Most organisms have internal circadian clocks that mediate responses to daily environmental changes in order to synchronize biological functions to the correct times of the day. Previous studies have focused on plants found in temperate and sub-tropical climates, and little is known about the circadian transcriptional networks of plants that typically grow under conditions with relatively constant day lengths and temperatures over the year. In this study we conducted a genomic and computational analysis of the circadian biology of Carica papaya, a tropical tree. We found that predicted papaya circadian clock genes cycle with the same phase as Arabidopsis genes. The patterns of time-of-day overrepresentation of circadian-associated promoter elements were nearly identical across papaya, Arabidopsis, rice, and poplar. Evolution of promoter structure predicts the observed morning- and evening-specific expression profiles of the papaya PRR5 paralogs. The strong conservation of previously identified circadian transcriptional networks in papaya, despite its tropical habitat and distinct life-style, suggest that circadian timing has played a major role in the evolution of plant genomes, consistent with the selective pressure of anticipating daily environmental changes. Further studies could exploit this conservation to elucidate general design principles that will facilitate engineering plant growth pathways for specific environments. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1007/s12042-008-9020-3) contains supplementary material, which is available to authorized users.

中文翻译：

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Carica papaya 中的保守日常转录程序。

大多数生物都有内部生物钟，可以调节对日常环境变化的反应，以使生物功能与一天中的正确时间同步。以前的研究集中在温带和亚热带气候中发现的植物，而对通常在一年中昼长和温度相对恒定的条件下生长的植物的昼夜节律转录网络知之甚少。在这项研究中，我们对热带树番木瓜的昼夜节律生物学进行了基因组和计算分析。我们发现预测的木瓜生物钟基因与拟南芥基因的周期相同。在木瓜、拟南芥、水稻和杨树中，昼夜节律相关启动子元件的昼夜节律过度表达模式几乎相同。启动子结构的进化预测了观察到的木瓜 PRR5 旁系同源物的早晚特异性表达谱。尽管木瓜的热带栖息地和独特的生活方式，先前确定的昼夜节律转录网络的强烈保护表明，昼夜节律时间在植物基因组的进化中发挥了重要作用，这与预测日常环境变化的选择压力是一致的。进一步的研究可以利用这种保护来阐明一般设计原则，这将有助于为特定环境设计植物生长途径。电子补充材料：本文的网络版（doi:10.1007/s12042-008-9020-3）包含补充材料，可供授权用户使用。