State Key Laboratory of Cotton Biology, Institute of Cotton Research, Chinese Academy of Agricultural Sciences, Anyang, 455000, China.
Art and Science College, University of Saskatchewan, Saskatoon, S7N 5A5, Canada.
Theor Appl Genet. 2019 Jan;132(1):97-112. doi: 10.1007/s00122-018-3197-0. Epub 2018 Oct 4.
Nulliplex-branch (nb) mutants in cotton display a specific architecture. The gene responsible for the nb phenotype was identified, and its modulation mode was further studied. Plant architecture is an important agronomic factor influencing various traits such as yield and variety adaptability in crop plants. Cotton (Gossypium) simultaneously displays monopodial and sympodial growth. Nulliplex-branch (nb) mutants showing determinate sympodial shoots have been reported in both G. hirsutum (Ghnb) and G. barbadense (Gbnb). In this study, the gene responsible for the nb phenotype was identified. GhNB and GbNB were found to be allelic loci and are TERMINAL FLOWER 1 orthologs on the Dt subgenome, though the At copies remain native. Sequencing and association analyses identified four (Gh-nb1-Gh-nb4) and one (Gb-nb1) type of point mutation in the coding sequences of Ghnb and Gbnb, respectively. The NB gene was mainly expressed in the root and shoot apex, and expression rhythms were also observed in these tissues, suggesting that the expression of the NB gene could be regulated by photoperiod. Constitutive overexpression of GhNB suppresses the differentiation of the reproductive shoots. Knockout of both copies of GhNB caused the main and lateral shoots to terminate in flowers, which is a more determinate architecture than that of the nb mutants and implies that its function might be dosage dependent. A protein lipid overlay assay indicated that the amino acid substitutions in Gh-nb1 and Gb-nb1 weaken the ligand-binding activity of the NB protein in vitro. These findings suggest that the NB gene plays crucial roles in regulating the determinacy of shoots, and the modulation of this gene should constitute an effective crop improvement approach through adjusting the growth habit of cotton.
棉株单枝（nb）突变体表现出特定的结构。鉴定出负责 nb 表型的基因，并进一步研究其调控模式。植物结构是影响作物产量和品种适应性等各种性状的重要农艺因素。棉花（Gossypium）同时表现出单轴和合轴生长。在 G. hirsutum（Ghnb）和 G. barbadense（Gbnb）中都报道了表现出有限合轴生长的单枝突变体。在本研究中，鉴定出负责 nb 表型的基因。GhNB 和 GbNB 被发现是等位基因，是 Dt 亚基因组上的 TERMINAL FLOWER 1 同源物，尽管 At 拷贝仍然是原生的。测序和关联分析分别在 Ghnb 和 Gbnb 的编码序列中鉴定出 4 种（Gh-nb1-Gh-nb4）和 1 种（Gb-nb1）类型的点突变。NB 基因主要在根和茎尖中表达，在这些组织中也观察到表达节律，表明 NB 基因的表达可能受到光周期的调控。GhNB 的组成型过表达抑制生殖枝的分化。GhNB 的两个拷贝的敲除导致主枝和侧枝在花中终止，这是一种比 nb 突变体更有限的结构，这意味着其功能可能是剂量依赖性的。蛋白质脂质覆盖测定表明，Gh-nb1 和 Gb-nb1 中的氨基酸取代削弱了 NB 蛋白在体外的配体结合活性。这些发现表明，NB 基因在调节枝条的确定性方面起着关键作用，通过调节棉花的生长习性，该基因的调控可能构成一种有效的作物改良方法。
