Bioengineering beans for phosphate-deficient soils in southern Africa
APPROXIMATELY EIGHT SPECIES OF SOUTHern African legumes are currently used as sustainable food crops. Biotechnology has the potential to improve the productivity of growing these plants by small-scale farmers who cannot afford sufficient phosphate fertilizer to optimize their nitrogen fixation and hence conversion to edible protein. The metabolic adaptations that enable legumes to fix atmospheric nitrogen are currently being investigated by our group for the purpose of genetic modification to enhance crop yields. Until now, attempts at modifying host plants or symbiotic bacteria have not significantly enhanced N2 fixation. We propose, instead, to bioengineer the key enzymes that control the mechanisms involved in protein formation. This may lead to enhanced seed protein content, which would be of advantage to poor communities that rely on this source of food. We postulate that misregulation of phosphoenolpyruvate carboxylase (PEPc) could be exploited by biotechnology to improve N2 fixation and protein content. We have found that, as distinct from their roots, legume nodules are under permanent phosphate stress, even during optimal phosphate supply to the host plant, implying that the development of phosphate stress may engage different forms of PEPc to ensure continued nodule functioning.