Institute of Fruit Tree and Tea Science (NIFTS), National Agriculture and Food Research Organization (NARO), Shizuoka 424-0292, Japan.
Faculty of Agriculture, Shizuoka University, Shizuoka 422-8529, Japan.
Tree Physiol. 2018 May 1;38(5):755-771. doi: 10.1093/treephys/tpx145.
After a long juvenile period, citrus trees undergo seasonal flowering cycles. Under natural conditions, citrus flowering is regulated mainly by low ambient temperatures around 15-20 °C and water deficit stress. Recent studies have revealed that fluctuations in the expression of citrus homologs of FLOWERING LOCUS T (FT, encoding a flowering integrator) are correlated with their presumed role as flower-promoting signals. Previous ectopic expression analyses have demonstrated the flower-promoting function of citrus FT homologs. In this study, we examined whether abscisic acid (ABA) affects the expression of FT homologs and the flowering induced by low ambient temperatures. Application of exogenous ABA to potted Satsuma mandarin (Citrus unshiu Marc.) trees resulted in transient accumulation of citrus FT homolog transcripts. The promoter of one citrus FT homolog, CiFT3, was active in transgenic A. thaliana (Arabidopsis thaliana) and responded to exogenous and endogenous ABA. CiFT3 is preferentially expressed in shoots, and its expression was affected by flower-inductive treatments. Endogenous ABA accumulated in mandarin shoots during the floral induction period at 15 °C and under field conditions. The accumulation of ABA was correlated with the accumulation of FT homolog transcripts and flowering intensity. It was consistent with changes in the expression of genes related to ABA metabolism. The abundance of carotenoid precursors that serve as substrates for ABA biosynthesis decreased in leaves during the accumulation of ABA. Our data indicate that ABA and carotenoid precursors in leaves influence the flowering of mandarin trees induced by low temperature.
经过漫长的幼年期后，柑橘树会经历季节性开花周期。在自然条件下，柑橘开花主要受 15-20°C 左右的环境低温和水分亏缺胁迫的调节。最近的研究表明，柑橘与开花整合因子（FT）同源物的表达波动与其作为促进开花信号的假定作用有关。先前的异位表达分析已经证明了柑橘 FT 同源物的促花功能。在这项研究中，我们研究了脱落酸（ABA）是否影响 FT 同源物的表达以及低温诱导的开花。将外源 ABA 应用于盆栽温州蜜柑（Citrus unshiu Marc.）树上，导致柑橘 FT 同源物转录本的瞬时积累。一个柑橘 FT 同源物的启动子 CiFT3 在转基因拟南芥（Arabidopsis thaliana）中具有活性，并对内外源 ABA 有反应。CiFT3 在芽中优先表达，其表达受诱导开花处理的影响。在 15°C 的开花诱导期和田间条件下，ABA 在温州蜜柑芽中积累。ABA 的积累与 FT 同源物转录本的积累和开花强度相关。这与 ABA 代谢相关基因表达的变化一致。作为 ABA 生物合成底物的类胡萝卜素前体的丰度在叶片中 ABA 积累期间下降。我们的数据表明，叶片中的 ABA 和类胡萝卜素前体影响低温诱导的蜜柑树的开花。
