Department of Biology, The Pennsylvania State University, University Park, PA, 16802, USA.
Center for Lignocellulose Structure and Formation, The Pennsylvania State University, University Park, PA, 16802, USA.
Plant J. 2018 Jun;94(6):956-974. doi: 10.1111/tpj.13909. Epub 2018 Apr 17.
In plants, UDP-glucose is the direct precursor for cellulose biosynthesis, and can be converted into other NDP-sugars required for the biosynthesis of wall matrix polysaccharides. UDP-glucose is generated from sucrose by two distinct metabolic pathways. The first pathway is the direct conversion of sucrose to UDP-glucose and fructose by sucrose synthase. The second pathway involves sucrose hydrolysis by cytosolic invertase (CINV), conversion of glucose to glucose-6-phosphate and glucose-1-phosphate, and UDP-glucose generation by UDP-glucose pyrophosphorylase (UGP). Previously, Barratt et al. (Proc. Natl Acad. Sci. USA, 106, 2009 and 13124) have found that an Arabidopsis double mutant lacking CINV1 and CINV2 displayed drastically reduced growth. Whether this reduced growth is due to deficient cell wall production caused by limited UDP-glucose supply, pleiotropic effects, or both, remained unresolved. Here, we present results indicating that the CINV/UGP pathway contributes to anisotropic growth and cellulose biosynthesis in Arabidopsis. Biochemical and imaging data demonstrate that cinv1 cinv2 seedlings are deficient in UDP-glucose production, exhibit abnormal cellulose biosynthesis and microtubule properties, and have altered cellulose organization without substantial changes to matrix polysaccharide composition, suggesting that the CINV/UGP pathway is a key metabolic route to UDP-glucose synthesis in Arabidopsis. Furthermore, differential responses of cinv1 cinv2 seedlings to exogenous sugar supplementation support a function of CINVs in influencing carbon partitioning in Arabidopsis. From these data and those of previous studies, we conclude that CINVs serve central roles in cellulose biosynthesis and carbon allocation in Arabidopsis.
在植物中，UDP-葡萄糖是纤维素生物合成的直接前体，可以转化为合成细胞壁基质多糖所需的其他 NDP-糖。UDP-葡萄糖由两种不同的代谢途径从蔗糖生成。第一条途径是蔗糖合酶直接将蔗糖转化为 UDP-葡萄糖和果糖。第二条途径涉及细胞质转化酶（CINV）水解蔗糖，将葡萄糖转化为葡萄糖-6-磷酸和葡萄糖-1-磷酸，并由 UDP-葡萄糖焦磷酸化酶（UGP）生成 UDP-葡萄糖。以前，Barratt 等人（Proc. Natl Acad. Sci. USA，106，2009 和 13124）发现，缺乏 CINV1 和 CINV2 的拟南芥双突变体生长明显减慢。这种生长减缓是由于 UDP-葡萄糖供应有限导致细胞壁生成不足、多效性影响还是两者兼而有之，仍未得到解决。在这里，我们提供的结果表明，CINV/UGP 途径有助于拟南芥的各向异性生长和纤维素生物合成。生化和成像数据表明，cinv1 cinv2 幼苗中 UDP-葡萄糖的产生减少，表现出异常的纤维素生物合成和微管特性，以及改变的纤维素组织，而基质多糖组成没有实质性变化，表明 CINV/UGP 途径是拟南芥 UDP-葡萄糖合成的关键代谢途径。此外，cinv1 cinv2 幼苗对外源糖补充的不同反应支持 CINVs 在影响拟南芥碳分配中的作用。从这些数据和以前的研究数据得出结论，CINVs 在拟南芥的纤维素生物合成和碳分配中起核心作用。
