Dou Junling, Yang Huihui, Sun Dongling, Yang Sen, Sun Shouru, Zhao Shengjie, Lu Xuqiang, Zhu Huayu, Liu Dongming, Ma Changsheng, Liu Wenge, Yang Luming
College of Horticulture, Henan Agricultural University, 63 Nongye Road, Zhengzhou, 450002, China.
Zhengzhou Fruit Research Institute, Chinese Academy of Agricultural Sciences, Zhengzhou, 450009, China.
Theor Appl Genet. 2022 Jan;135(1):65-79. doi: 10.1007/s00122-021-03952-6. Epub 2021 Sep 25.
A SNP mutation in Clbl gene encoding TERMINAL FLOWER 1 protein is responsible for watermelon branchless. Lateral branching is one of the most important traits, which directly determines plant architecture and crop productivity. Commercial watermelon has the characteristics of multiple lateral branches, and it is time-consuming and labor-costing to manually remove the lateral branches in traditional watermelon cultivation. In our present study, a lateral branchless trait was identified in watermelon material WCZ, and genetic analysis revealed that it was controlled by a single recessive gene, which named as Clbl (Citrullus lanatus branchless). A bulked segregant sequencing (BSA-seq) and linkage analysis was conducted to primarily map Clbl on watermelon chromosome 4. Next-generation sequencing-aided marker discovery and a large mapping population consisting of 1406 F plants were used to further map Clbl locus into a 9011-bp candidate region, which harbored only one candidate gene Cla018392 encoding a TERMINAL FLOWER 1 protein. Sequence comparison of Cla018392 between two parental lines revealed that there was a SNP detected from C to A in the coding region in the branchless inbred line WCZ, which resulted in a mutation from alanine (GCA) to glutamate (GAA) at the fourth exon. A dCAPS marker was developed from the SNP locus, which was co-segregated with the branchless phenotype in both BC and F population, and it was further validated in 152 natural watermelon accessions. qRT-PCR and in situ hybridization showed that the expression level of Cla018392 was significantly reduced in the axillary bud and apical bud in branchless line WCZ. Ectopic expression of ClTFL1 in Arabidopsis showed an increased number of lateral branches. The results of this study will be helpful for better understanding the molecular mechanism of lateral branch development in watermelon and for the development of marker-assisted selection (MAS) for new branchless watermelon cultivars.
编码TERMINAL FLOWER 1蛋白的Clbl基因中的一个SNP突变导致西瓜无侧枝。侧枝是最重要的性状之一，直接决定植株形态和作物产量。商业西瓜具有多个侧枝的特征，在传统西瓜种植中人工去除侧枝既费时又费工。在我们目前的研究中，在西瓜材料WCZ中鉴定出一个无侧枝性状，遗传分析表明它由一个单隐性基因控制，该基因命名为Clbl（西瓜无侧枝）。进行了混合分组分析法（BSA-seq）和连锁分析，将Clbl初步定位在西瓜4号染色体上。利用新一代测序辅助标记发现法和由1406株F植株组成的大型作图群体，将Clbl基因座进一步定位到一个9011 bp的候选区域，该区域仅含有一个候选基因Cla018392，编码TERMINAL FLOWER 1蛋白。两个亲本系之间Cla018392的序列比较表明，在无侧枝自交系WCZ的编码区检测到一个从C到A的SNP，导致第四外显子处从丙氨酸（GCA）突变为谷氨酸（GAA）。从该SNP位点开发了一个dCAPS标记，它在BC和F群体中均与无侧枝表型共分离，并在152份天然西瓜种质中进一步验证。qRT-PCR和原位杂交表明，Cla018392在无侧枝系WCZ的腋芽和顶芽中的表达水平显著降低。ClTFL1在拟南芥中的异位表达显示侧枝数量增加。本研究结果将有助于更好地理解西瓜侧枝发育的分子机制，并有助于开发无侧枝西瓜新品种的分子标记辅助选择（MAS）。
