Plant productivity and yield are dependent on source-sink relationships, i.e. the capacity of source leaves to fix CO2 and the capacity of developing sink tissues and organs to assimilate and convert this fixed carbon into dry matter. Studies from our laboratories as well as others have demonstrated that rice productivity and yield are mainly sink-limited during its development because of limited capacity to utilize the initial photosynthetic product (triose phosphate). This limitation in triose phosphate utilization, evident at both the vegetative and reproductive stages of rice development, may be associated with limited capacity for carbohydrate synthesis in rice leaves (which are poor accumulators of starch) or feedback due to limited sink strength of developing seeds. Strategies in improving triose phosphate utilization by enhancing starch production in leaves and developing seeds by the expression of engineered genes for ADP glucose pyrophosphorylase, a key regulatory enzyme of starch biosynthesis, are discussed.