Plant Physiol. |山东大学谭保才团队揭示维生素B6（VB6）在玉米籽粒发育过程中的作用

近日，植物学期刊Plant Physiology在线发表了山东大学谭保才教授团队题为“Small kernel2 encodes a glutaminase in vitamin B6 biosynthesis essential for maize seed development”的研究论文，揭示了维生素B6（VB6）在玉米籽粒发育过程中的作用。

Figure 1. Seed development is affected in the smk2-1 mutant.

A, An ear segregating smk2-1 mutants (arrows). B, Germinal face of the WT and smk2-1 mutant kernels at 18 DAP. C, Section of mature WT and smk2-1 kernels. D-G, Cytological sections of WT (D, F) and smk2-1 mutant kernels (E, G) at 18 DAP. LP, leaf primordia; RAM, root apical meristem; SAM, shoot apical meristem; SC, scutellum; Em, Embryo. Scale bars=0.5 cm in (A-C), 1 mm in (D) and (E), 500 µm in (F), and 100 µm in (G).

维生素B6作为一种重要的辅酶和抗氧化物质，对植物的生长发育及应对外界胁迫起着重要的作用。该研究团队鉴定并克隆了一个影响玉米籽粒发育的基因Smk2，该基因编码VB6合成途径中的谷氨酰胺酶。Smk2的突变严重阻碍了胚的发育，但对胚乳发育影响较小。分析表明，smk2突变体胚和胚乳中都含有微量VB6，说明种子中VB6的含量对胚的发育十分关键，而对胚乳发育的影响相对较小。微量的VB6可能是母体组织向籽粒运输的，但这些VB6不足以维持种子正常发育，大量VB6需要种子自身合成。研究还发现，VB6可能以磷酸吡哆胺的形式累积在胚乳中。

Small kernel2 encodes a glutaminase in vitamin B6 biosynthesis essential for maize seed development

Yan-Zhuo Yang, Shuo Ding, Yong Wang, Cui-Ling Li, Yun Shen, Robert Meeley,Donald R. McCarty, and Bao-Cai Tan

Vitamin B6, an essential co-factor for a range of biochemical reactions and a potent antioxidant, plays important roles in plant growth, development, and stress tolerance. Vitamin B6 deficiency causes embryo lethality in Arabidopsis, but the specific role of vitamin B6 synthesis in endosperm development has not been fully addressed, especially in monocot crops where endosperm constitutes the major portion of the grain. Through molecular characterization of a small kernel2 (smk2) mutant in maize, we reveal that vitamin B6 has differential effects on embryogenesis and endosperm development in maize. The B6 vitamer 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 the transition stage, endosperm formation is nearly normal. Cloning reveals that Smk2 encodes the glutaminase subunit of the PLP synthase complex involved in vitamin B6 biosynthesis de novo. Smk2 partially complements the Arabidopsis vitamin B6 deficient mutant pdx2.1 and Saccharomyces cerevisiae pyridoxine auxotrophic mutant MML21. Smk2 is constitutively expressed in the maize plant including developing embryos. Analysis of B6 vitamers indicates that the endosperm accumulates a large amount of pyridoxamine 5′-phosphate (PMP). These results indicate that vitamin B6 is essential to embryogenesis but has a reduced role in endosperm development in maize. The vitamin B6 required for seed development is synthesized in the seed and the endosperm accumulates PMP probably as a storage form of vitamin B6.

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