School of Biological Sciences, University of Southampton, Boldrewood Campus, Southampton SO16 7PX, United Kingdom.
Plant Physiol. 2010 Jun;153(2):542-54. doi: 10.1104/pp.110.154971. Epub 2010 Apr 27.
The hemicellulose glucuronoxylan (GX) is a major component of plant secondary cell walls. However, our understanding of GX synthesis remains limited. Here, we identify and analyze two new genes from Arabidopsis (Arabidopsis thaliana), IRREGULAR XYLEM9-LIKE (IRX9-L) and IRX14-LIKE (IRX14-L) that encode glycosyltransferase family 43 members proposed to function during xylan backbone elongation. We place IRX9-L and IRX14-L in a genetic framework with six previously described glycosyltransferase genes (IRX9, IRX10, IRX10-L, IRX14, FRAGILE FIBER8 [FRA8], and FRA8 HOMOLOG [F8H]) and investigate their function in GX synthesis. Double-mutant analysis identifies IRX9-L and IRX14-L as functional homologs of IRX9 and IRX14, respectively. Characterization of irx9 irx10 irx14 fra8 and irx9-L irx10-L irx14-L f8h quadruple mutants allows definition of a set of genes comprising IRX9, IRX10, IRX14, and FRA8 that perform the main role in GX synthesis during vegetative development. The IRX9-L, IRX10-L, IRX14-L, and F8H genes are able to partially substitute for their respective homologs and normally perform a minor function. The irx14 irx14-L double mutant virtually lacks xylan, whereas irx9 irx9-L and fra8 f8h double mutants form lowered amounts of GX displaying a greatly reduced degree of backbone polymerization. Our findings reveal two distinct sets of four genes each differentially contributing to GX biosynthesis.
半纤维素木葡聚糖（GX）是植物次生细胞壁的主要成分。然而，我们对半纤维素 GX 的合成机制仍知之甚少。本研究从拟南芥（Arabidopsis thaliana）中鉴定并分析了两个新基因，IRREGULAR XYLEM9-LIKE（IRX9-L）和 IRX14-LIKE（IRX14-L），它们编码糖苷转移酶家族 43 成员，推测在木聚糖骨架延伸过程中发挥作用。我们将 IRX9-L 和 IRX14-L 置于一个遗传框架中，该框架包含六个先前描述的糖苷转移酶基因（IRX9、IRX10、IRX10-L、IRX14、FRAGILE FIBER8 [FRA8] 和 FRA8 HOMOLOG [F8H]），并研究它们在 GX 合成中的功能。双突变分析确定 IRX9-L 和 IRX14-L 分别为 IRX9 和 IRX14 的功能同源物。对 irx9 irx10 irx14 fra8 和 irx9-L irx10-L irx14-L f8h 四重突变体的表征，定义了一组基因，包括 IRX9、IRX10、IRX14 和 FRA8，它们在营养生长发育过程中主要参与 GX 的合成。IRX9-L、IRX10-L、IRX14-L 和 F8H 基因能够部分替代其相应的同源物，并发挥次要功能。irx14 irx14-L 双突变体几乎不含木聚糖，而 irx9 irx9-L 和 fra8 f8h 双突变体形成的 GX 量降低，其骨架聚合度大大降低。我们的研究结果揭示了两组各由四个基因组成的基因，它们在 GX 生物合成中发挥不同的作用。
