INRAE, UR BIA, F-44316 Nantes, France.
DOE Joint Genome Institute, Berkeley, CA 94720, USA.
Int J Mol Sci. 2023 Apr 6;24(7):6821. doi: 10.3390/ijms24076821.
Seeds of the model grass are unusual because they contain very little starch and high levels of mixed-linkage glucan (MLG) accumulated in thick cell walls. It was suggested that MLG might supplement starch as a storage carbohydrate and may be mobilised during germination. In this work, we observed massive degradation of MLG during germination in both endosperm and nucellar epidermis. The enzymes responsible for the MLG degradation were identified in germinated grains and characterized using heterologous expression. By using mutants targeting MLG biosynthesis genes, we showed that the expression level of genes coding for MLG and starch-degrading enzymes was modified in the germinated grains of knocked-out mutants depleted in MLG but with higher starch content. Our results suggest a substrate-dependent regulation of the storage sugars during germination. These overall results demonstrated the function of MLG as the main carbohydrate source during germination of Brachypodium grain. More astonishingly, Brachypodium mutants are able to adapt their metabolism to the lack of MLG by modifying the energy source for germination and the expression of genes dedicated for its use.
该模型草的种子很不寻常，因为它们的淀粉含量非常低，而细胞壁中则积累了大量的混合链葡聚糖（MLG）。有人提出，MLG 可以替代淀粉作为储存碳水化合物，并可能在萌发过程中被动员起来。在这项工作中，我们观察到 MLG 在胚乳和珠心表皮的萌发过程中大量降解。负责 MLG 降解的酶在萌发的谷物中被鉴定出来，并通过异源表达进行了表征。通过使用针对 MLG 生物合成基因的突变体，我们表明，在 MLG 耗尽但淀粉含量更高的突变体萌发的谷物中，编码 MLG 和淀粉降解酶的基因的表达水平发生了改变。我们的结果表明，在萌发过程中，储存糖的表达受到底物的调节。这些结果表明 MLG 是拟南芥种子萌发过程中主要的碳水化合物来源。更令人惊讶的是，拟南芥突变体能够通过改变萌发的能量来源和用于其利用的基因的表达来适应缺乏 MLG 的情况。
