Main conclusionFive laccase genes are potentially involved in developmental lignification in the model C4 grass Setaria viridis and their different tissue specificities suggest subfunctionalization events.AbstractPlant laccases are copper-containing glycoproteins involved in monolignol oxidation and, therefore, their activity is essential for lignin polymerization. Although these enzymes belong to large multigene families with highly redundant members, not all of them are thought to be involved in lignin metabolism. Here, we report on the genome-wide characterization of the laccase gene family in the model C4 grass Setaria viridis and further identification of the members potentially involved in monolignol oxidation. A total of 52 genes encoding laccases (SvLAC1 to SvLAC52) were found in the genome of S. viridis, and phylogenetic analyses showed that these genes were heterogeneously distributed among the characteristic six subclades of the family and are under relaxed selective constraints. The observed expansion in the total number of genes in this species was mainly caused by tandem duplications within subclade V, which accounts for 68% of the whole family. Comparative phylogenetic analyses showed that the expansion of subclade V is specifically observed for the Paniceae tribe within the Panicoideae subfamily in grasses. Five SvLAC genes (SvLAC9, SvLAC13, SvLAC15, SvLAC50, and SvLAC52) fulfilled the criteria established to identify lignin-related candidates: (1) phylogenetic proximity to previously characterized lignin-related laccases from other species, (2) similar expression pattern to that observed for lignin biosynthetic genes in the S. viridis elongating internode, and (3) high expression in S. viridis tissues undergoing active lignification. In addition, in situ hybridization experiments not only confirmed that these selected SvLAC genes were expressed in lignifying cells, but also that their expression showed different tissue specificities, suggesting subfunctionalization events within the family. These five laccase genes are strong candidates to be involved in lignin polymerization in S. viridis and might be good targets for lignin bioengineering strategies.

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狗尾草漆酶基因家族的全基因组特征揭示了可能参与木质化的成员

主要结论五个漆酶基因可能参与模型C4草狗尾草的发育木质化，它们不同的组织特异性表明亚功能化事件。摘要植物漆酶是参与木质素单体氧化的含铜糖蛋白，因此它们的活性对于木质素聚合是必不可少的。尽管这些酶属于具有高度冗余成员的大型多基因家族，但并非所有这些酶都被认为参与木质素代谢。在这里，我们报告了模型 C4 草狗尾草中漆酶基因家族的全基因组特征，并进一步鉴定了可能参与木酚氧化的成员。在 S. viridis 的基因组中发现了总共 52 个编码漆酶的基因（SvLAC1 至 SvLAC52），和系统发育分析表明，这些基因在该家族的六个特征亚群中异质分布，并且处于宽松的选择约束下。观察到的该物种基因总数的增加主要是由亚进化枝 V 内的串联重复引起的，占整个家族的 68%。比较系统发育分析表明，在禾本科的 Panicoideae 亚科中的 Paniceae 部落中特别观察到 subclade V 的扩展。五个 SvLAC 基因（SvLAC9、SvLAC13、SvLAC15、SvLAC50 和 SvLAC52）满足为鉴定与木质素相关的候选物而建立的标准：（1）系统发育接近于来自其他物种的先前表征的木质素相关漆酶，（2）相似的表达模式在 S. 中观察到木质素生物合成基因。viridis 伸长节间，和 (3) 在 S. viridis 组织中的高表达正在经历活跃的木质化。此外，原位杂交实验不仅证实了这些选定的 SvLAC 基因在木质化细胞中表达，而且它们的表达表现出不同的组织特异性，表明家族内的亚功能化事件。这五种漆酶基因是参与绿色链球菌中木质素聚合的有力候选者，可能是木质素生物工程策略的良好靶点。暗示家庭内的亚功能化事件。这五种漆酶基因是参与绿色链球菌中木质素聚合的有力候选者，可能是木质素生物工程策略的良好靶点。暗示家庭内的亚功能化事件。这五种漆酶基因是参与绿色链球菌中木质素聚合的有力候选者，可能是木质素生物工程策略的良好靶点。