Modification of sugar composition in strawberry fruit by antisense suppression of an ADP-glucose pyrophosphorylase

Abstract

Cultivated strawberry (Fragaria x ananassa Duch.) is an economically very important fruit crop in the world. The aim of this study was to investigate the changes of soluble sugar composition in strawberry fruit. We isolated full cDNA encoding an AGPase small subunit (FagpS) from strawberry cv. Niyobou. The nucleotide length of FagpS cDNA clone was 1826bp. which the cDNA has an open reading frame deriving 57kDa. To modulate the soluble sugar contents of fruits, we obtained transgenic plants that incorporate an antisense orientation of FagpS in strawberry cv. Anther under the control of the fruit-dominant ascorbate peroxidase (APX) promoter. Several independent transgenic and regenerated plants were obtained and propagated in the greenhouse for agronomical tract analysis. Most transgenic fruits did not show significant differences in weight, and hardness when compared with control fruits of strawberry. While starch contents in fruit of transgenic lines were decreased about 27% to 69%, total soluble sugar contents were increased about 16% to 37% in transgenic plants. These results show HPLC analysis of sugar composition at four stages of fruit development, the increase of sugar contents of fruits in transgenic lines compared with wild plants particularly detected in the transition from the turning to the red stage. This results were confirmed by northern analysis which showed the steady-state levels of AGPase mRNA drastically reduced in red stage of fruits in all the transgenic plants. Therefore, these results supported that AGPase expression in the transgenic lines was controlled by APX promoter. The analysis of AGPase transcript levels in other tissues transgenic plants showed that AGPase mRNA expression is similar to control plants. Starch staining of leaf and pollen by I2-KI also show the similar data compared with wild plants. Therefore, our results indicated that AGPase gene is a candidate for changes of sugar composition in strawberry fruit.