The synthesis of 5-aminolevulinic acid (ALA) is a key regulatory step for the production of hemes and chlorophyll via the tetrapyrrole synthesis pathway. The first enzyme committed to ALA synthesis is glutamyl-tRNA reductase encoded in Arabidopsis by a small family of nuclear-encoded HEMA genes. To better understand the regulation of the tetrapyrrole synthesis pathway we have made a detailed study of HEMA2 expression with transgenic Arabidopsis thaliana L. Col. plants carrying chimeric HEMA2 promoter:gusA fusion constructs. Our results show that the HEMA2 promoter directs expression predominantly to roots and flowers, but that HEMA2 is also expressed at low levels in photosynthetic tissues. Deletion analysis of the HEMA2 promoter indicates that a ca. 850 bp fragment immediately upstream of the HEMA2 coding region is sufficient to drive regulated gusA expression. In contrast to HEMA1, HEMA2 is not up-regulated by red, far-red, blue, UV or white light. In addition, elimination of a promotive plastid signal by Norflurazon-induced photobleaching of plastids had no effect on HEMA2 expression while being required for normal white-light induction of HEMA1. HEMA2 expression in the cotyledons is inhibited by the presence of sucrose or glucose, but not fructose, and this response is light-independent. HEMA1 expression in cotyledons is also inhibited by sugars, but in a strictly light-dependent manner. The roles of HEMA1 and HEMA2 in meeting cellular tetrapyrrole requirements are discussed.

中文翻译：

---

拟南芥中编码谷氨酰-tRNA还原酶的HEMA基因家族的差异性调节：HEMA2的表达受糖的调节，但独立于轻质信号。

5-氨基乙酰丙酸（ALA）的合成是通过四吡咯合成途径生产血红素和叶绿素的关键调控步骤。致力于ALA合成的第一个酶是拟南芥中由一小部分核编码的HEMA基因编码的谷氨酰tRNA还原酶。为了更好地理解四吡咯合成途径的调控，我们对携带嵌合HEMA2启动子：gusA融合构建体的转基因拟南芥植物进行了HEMA2表达的详细研究。我们的结果表明，HEMA2启动子主要指导根和花的表达，但HEMA2在光合作用组织中的表达也很低。HEMA2启动子的缺失分析表明，ca。HEMA2编码区上游的850 bp片段足以驱动gusA的表达。与HEMA1相反，HEMA2不受红色，远红色，蓝色，UV或白色光的上调。另外，通过诺氟拉松诱导的质体光漂白消除促性质体信号对HEMA2表达没有影响，而正常的白光诱导HEMA1则是必需的。子叶中HEMA2的表达受到蔗糖或葡萄糖的抑制，但不受果糖的抑制，并且这种反应是光独立的。子叶中的HEMA1表达也受到糖的抑制，但以严格的光依赖性方式。讨论了HEMA1和HEMA2在满足细胞四吡咯要求中的作用。另外，通过诺氟拉松诱导的质体光漂白消除促性质体信号对HEMA2表达没有影响，而正常的白光诱导HEMA1则是必需的。子叶中HEMA2的表达受到蔗糖或葡萄糖的抑制，但不受果糖的抑制，并且这种反应是光独立的。子叶中的HEMA1表达也受到糖的抑制，但以严格的光依赖性方式。讨论了HEMA1和HEMA2在满足细胞四吡咯要求中的作用。另外，通过诺氟拉松诱导的质体光漂白消除促性质体信号对HEMA2表达没有影响，而正常的白光诱导HEMA1则是必需的。子叶中HEMA2的表达受到蔗糖或葡萄糖的抑制，但不受果糖的抑制，并且这种反应是光独立的。子叶中的HEMA1表达也受到糖的抑制，但以严格的光依赖性方式。讨论了HEMA1和HEMA2在满足细胞四吡咯要求中的作用。而且此响应与光无关。子叶中的HEMA1表达也受到糖的抑制，但以严格的光依赖性方式。讨论了HEMA1和HEMA2在满足细胞四吡咯要求中的作用。而且此响应与光无关。子叶中的HEMA1表达也受到糖的抑制，但以严格的光依赖性方式。讨论了HEMA1和HEMA2在满足细胞四吡咯要求中的作用。