Departamento de Biologia Vegetal, Instituto de Biologia, Universidade Estadual de Campinas, CP 6109, Campinas, SP, 13083-970, Brazil.
Centro Avançado da Pesquisa Tecnológica do Agronegócio de Cana, Instituto Agronômico de Campinas, CP 206, Ribeirão Preto, SP, 14001-970, Brazil.
Mol Genet Genomics. 2017 Dec;292(6):1323-1340. doi: 10.1007/s00438-017-1349-6. Epub 2017 Jul 11.
Dirigent (DIR) proteins, encoded by DIR genes, are referred to as "dirigent" because they direct the outcome of the coupling of the monolignol coniferyl alcohol into (+) or (-) pinoresinol, the first intermediates in the enantiocomplementary pathways for lignan biosynthesis. DIR domain-containing or DIR-like proteins are, thus, termed for not having a clear characterization. A transcriptome- and genome-wide survey of DIR domain-containing proteins in sugarcane was carried out, in addition to phylogenetic, physicochemical and transcriptional analyses. A total of 120 non-redundant sequences containing the DIR domain were identified and classified into 64 groups according to phylogenetic and sequence alignment analyses. In silico analysis of transcript abundance showed that these sequences are expressed at low levels in leaves and genes in the same phylogenetic clade have similar expression patterns. Expression analysis of ShDIR1-like transcripts in the culm internodes of sugarcane demonstrates their abundance in mature internodes, their induction by nitrogen fertilization and their predominant expression in cells that have a lignified secondary cell wall, such as vascular bundles of young internodes and parenchymal cells of the pith of mature internodes. Due to the lack of information about the functional role of DIR in plants, a possible relationship is discussed between the ShDIR1-like transcriptional profile and cell wall development in parenchyma cells of sugarcane culm, which typically accumulates large amounts of sucrose. The number of genes encoding the DIR domain-containing proteins in sugarcane is intriguing and is an indication per se that these proteins may have an important metabolic role and thus deserve to be better studied.
DIR 蛋白（DIR）由 DIR 基因编码，因其能够指导松柏醇与 (+)或(-)松脂醇的偶联结果而得名，这是木质素生物合成对映体互补途径中的第一个中间产物。因此，含有 DIR 结构域的蛋白或类似 DIR 结构域的蛋白被称为没有明确特征的蛋白。除了进行系统发育、物理化学和转录分析外，我们还对甘蔗中的 DIR 结构域蛋白进行了转录组和基因组范围的调查。总共鉴定出 120 个非冗余序列，这些序列含有 DIR 结构域，并根据系统发育和序列比对分析将其分为 64 组。通过对转录丰度的计算机分析发现，这些序列在叶片中的表达水平较低，并且在同一系统发育分支中的基因具有相似的表达模式。ShDIR1 样转录物在甘蔗节间中的表达分析表明，它们在成熟节间中丰度较高，氮素施肥诱导其表达，并且在具有木质化次生细胞壁的细胞中优先表达，如年轻节间的维管束和成熟节间的髓质细胞。由于缺乏 DIR 在植物中功能作用的信息，我们讨论了 ShDIR1 样转录谱与甘蔗节间髓质细胞细胞壁发育之间的可能关系，甘蔗节间髓质细胞通常积累大量的蔗糖。甘蔗中编码 DIR 结构域蛋白的基因数量令人好奇，本身就表明这些蛋白可能具有重要的代谢作用，因此值得进一步研究。
