Changes in the expression of ADP-glucose pyrophosphorylase genes during fruit ripening in strawberry

Abstract

Starch contents play important roles in determining the fruit quality. Stawberry accumulates starch in the early stages and then mobilized into soluble sugars during fruit ripening. To date the molecular studies on the ADP-glucose pyrophosphorylase (AGPase), a key enzyme of starch biosynthesis, were not reported. cDNAs encoding small (FagpS) and large (FagpL1 and FaspL2) AGPase subunits were isolated from strawberry (Fragaria x ananassa Duch. cv. Niyobou). Both FagpS and FagpL1 cDNAs have open reading frames deriving 55-58 kDa polypeptides, where FagpL2 contains a partial fragment. Sequence analyses showed that FagpS has a glutamate-threonine-cysteine-leucine (ETCL) instead of a glutaminethreonine-cysteine-leucine (QTCL) motif found in all the dicot plants except for Citrus. In fruits, FagpS and FagpL1 were expressed in all stages with a little change in the amounts of transcripts. In the case of FagpL2 we were not able to detect any signal from all stages of fruit development and all tissues except for very a weak signal from the leaf. The results indicate that FagpL1 and FagpL2 show ubiquitous and leaf-specific expression patterns, respectively. The studies suggest that the starch contents in strawberry might be controlled by the expression of AGPase gene at both the transcriptional and posttranscriptional levels during fruit development.