Enhancement of vitamin B₆ levels in rice expressing Arabidopsis vitamin B₆ biosynthesis de novo genes

Abstract

SummaryVitamin B6 (pyridoxine) is vital for key metabolic reactions and reported to have antioxidant properties in planta. Therefore, enhancement of vitamin B6 content has been hypothesized to be a route to improve resistance to biotic and abiotic stresses. Most of the current studies on vitamin B6 in plants are on eudicot species, with monocots remaining largely unexplored. In this study, we investigated vitamin B6 biosynthesis in rice, with a view to examining the feasibility and impact of enhancing vitamin B6 levels. Constitutive expression in rice of two Arabidopsis thaliana genes from the vitamin B6 biosynthesis de novo pathway, AtPDX1.1 and AtPDX2, resulted in a considerable increase in vitamin B6 in leaves (up to 28.3‐fold) and roots (up to 12‐fold), with minimal impact on general growth. Rice lines accumulating high levels of vitamin B6 did not display enhanced tolerance to abiotic stress (salt) or biotic stress (resistance to Xanthomonas oryzae infection). While a significant increase in vitamin B6 content could also be achieved in rice seeds (up to 3.1‐fold), the increase was largely due to its accumulation in seed coat and embryo tissues, with little enhancement observed in the endosperm. However, seed yield was affected in some vitamin B6‐enhanced lines. Notably, expression of the transgenes did not affect the expression of the endogenous rice PDX genes. Intriguingly, despite transgene expression in leaves and seeds, the corresponding proteins were only detectable in leaves and could not be observed in seeds, possibly pointing to a mode of regulation in this organ.

Vitamins in Cereals: A Critical Review of Content, Health Effects, Processing Losses, Bioaccessibility, Fortification, and Biofortification Strategies for Their Improvement

“…Germplasm screening of crops has revealed limited variations (<2-fold) in the vitamin B6 composition of wheat ( 98 ). Constitutive expression of two Arabidopsis pyridoxal 5′-phosphate synthase genes (PDX1 and PDX2) has resulted in a considerable increase in the level of vitamin B6 in rice leaves (up to 28.3-fold), roots (up to 12-fold), and seeds (up to 3.1-fold) ( 74 ).…”

Label-Free Quantitative Proteomics Unravel the Impacts of Salt Stress on Dendrobium huoshanense

“…Massive free radicals (especially hydrogen peroxide) and MAPK signal transduction may be the reasons for the formation of free radical scavenging enzymes and antioxidants in D. huoshanense . SOS4 encodes a pyridoxine kinase that catalyzes the conversion of vitamin B6 to pyridoxal phosphate ( Rueschhoff et al, 2013 ; Mangel et al, 2019 ). The sos4 mutant accumulated more sodium ions and fewer potassium ions than the wild type under salt stress.…”

B vitamin supply in plants and humans: the importance of vitamer homeostasis

“…The expression of Arabidopsis PDX1.1 and PDX2 in Manihot esculenta (cassava) resulted in an almost six‐fold increase of total vitamin B 6 in storage roots, which would reach the recommended daily intake in average food portions (Li et al., 2015). However, the same approach in rice did not lead to an accumulation in polished grains, although the leaf tissue had a 30‐fold increase (Mangel et al., 2019). By contrast, engineering GTPCHI and ADCS for pterin and p ‐ABA, respectively, in combination with a synthetic folate binding protein (sFBP) in rice resulted in a 150‐fold increase in the folate content of polished raw grains (Blancquaert et al., 2015; Storozhenko et al., 2007).…”