Distelfeld Assaf, Tranquilli Gabriela, Li Chengxia, Yan Liuling, Dubcovsky Jorge
Department of Plant Sciences, University of California, Davis, California 95616-8515, USA.
Plant Physiol. 2009 Jan;149(1):245-57. doi: 10.1104/pp.108.129353. Epub 2008 Nov 12.
Winter wheat (Triticum spp.) varieties require long exposures to low temperatures to flower, a process called vernalization. The VRN2 locus includes two completely linked zinc finger-CCT domain genes (ZCCT1 and ZCCT2) that act as flowering repressors down-regulated during vernalization. Deletions or mutations in these two genes result in the elimination of the vernalization requirement in diploid wheat (Triticum monococcum). However, natural allelic variation in these genes has not been described so far in polyploid wheat (tetraploid Triticum turgidum and hexaploid Triticum aestivum). A tetraploid wheat population segregating for both VRN-A2 and VRN-B2 loci facilitated the characterization of different alleles. Comparisons between functional and nonfunctional alleles revealed that both ZCCT1 and ZCCT2 genes are able to confer vernalization requirement and that different ZCCT genes are functional in different genomes. ZCCT1 and ZCCT2 proteins from nonfunctional vrn2 alleles have mutations at arginine amino acids at position 16, 35, or 39 of the CCT domain. These positions are conserved between CCT and HEME ACTIVATOR PROTEIN2 (HAP2) proteins, supporting a model in which the action of CCT domains is mediated by their interactions with HAP2/HAP3/HAP5 complexes. This study also revealed natural variation in gene copy number, including a duplication of the functional ZCCT-B2 gene and deletions or duplications of the complete VRN-B2 locus. Allelic variation at the VRN-B2 locus was associated with a partially dominant effect, which suggests that variation in the number of functional ZCCT genes can be used to expand allelic diversity for heading time in polyploid wheat and, hopefully, improve its adaptation to different environments.
冬小麦（小麦属）品种需要长时间暴露在低温下才能开花，这一过程称为春化作用。VRN2位点包含两个完全连锁的锌指-CCT结构域基因（ZCCT1和ZCCT2），它们作为开花抑制因子，在春化作用期间被下调。这两个基因的缺失或突变导致二倍体小麦（一粒小麦）不再需要春化作用。然而，到目前为止，在多倍体小麦（四倍体硬粒小麦和六倍体普通小麦）中尚未描述这些基因的自然等位变异。一个同时在VRN-A2和VRN-B2位点分离的四倍体小麦群体有助于对不同等位基因进行表征。功能性和非功能性等位基因之间的比较表明，ZCCT1和ZCCT2基因都能够赋予对春化作用的需求，并且不同的ZCCT基因在不同的基因组中发挥作用。来自非功能性vrn2等位基因的ZCCT1和ZCCT2蛋白在CCT结构域的第16、35或39位精氨酸氨基酸处发生突变。这些位置在CCT和血红素激活蛋白2（HAP2）蛋白之间是保守的，支持了一种模型，即CCT结构域的作用是通过它们与HAP2/HAP3/HAP5复合物的相互作用来介导的。这项研究还揭示了基因拷贝数的自然变异，包括功能性ZCCT-B2基因的重复以及完整VRN-B2位点的缺失或重复。VRN-B2位点的等位变异与部分显性效应相关，这表明功能性ZCCT基因数量的变异可用于扩大多倍体小麦抽穗期的等位基因多样性，并有望改善其对不同环境的适应性。
