The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, Edinburgh, EH9 3BF, UK.
The Edinburgh Cell Wall Group, Institute of Molecular Plant Sciences, The University of Edinburgh, Edinburgh, EH9 3BF, UK.
J Plant Physiol. 2021 Jul;262:153446. doi: 10.1016/j.jplph.2021.153446. Epub 2021 May 21.
The shoot epidermal cell wall in land-plants is associated with a polyester, cutin, which controls water loss and possibly organ expansion. Covalent bonds between cutin and its neighbouring cell-wall polysaccharides have long been proposed. However, the lack of biochemical evidence makes cutin-polysaccharide linkages largely conjectural. Here we optimised a portfolio of radiochemical assays to look for cutin-polysaccharide ester bonds in the epidermis of pea epicotyls, ice-plant leaves and tomato fruits, based on the hypothesis that a transacylase remodels cutin in a similar fashion to cutin synthase and cutin:cutin transacylase activities. Through in-situ enzyme assays and chemical degradations coupled with chromatographic analysis of the H-labelled products, we observed that among several wall-related oligosaccharides tested, only a xyloglucan oligosaccharide ([H]XXXGol) could acquire ester-bonds from endogenous cutin, suggesting a cutin:xyloglucan transacylase (CXT). CXT activity was heat-labile, time-dependent, and maximal at near-neutral pH values. In-situ CXT activity peaked in nearly fully expanded tomato fruits and ice-plant leaves. CXT activity positively correlated with organ growth rate, suggesting that it contributes to epidermal integrity during rapid expansion. This study uncovers hitherto unappreciated re-structuring processes in the plant epidermis and provides a step towards the identification of CXT and its engineering for biotechnological applications.
陆生植物的茎表皮细胞壁与聚酯角质有关，角质控制水分流失并可能影响器官扩张。角质与其相邻细胞壁多糖之间的共价键早已被提出。然而，缺乏生化证据使得角质-多糖键的联系在很大程度上仍是推测性的。在这里，我们根据转酰基酶以类似于角质合成酶和角质：角质转酰基酶的方式重塑角质的假设，优化了一系列放射性化学分析，以寻找豌豆上胚轴、冰叶日中花叶片和番茄果实表皮中的角质-多糖酯键。通过原位酶分析和化学降解以及对 H 标记产物的色谱分析，我们观察到在所测试的几种细胞壁相关寡糖中，只有木葡聚糖寡糖（[H]XXXGol）可以从内源性角质获得酯键，这表明存在角质-木葡聚糖转酰基酶（CXT）。CXT 活性是热不稳定的、时间依赖性的，在接近中性 pH 值时达到最大值。原位 CXT 活性在几乎完全展开的番茄果实和冰叶日中花叶片中达到峰值。CXT 活性与器官生长速率呈正相关，这表明它有助于表皮在快速扩张过程中的完整性。本研究揭示了植物表皮中迄今未被重视的重组过程，并为鉴定 CXT 及其在生物技术应用中的工程化提供了一个步骤。
