Wood provides an important biomass resource for biofuel production around the world. The radial growth of tree stems is central to biomass production for forestry and biofuels, but it is challenging to dissect genetically because it is a complex trait influenced by many genes. In this study, we adopted methods of physiology, transcriptomics and genetics to investigate the regulatory mechanisms of tree radial growth and wood development. Physiological comparison showed that two Populus genotypes presented different rates of radial growth of stems and accumulation of woody biomass. A comparative transcriptional network approach was used to define and characterize functional differences between two Populus genotypes. Analyses of transcript profiles from wood-forming tissue of the two genotypes showed that 1542, 2295 and 2110 genes were differentially expressed in the pre-growth, fast-growth and post-growth stages, respectively. The co-expression analyses identified modules of co-expressed genes that displayed distinct expression profiles. Modules were further characterized by correlating transcript levels with genotypes and physiological traits. The results showed enrichment of genes that participated in cell cycle and division, whose expression change was consistent with the variation of radial growth rates. Genes related to secondary vascular development were up-regulated in the faster-growing genotype in the pre-growth stage. We characterized a BEL1-like (BELL) transcription factor, PeuBELL15, which was up-regulated in the faster-growing genotype. Analyses of transgenic Populus overexpressing as well as CRISPR/Cas9-induced mutants for BELL15 showed that PeuBELL15 improved accumulation of glucan and lignin, and it promoted secondary vascular growth by regulating the expression of genes relevant for cellulose synthases and lignin biosynthesis. This study illustrated that active division and expansion of vascular cambium cells and secondary cell wall deposition of xylem cells contribute to stem radial increment and biomass accumulation, and it identified relevant genes for these complex growth traits, including a BELL transcription factor gene PeuBELL15. This provides genetic resources for improving and breeding elite genotypes with fast growth and high wood biomass.

中文翻译：

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比较转录组分析定义了具有对比茎生长速率的两种杨属基因型之间不同的基因和基因模块。


木材为世界各地的生物燃料生产提供了重要的生物质资源。树干的径向生长对于林业和生物燃料的生物质生产至关重要，但从遗传学角度剖析具有挑战性，因为它是一个受许多基因影响的复杂性状。本研究采用生理学、转录组学和遗传学的方法来研究树木径向生长和木材发育的调控机制。生理比较表明，两种杨属基因型呈现出不同的茎径向生长速率和木质生物量积累速率。使用比较转录网络方法来定义和表征两种杨属基因型之间的功能差异。对两种基因型木材形成组织转录谱的分析表明，1542、2295和2110个基因分别在生长前期、快速生长和生长后阶段存在差异表达。共表达分析鉴定出表现出不同表达谱的共表达基因模块。通过将转录水平与基因型和生理特征相关联来进一步表征模块。结果显示参与细胞周期和分裂的基因富集，其表达变化与径向生长速率的变化一致。在生长前期，生长较快的基因型中与次生血管发育相关的基因上调。我们鉴定了一种 BEL1 样 (BELL) 转录因子 PeuBELL15，它在生长较快的基因型中表达上调。 对转基因杨树过表达以及 CRISPR/Cas9 诱导的 BELL15 突变体的分析表明，PeuBELL15 改善了葡聚糖和木质素的积累，并通过调节与纤维素合酶和木质素生物合成相关的基因的表达来促进次生维管生长。本研究表明，维管形成层细胞的活跃分裂和扩张以及木质部细胞的次生细胞壁沉积有助于茎径向增量和生物量积累，并鉴定了这些复杂生长性状的相关基因，包括BELL转录因子基因PeuBELL15。这为改良和培育生长快、木材生物量高的优良基因型提供了遗传资源。