Department of Botany, Graduate School of Science, Kyoto University, Sakyo-ku, Kyoto, 606-8502 Japan.
Plant Cell Physiol. 2011 Aug;52(8):1340-53. doi: 10.1093/pcp/pcr079. Epub 2011 Jun 20.
Polarity along the adaxial-abaxial axis of the leaf is essential for leaf development and morphogenesis. One of the genes that encodes a putative transcription factor regulating adaxial-abaxial polarity, FILAMENTOUS FLOWER (FIL), is expressed in the abaxial region of the leaf primordia. However, the molecular mechanisms controlling the polarized expression of FIL remain unclear. Here, we analyzed an enlarged fil expression domain1 (enf1) mutant of Arabidopsis, which forms both abaxialized leaves and adaxialized leaves. The ENF1 gene encodes SUCCINIC SEMIALDEHYDE DEHYDROGENASE (SSADH), which catalyzes the conversion of succinic semialdehyde (SSA) to succinate. The enf1 phenotype was suppressed by an additional mutation in GAMMA-AMINOBUTYRIC ACID AMINOTRANSFERASE1 (GABAT1), which encodes an SSA-producing enzyme, suggesting that SSA or its derivatives is the metabolite responsible for the defect in the adaxial-abaxial axis-dependent gene expression of enf1. In the shoot apical meristem, GABAT1 was expressed in the outermost layer but SSADH was not. Exogenous application of SSA induced adaxial characters on the abaxial side of the newly developed leaves. We suggest that a GABA shunt metabolite, SSA or its close derivatives, is involved in the robust leaf patterning and structure along the adaxial-abaxial axis.
叶片的近轴-远轴极性对叶片发育和形态发生至关重要。编码一个假定的转录因子的基因，调节近轴-远轴极性，FILAMENTOUS FLOWER（FIL），在叶片原基的远轴区域表达。然而，控制 FIL 极性表达的分子机制尚不清楚。在这里，我们分析了拟南芥中一个扩大的 fil 表达域 1（enf1）突变体，它形成了近轴化的叶片和远轴化的叶片。ENF1 基因编码 SUCCINIC SEMIALDEHYDE DEHYDROGENASE（SSADH），它催化琥珀酸半醛（SSA）转化为琥珀酸。ENF1 表型被另外一个突变抑制，该突变在 GAMMA-AMINOBUTYRIC ACID AMINOTRANSFERASE1（GABAT1）中，它编码一个 SSA 产生酶，表明 SSA 或其衍生物是负责 enf1 在近轴-远轴轴依赖性基因表达缺陷的代谢物。在茎尖分生组织中，GABAT1 在最外层表达，但 SSADH 没有。SSA 的外源应用诱导了新发育叶片的远轴侧的近轴特征。我们认为 GABA 分流代谢物，SSA 或其近衍生物，参与了沿近轴-远轴轴的强烈叶片图案化和结构。
