Department of Plant Biology and Forest Genetics, Uppsala BioCenter, Swedish University of Agricultural Sciences, PO Box 7090, SE-750 07 Uppsala, Sweden.
BMC Genomics. 2010 Feb 23;11:129. doi: 10.1186/1471-2164-11-129.
Salix (willow) and Populus (poplar) are members of the Salicaceae family and they share many ecological as well as genetic and genomic characteristics. The interest of using willow for biomass production is growing, which has resulted in increased pressure on breeding of high yielding and resistant clones adapted to different environments. The main purpose of this work was to develop dense genetic linkage maps for mapping of traits related to yield and resistance in willow. We used the Populus trichocarpa genome to extract evenly spaced markers and mapped the orthologous loci in the willow genome. The marker positions in the two genomes were used to study genome evolution since the divergence of the two lineages some 45 mya.
We constructed two linkage maps covering the 19 linkage groups in willow. The most detailed consensus map, S1, contains 495 markers with a total genetic distance of 2477 cM and an average distance of 5.0 cM between the markers. The S3 consensus map contains 221 markers and has a total genetic distance of 1793 cM and an average distance of 8.1 cM between the markers. We found high degree of synteny and gene order conservation between willow and poplar. There is however evidence for two major interchromosomal rearrangements involving poplar LG I and XVI and willow LG Ib, suggesting a fission or a fusion in one of the lineages, as well as five intrachromosomal inversions. The number of silent substitutions were three times lower (median: 0.12) between orthologs than between paralogs (median: 0.37 - 0.41).
The relatively slow rates of genomic change between willow and poplar mean that the genomic resources in poplar will be most useful in genomic research in willow, such as identifying genes underlying QTLs of important traits. Our data suggest that the whole-genome duplication occurred long before the divergence of the two genera, events which have until now been regarded as contemporary. Estimated silent substitution rates were 1.28 x 10-9 and 1.68 x 10-9 per site and year, which are close to rates found in other perennials but much lower than rates in annuals.
柳树（柳树）和杨树（杨树）是杨柳科的成员，它们具有许多生态以及遗传和基因组特征。利用柳树进行生物质生产的兴趣日益浓厚，这导致了对适应不同环境的高产和抗性克隆的选育压力增大。这项工作的主要目的是为柳树的产量和抗性相关性状的图谱绘制开发高密度遗传连锁图谱。我们使用杨属黑杨基因组提取均匀间隔的标记，并在柳树基因组中映射同源基因座。这两个基因组中的标记位置用于研究自 4500 万年前两个谱系分化以来的基因组进化。
我们构建了覆盖柳树 19 个连锁群的两个连锁图谱。最详细的共识图谱 S1 包含 495 个标记，总遗传距离为 2477cM，标记之间的平均距离为 5.0cM。S3 共识图谱包含 221 个标记，总遗传距离为 1793cM，标记之间的平均距离为 8.1cM。我们发现柳树和杨树之间存在高度的同线性和基因顺序保守性。然而，有证据表明涉及杨属 LG I 和 XVI 和柳树 LG Ib 的两个主要染色体间重排，这表明一个谱系发生了融合或分裂，以及五个染色体内倒位。在直系同源物之间，沉默替代的数量要低三倍（中位数：0.12），而在旁系同源物之间（中位数：0.37-0.41）。
柳树和杨属之间基因组变化的相对缓慢速度意味着杨属的基因组资源在柳树的基因组研究中最有用，例如鉴定重要性状 QTL 的基因。我们的数据表明，全基因组复制发生在两个属分化之前很久，直到现在，这两个事件一直被认为是同时发生的。估计的沉默替换率分别为每个位点和每年 1.28x10-9 和 1.68x10-9，接近在其他多年生植物中发现的速率，但远低于在一年生植物中发现的速率。
