Iwate Biotechnology Research Center, Kitakami, Iwate, Japan.
Plant Cell Physiol. 2011 Jun;52(6):1031-41. doi: 10.1093/pcp/pcr055. Epub 2011 Apr 29.
Gentians are herbaceous perennials blooming in summer through autumn. Although they are popular ornamental flowers in Japan, the regulation of their timing of flowering has not been studied. We identified and characterized gentian orthologs of the Arabidopsis FT/TFL1 gene family to elucidate the mechanisms of flowering initiation. We isolated three gentian orthologs of FT and TFL1, denoted GtFT1, GtFT2 and GtTFL1. Since up-regulation of GtFT1 and GtFT2 as well as down-regulation of GtTFL1 promoted floral initiation in gentian plantlets, these genes affected floral initiation in a similar way to Arabidopsis FT and TFL1. The expression levels of GtFT1 and GtFT2 in leaves of late-flowering gentian increased prior to floral initiation, whereas GtTFL1 was highly expressed in shoot apical meristem at the vegetative stage and decreased drastically just before flowering initiation. Comparison of gene expression patterns showed that GtFT1 expression increased earlier in early-flowering than in late-flowering gentian, whereas the timing of the increase in GtFT2 expression was similar in early- and late-flowering plants. The GtTFL1 expression in early-flowering gentian was extremely low throughout the vegetative and reproductive stages. These results indicated that either the up-regulation of GtFT1 or the down-regulation of GtTFL1 may determine flowering time. Furthermore, we found that early-flowering but not late-flowering gentians have a 320 bp insertion in the promoter region of GtTFL1. Thus, the negligible expression of GtTFL1 in early-flowering lines may be due to this insertion, resulting in a shortened vegetative stage.
龙胆是一种夏季到秋季开花的草本多年生植物。虽然它们在日本是很受欢迎的观赏花卉，但它们开花时间的调节机制尚未得到研究。我们鉴定并描述了拟南芥 FT/TFL1 基因家族的龙胆同源物，以阐明开花起始的机制。我们分离了三个龙胆 FT 和 TFL1 的同源物，分别命名为 GtFT1、GtFT2 和 GtTFL1。由于 GtFT1 和 GtFT2 的上调以及 GtTFL1 的下调促进了龙胆植物的花起始，这些基因以类似于拟南芥 FT 和 TFL1 的方式影响花起始。晚花龙胆叶片中 GtFT1 和 GtFT2 的表达水平在花起始前增加，而 GtTFL1 在营养阶段的茎尖分生组织中高度表达，并在花起始前急剧下降。基因表达模式的比较表明，早花龙胆中 GtFT1 的表达比晚花龙胆更早增加，而 GtFT2 表达增加的时间在早花和晚花植物中相似。早花龙胆的 GtTFL1 表达在整个营养和生殖阶段都极低。这些结果表明，GtFT1 的上调或 GtTFL1 的下调可能决定开花时间。此外，我们发现早花龙胆但不是晚花龙胆在 GtTFL1 的启动子区域有一个 320 bp 的插入。因此，早花系中 GtTFL1 的低表达可能是由于这种插入，导致营养阶段缩短。
