Szymanski D B, Jilk R A, Pollock S M, Marks M D
Department of Genetics, University of Minnesota, St. Paul, MN 55108-1095, USA.
Development. 1998 Apr;125(7):1161-71. doi: 10.1242/dev.125.7.1161.
More than twenty genes are required for the correct initiation, spacing, and morphogenesis of trichomes in Arabidopsis. The initial selection of trichome precursors requires the activity of both the GLABROUS1 (GL1) and TRANSPARENT TESTA GLABROUS (TTG) genes. The GLABRA2 (GL2) gene is required for subsequent phases of trichome morphogenesis such as cell expansion, branching, and maturation of the trichome cell wall. Previous studies have shown that GL2 is a member of the homeodomain class of transcription factors. Here we report a detailed analysis of GL2 expression in the shoot using anti-GL2 antibodies and the GUS reporter gene fused to the GL2 promoter. The GL2 expression profile in the shoot is complex, and involves spatial and temporal variation in developing leaves and trichomes. Two separate promoter domains that are expressed in trichomes were identified. GL2, like GL1, is expressed in developing trichomes and in cells surrounding trichomes during early stages of trichome development. Unlike GL1, GL2 expression persists in mature trichomes. It was found that while GL1 and TTG were not required for the initiation of GL2 expression in the non-trichome cells, the presence of a functional GL1 or TTG gene was able to increase GL2 expression in these cells compared to ttg gl1 plants. The hypothesis that GL1 regulates aspects of GL2 expression is consistent with epistatic analysis of gl1 and gl2 and the expression patterns of GL1 and GL2. In support of this hypothesis, it was found that ectopic expression of GL1 in the presence of ectopic expression of the maize R gene, which can bypass the requirement for TTG, can ectopically activate GL2 transcription.
拟南芥中毛状体的正确起始、间隔和形态发生需要二十多个基因。毛状体前体的初始选择需要GLABROUS1（GL1）和TRANSPARENT TESTA GLABROUS（TTG）基因的活性。GLABRA2（GL2）基因是毛状体形态发生后续阶段所必需的，如细胞扩张、分支和毛状体细胞壁的成熟。先前的研究表明，GL2是同源结构域类转录因子的成员。在此，我们使用抗GL2抗体和与GL2启动子融合的GUS报告基因，对茎中GL2的表达进行了详细分析。茎中GL2的表达模式很复杂，在发育中的叶片和毛状体中涉及空间和时间上的变化。鉴定出了在毛状体中表达的两个独立的启动子结构域。与GL1一样，GL2在毛状体发育早期在发育中的毛状体和毛状体周围的细胞中表达。与GL1不同的是，GL2在成熟毛状体中持续表达。结果发现，虽然在非毛状体细胞中GL2表达的起始不需要GL1和TTG，但与ttg gl1植物相比，功能性GL1或TTG基因的存在能够增加这些细胞中GL2的表达。GL1调节GL2表达的某些方面这一假设与gl1和gl2的上位性分析以及GL1和GL2的表达模式一致。为支持这一假设，发现在玉米R基因异位表达的情况下GL1的异位表达可以绕过对TTG的需求，能够异位激活GL2转录。
