Abstract: Taking Salix matsudana and S. babylonica as test materials, branches from different positions were sectioned and stained to determine their cellulose content. Based on the whole-genome sequencing of S. matsudana and S. babylonica, cellulose synthase genes were identified. A variety of approaches, including phylogenetic analysis, chromosome mapping, and RNA-seq data, were employed. Structural variation sites were also jointly analyzed with chromosome localization. The results indicate that branches of S. babylonica have thinner cell wall thickness and lower cellulose content at the same positions compared to S. matsudana. Based on the conserved domain features of cellulose synthase, we identified 25 and 29 cellulose synthase genes in the whole-genome sequencing results of S. matsudana and S. babylonica, respectively. Phylogenetic analysis indicated that the family members could be divided into 10 subgroups, and chromosome mapping showed that CesA genes in S. babylonica were unevenly distributed across 17 chromosomes. RNA-seq data analysis revealed that CesA4/7/8 were significantly highly expressed in S. matsudana, suggesting their important role in cellulose synthesis. Joint analysis of structural variation sites and gene localization found that inversions on chromosomes C18, C11, and D11 altered the structure of the promoter regions of CesA7-3, CesA8-3 and CesA8-4, while insertions and deletions on chromosomes D2 and D4 affected the gene sequences of CesA4-2 and CesA8-2. Chromosomal structural variations have impacted the expression of cellulose synthase genes CesA4/7/8 in S. matsudana and S. babylonica, altering the cellulose content and cell wall thickness. These changes ultimately lead to the differences in branch morphology between S. matsudana and S. babylonica.

Key words: Salix matsudana; Salix babylonica; cellulose; cellulose synthase genes; structural variatio

摘要： 以旱柳Salix matsudana和垂柳S. babylonica为试材，取不同位置枝条观察木质部细胞形态并测定其纤维素含量；在旱柳和垂柳全基因组测序基础上，鉴定纤维素合成酶基因CesA，并运用进化分析、染色体定位以及RNA-seq数据等多种手段，将结构变异位点与染色体定位进行联合分析。结果表明，垂柳枝条在相同位置木质部具有更薄的细胞壁和更低的纤维素含量。在旱柳和垂柳的全基因组序列中分别鉴定出25个和29 个CesA；该家族成员可分为10 个亚组，垂柳CesA基因不均等地分布在17条染色体上；CesA4/7/8在旱柳中显著高表达，推测其在纤维素合成中发挥着重要作用；染色体C18、C11和D11上的倒位改变了CesA7-3、CesA8-3和CesA8-4启动子区结构，染色体D2和D4的插入缺失影响CesA4-2和CesA8-2基因序列。因此，认为染色体结构变异影响了旱柳、垂柳中纤维素合酶基因CesA4/7/8表达，并改变纤维素含量与细胞壁厚度，最终造成旱柳与垂柳枝条形态的差异。

关键词: 旱柳；垂柳；纤维素；纤维素合酶基因；结构变异