Data_Sheet_1_Protein Kinase Activity of Phytochrome A Positively Correlates With Photoresponses in Arabidopsis.PDF

Plant phytochromes are known as autophosphorylating serine/threonine protein kinases. However, the functional importance of their kinase activity is not fully elucidated. Previously, the kinase activity is shown to be necessary for the function of Avena sativa phytochrome A (AsphyA) using transgenic plants with mutants displaying reduced kinase activity, such as K411L and T418D. In this study, we isolated and analyzed two AsphyA mutants, K411R and T418V, that showed increased kinase activity. Transgenic phyA-201 plants with these mutants showed hypersensitive responses to far-red (FR) light, such as shorter hypocotyls and more expanded cotyledons than those of control plant (i.e., transgenic phyA-201 plant with wild-type AsphyA). Contrary to the mutants with reduced kinase activity, these mutants accelerated FR-induced phosphorylation and subsequent degradation of phytochrome-interacting factor 3 (PIF3) in Arabidopsis. Moreover, elongated hypocotyl 5 (HY5), a critical positive regulator of photoresponses in plants, accumulated in higher amounts in the transgenic plants under FR light than in the control plant. In addition, PIF1 degradation was accelerated in the transgenic plants. Consequently, the transgenic plants exhibit higher germination frequencies than the control plant. Collectively, our results demonstrate that the AsphyA mutants with increased kinase activity are hyperactive in plants, supporting a positive relationship between the kinase activity of phytochromes and photoresponses in plants.

植物光敏色素（phytochrome）属于自磷酸化丝氨酸/苏氨酸蛋白激酶。然而，其激酶活性的功能重要性尚未完全阐明。此前，通过使用携带激酶活性降低突变体（如K411L与T418D）的转基因植株，已证实激酶活性对燕麦光敏色素A（AsphyA）的功能是必需的。本研究中，我们分离并分析了两个激酶活性升高的AsphyA突变体：K411R与T418V。携带上述突变体的phyA-201转基因植株对远红光（FR）表现出超敏响应：其下胚轴更短，子叶扩张程度较对照组（即携带野生型AsphyA的phyA-201转基因植株）更大。与激酶活性降低的突变体相反，这些突变体加速了拟南芥中远红光诱导的光敏色素互作因子3（PIF3）的磷酸化及后续降解过程。此外，作为植物光响应关键正向调控因子的下胚轴伸长5（HY5），在远红光条件下的转基因植株中积累量较对照组更高。同时，转基因植株中光敏色素互作因子1（PIF1）的降解过程也得到加速。因此，转基因植株的萌发频率较对照组更高。综上，本研究结果证实，激酶活性升高的AsphyA突变体在植株中表现出超活性，支持了植物光敏色素的激酶活性与光响应之间存在正相关关系这一结论。