Characterization of cDNAs encoding small and large subunits of ADP-glucose pyrophosphorylases from watermelon (Citrullus vulgaris S.)

Three cDNA clones encoding ADP-glucose pyrophosphorylases were isolated from a full red fruit cDNA library of watermelon (Citrullus vulgaris S.). Sequence analyses indicated that one clone, wms1, corresponds to the small subunit, and two clones, wml1 and wml2 (a partial gene), are the large subunits of AGPase, The presumed AGPase proteins encoded by wms1, wml1, and wml2 have 526, 526, and 481 amino acids, respectively. The protein sequences have the conserved amino acids important for the substrate or regulator binding site, with some variation, Developmental changes in the amounts of wms1, wml1, and wml2 transcripts in fruits were measured by northern blot analysis, Their expression levels decreased from the small green to medium green stages, then increased in accordance with fruit ripening, which was different from those of tomato and oriental melon.