L-ascorbic acid (vitamin C) is an essential water-soluble antioxidant and acts as an enzymes cofactor involved in the biosynthesis of necessary molecules. It is requisite for both plants and animals. In the past two decades, metabolic pathways and genetic regulation of ascorbate biosynthesis have been explored. A plethora of studies proposed that the Smirnoff-Wheeler pathway contributes to the major content of ascorbic acid. So far, attempts have been made to regulate metabolic pathways by cloning and overexpressing genes of biosynthetic pathways to enhance ascorbic acid content. The diversity and variability of L-ascorbic acid among different plant tissues remain the challenge. Thus, in this review, gene cloning strategies of GGP (GDP-L-Galactose Phosphorylase), GalDH (L-galactose Dehydrogenase), GLDH (L-Galactono-1,4-Lactone Dehydrogenase), and consequences of their overexpression or suppression on ascorbate content and overall plant growth including tolerance has been discussed. Overexpression of GGP and GLDH in model plants showed reasonable results. However, stable translation of these results in consumable crops to improve nutritional superiority will necessitate a novel targeted approach. Moreover, additional interventions are being explored so that can be employted to enhance the L-ascorbic acid content in different species of crop by using different molecular approaches.

Ascorbic acid, Vitamin C, L-galactose dehydrogenase, GDP-L-Galactose Phosphorylase, L-Galactono-1,4-Lactone Dehydrogenase, Gene cloning, ascorbate biosynthesis.

Advancement in the field of ascorbic acid biochemistry, including metabolism and biosynthesis, opens a new path for enhancing ascorbic acid content in plants and microbes. This also favored the cloning of genes involved in ascorbate biosynthesis, most of the genes are well explored, and many cloning strategies have been published inthe last two decades. Transgenic plants have been developed by cloning and expressing genes of different ascorbic acid biosynthetic pathways. These transgenic plants are made conducive to optimize ascorbic acid biosynthesis. Some model plants, such as A. thaliana, Oryza sativa, tobacco, etc., showed increased synthesis and accumulation of ascorbic acid by overexpression of genes of the ascorbate biosynthetic pathway. However, overexpression of a single gene can be supplementary rate-limiting and has restricted significance. It is concluded that enhanced enzyme activity may correlate with increased ascorbate biosynthesis/accumulation, but it is not unswervingly proportional. For further studies combination of two or more biosynthetic genes can be used in a single model plant to regulate ascorbate synthesis, and the effect of other metabolic products might be exploited. Till now, leaves have been in focus for expressing cloned genes. Therefore the impact of cloned genes could also be explored on other plant parts such as flowers, fruit, etc. An ideal protocol must be developed to transform the result observed in the model plant into crops that can be consumed.

Ayush Srivastava, Daljeet Singh Dhanjal, Reena Singh and Chirag Chopra (2022). Biochemical and Biotechnological Perspectives of GDP-L-Galactose Phosphorylase, L-galactose Dehydrogenase, L-Galactono-1,4-Lactone Dehydrogenase: A Review. Biological Forum – An International Journal, 14(2): 486-497.