Instituto de Biologia Experimental e Tecnológica (iBET), Apartado 12, 2780-901, Oeiras, Portugal.
Instituto de Tecnologia Química e Biológica António Xavier, Universidade Nova de Lisboa (ITQB NOVA), Av. da República, 2780-157, Oeiras, Portugal.
BMC Plant Biol. 2018 Dec 29;18(1):379. doi: 10.1186/s12870-018-1564-2.
There are clear differences in embryo development between angiosperm and gymnosperm species. Most of the current knowledge on gene expression and regulation during plant embryo development has derived from studies on angiosperms species, in particular from the model plant Arabidopsis thaliana. The few published studies on transcript profiling of conifer embryogenesis show the existence of many putative embryo-specific transcripts without an assigned function. In order to extend the knowledge on the transcriptomic expression during conifer embryogenesis, we sequenced the transcriptome of zygotic embryos for several developmental stages that cover most of Pinus pinaster (maritime pine) embryogenesis.
Total RNA samples collected from five zygotic embryo developmental stages were sequenced with Illumina technology. A de novo transcriptome was assembled as no genome sequence is yet published for Pinus pinaster. The transcriptome of reference for the period of zygotic embryogenesis in maritime pine contains 67,429 transcripts, which likely encode 58,527 proteins. The annotation shows a significant percentage, 31%, of predicted proteins exclusively present in pine embryogenesis. Functional categories and enrichment analysis of the differentially expressed transcripts evidenced carbohydrate transport and metabolism over-representation in early embryo stages, as highlighted by the identification of many putative glycoside hydrolases, possibly associated with cell wall modification, and carbohydrate transport transcripts. Moreover, the predominance of chromatin remodelling events was detected in early to middle embryogenesis, associated with an active synthesis of histones and their post-translational modifiers related to increased transcription, as well as silencing of transposons.
Our results extend the understanding of gene expression and regulation during zygotic embryogenesis in conifers and are a valuable resource to support further improvements in somatic embryogenesis for vegetative propagation of conifer species. Specific transcripts associated with carbohydrate metabolism, monosaccharide transport and epigenetic regulation seem to play an important role in pine early embryogenesis and may be a source of reliable molecular markers for early embryogenesis.
被子植物和裸子植物物种的胚胎发育存在明显差异。目前关于植物胚胎发育过程中基因表达和调控的大部分知识都来自于对被子植物物种的研究，尤其是模式植物拟南芥。少数关于针叶树胚胎发生转录谱的已发表研究表明，存在许多假定的胚胎特异性转录本，但没有赋予其功能。为了扩展对针叶树胚胎发生过程中转录组表达的认识，我们对涵盖几个胚胎发育阶段的马尾松合子胚胎进行了测序，这些阶段涵盖了马尾松胚胎发生的大部分过程。
从五个合子胚胎发育阶段收集的总 RNA 样本进行了 Illumina 技术测序。由于尚未为 Pinus pinaster 发布基因组序列，因此组装了从头转录组。马尾松胚胎发生时期的参考转录组包含 67,429 个转录本，这些转录本可能编码 58,527 个蛋白质。注释显示，预测蛋白质中 31%仅存在于松属胚胎发生中，这表明存在显著比例的特有蛋白质。差异表达转录本的功能类别和富集分析表明，在早期胚胎阶段碳水化合物的运输和代谢过表达，这突出了许多假定的糖苷水解酶的鉴定，这些酶可能与细胞壁修饰和碳水化合物运输转录本有关。此外，在早期到中期胚胎发生过程中检测到染色质重塑事件占主导地位，这与组蛋白的合成增加及其与转录增加和转座子沉默相关的翻译后修饰物有关。
我们的研究结果扩展了对裸子植物合子胚胎发生过程中基因表达和调控的理解，并且为进一步改进针叶树物种的营养繁殖体的体细胞胚胎发生提供了有价值的资源。与碳水化合物代谢、单糖运输和表观遗传调控相关的特定转录本似乎在马尾松早期胚胎发生中发挥重要作用，并且可能是早期胚胎发生的可靠分子标记的来源。
