Abstract To assess the genetic and environmental components of gene-expression variation among trees we used RNA-seq technology and Eucalyptus urophylla x grandis hybrid clones tested in field conditions. Leaf and xylem transcriptomes of three 20 month old clones differing in terms of growth, repeated in two blocks, were investigated. Transcriptomes were very similar between ramets. The number of expressed genes was significantly (P<0.05) higher in leaf (25,665±634) than in xylem (23,637±1,241). A pairwise clone comparisons approach showed that 4.5 to 14 % of the genes were differentially expressed (false discovery rate [FDR]<0.05) in leaf and 7.1 to 16 % in xylem. An assessment of among clone variance components revealed significant results in leaf and xylem in 3431 (248) genes (at FDR<0.2) and 160 (3) (at FDR<0.05), respectively. These two complementary approaches displayed correlated results. A focus on the phenylpropanoid, cellulose and xylan pathways revealed a large majority of low expressed genes and a few highly expressed ones, with RPKM values ranging from nearly 0 to 600 in leaf and 10,000 in xylem. Out of the 115 genes of these pathways, 45 showed differential expression for at least one pair of genotype, five of which displaying also clone variance components. These preliminary results are promising in evaluating whether gene expression can serve as possible ‘intermediate phenotypes’ that could improve the accuracy of selection of grossly observable traits.

中文翻译：

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田间条件下尾叶桉 x 大叶桉叶和木质部转录组变异的遗传效应

摘要 为了评估树木基因表达变异的遗传和环境成分，我们使用了 RNA-seq 技术和在田间条件下测试的 Eucalyptus urophylla x grandis 杂交克隆。研究了在生长方面不同的三个 20 个月大的克隆的叶和木质部转录组，在两个区块中重复。分株之间的转录组非常相似。叶中表达基因的数量（25,665±634）显着（P<0.05）高于木质部（23,637±1,241）。成对克隆比较方法表明，4.5% 到 14% 的基因在叶中差异表达（错误发现率 [FDR]<0.05），在木质部中差异表达为 7.1% 到 16%。对克隆方差分量的评估显示，叶和木质部分别在 3431 (248) 个基因 (FDR < 0.2) 和 160 (3) (FDR < 0.05) 中有显着结果。这两种互补的方法显示了相关的结果。对苯丙烷、纤维素和木聚糖途径的关注揭示了大部分低表达基因和少数高表达基因，叶中的 RPKM 值范围从近 0 到 600，木质部中的 RPKM 值范围为 10,000。在这些途径的 115 个基因中，45 个显示至少一对基因型的差异表达，其中 5 个还显示克隆变异成分。这些初步结果在评估基因表达是否可以作为可能的“中间表型”发挥作用，从而提高选择粗略可观察性状的准确性时很有希望。叶中的 RPKM 值从近 0 到 600 不等，木质部为 10,000。在这些途径的 115 个基因中，45 个显示至少一对基因型的差异表达，其中 5 个也显示克隆变异成分。这些初步结果在评估基因表达是否可以作为可能的“中间表型”发挥作用，从而提高选择粗略可观察性状的准确性时很有希望。叶中的 RPKM 值从近 0 到 600 不等，木质部为 10,000。在这些途径的 115 个基因中，45 个显示至少一对基因型的差异表达，其中 5 个还显示克隆变异成分。这些初步结果在评估基因表达是否可以作为可能的“中间表型”发挥作用，从而提高选择粗略可观察性状的准确性时很有希望。