The Pseudoenzyme PDX1.2 Boosts Vitamin B6 Biosynthesis under Heat and Oxidative Stress in Arabidopsis

Background: A non-catalytic vitamin B-6 biosynthesis protein (PDX1.2) exists in plants, but its role is unknown. Results: PDX1.2 interacts with its catalytic counterparts, enhancing their activity and forming a dodecameric complex induced under abiotic stress. Conclusion: PDX1.2 is a pesudoenzyme that regulates vitamin B-6 biosynthesis under abiotic stress. Significance: This work presents a model for regulation of vitamin B-6 biosynthesis and the existence/significance of pseudoenzymes in plants. Vitamin B-6 is an indispensable compound for survival, well known as a cofactor for numerous central metabolic enzymes and more recently for playing a role in several stress responses, particularly in association with oxidative stress. Regulatory aspects for the use of the vitamin in these roles are not known. Here we show that certain plants carry a pseudoenzyme (PDX1.2), which is involved in regulating vitamin B-6 biosynthesis de novo under stress conditions. Specifically, we demonstrate that Arabidopsis PDX1.2 enhances the activity of its catalytic paralogs by forming a heterododecameric complex. PDX1.2 is strongly induced by heat as well as singlet oxygen stress, concomitant with an enhancement of vitamin B-6 production. Analysis of pdx1.2 knockdown lines demonstrates that boosting vitamin B-6 content is dependent on PDX1.2, revealing that this pseudoenzyme acts as a positive regulator of vitamin B-6 biosynthesis during such stress conditions in plants.