Gayral Mathieu, Elmorjani Khalil, Dalgalarrondo Michèle, Balzergue Sandrine M, Pateyron Stéphanie, Morel Marie-Hélène, Brunet Sylvie, Linossier Laurent, Delluc Caroline, Bakan Bénédicte, Marion Didier
Biopolymers, Interactions, Assemblies, Institut National de la Recherche AgronomiqueNantes, France.
POPS (transcriptOmic Platform of iPS2) Platform, Centre National de la Recherche Scientifique, Institute of Plant Sciences Paris Saclay, Institut National de la Recherche Agronomique, Université Paris-Sud, Université Evry, Université Paris-SaclayOrsay, France.
Front Plant Sci. 2017 Apr 13;8:557. doi: 10.3389/fpls.2017.00557. eCollection 2017.
Major nutritional and agronomical issues relating to maize () grains depend on the vitreousness/hardness of its endosperm. To identify the corresponding molecular and cellular mechanisms, most studies have been conducted on opaque/floury mutants, and recently on Quality Protein Maize, a reversion of an mutation by modifier genes. These mutant lines are far from conventional maize crops. Therefore, a dent and a flint inbred line were chosen for analysis of the transcriptome, amino acid, and sugar metabolites of developing central and peripheral endosperm that is, the forthcoming floury and vitreous regions of mature seeds, respectively. The results suggested that the formation of endosperm vitreousness is clearly associated with significant differences in the responses of the endosperm to hypoxia and endoplasmic reticulum stress. This occurs through a coordinated regulation of energy metabolism and storage protein (i.e., zein) biosynthesis during the grain-filling period. Indeed, genes involved in the glycolysis and tricarboxylic acid cycle are up-regulated in the periphery, while genes involved in alanine, sorbitol, and fermentative metabolisms are up-regulated in the endosperm center. This spatial metabolic regulation allows the production of ATP needed for the significant zein synthesis that occurs at the endosperm periphery; this finding agrees with the zein-decreasing gradient previously observed from the sub-aleurone layer to the endosperm center. The massive synthesis of proteins transiting through endoplasmic reticulum elicits the unfolded protein responses, as indicated by the splicing of bZip60 transcription factor. This splicing is relatively higher at the center of the endosperm than at its periphery. The biological responses associated with this developmental stress, which control the starch/protein balance, leading ultimately to the formation of the vitreous and floury regions of mature endosperm, are discussed.
与玉米籽粒相关的主要营养和农艺问题取决于其胚乳的玻璃质化/硬度。为了确定相应的分子和细胞机制，大多数研究是在不透明/粉质突变体上进行的，最近也在优质蛋白玉米上进行了研究，优质蛋白玉米是通过修饰基因对突变的回复。这些突变系与传统玉米作物相差甚远。因此，选择了一个马齿型和一个硬粒型自交系，分别对发育中的中央和外周胚乳（即成熟种子即将形成的粉质和玻璃质区域）的转录组、氨基酸和糖代谢产物进行分析。结果表明，胚乳玻璃质化的形成明显与胚乳对缺氧和内质网应激反应的显著差异有关。这是通过在灌浆期对能量代谢和贮藏蛋白（即醇溶蛋白）生物合成的协同调节来实现的。事实上，参与糖酵解和三羧酸循环的基因在外周上调，而参与丙氨酸、山梨醇和发酵代谢的基因在胚乳中心上调。这种空间代谢调节使得在胚乳外周发生的大量醇溶蛋白合成所需的ATP得以产生；这一发现与先前从亚糊粉层到胚乳中心观察到的醇溶蛋白递减梯度一致。如bZip60转录因子的剪接所示，在内质网中转运的蛋白质的大量合成引发了未折叠蛋白反应。这种剪接在胚乳中心比在外周相对更高。本文讨论了与这种发育应激相关的生物学反应，这些反应控制着淀粉/蛋白质平衡，最终导致成熟胚乳玻璃质和粉质区域的形成。
