Gerna Davide, Clara David, Antonielli Livio, Mitter Birgit, Roach Thomas
Department of Botany and Center for Molecular Biosciences Innsbruck, University of Innsbruck, 6020 Innsbruck, Austria.
Center for Health & Bioresources, Bioresources Unit, AIT Austrian Institute of Technology GmbH, 3430 Tulln, Austria Accepted for publication 17 August 2023.
Phytobiomes J. 2022 Aug 31;8(1):21-33. doi: 10.1094/PBIOMES-03-23-0019-MF. Epub 2022 Jul 18.
Seed germination critically determines successful plant establishment and agricultural productivity. In the plant holobiont's life cycle, seeds are hubs for microbial communities' assembly, but what exactly shapes the holobiont during germination remains unknown. Here, 16S rRNA gene amplicon sequencing characterized the bacterial communities in embryonic compartments (cotyledons and axes) and on seed coats pre- and post-germination of four soybean () cultivars, in the presence or absence of exogenous abscisic acid (ABA), which prevented germination and associated metabolism of seeds that had imbibed. Embryonic compartments were metabolically profiled during germination to design minimal media mimicking the seed endosphere for bacterial growth assays. The distinction between embryonic and seed coat bacterial microbiomes of dry seeds weakened during germination, resulting in the plumule, radicle, cotyledon, and seed coat all hosting the same most abundant and structurally influential genera in germinated seeds of every cultivar. Treatment with ABA prevented the increase of bacterial microbiomes' richness, but not taxonomic homogenization across seed compartments. Growth assays on minimal media containing the most abundant metabolites that accumulated in germinated seeds revealed that seed reserve mobilization promoted enrichment of copiotrophic bacteria. Our data show that seed imbibition enabled distribution of seed-coat-derived epiphytes into embryos irrespective of germination, while germinative metabolism promoted proliferation of copiotrophic taxa, which predominated in germinated seeds.
种子萌发对于植物的成功定植和农业生产力至关重要。在植物全生物的生命周期中，种子是微生物群落组装的中心，但在萌发过程中究竟是什么塑造了全生物仍不清楚。在这里，16S rRNA基因扩增子测序对四个大豆品种萌发前后胚区（子叶和胚轴）以及种皮上的细菌群落进行了表征，实验设置了添加或不添加外源脱落酸（ABA）的处理，ABA可抑制已吸胀种子的萌发及相关代谢。在萌发过程中对胚区进行代谢谱分析，以设计模拟种子内圈环境的基本培养基用于细菌生长测定。干种子的胚区和种皮细菌微生物群之间的差异在萌发过程中减弱，导致每个品种萌发种子的胚芽、胚根、子叶和种皮都含有相同的最丰富且在结构上有影响力的属。ABA处理阻止了细菌微生物群丰富度的增加，但并未阻止种子各部分之间的分类同质化。在含有萌发种子中积累的最丰富代谢物的基本培养基上进行的生长测定表明，种子储备动员促进了富营养细菌的富集。我们的数据表明，无论是否萌发，种子吸胀都能使种皮来源的附生植物分布到胚中，而萌发代谢促进了富营养类群的增殖，这些类群在萌发种子中占主导地位。
