Plant Breeding Institute, Kiel University, D-24108 Kiel, Germany; and.
CeBiTec and Department of Biology, Bielefeld University, D-33594 Bielefeld, Germany.
Proc Natl Acad Sci U S A. 2014 Jul 15;111(28):10365-70. doi: 10.1073/pnas.1404829111. Epub 2014 Jun 25.
Sugar beet (Beta vulgaris) is a biennial root crop that grows vegetatively in the first year and starts shoot elongation (bolting) and flowering after exposure to cold temperatures over winter. Early bolting before winter is controlled by the dominant allele of the B locus. Recently, the BOLTING time control 1 (BTC1) gene has been cloned from this locus. BTC1 promotes early bolting through repression of the downstream bolting repressor B. vulgaris flowering locus T1 (BvFT1) and activation of the downstream floral activator BvFT2. We have identified a new bolting locus B2 acting epistatically to B. B2 houses a transcription factor which is diurnally regulated and acts like BTC1 upstream of BvFT1 and BvFT2. It was termed BvBBX19 according to its closest homolog from Arabidopsis thaliana. The encoded protein has two conserved domains with homology to zinc finger B-boxes. Ethyl methanesulfonate-induced mutations within the second B-box caused up-regulation of BvFT1 and complete down-regulation of BvFT2. In Arabidopsis, the expression of FT is promoted by the B-box containing protein CONSTANS (CO). We performed a phylogenetic analysis with B-box genes from beet and A. thaliana but only BvCOL1 clustered with CO. However, BvCOL1 had been excluded as a CO ortholog by previous studies. Therefore, a new model for flowering induction in beet is proposed in which BTC1 and BvBBX19 complement each other and thus acquire a CO function to regulate their downstream targets BvFT1 and BvFT2.
糖甜菜（Beta vulgaris）是一种二年生块根作物，在第一年以营养生长方式生长，在冬季经历低温后开始进行抽薹伸长（开花）。冬季前的早期抽薹由 B 位点的显性等位基因控制。最近，该位点的 BOLTING time control 1（BTC1）基因已被克隆。BTC1 通过抑制下游开花抑制物 B. vulgaris flowering locus T1（BvFT1）和激活下游花激活物 BvFT2 来促进早期抽薹。我们已经鉴定出一个新的开花位点 B2，它与 B 位点的等位基因上位性作用。B2 座含有一个转录因子，该转录因子受昼夜节律调节，其作用类似于 BvFT1 和 BvFT2 上游的 BTC1。根据其与拟南芥的同源物，将其命名为 BvBBX19。该编码蛋白具有两个与锌指 B 盒同源的保守结构域。在第二个 B 盒内的乙基甲磺酸诱导突变导致 BvFT1 的上调和 BvFT2 的完全下调。在拟南芥中，FT 的表达受含有 B 盒的蛋白 CONSTANS（CO）的促进。我们对甜菜和拟南芥的 B 盒基因进行了系统发育分析，但只有 BvCOL1 与 CO 聚类。然而，BvCOL1 之前的研究已被排除为 CO 的同源物。因此，提出了一个新的甜菜开花诱导模型，其中 BTC1 和 BvBBX19 相互补充，从而获得 CO 功能来调节它们的下游靶标 BvFT1 和 BvFT2。
