Jang Seonghoe, Choi Sang-Chul, Li Hsing-Yi, An Gynheung, Schmelzer Elmon
Biotechnology Center in Southern Taiwan, Academia Sinica, Tainan County, 741, Taiwan; Agricultural Biotechnology Research Center, Academia Sinica, Taipei, 115, Taiwan.
Crop Biotechnology Center, Kyunghee University, Yongin, 446-701, Korea.
PLoS One. 2015 Aug 28;10(8):e0134987. doi: 10.1371/journal.pone.0134987. eCollection 2015.
We show that the key flowering regulators encoded by Phalaenopsis aphrodite FLOWERING LOCUS T1 (PaFT1) and PaFD share high sequence homologies to these from long-day flowering Arabidopsis and short-day flowering rice. Interestingly, PaFT1 is specifically up-regulated during flowering inductive cooling treatment but is not subjected to control by photoperiod in P. aphrodite. Phloem or shoot apex-specific expression of PaFT1 restores the late flowering of Arabidopsis ft mutants. Moreover, PaFT1 can suppress the delayed flowering caused by SHORT VEGATATIVE PHASE (SVP) overexpression as well as an active FRIGIDA (FRI) allele, indicating the functional conservation of flowering regulatory circuit in different plant species. PaFT1 promoter:GUS in Arabidopsis showed similar staining pattern to that of Arabidopsis FT in the leaves and guard cells but different in the shoot apex. A genomic clone or heat shock-inducible expression of PaFT1 is sufficient to the partial complementation of the ft mutants. Remarkably, ectopic PaFT1 expression also triggers precocious heading in rice. To further demonstrate the functional conservation of the flowering regulators, we show that PaFD, a bZIP transcription factor involved in flowering promotion, interacts with PaFT1, and PaFD partially complemented Arabidopsis fd mutants. Transgenic rice expressing PaFD also flowered early with increased expression of rice homologues of APETALA1 (AP1). Consistently, PaFT1 knock-down Phalaenopsis plants generated by virus-induced gene silencing exhibit delayed spiking. These studies suggest functional conservation of FT and FD genes, which may have evolved and integrated into distinct regulatory circuits in monopodial orchids, Arabidopsis and rice that promote flowering under their own inductive conditions.
我们发现，蝴蝶兰成花素基因T1（PaFT1）和PaFD编码的关键开花调控因子与长日照开花的拟南芥和短日照开花的水稻中的这些因子具有高度的序列同源性。有趣的是，PaFT1在开花诱导冷处理期间特异性上调，但不受蝴蝶兰光周期的调控。PaFT1在韧皮部或茎尖特异性表达可恢复拟南芥ft突变体的晚花表型。此外，PaFT1可以抑制由SHORT VEGATATIVE PHASE（SVP）过表达以及活性FRIGIDA（FRI）等位基因引起的开花延迟，这表明不同植物物种中开花调控回路具有功能保守性。拟南芥中PaFT1启动子驱动的GUS在叶片和保卫细胞中的染色模式与拟南芥FT相似，但在茎尖不同。PaFT1的基因组克隆或热激诱导表达足以部分互补ft突变体。值得注意的是，异位表达PaFT1也会促使水稻提前抽穗。为了进一步证明开花调控因子的功能保守性，我们发现参与促进开花的bZIP转录因子PaFD与PaFT1相互作用，并且PaFD部分互补了拟南芥fd突变体。表达PaFD的转基因水稻也提前开花，且APETALA1（AP1）水稻同源基因的表达增加。同样，通过病毒诱导基因沉默产生的PaFT1基因敲低蝴蝶兰植株表现出延迟抽穗。这些研究表明FT和FD基因具有功能保守性，它们可能已经进化并整合到单轴兰花、拟南芥和水稻中不同的调控回路中，以在各自的诱导条件下促进开花。
