Modulating Plant Calcium for Better Nutrition and Stress Tolerance

External Ca 2+ supplementation helps plants to recover from stress. This paper considers genetic methods for increasing Ca 2+ to augment stress tolerance in plants and to increase their nutritional value. The transport of Ca 2+ must be carefully controlled to minimize fluctuations in the cytosol while providing both structural support to new cell walls and membranes, and intracellular stores of Ca 2+ for signaling. It is not clear how this is accomplished in meristems, which are remote from active transpiration—the driving force for Ca 2+ movement into shoots. Meristems have high levels of calreticulin (CRT), which bind a 50-fold excess of Ca 2+ and may facilitate Ca 2+ transport between cells across plasmodesmatal ER. Transgenes based on the high-capacity Ca 2+ -binding C-domain of CRT1 have increased the total plant Ca 2+ by 15%–25% and also increased the abiotic stress tolerance. These results are compared to the overexpression of sCAX1 , which not only increased total Ca 2+ up to 3-fold but also caused Ca 2+ deficiency symptoms. Coexpression of sCAX1 and CRT1 resolved the symptoms and led to high levels of Ca 2+ without Ca 2+ supplementation. These results imply an important role for ER Ca 2+ in stress tolerance and signaling and demonstrate the feasibility of using Ca 2+ -modulating proteins to enhance both agronomic and nutritional properties.