Transcription expression dynamics of genes involved in L-ascorbic acid biosynthesis during fruit development and maturation in Kinnow mandarin

Abstract

Citrus fruits are major sources of vitamin C (L-ascorbic acid), a key antioxidant that protects human cells
against reactive oxygen species (ROS) generated during metabolism and environmental stress. This study
examined the transcriptional regulation of genes involved in ascorbic acid (AsA) biosynthesis and recycling
during fruit development in Kinnow mandarin (Citrus reticulata). Fruits were collected at three developmental
stages, and gene expression was analyzed in flavedo, albedo, and pulp tissues using quantitative real-time PCR.
Thirteen genes representing L-galactose, myo-inositol, and D-galacturonate pathways, along with the recycling
pathway, were evaluated. Distinct tissue-specific and stage-dependent expression patterns were observed.
L-galactose pathway genes showed strong upregulation in flavedo during maturation, indicating its central
role in AsA biosynthesis. In contrast, myo-inositol and D-galacturonate pathway genes were downregulated,
suggesting reduced contribution at later stages. Recycling pathway genes also declined, particularly in pulp
tissues. These findings reveal coordinated regulation of AsA metabolism and highlight the pivotal role of flavedo
in vitamin C accumulation, providing targets for improving citrus fruit nutritional quality.