Alternative pathways leading to ascorbate biosynthesis in plants: lessons from the last 25 years

Area of Science:

• Plant Physiology
• Biochemistry
• Plant Biotechnology

Background:

• l-Ascorbic acid (AsA) is a vital antioxidant in plants and essential nutrient for humans.
• Humans require dietary AsA due to their inability to synthesize it.
• Plant AsA biosynthesis involves a complex metabolic network with multiple pathways.

Purpose of the Study:

• To review and present evidence for three alternative AsA biosynthesis pathways in plants: d-galacturonate, l-gulose, and myo-inositol.
• To discuss the role of these alternative pathways in plant stress response and AsA production.
• To highlight the potential of these pathways for developing climate-tolerant crops.

Main Methods:

• Critical discussion of feeding studies using AsA precursors and their conversion in plant organs.
• Analysis of research on gene expression of key enzymes in alternative pathways.
• Evaluation of AsA content increase and stress tolerance in transgenic plants.

Main Results:

• Evidence supports the operation of d-galacturonate, l-gulose, and myo-inositol pathways in various plant species.
• Overexpression of key genes in alternative pathways led to >100% AsA increase in transgenics.
• Enhanced AsA levels correlated with improved tolerance to multiple stresses.

Conclusions:

• Alternative AsA biosynthesis pathways are vital for plant adaptation to stress and compensation for reduced flux in the main pathway.
• Characterized genes and enzymes from alternative pathways offer valuable tools for crop improvement.
• These findings contribute to developing more climate-resilient crops through enhanced AsA production.