Regulation of ascorbic acid synthesis in plants.

Ascorbic acid (AsA) is a major antioxidant and plays an important role in plant growth and development. There are two aspects to improve AsA content, including de novo synthesis and recycling from its oxidized form. However, the knowledge of regulatory mechanisms of AsA synthesis pathways and metabolism still remains limited. We have determined that AsA synthesis process was modulated on both transcriptional and post-transcriptional levels in Arabidopsis. GDP-mannose pyrophosphorylase (VTC1) is the initial AsA biosynthetic enzyme in L-galactose pathway, we previously showed that Arabidopsis ERF98 transcriptionally activates gene expression of VTC1 to improve AsA content and respond salt stress; recent discovery of the interaction between photomorphogenic factor COP9 signalosome (CSN) subunit CSN5B and VTC1 indicates that CSN5B promotes VTC1 degradation in the dark, which keeps the change of AsA content from day to night. This mini-review integrates previous reports and recent evidence to better understand the regulatory mechanisms involved in AsA synthesis.