Department of Plant Biotechnology, Faculty of Biochemistry, Biophysics and Biotechnology, Jagiellonian University, Gronostajowa 7, Krakow, 30-387, Poland.
Department of Biochemistry, University of Cambridge, Tennis Court Road, Cambridge, CB2 1QW, UK.
New Phytol. 2021 Sep;231(5):1720-1733. doi: 10.1111/nph.17531. Epub 2021 Jul 6.
Wood of coniferous trees (softwood), is a globally significant carbon sink and an important source of biomass. Despite that, little is known about the genetic basis of softwood cell wall biosynthesis. Branching of xylan, one of the main hemicelluloses in softwood secondary cell walls, with glucuronic acid (GlcA) is critical for biomass recalcitrance. Here, we investigate the decoration patterns of xylan by conifer GlucUronic acid substitution of Xylan (GUX) enzymes. Through molecular phylogenetics we identify two distinct conifer GUX clades. Using transcriptional profiling we show that the genes are preferentially expressed in secondary cell wall forming tissues. With in vitro and in planta assays we demonstrate that conifer GUX enzymes from both clades are active glucuronyltransferases. Conifer GUX enzymes from each clade have different specific activities. While members of clade one add evenly spaced GlcA branches, the members of clade two are also capable of glucuronidating two consecutive xyloses. Importantly, these types of xylan patterning are present in softwood. As xylan patterning might modulate xylan-cellulose and xylan-lignin interactions, our results further the understanding of softwood cell wall biosynthesis and provide breeding or genetic engineering targets that can be used to modify softwood properties.
针叶树木材（软木）是全球重要的碳汇，也是生物质的重要来源。尽管如此，人们对软木细胞壁生物合成的遗传基础知之甚少。半纤维素木聚糖的支化，与木聚糖中的葡萄糖醛酸（GlcA）结合，对生物质的抗降解性至关重要。在这里，我们研究了针叶树 GlucUronic acid substitution of Xylan（GUX）酶对木聚糖的修饰模式。通过分子系统发生学，我们确定了两个不同的针叶树 GUX 分支。通过转录谱分析，我们表明这些基因在次生细胞壁形成组织中优先表达。通过体外和体内实验，我们证明了来自两个分支的针叶树 GUX 酶都是具有活性的糖基转移酶。两个分支的 GUX 酶具有不同的比活性。虽然第一分支的成员能够均匀地添加 GlcA 分支，但第二分支的成员也能够对两个连续的木糖进行糖基化。重要的是，这种类型的木聚糖模式存在于软木中。由于木聚糖的模式可能调节木聚糖-纤维素和木聚糖-木质素的相互作用，我们的结果进一步了解了软木细胞壁的生物合成，并提供了可以用于修饰软木性质的育种或遗传工程靶点。
