Abstract
We investigate the function of nucleotide pyrophosphatase/phosphodiesterase (NPP) in rice. Six NPP isozyme genes have been found in rice. Previously, we purified and characterized NPP1, 2 and 6. NPP1 and 6 were divided into ADP-glucose hydrolyzing type, while NPP2 was nucleotide hydrolyzing type. All NPP isozymes were conjugated with Con A-recognized saccharide chains, and existed as 70-74 kDa homooligomeric forms. Furthermore, the expression and targeting of NPP-GFP fusion genes revealed that NPPs localize within the chloroplasts. In the present study, we analyzed phenotypic divergence, starch and free sugar contents in NPP1 overexpressed and knocked-out mutant plants. The former plants exhibited growth stimulation of young roots, decrease of starch accumulation and increase of free sugar contents. Intriguingly, the weights of grains harvested from npp1 or npp6 mutants were significantly increased. The overall results strongly suggested that ADP-glucose hydrolyzing NPPs are involved in controlling root elongation through regulating the starch synthesis.
