Department of Biochemistry, University of Cambridge, Hopkins Building, The Downing Site, Tennis Court Road, Cambridge CB2 1QW, UK.
Department of Physics, University of Warwick, Coventry CV4 7AL, UK.
Plant Cell. 2022 Oct 27;34(11):4600-4622. doi: 10.1093/plcell/koac238.
Hemicellulose polysaccharides influence assembly and properties of the plant primary cell wall (PCW), perhaps by interacting with cellulose to affect the deposition and bundling of cellulose fibrils. However, the functional differences between plant cell wall hemicelluloses such as glucomannan, xylan, and xyloglucan (XyG) remain unclear. As the most abundant hemicellulose, XyG is considered important in eudicot PCWs, but plants devoid of XyG show relatively mild phenotypes. We report here that a patterned β-galactoglucomannan (β-GGM) is widespread in eudicot PCWs and shows remarkable similarities to XyG. The sugar linkages forming the backbone and side chains of β-GGM are analogous to those that make up XyG, and moreover, these linkages are formed by glycosyltransferases from the same CAZy families. Solid-state nuclear magnetic resonance indicated that β-GGM shows low mobility in the cell wall, consistent with interaction with cellulose. Although Arabidopsis β-GGM synthesis mutants show no obvious growth defects, genetic crosses between β-GGM and XyG mutants produce exacerbated phenotypes compared with XyG mutants. These findings demonstrate a related role of these two similar but distinct classes of hemicelluloses in PCWs. This work opens avenues to study the roles of β-GGM and XyG in PCWs.
半纤维素多糖影响植物初生细胞壁 (PCW) 的组装和性质，可能通过与纤维素相互作用来影响纤维素纤维的沉积和束集。然而，植物细胞壁半纤维素（如葡甘露聚糖、木聚糖和木葡聚糖（XyG））之间的功能差异仍不清楚。作为最丰富的半纤维素，XyG 被认为在真双子叶植物 PCWs 中很重要，但缺乏 XyG 的植物表现出相对温和的表型。我们在这里报告，一种有图案的 β-半乳葡甘露聚糖（β-GGM）广泛存在于真双子叶植物 PCWs 中，并且与 XyG 表现出显著的相似性。形成 β-GGM 主链和侧链的糖键与构成 XyG 的糖键类似，而且，这些键是由同一 CAZy 家族的糖基转移酶形成的。固态核磁共振表明，β-GGM 在细胞壁中移动性低，与纤维素相互作用一致。尽管拟南芥 β-GGM 合成突变体没有明显的生长缺陷，但 β-GGM 和 XyG 突变体之间的遗传杂交产生的表型比 XyG 突变体更严重。这些发现表明这两种类似但不同的半纤维素类在 PCWs 中具有相关作用。这项工作为研究β-GGM 和 XyG 在 PCWs 中的作用开辟了途径。
