Data_Sheet_1_Long-day photoperiod and cool temperature induce flowering in cassava: Expression of signaling genes.PDF

Cassava is a staple food crop in the tropics, and is of particular importance in Africa. Recent development of genomic selection technology have improved the speed of cassava breeding; however, cassava flower initiation and development remains a bottleneck. The objectives of the current studies were to elucidate the effect of photoperiod, temperature and their interactions on the time of flowering and flower development in controlled environments, and to use RNA-sequencing to identify transcriptome expression underlying these environmental responses. Compared to a normal tropical day-length of 12 h, increasing the photoperiod by 4 h or decreasing the air temperature from 34/31 to 22°/19°C (day/night) substantially hastened the time to flowering. For both photoperiod and temperature, the environment most favorable for flowering was opposite the one for storage root harvest index. There was a pronounced treatment interaction: at warm day-time temperatures, percent flowering was low, and photoperiod had little effect. In contrast, at cooler temperatures, percent flowering increased, and long-day (LD) photoperiod had a strong effect in hastening flowering. In response to temperature, many differentially expressed genes in the sugar, phase-change, and flowering-time-integrator pathways had expression/flowering patterns in the same direction as in Arabidopsis (positive or negative) even though the effect of temperature on flowering operates in the reverse direction in cassava compared to Arabidopsis. Three trehalose-6-phosphate-synthase-1 (TPS1) genes and four members of the SPL gene family had significantly increased expression at cool temperature, suggesting sugar signaling roles in flower induction. In response to LD photoperiod, regulatory genes were expressed as in Arabidopsis and other LD flowering plants. Several hormone-related genes were expressed in response to both photoperiod and temperature. In summary, these findings provide insight on photoperiod and temperature responses and underlying gene expression that may assist breeding programs to manipulate flowering for more rapid crop improvement.

木薯（Cassava）是热带地区的主粮作物，在非洲具有特殊重要性。近年来基因组选择技术的发展提升了木薯育种的速度，但木薯的花起始与发育仍是育种进程中的瓶颈。本研究的目标为：阐明光周期、温度及其交互作用对可控环境下开花时间与花发育的影响，并借助RNA测序（RNA-sequencing）解析这些环境响应背后的转录组表达调控模式。相较于热带地区常规的12小时日照长度，将光周期延长4小时，或把昼夜温度从34/31℃调整至22/19℃，均可显著提早开花时间。对于光周期与温度两个因素而言，最利于开花的环境条件，与储藏块根收获指数的最优条件恰好相反。处理间存在显著交互效应：在日间高温环境下，开花率较低，光周期几乎无调控效果；与之相反，在低温环境下，开花率显著提升，长日照（LD）光周期对提早开花具有极强的促进作用。在温度响应层面，糖代谢、相变及开花时间整合通路中的大量差异表达基因，其表达模式与开花时间的关联趋势与拟南芥（Arabidopsis）一致（正向或负向）——尽管木薯中温度对开花的调控方向与拟南芥恰好相反。3个海藻糖-6-磷酸合酶1（TPS1）基因与SPL基因家族的4个成员，在低温环境下的表达量显著上调，提示糖信号通路在花诱导过程中发挥关键作用。在长日照光周期响应过程中，调控基因的表达模式与拟南芥及其他长日照开花植物一致。另有多种激素相关基因同时响应光周期与温度变化。综上，本研究揭示了木薯对光周期与温度的响应机制及其背后的基因表达调控规律，可为通过调控开花进程以加速作物遗传改良的育种项目提供重要理论参考。