CmBBX8 accelerating flowering by targeting CmFTL1 directly in summer chrysanthemum

First author: Lijun Wang; Affiliations: Nanjing Agricultural University (南京农业大学): Nanjing, China

Corresponding author: Jiafu Jiang

For a flowering plant, the transition from vegetative stage to reproductive growth is probably the most critical developmental switch. In the model plant Arabidopsis thaliana, the product of BBX7, group II member of BBX family, acts to delay floral transition. In this study, a presumed chrysanthemum homolog of a second group gene AtBBX8, designated CmBBX8, had been isolated and characterized. The transcription of CmBBX8 followed a diurnal rhythm as the chrysanthemum floral transition regulator. Over‐expression of CmBBX8 accelerated flowering, while its (artificial microRNAs) amiR‐enabled knock‐down delayed flowering in plants grown under both long and short day conditions. Global expression analysis revealed that genes associated with photoperiod were downregulated in amiR‐CmBBX8 lines compared with the wild type, which were verified to be upregulated in overexpressing lines (OX‐CmBBX8) by RT‐PCR. A number of in vitro assays were used to show that CmBBX8 targets CmFTL1. Furthermore, the function of CmFTL1 as a floral inducer under long day conditions was confirmed by the behavior of engineered summer‐flowering chrysanthemum plants. The conclusion is that the BBX8‐FT regulatory module is an important determinant of reproductive development in summer‐flowering chrysanthemum.

对于开花植物来说，从营养生长阶段转变为生殖生长阶段可能是最重要的发育转变。在模式植物拟南芥中，BBX基因家族中的II类基因BBX7作用于拟南芥成花转变的延迟。本文中，作者克隆了拟南芥II类BBX基因家族基因AtBBX8在菊花中的同源基因CmBBX8，并对其进行了功能验证。CmBBX8基因的转录遵循昼夜节律，是菊花的成花转变调控因子。无论是在长日照或是短日照条件下，过表达CmBBX8基因能够促进开花，而其人工miRNA干扰突变体则延迟了植株的开花。基因表达谱分析显示，与野生型相比，跟光周期相关的基因在amiR‐CmBBX8株系中下调表达，而通过RT‐PCR试验显示这类基因在CmBBX8基因过表达株系中上调表达。作者进行了一系列的体外试验，结果均显示CmBBX8蛋白能够靶向CmFTL1基因。此外，CmFTL1基因的功能是在长日照条件下诱导开花，而经过改造的夏季开花菊花品种也证明了这一点。本文的研究揭示了BBX8‐FT调控模块是决定夏季开花的菊花品种生殖发育的关键因子。

通讯：蒋甲福 (http://yyxy.njau.edu.cn/jjf.pdf)

个人简介：1995-1999年，南京农业大学，学士；1999-2002年，南京农业大学，硕士；2002-2006年，中国科学院植物研究所，博士；2006-2007年，新加坡国立大学，博士后；2007-2010年，美国得州理工大学，博士后。

研究方向：菊花开花分子机理调控。

doi: https://doi.org/10.1111/pbi.13322

Journal: Plant Biotechnology Journal

Published date: December 28, 2019