Abstract：
Polysaccharide structural complexity not only influences cell wall strength and extensibility but also hinders pathogenic and biotechnological attempts to saccharify the wall. In certain species and tissues, glucuronic acid side groups on xylan exhibit arabinopyranose or galactose decorations whose genetic and evolutionary basis is completely unknown, impeding efforts to understand their function and engineer wall digestibility. Genetics and polysaccharide profiling were used to identify the responsible loci in Arabidopsis and Eucalyptus from proposed candidates, while phylogenies uncovered a shared evolutionary origin. GH30-family endo-glucuronoxylanase activities were analysed by electrophoresis, and their differing specificities were rationalised by phylogeny and structural analysis. The newly identified xylan arabinopyranosyltransferases comprise an overlooked subfamily in the GT47-A family of Golgi glycosyltransferases, previously assumed to comprise mainly xyloglucan galactosyltransferases, highlighting an unanticipated adaptation of both donor and acceptor specificities. Further neofunctionalisation has produced a Myrtaceae-specific xylan galactosyltransferase. Simultaneously, GH30 endo-glucuronoxylanases have convergently adapted to overcome these decorations, suggesting a role for these structures in defence. The differential expression of glucuronoxylan-modifying genes across Eucalyptus tissues, however, hints at further functions. Our results demonstrate the rapid adaptability of biosynthetic and degradative carbohydrate-active enzyme activities, providing insight into plant-pathogen interactions and facilitating plant cell wall biotechnological utilisation.
摘要：
多糖结构的复杂性不仅影响细胞壁的强度和延伸性，而且阻碍了病原和生物技术对细胞壁进行糖化的尝试。在某些物种和组织中，木聚糖上的葡糖醛酸侧基表现出阿拉伯吡喃糖或半乳糖装饰，其遗传和进化基础完全未知，阻碍理解它们的功能和工程师壁消化率的努力。遗传学和多糖分析用于从拟议的候选物中鉴定拟南芥和桉树中的负责基因座，而系统发育揭示了一个共同的进化起源。通过电泳分析了GH30家族的内切葡糖醛酸木聚糖酶活性，它们的不同特异性通过系统发育和结构分析得到合理化。新鉴定的木聚糖阿拉伯吡喃糖基转移酶包含高尔基体糖基转移酶GT47-A家族中一个被忽视的亚家族，以前认为主要包含木葡聚糖半乳糖基转移酶，强调供体和受体特异性的意外适应。进一步的新官能化产生了桃金娘科特异性的木聚糖半乳糖基转移酶。同时,GH30内切葡糖醛酸木聚糖酶已经收敛地适应了克服这些装饰，建议这些结构在防御中的作用。葡糖醛酸木聚糖修饰基因在桉树组织中的差异表达，然而,提示进一步的功能。我们的结果表明生物合成和降解碳水化合物活性酶活性的快速适应性，提供对植物-病原体相互作用的洞察，并促进植物细胞壁生物技术的利用。
