A highly conserved gene for vitamin B biosynthesis may have consequences for stress and hormone responses in plants

Pyridoxine (vitamin B(6)) is not only an essential cofactor in amino acid biosynthesis but has recently been added to the list of potent antioxidants found in plants (Bilski et al., 71: 129-134, 2000). Herein the cloning of a gene (pvPDX1) from Phaseolus vulgaris that has a high degree of similarity to PDX1 from Cercospora nicotianae is reported. In C. nicotianae, PDX1 is involved in the biosynthesis of pyridoxine as null mutants exhibit pyridoxine auxotrophy (Ehrenshaft et al., Proc Natl Acad Sci USA 96: 9374-9378, 1999). Expression of pvPDX1 in PDX1 mutants of C. nicotianae partially complements pyridoxine auxotrophy suggesting that a similar biosynthetic pathway for pyridoxine exists in both plants and fungi. In P. vulgaris, expression of pvPDX1 was induced by mechanical wounding via a mechanism that is independent of the production of AOS (active oxygen species). Furthermore, whereas the expression of pvPDX1 in P. vulgaris was up-regulated by treatment with 1-aminocyclopropane-1- carboxylic acid (ACC) treatment in a time course similar to that observed with wounding, expression was not consistently regulated by other treatments that caused a similar increase in ethylene production suggesting a more complicated regulatory pathway.