追氮时期对小麦籽粒蛋白品质空间分布的调控机制

The contradictions between yield and quality are becoming increasingly pronounced in China, resulting in a large quantity of importation of strong- and weak-gluten wheat. It has been observed that protein content largely varies within different layers of grain, and this spatial variation differently responds to nitrogen topdressing timing. This provides a potential approach to maintain high grain yield with satisfied quality of wheat. However, the underlying mechanisms on formation of protein spatial variation are unknown. We have observed that grain protein content can be modified by nitrogen topdressing timing in previous work. The modifications were mediated by the supply of protein synthesis substrate and the capacity of protein synthesis, which were deduced to be critical factors affecting protein spatial variation. Here, we will use selected representative strong- and weak-gluten varieties differing in response to nitrogen fertilization. Laser capture microdissection will be conducted to precisely collect cells from different layers. In combination with transcriptomics and metabolomics, we will study tempo-spatial distribution of amino acids in grain during filling stage and tempo-spatial pattern of genes encoding storage protein synthesis and processing. Grain pearling as well as protein and baking quality quantification were exerted to compare the responses of protein spatial variation of strong- or weak-gluten variety to nitrogen topdressing timing. The underlying mechanisms on formation of protein spatial variation will be explained. The results should help construct integrated cultivation protocols of specialty wheat with both high yield and qualified quality.

在我国小麦生产中，产量和品质的矛盾日益显著，导致优质的强筋和弱筋小麦原料主要依靠进口。小麦籽粒不同部位面粉蛋白组分含量差异显著，并受追氮时期的调控，为协调小麦优质和高产提供了新思路，但籽粒蛋白空间差异的形成机制不详。申请人前期研究发现改变氮肥追施时期可以通过调控蛋白合成底物供应及籽粒蛋白合成能力而改变籽粒蛋白含量，因此推测氨基酸的供应水平和籽粒不同部位蛋白合成能力差异是导致籽粒蛋白空间分布形成的关键机制。本项目拟使用代表性强弱筋小麦品种，运用激光显微切割技术，精准获取胚乳不同部位样品，用于转录组学及代谢组学分析，研究蛋白合成底物氨基酸在灌浆期籽粒中的时空分布及胚乳重要贮藏蛋白组分合成及加工能力等的空间差异；通过成熟期籽粒分层磨粉和蛋白及烘焙品质测定，比较追氮时期对不同筋力小麦蛋白空间分布的调控效应，阐明籽粒蛋白品质空间分布形成的机理与调控途径，为小麦优质高产栽培提供理论与技术支撑。

在我国小麦生产中，产量和品质的矛盾日益显著，导致优质的强筋和弱筋小麦原料主要依靠进口。小麦籽粒不同部位面粉蛋白组分含量差异显著，并受追氮时期的调控，为协调小麦优质和高产提供了新思路，但籽粒蛋白空间差异的形成机制不详。本项目使用代表性强中弱筋小麦品种，通过微型正电子发射断层扫描-计算机断层扫描(PET-CT)，直接且无损地观察到谷氨酰胺在颖果通过转移细胞运输至糊粉层，进而向内运输至外胚乳与内胚乳；进而运用激光显微切割技术，精准获取胚乳不同部位样品，通过代谢组测序明确了20种氨基酸及氨基酸衍生物在不同部位的代谢丰度，发现谷氨酰胺、谷氨酸、天冬氨酸、脯氨酸等在糊粉层中的代谢丰度在多个时间点要高于内外胚乳，证实了灌浆底物供应对蛋白梯度形成的重要性；利用转录组学分析胚乳蛋白生物合成能力的空间差异，发现编码贮藏蛋白的基因在各部位的基因表达差异与胚乳蛋白空间分布异质性不相符，同时明确了氨基酸代谢、核糖体生物合成、蛋白加工及运输过程与最终蛋白分布异质性规律具有相关性并筛选出了调控蛋白体空间异质性形成的关键基因。通过追氮时期和施氮量调控不同筋力小麦品种蛋白空间分布特征，发现随着追氮时期后移，糊粉层和外胚乳层中的谷蛋白及面包品质增加更为显著，追氮时期后移通过提升早期不同层次游离氨基酸的供应水平及后期蛋白合成及加工编码基因的表达水平，调控籽粒蛋白空间分布趋势；增施氮肥对宁麦13和扬麦16糊粉层和外胚乳的蛋白含量调控效果更好，而徐麦32的内胚乳蛋白对增施氮肥更为敏感。研究结果对于阐明籽粒蛋白品质空间分布形成的机理、实现小麦籽粒品质的定向调控途径，和促进优质高产小麦的发展具有重要的理论与实践意义。