Insights into role of STP13 in sugar driven signaling that leads to decrease in photosynthesis in dicot legume crop model (Phaseolus vulgaris L.) under Fe and Zn stress.

Mineral (Fe/Zn) stress significantly affects fundamental metabolic and physiological responses in plants that results in reduction of plant growth and development. Deficiency of these micronutrients leads to inhibition of photosynthesis by having impact on various crucial biological processes like protein synthesis, primary and secondary metabolism and carbohydrate partitioning between source and sink tissues. In the present study, common bean variety Shalimar French Bean-1 (SFB-1) plants were used as an experimental material and were grown under in vitro condition on four different MGRL media i.e. normal MGRL medium (Control), MGRL without Fe (0-Fe), MGRL without Zinc (0-Zn) and MGRL with excess Zn (300-Zn) for 21 days under optimum conditions. Shoot and root tissues from all the treatments were harvested and further subjected to estimation of total chlorophyll, total sugar and extraction of total RNA for differential gene expression of sugar transporter 13 (STP13). We observed significant decrease in total chlorophyll content in samples harvested from mineral stress plants. However, the concentration of total sugar and fold expression of STP13 gene was significantly higher in shoots of Fe/Zn stressed and in roots of 300-Zn plants. We observed higher accumulation of sugar under stress condition that correlated with high expression of sugar transporter 13 (STP 13). Further, we observed decrease in the chlorophyll content under stress conditions. Based on these findings, we propose the role of sugar driven signaling in decreasing photosynthesis in case of common bean. The decrease in photosynthesis is confirmed by observing significant decrease in chlorophyll content in stressed plants.