背景回顾：The timing of flowering is tightly controlled by signals that integrate environmental and endogenous cues. Sugars produced by carbon fixation in the chloroplast are a crucial endogenous cue for floral initiation. Chloroplasts also convey information directly to the nucleus through retrograde signaling to control plant growth and development. 

结果1-叶绿体抑制开花：Here, we show that mutants defective in chlorophyll biosynthesis and chloroplast development flowered early, especially under long-day conditions, although low sugar accumulation was seen in some mutants. Plants treated with the bleaching herbicide norflurazon also flowered early, suggesting that chloroplasts have a role in floral repression. 

结果2-GLK1/2作用于CO-FT下游，抑制开花：Among retrograde signaling mutants, the golden2-like 1 (glk1) glk2 double mutants showed early flowering under long-day conditions. This early flowering was completely suppressed by constans (co) and flowering locus t (ft) mutations. Leaf vascular-specific knockdown of both GLK1 and GLK2 phenocopied the glk1 glk2 mutants.  

结果3-GLK1/2-BBXs：GLK1 and GLK2 repress flowering by directly activating the expression of B-BOX DOMAIN PROTEIN 14 (BBX14), BBX15, and BBX16 via CCAATC cis-elements in the BBX genes.

结果4-BBX-CO-FT：BBX14/15/16 physically interact with CO in the nucleus and expression of BBXs hampered CO-mediated FT transcription. Simultaneous knockdown of BBX14/15/16 by artificial miRNA (35S::amiR-BBX14/15/16) caused early flowering with increased FT transcript levels, whereas BBX overexpression caused late flowering.

结果5-GLK1/2-BBXs对达草灭处理不敏感：Flowering of glk1/2 and 35S::amiR-BBX14/15/16 plants was insensitive to norflurazon treatment. 

结论：Taking these observations together, we propose that the GLK1/2–BBX14/15/16 module provides a novel mechanism explaining how the chloroplast represses flowering to balance plant growth and reproductive development.

A working model of the regulation of flowering time by chloroplast retrograde signaling through the GLK–BBX14/15/16 module.

开花时间同时受到外部环境和内部发育信号的紧密调控。由叶绿体碳固定产生的蔗糖对于成花转变来说是一个非常重要的内源信号。叶绿体也会通过逆行信号直接向细胞核传递信息，以控制植物的生长和发育。本文中，作者发现叶绿素生物合成和叶绿体发育缺陷的突变体虽然蔗糖积累水平较低，但却能够早花，尤其是在长日照条件下。利用除草剂达草灭（靶向PDS）处理也能够促进植株早花，说明叶绿体作用于成花抑制。在逆行信号突变体中，glk1 glk2双突变体在长日照条件下表现出早花的表型。然而，glk1 glk2的早花表型会被co和ft突变完全抑制。叶片维管特异性敲低GLK1和GLK2的表型与glk1 glk2双突的表型十分类似。GLK1和GLK2通过BBXs基因的CCAATC顺式调控元件，直接激活BBX14/15/16的表达。BBX14/15/16能够与CO在细胞核中互作，并且BBXs的表达阻碍了CO介导的FT转录激活。通过人工miRNA（35S::amiR-BBX14/15/16）同时敲低BBX14/15/16会导致FT表达增强及早花的表型，而BBX过表达则会导致晚花的表型。glk1/2和35S::amiR-BBX14/15/16植株的开花对于达草灭处理不敏感。综上，作者提出GLK1/2–BBX14/15/16模块为解释叶绿体如何抑制开花以平衡植物生长和生殖发育提供了一个新的机制。