Pectin and lignin are two enigmatic macromolecular components of cell wall, which are spatially and temporally deposited during plant growth. While the former is important for primary growth, the latter accumulates during secondary growth. With the evolution of land plants, the structural complexity of pectin increased to protect cell walls against the intrusion of pectinolytic pathogens besides offering multiple choices for its interaction with lignin. We reconstructed pectin biosynthesis pathways in an annual lignocellulosic bast fibre-producing crop jute ( Corchorus spp.) from hypocotyl transcriptomes and identified 27 isoforms of 17 genes and 12 isoforms of galacturonosyltransferase involved in nucleotide-sugar interconversion and pectin polymerization, respectively. Salvage pathways were found to be functional for replenishing nucleotide sugars in jute hypocotyls. Phylogenetic analyses revealed that the genes of pectin biosynthesis pathways are well conserved across taxa. For significant upregulation of the rhamnose biosynthesis gene ( RHM1 ), we traced its evolution, identified its two-domain protein structure proposed to have been evolved from charophycean green algae and generated a structural model explaining its functional conservation. Retting of jute stem with pectinolytic bacteria showed that pectin complexity and its interaction with lignin play crucial roles in resisting cell wall deconstruction that may have accrued from increased rhamnogalacturonan biosynthesis.

中文翻译：

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果胶生物合成途径适用于木质纤维素黄麻（Corchorus spp.）中较高的鼠李糖半乳糖醛酸形成

果胶和木质素是细胞壁的两种神秘大分子成分，它们在植物生长过程中在空间和时间上沉积。前者对初级生长很重要，而后者在次级生长过程中积累。随着陆生植物的进化，果胶的结构复杂性增加，除了为与木质素的相互作用提供多种选择外，还可以保护细胞壁免受果胶分解病原体的侵入。我们从下胚轴转录组重建了一年生木质纤维素韧皮纤维生产作物黄麻 (Corchorus spp.) 中的果胶生物合成途径，并分别鉴定了 17 个基因的 27 种同种型和参与核苷酸-糖相互转化和果胶聚合的半乳糖醛酸转移酶的 12 种同种型。发现补救途径可用于补充黄麻下胚轴中的核苷酸糖。系统发育分析表明，果胶生物合成途径的基因在整个分类群中都非常保守。对于鼠李糖生物合成基因 (RHM1) 的显着上调，我们追踪了它的进化，确定了它的双域蛋白质结构，推测它是从轮藻绿藻进化而来的，并生成了一个解释其功能保守性的结构模型。用果胶分解细菌对黄麻茎进行浸解表明，果胶的复杂性及其与木质素的相互作用在抵抗可能因鼠李糖半乳糖醛酸聚糖生物合成增加而产生的细胞壁解构方面起着至关重要的作用。对于鼠李糖生物合成基因 (RHM1) 的显着上调，我们追踪了它的进化，确定了它的双域蛋白质结构，推测它是从轮藻绿藻进化而来的，并生成了一个解释其功能保守性的结构模型。用果胶分解细菌对黄麻茎进行浸解表明，果胶的复杂性及其与木质素的相互作用在抵抗可能因鼠李糖半乳糖醛酸聚糖生物合成增加而产生的细胞壁解构方面起着至关重要的作用。对于鼠李糖生物合成基因 (RHM1) 的显着上调，我们追踪了它的进化，确定了它的双域蛋白质结构，推测它是从轮藻绿藻进化而来的，并生成了一个解释其功能保守性的结构模型。用果胶分解细菌对黄麻茎进行浸解表明，果胶的复杂性及其与木质素的相互作用在抵抗可能因鼠李糖半乳糖醛酸聚糖生物合成增加而产生的细胞壁解构方面起着至关重要的作用。