Department of Horticulture College, Northwest Agriculture & Forestry University, Yangling, 712100, China.
BMC Plant Biol. 2019 Mar 6;19(1):93. doi: 10.1186/s12870-019-1695-0.
Insufficient production of flower buds is an intractable problem in 'Fuji' apple orchards. Although cytokinin (CK) promotes flower bud formation in apple trees, little is known about the mechanisms regulating this phenomenon.
In the present study, high-throughput RNA sequencing (RNA-Seq) of 'Nagafu No. 2' buds was conducted to characterize the transcriptional response to 6-BA treatment during key period of floral transition. A weighted gene co-expression network analysis (WGCNA) of the differentially expressed genes identified hormone signal transduction pathways, totaling 84 genes were highly correlated with the expression pattern of flowering-time genes. The up-regulation of CK signal components and a gibberellin (GA) signal repressor were found to contribute to the promotion of floral transition. In relative comparison to non-treated buds, a series of sugar metabolism- and signal- related genes were associated with relatively high levels of sucrose, fructose, and glucose during floral induction in the 6-BA treated buds. Several transcription factors (i.e. SPLs, SOC1, FD, and COL) that are involved in GA, aging, and photoperiod-regulated flowering pathways were also upregulated by the 6-BA treatment. In addition, potential transcription factors integrating CK signaling to trigger floral induction in apple were also assessed; including PHYTO-CHROME-INTERACTING FACTOR (PIF1,3), WUSCHEL-related homeobox (WOX3,13), and CK response regulators (ARR2).
The present study provides insight into the response of flowering and development-related pathways and transcription factors to 6-BA during the period of floral transition in apple. It extends our knowledge of the fundamental mechanisms associated with CK-regulated floral transition in apple trees.
花蕾产量不足是富士苹果园的一个难题。虽然细胞分裂素（CK）能促进苹果树形成花蕾，但对调节这一现象的机制知之甚少。
本研究对‘长富 2 号’芽进行了高通量 RNA 测序（RNA-Seq），以研究在花转变关键时期 6-BA 处理对转录组的影响。对差异表达基因的加权基因共表达网络分析（WGCNA）表明，激素信号转导途径与开花时间基因的表达模式高度相关，共有 84 个基因。CK 信号成分和赤霉素（GA）信号抑制剂的上调被认为有助于促进花转变。与未处理的芽相比，在 6-BA 处理的芽中，一系列与糖代谢和信号相关的基因在花诱导过程中与相对较高的蔗糖、果糖和葡萄糖水平相关。参与 GA、衰老和光周期调控开花途径的几个转录因子（如 SPLs、SOC1、FD 和 COL）也被 6-BA 处理上调。此外，还评估了将 CK 信号整合到苹果中触发花诱导的潜在转录因子；包括 PHYTO-CHROME-INTERACTING FACTOR（PIF1,3）、WUSCHEL 相关同源盒（WOX3,13）和 CK 反应调节因子（ARR2）。
本研究深入了解了苹果花转变时期与开花和发育相关途径及转录因子对 6-BA 的反应，扩展了我们对 CK 调控苹果花转变的基本机制的认识。
