Lignin deficiency in the endocarp of walnuts causes kernel bare, leads to inconvenient processing and transportation of walnuts, and easily produces insect damage and mildew, thereby affecting the quality of walnuts. Cinnamyl alcohol dehydrogenase (CAD) is one of the key rate-limiting enzymes in lignin synthesis and plays an important role in the synthesis of lignin in the endocarp of walnut. However, knowledge about CAD gene family members and their evolutionary and functional characteristics in walnuts is limited. In this study, all 18 JrCADs were identified, and phylogenetic relationships, gene structure, protein motifs, collinearity analysis, and expression patterns of the JrCADs were also analyzed. All JrCADs could be divided into three groups based on the phylogenetic tree, gene structure, and motif analysis also support this grouping. Transcriptome data demonstrated that JrCADs have different expression patterns in walnut endocarps at different developmental stages. Combined with qRT–PCR data, we finally identified several candidate JrCADs involved in the process of endocarp sclerosis. This study showed that the JrCAD family members are highly conservative in evolutionary characteristics and they might participate in a variety of hormone responses. JrCAD17 and JrCAD18 are highly expressed in all periods of walnut endocarp harding, they are closely related to lignin accumulation.

核桃内果皮木质素缺乏导致核桃仁裸露，导致核桃加工和运输不便，易产生虫害和霉变，从而影响核桃品质。肉桂醇脱氢酶(CAD)是木质素合成的关键限速酶之一，对核桃内果皮木质素的合成具有重要作用。然而，关于核桃CAD基因家族成员及其进化和功能特征的知识是有限的。在本研究中，鉴定了所有 18 个JrCAD ，并分析了 JrCAD 的系统发育关系、基因结构、蛋白质基序、共线性分析和表达模式。所有JrCAD基于系统发育树、基因结构和基序分析可以分为三组，也支持这种分组。转录组数据表明，JrCADs在不同发育阶段的核桃内果皮中具有不同的表达模式。结合 qRT-PCR 数据，我们最终确定了几个参与果皮硬化过程的候选JrCAD 。本研究表明，JrCAD家族成员在进化特征上高度保守，可能参与了多种激素反应。JrCAD17和JrCAD18在核桃内果皮硬化各时期均有高表达，与木质素积累密切相关。