Metabolic Engineering of Wheat for Enhanced Vitamin B6 to Combat Hidden Hunger

Vitamin B6 is an essential micronutrient for humans which is synthesized in plants via de novo pathway. Since this pathway involves only two enzymes, it can be easily exploited to develop biofortified crops. In the present study, we investigated the effect of overexpressing PDX2 gene from Arabidopsis under endosperm-specific promoter for enhancing B6 levels in wheat seeds. Calli of two elite wheat varieties, Faisalabad-2008 and Galaxy, were transformed with PDX2 construct in expression vector via Agrobacterium-mediated transformation with the efficiency of 2.11% and 1.09%, respectively. Among the ten transgenic lines evaluated, the highest gene expression observed was 22.49-fold leading to 6.49-fold increase in B6 accumulation in mature seeds determined via HPLC. Vitamin B6 accumulation did not alter the chlorophyll content. However, the soluble protein content significantly decreased in some transgenic lines as compared to control plants. Some Faisalabad-2008 transgenic lines exhibited significant increase while all Galaxy transgenic lines showed significant decrease in their carbohydrate content than control plants. Moreover, seed yield increased in some transgenic lines without posing any variation in other agro-economically important traits. Previously vitamin B6 accumulation has been reported to confer resistance to abiotic factors because of its antioxidant properties. However, the transgene expression and vitamin B6 accumulation in the seed did not confer salt resistance to the transgenic lines. The amount of proline increased in salt-stressed plants while chlorophyll, protein, carbohydrate, and relative water content decreased. Thus, overexpression of PDX2 under seed-specific promoter enhances accumulation of vitamin B6 without conferring any resistance to salt stress conditions.

Automated summary

In this study, overexpression of the PDX2 gene from Arabidopsis under an endosperm-specific promoter was shown to enhance vitamin B6 accumulation in wheat seeds. Transgenic lines of two wheat varieties were generated with transformation efficiencies of 2.11% and 1.09%. The highest gene expression level observed was 22.49-fold, resulting in a 6.49-fold increase in B6 accumulation. Vitamin B6 accumulation did not affect chlorophyll content but significantly decreased soluble protein content in some transgenic lines. In addition, some transgenic lines exhibited increased seed yield without changes in other important traits. However, the transgenic lines did not show enhanced resistance to salt stress despite the increased vitamin B6 accumulation.