Department of Botany, University of British Columbia, Vancouver, British Columbia V6T 1Z4, Canada.
Institut National de la Recherche Agronomique (INRA), Nantes 44316, France.
Plant Cell. 2019 Apr;31(4):809-831. doi: 10.1105/tpc.18.00954. Epub 2019 Mar 8.
Cell-to-cell adhesion is essential for establishment of multicellularity. In plants, such adhesion is mediated through a middle lamella composed primarily of pectic polysaccharides. The molecular interactions that influence cell-to-cell adhesion are not fully understood. We have used Arabidopsis () seed coat mucilage as a model system to investigate interactions between cell wall carbohydrates. Using a forward-genetic approach, we have discovered a gene, (), encoding a protein that is annotated as a member of the Auxiliary Activity 5 (AA5) family of Carbohydrate-Active Enzymes (Gal/glyoxal oxidases) and is secreted to the apoplast late in the differentiation of seed coat epidermal cells. We show that Y is required for the Gal oxidase activity of intact seeds; the oxidation of Gal in side-chains of rhamnogalacturonan-I (RG-I) present in () mucilage, but not in wild-type mucilage; the retention of branched RG-I in the seed following extrusion; and the enhancement of cell-to-cell adhesion in the seed coat epidermis. These data support the hypothesis that RUBY is a Gal oxidase that strengthens pectin cohesion within the middle lamella, and possibly the mucilage of wild-type seed coat epidermal cells, through oxidation of RG-I Gal side-chains.
细胞间黏附对于多细胞生物的建立至关重要。在植物中，这种黏附是通过主要由果胶多糖组成的中层来介导的。影响细胞间黏附的分子相互作用尚未完全了解。我们使用拟南芥（Arabidopsis）种皮黏液作为模型系统来研究细胞壁碳水化合物之间的相互作用。我们采用正向遗传学方法，发现了一个基因，（），编码一种蛋白质，该蛋白质被注释为辅助活性 5（AA5）家族碳水化合物活性酶（半乳糖/乙二醛氧化酶）的成员，并在种皮表皮细胞分化后期分泌到质外体。我们表明，Y 是完整种子中半乳糖氧化酶活性所必需的；氧化存在于（）黏液中但不存在于野生型黏液中的 RG-I 侧链中的半乳糖；在挤出后保留分支 RG-I 在种子中；并增强种皮表皮细胞的细胞间黏附。这些数据支持 RUBY 是一种半乳糖氧化酶的假设，该酶通过氧化 RG-I 半乳糖侧链，增强中层内果胶的内聚力，并可能增强野生型种皮表皮细胞的黏液的内聚力。
