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Plant Cell. 2016 Feb;28(2):439-53. doi: 10.1105/tpc.15.01033. Epub 2016 Feb 8.

Balancing of B6 Vitamers Is Essential for Plant Development and Metabolism in Arabidopsis.

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Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland.
Institute of Plant Biochemistry, Cluster of Excellence on Plant Science, Heinrich-Heine-University, 40225 Düsseldorf, Germany.
Max-Planck-Institute for Molecular Plant Physiology, 14476 Potsdam-Golm, Germany.
Department of Botany and Plant Biology, University of Geneva, 1211 Geneva, Switzerland


Vitamin B6 comprises a family of compounds that is essential for all organisms, most notable among which is the cofactor pyridoxal 5'-phosphate (PLP). Other forms of vitamin B6 include pyridoxamine 5'-phosphate (PMP), pyridoxine 5'-phosphate (PNP), and the corresponding nonphosphorylated derivatives. While plants can biosynthesize PLP de novo, they also have salvage pathways that serve to interconvert the different vitamers. The selective contribution of these various pathways to cellular vitamin B6 homeostasis in plants is not fully understood. Although biosynthesis de novo has been extensively characterized, the salvage pathways have received comparatively little attention in plants. Here, we show that the PMP/PNP oxidase PDX3 is essential for balancing B6 vitamer levels in Arabidopsis thaliana. In the absence of PDX3, growth and development are impaired and the metabolite profile is altered. Surprisingly, RNA sequencing reveals strong induction of stress-related genes in pdx3, particularly those associated with biotic stress that coincides with an increase in salicylic acid levels. Intriguingly, exogenous ammonium rescues the growth and developmental phenotype in line with a severe reduction in nitrate reductase activity that may be due to the overaccumulation of PMP in pdx3. Our analyses demonstrate an important link between vitamin B6 homeostasis and nitrogen metabolism.

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