Suppressed Expression of Ascorbate Oxidase Gene Promotes Ascorbic Acid Accumulation in Tomato Fruit

Abstract

Reduced ascorbic acid (AsA) can be converted into oxidized state by ascorbate oxidase (AO). In present study, AO gene was down-regulated by RNA interference in tomato via Agrobacterium-mediated transformation. The existence of the RNA interference T-DNA in transformed plants and their progenies were confirmed by polymerase chain reaction amplification and Southern blotting. AO expression levels in transgenic lines were monitored by semi-quantitative reverse transcriptase-polymerase chain reaction. The decreased AO enzyme activity and significantly improved AsA content in tomato fruit were observed to be correlated with AO gene suppression. Transgenic plants with AO suppression and AsA improvement exhibited higher photosynthesis capacity than untransformed control under drought stress. This report demonstrates the AsA oxidation pathway by RNA interference, and provides a feasible approach to improve AsA content in horticultural plants by regulating genes related to AsA metabolism.

Ascorbate oxidase: The unexpected involvement of a ‘wasteful enzyme’ in the symbioses with nitrogen-fixing bacteria and arbuscular mycorrhizal fungi

“…AO over-expressing plants are prone to ozone [3] and salt [4] stresses, whereas lower expression apparently confers resistance to unfavorable environmental conditions [4]. Therefore, AO activity appears at best not necessary, if not even dangerous, and the silencing of AO genes seems a valuable strategy to increase AsA content in crops [5]. In this context, the widespread presence of multiple copies of putative AO-encoding genes in virtually all plant taxa, as evidenced by EST analysis, seems inexplicable.…”

Cloning and Expression Analysis of an Ascorbate Oxidase (AO) Gene from Strawberry (Fragaria×ananassa cv. Toyonaka)

“…As mentioned in introduction, AO catalyzes the oxidative reaction of AA and plays an important role on regulation of the redox state and content of AA pool (Sanmartin et al, 2003a;Zhang et al, 2011). With increasing research on the function of AO, an opinion prevailed that AO controls cell expansion during plant development and growth, although the actual mechanism of its action remains unknown (Kato et al, 2000;Lin et al, 1991;Mertz, 1961).…”

Biotechnology for Enhanced Nutritional Quality in Plants

“…An RNAi strategy was recently employed in order to obtain higher levels of vitamin C by modulating the expression of enzymes related to ascorbate metabolism (Zhang et al, 2011a;2011b). AO (ascorbate oxidase) and APX (ascorbate peroxidase) are the enzymes that oxidize ascorbic acid to MDHA (monodehydroascorbate) in plants.…”

“…AO (ascorbate oxidase) and APX (ascorbate peroxidase) are the enzymes that oxidize ascorbic acid to MDHA (monodehydroascorbate) in plants. Zhang et al (2011a;2011b) used RNAi to down-regulate the expression of both enzymes in tomato. RNAi suppression of AO expression resulted in up to 155% improvement of fruit ascorbate content (Zhang et al, 2011a).…”

“…Zhang et al (2011a;2011b) used RNAi to down-regulate the expression of both enzymes in tomato. RNAi suppression of AO expression resulted in up to 155% improvement of fruit ascorbate content (Zhang et al, 2011a). Similarly, RNAi suppression of a mitochondrial APX resulted in 1.4-to 2.2-fold increases in fruit ascorbate content compared to wild type control.…”