Lu Y T, Hidaka H, Feldman L J
Department of Plant Biology, University of California, Berkeley 94720, USA.
Planta. 1996;199(1):18-24. doi: 10.1007/BF00196876.
Roots of many species respond to gravity (gravitropism) and grow downward only if illuminated. This light-regulated root gravitropism is phytochrome-dependent, mediated by calcium, and inhibited by KN-93, a specific inhibitor of calcium/calmodulin-dependent protein kinase II (CaMK II). A cDNA encoding MCK1, a maize homolog of mammalian CaMK, has been isolated from roots of maize (Zea mays L.). The MCK1 gene is expressed in root tips, the site of perception for both light and gravity. Using the [35S]CaM gel-overlay assay we showed that calmodulin-binding activity of the MCK1 is abolished by 50 microM KN-93, but binding is not affected by 5 microM KN-93, paralleling physiological findings that light-regulated root gravitropism is inhibited by 50 microM KN-93, but not by 5 microM KN-93. KN-93 inhibits light-regulated gravitropism by interrupting transduction of the light signal, not light perception, suggesting that MCK1 may play a role in transducing light. This is the first report suggesting a physiological function for a CaMK homolog in light signal transduction.
许多物种的根对重力有反应（向地性），并且只有在有光照时才向下生长。这种光调节的根向地性是依赖于光敏色素的，由钙介导，并被KN - 93抑制，KN - 93是钙/钙调蛋白依赖性蛋白激酶II（CaMK II）的一种特异性抑制剂。从玉米（Zea mays L.）的根中分离出了一个编码MCK1的cDNA，MCK1是哺乳动物CaMK的玉米同源物。MCK1基因在根尖表达，根尖是光和重力感知的部位。使用[35S]CaM凝胶覆盖试验，我们发现50微摩尔的KN - 93可消除MCK1的钙调蛋白结合活性，但5微摩尔的KN - 93对结合没有影响，这与光调节的根向地性被50微摩尔的KN - 93抑制但不被5微摩尔的KN - 93抑制的生理学发现相似。KN - 93通过中断光信号的转导而非光感知来抑制光调节的向地性，这表明MCK1可能在光信号转导中起作用。这是首次报道表明CaMK同源物在光信号转导中的生理功能。
