Lam E, Benedyk M, Chua N H
Laboratory of Plant Molecular Biology, Rockefeller University, New York, New York 10021.
Mol Cell Biol. 1989 Nov;9(11):4819-23. doi: 10.1128/mcb.9.11.4819-4823.1989.
A photoautotrophic suspension culture of soybeans was found to exhibit light-dependent expression of the genes encoding the major chlorophyll a- and b-binding protein (CAB). The expression was mediated by phytochrome, since it was induced by red light and reversed by far-red light. The maximal level as well as the kinetics of the induction were comparable between the suspension culture and soybean seedlings. Using this cell culture, we addressed the question of whether a calcium- and/or calmodulin-mediated step is involved in the signal transduction process between phytochrome and CAB expression. We found that W-7, a potent calmodulin antagonist, severely attenuated the induction of CAB mRNA by light, whereas W-5, a weak calmodulin antagonist, had little effect. Control experiments demonstrated that W-7 treatment did not block the induction of hsp-75 by heat shock. The addition of ionomycin, a calcium ionophore, induced a low level of CAB mRNA accumulation in the dark which could be further enhanced by light treatment. We propose that calmodulin activation by light is necessary but not sufficient to induce maximal CAB expression.
研究发现，大豆的光合自养悬浮培养物中，编码主要叶绿素a和b结合蛋白（CAB）的基因呈现出光依赖性表达。这种表达由光敏色素介导，因为它可被红光诱导，并可被远红光逆转。悬浮培养物和大豆幼苗之间，诱导的最大水平以及动力学情况相当。利用这种细胞培养物，我们探讨了在光敏色素与CAB表达之间的信号转导过程中，是否涉及钙和/或钙调蛋白介导的步骤。我们发现，强效钙调蛋白拮抗剂W-7可严重减弱光对CAB mRNA的诱导作用，而弱效钙调蛋白拮抗剂W-5几乎没有影响。对照实验表明，W-7处理不会阻断热休克对hsp-75的诱导。添加钙离子载体离子霉素可在黑暗中诱导低水平的CAB mRNA积累，光照处理可进一步增强这种积累。我们提出，光激活钙调蛋白对于诱导最大程度的CAB表达是必要的，但并不充分。
