Vitamin B6 Is Essential for Maize Embryogenesis

Vitamin B₆ is synthesized de novo in plants, fungi, archeae, and most eubacteria, but not in animals, including humans, which have to obtain it from dietary sources. Vitamin B₆ is an essential cofactor for a range of biochemical reactions and a potent antioxidant. In plants, it plays important roles in plant growth and development, and stress tolerance. Although vitamin B₆ biosynthesis is essential for embryogenesis in Arabidopsis, the roles of vitamin B₆ in embryogenesis and endosperm development in grasses has not been addressed. Whereas Arabidopsis seeds develop transient endosperm that is quickly consumed by the developing embryo leaving a single layer of aleurone cells in mature seeds, endosperm is a major component of the mature grass seed. By means of a molecular characterization of the small kernel2 (smk2) mutant in maize (Zea mays), Yang et al. (10.​1104/​pp.​16.​01295 ) reveal that vitamin B₆ has differential effects on embryogenesis and endosperm development Vitamin B₆ levels are decreased dramatically in both the endosperm an embryo of the smk2 mutant, indicating that embryogenesis is more sensitive to reduced vitamin B₆ levels than endosperm development. In particular, a vitamer having some vitamin B₆ activity, namely pyridoxal 5’-phosphate (PLP), is drastically reduced in both the smk2 embryo and the endosperm. However, whereas embryogenesis of the smk2 mutant is arrested at an early transition stage, endosperm formation is nearly normal. Molecular analyses indicate that Smk2 encodes the glutaminase subunit of the PLP synthase complex involved in vitamin B₆ biosynthesis de novo. Smk2 is constitutively expressed in the maize plant, including developing embryos. These results indicate that vitamin B₆ is essential to embryogenesis but has a reduced role in endosperm development in maize.