Phytochrome-interacting factors (PIFs) are basic helix-loop-helix transcription factors that regulate light responses downstream of phytochromes. In Arabidopsis (Arabidopsis thaliana), eight PIFs (PIF1-8) regulate light responses, either redundantly or distinctively. Distinctive roles of PIFs may be attributed to differences in mRNA expression patterns governed by promoters or variations in molecular activities of proteins. However, elements responsible for the functional diversification of PIFs have yet to be determined. Here, we investigated the role of promoters and proteins in the functional diversification of PIF1 and PIF4 by analyzing transgenic lines expressing promoter-swapped PIF1 and PIF4, as well as chimeric PIF1 and PIF4 proteins. For seed germination, PIF1 promoter played a major role, conferring dominance to PIF1 gene with a minor contribution from PIF1 protein. Conversely, for hypocotyl elongation under red light, PIF4 protein was the major element conferring dominance to PIF4 gene with the minor contribution from PIF4 promoter. In contrast, both PIF4 promoter and PIF4 protein were required for the dominant role of PIF4 in promoting hypocotyl elongation at high ambient temperatures. Together, our results support that the functional diversification of PIF1 and PIF4 genes resulted from contributions of both promoters and proteins, with their relative importance varying depending on specific light responses.

中文翻译：

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由于启动子和蛋白质的差异，光敏色素相互作用因子基因 PIF1 和 PIF4 在功能上多样化

光敏色素相互作用因子（PIF）是基本的螺旋-环-螺旋转录因子，调节光敏色素下游的光反应。在拟南芥 (Arabidopsis thaliana) 中，八个 PIF (PIF1-8) 冗余或独特地调节光响应。 PIF 的独特作用可能归因于启动子控制的 mRNA 表达模式的差异或蛋白质分子活性的变化。然而，负责 PIF 功能多样化的要素尚未确定。在这里，我们通过分析表达启动子交换的 PIF1 和 PIF4 以及嵌合 PIF1 和 PIF4 蛋白的转基因系，研究了启动子和蛋白在 PIF1 和 PIF4 功能多样化中的作用。对于种子萌发，PIF1 启动子发挥了主要作用，赋予 PIF1 基因主导地位，而 PIF1 蛋白的贡献较小。相反，对于红光下的下胚轴伸长，PIF4蛋白是赋予PIF4基因优势的主要元件，PIF4启动子的贡献较小。相比之下，PIF4启动子和PIF4蛋白都是PIF4在高环境温度下促进下胚轴伸长的主导作用所必需的。总之，我们的结果支持 PIF1 和 PIF4 基因的功能多样化是启动子和蛋白质共同作用的结果，其相对重要性根据特定的光反应而变化。