to 2 & mu;M). Phenotypic changes, Zn uptake, enzyme activities, and zinc-regulated, iron-regulated transporter-like proteins (ZIP) transporter and root architecture-related candidate gene expression were analyzed. The better response for phenotypic traits of all seven millets was seen under 0.50 to 2 & mu;M Zn supply than deficient Zn (0.05 & mu;M). All the millets grown under deficient Zn conditions showed significantly lower mean Zn contents in the leaf and root tissue. The antioxidant enzyme activity increased in the leaves of all millets under Zn deficiency conditions. Root-related traits such as root hair density, lateral root length, and the number increased under Zn deficiency conditions in all millets. The molecular studies indicate that higher root-specific gene expression levels correlate with root phenotypic traits. Under Zn deficiency conditions, the root architecture-modifying genes such as transport inhibitor response 1 (TIR1) and root hair defective 3 (RHD3) are highly up-regulated in the root tissues. The ZIP family transporter genes were expressed under both Zn sufficient and deficient conditions in all millets. We have determined the optimum concentration of Zn for the growth and yield of seven millets. It will help to reduce the over-application of Zn fertilizer and increase millet production. This study also provides insight into the role of root-specific traits for improving Zn-uptake in millets under the Zn deficiency condition.