BACKGROUND Boehmeria nivea L. Gaud (Ramie) produces one of the longest natural fibers in nature. The bark of ramie mainly comprises of the phloem tissue of stem and is the raw material for fiber. Therefore, identifying the molecular regulation of phloem development is important for understanding of bast fiber biosynthesis and improvement of fiber quality in ramie. RESULTS In this study, we collected top bud (TB), bark from internode elongating region (ER) and bark from internode fully elongated region (FER) from the ramie variety Zhongzhu No. 1. Histological study indicated that these samples contain phloem tissues at different developmental and maturation stages, with a higher degree of maturation of phloem tissue in FER. RNA sequencing (RNA-seq) was performed and de novo transcriptome was assembled. Unigenes and differentially expressed genes (DEGs) in these three samples were identified. The analysis of DEGs by using Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) revealed clear differences in gene expression between ER and FER. Some unigenes involved in secondary cell wall biosynthesis were up-regulated in both ER and FER, while unigenes for some cell wall components or cell wall modifications showed differential expression between ER and FER. In addition, the ethylene respond factors (ERFs) in the ethylene signaling pathway were up-regulated in FER, and ent-kaurenoic acid oxidase (KAO) and GA 20-oxidase (GA20ox) for gibberellins biosynthesis were up-regulated while GA 2-oxidase (GA2ox) for gibberellin inactivation was down-regulated in FER. CONCLUSIONS Both morphological study and gene expression analysis supported a burst of phloem and vascular developmental processes during the fiber maturation in the ramie stem, and ethylene and gibberellin are likely to be involved in this process. Our findings provide novel insights into the phloem development and fiber maturation in ramie, which could be useful for fiber improvement in ramie and other fiber crops.

中文翻译：

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茎皮的比较转录组学揭示了与Boehmeria nivea L. gaud（ram麻）韧皮纤维发育相关的基因。

背景技术伯尼米猪笼草（Ramie）生产自然界中最长的天然纤维之一。of麻的树皮主要由茎的韧皮部组织组成，是纤维的原料。因此，确定韧皮部发育的分子调控对于了解麻纤维的生物合成和improvement麻纤维质量的改善非常重要。结果在本研究中，我们从Zhong麻中种1号采集了顶芽（TB），节间伸长区（ER）的树皮和节间完全伸长区（FER）的树皮。组织学研究表明，这些样品中含有韧皮部组织FER中韧皮部组织的成熟度较高，因此发育和成熟阶段不同。进行RNA测序（RNA-seq）并组装从头转录组。确定了这三个样品中的单基因和差异表达基因（DEG）。通过使用基因本体论（GO）和《京都基因与基因组百科全书》（KEGG）对DEG进行分析，发现ER和FER之间的基因表达存在明显差异。参与二次细胞壁生物合成的某些单基因在ER和FER中均上调，而某些细胞壁成分或细胞壁修饰的单基因显示ER和FER之间存在差异表达。此外，FER中乙烯信号传导途径中的乙烯反应因子（ERFs）上调，而赤霉素生物合成的ENT-月桂酸酸氧化酶（KAO）和GA 20-氧化酶（GA20ox）上调，而GA 2-用于赤霉素灭活的氧化酶（GA2ox）在FER中被下调。结论形态学研究和基因表达分析均支持the麻茎纤维成熟过程中韧皮部和血管发育过程的爆发，乙烯和赤霉素可能参与了这一过程。我们的发现为into麻的韧皮部发育和纤维成熟提供了新颖的见解，这可能对improvement麻和其他纤维作物的纤维改良有用。