Differential Expression of Genes Involved in Sucrose Synthesis in Source and Sink Organs of Cassava Plants Undergoing Seasonal Drought Stress

Sucrose functions as a regulator of gene expression allowing plants to respond to cellular energy demands during both normal and stress conditions. Previous studies indicated that drought followed with onset of rain could negatively affect yield of starch in storage roots of cassava. In this study, molecular approaches were conducted to investigate expression profiling of sucrose phosphate synthase (SPS), sucrose phosphatase (SPP) and 14-3-3, which are importance as regulatory points to modulate availability of sucrose in cassava. In source organs, expression of cassava (Manihot esculenta Crantz.) sucrose phosphate synthase (MeSPS) and cassava sucrose phosphatase (MeSPP) varied depending on developmental stage and day/night cycle. In sink organ, the levels of MeSPS, MeSPP and Me14-3-3 transcripts were affected to a much greater degree by different planting season than by root developmental stage. In response to fluctuating level of rainfall, a correlation between MeSPS and Me14-3-3 expression patterns was observed. This finding suggests the role of these enzymes and the importance of sucrose metabolism in seasonal drought stress response in cassava. Given the identified new role for cassava as an important biofuel crop as well as its current usage as a food crop, understanding on the most appropriate time to plant and harvest cassava in order to maximize starch quantity and quality is warranted.