Regulation of the major vacuolar Ca2+ transporter genes, by intercellular Ca2+ concentration and abiotic stresses, in tip-burn resistant Brassica oleracea

Abstract

Calcium is an essential plant macronutrient that has unique structural and signaling roles related to tip-burn disorder in Brassica spp. crops. For two types of cabbage inbred lines, tip-burn susceptible and resistant, we measured and compared major macronutrient cations, including Ca2+, in leaves. In both lines, Ca2+, Mg2+, Na+, and K +, accumulated more in leaf base than in leaf apex. Ca2+ and K+ were >2 times more abundant in the tip-burn resistant line, while Na+ was higher in the susceptible line. Ca2+ differences between the two lines resulted from differential accumulation of calcium into cell vacuoles. We profiled major vacuolar Ca2+ transporters, in both cabbage lines, by growth time and intercellular Ca 2+ concentration. Expression pattern of several Ca2+ transporter genes differed between tip-burn susceptible and resistant lines by growth time points. We also identified promoter regions of the major Ca 2+ vacuole transporter genes, CAX1, ACA4, and ACA11, which displayed hormonal, light and defense-related cis-acting regulatory elements. Finally, transporter genes in the two cabbage lines responded differently to abiotic stresses, demonstrating diversity in gene regulation among orthologous genes.