Alternative promoter usage is a proteome-expanding mechanism that allows multiple pre-mRNAs to be transcribed from a single gene. The impact of this mechanism on the proteome and whether it is positively exploited in normal organismal responses remain unclear. We found that the plant photoreceptor phytochrome induces genome-wide changes in alternative promoter selection in Arabidopsis thaliana. Through this mechanism, protein isoforms with different N termini are produced that display light-dependent differences in localization. For instance, shade-grown plants accumulate a cytoplasmic isoform of glycerate kinase (GLYK), an essential photorespiration enzyme that was previously thought to localize exclusively to the chloroplast. Cytoplasmic GLYK constitutes a photorespiratory bypass that alleviates fluctuating light-induced photoinhibition. Therefore, phytochrome controls alternative promoter selection to modulate protein localization in response to changing light conditions. This study suggests that alternative promoter usage represents another ubiquitous layer of gene expression regulation in eukaryotes that contributes to diversification of the proteome.

中文翻译：

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光通过植物色素介导的替代启动子选择来控制蛋白质的定位。

替代启动子的使用是蛋白质组扩展机制，它允许从单个基因转录多个pre-mRNA。尚不清楚该机制对蛋白质组的影响以及它是否在正常的生物反应中得到了积极利用。我们发现植物光感受器植物色素诱导拟南芥中的替代启动子选择的全基因组变化。通过这种机制，可以产生具有不同N末端的蛋白同工型，这些蛋白同工型在定位上显示出光依赖性。例如，生长在阴凉处的植物会积聚甘油酸激酶（GLYK）的胞质同工型，这是一种必不可少的光呼吸酶，以前被认为只能定位在叶绿体上。细胞质GLYK构成光呼吸旁路，可减轻波动的光诱导光抑制作用。因此，植物色素控制替代启动子的选择，以响应不断变化的光照条件来调节蛋白质的定位。这项研究表明，替代启动子的使用代表了真核生物中另一个普遍存在的基因表达调控层，有助于蛋白质组的多样化。