Raghuram N, Sopory S K
Molecular Plant Physiology Laboratory, School of Life Sciences, Jawaharlal Nehru University, New Delhi, India.
Plant Mol Biol. 1995 Oct;29(1):25-35. doi: 10.1007/BF00019116.
We have explored the possible involvement of the phosphoinositide (PI) cycle and protein kinase C (PKC) in the phytochrome (Pfr)-mediated light signal transduction pathway using nitrate reductase (NR) and phytochrome-I (PhyI) genes as model systems. We have shown earlier that phorbol myristate acetate (PMA) completely replaces the red light effect in stimulating nitrate reductase activity and transcript levels in maize. In this paper, we present detailed evidence to show that PMA mimics the red light effect and follows similar kinetics to enhance NR steady-state transcript accumulation in a nitrate-dependent manner. We also show that PMA inhibits phyI steady-state transcript accumulation in a manner similar to red light, indicating that a PKC-type enzyme(s) may be involved in mediating the light effect in both cases. Serotonin or 5-hydroxytryptamine (5-HT), a stimulator of PI turnover, was also found to mimic the red light effect in enhancing NR transcript levels and inhibiting phyI transcript accumulation, indicating the role of the PI cycle in generating second messengers for regulating the two genes. These results indicate that phytochrome-mediated light regulation of NR and phyI gene expression may involve certain common steps in the signal transduction pathway such as the PI cycle and protein phosphorylation by a PKC-type enzyme.
我们以硝酸还原酶（NR）和光敏色素-I（PhyI）基因为模型系统，探讨了磷酸肌醇（PI）循环和蛋白激酶C（PKC）在光敏色素（Pfr）介导的光信号转导途径中的可能作用。我们之前已经表明，佛波酯（PMA）在刺激玉米硝酸还原酶活性和转录水平方面完全取代了红光效应。在本文中，我们提供了详细证据表明，PMA模拟红光效应，并遵循相似的动力学以硝酸盐依赖的方式增强NR稳态转录本积累。我们还表明，PMA以类似于红光的方式抑制phyI稳态转录本积累，表明PKC型酶可能在这两种情况下介导光效应。血清素或5-羟色胺（5-HT），一种PI周转的刺激剂，也被发现模拟红光效应，增强NR转录水平并抑制phyI转录本积累，表明PI循环在产生用于调节这两个基因的第二信使中的作用。这些结果表明，光敏色素介导的对NR和phyI基因表达的光调节可能涉及信号转导途径中的某些共同步骤，如PI循环和PKC型酶介导的蛋白质磷酸化。
