The present invention relates to nucleic acid fragments encoding amino
acid sequences for organic acid biosynthetic enzymes in plants, and the
use thereof for the modification of, for example, organic acid
biosynthesis and secretion in plants. In particularly preferred
embodiments, the invention relates to the combinatorial expression of
citrate synthase (CS) and/or malate dehydrogenase (MDH) and/or
phosphoenolpyruvate carboxylase (PEPC) in plants to modify, for example,
organic acid synthesis and secretion.