Department of Molecular Genetics, University of Mainz, 55128 Mainz, Germany.
Gene. 2012 May 1;498(2):223-30. doi: 10.1016/j.gene.2012.01.078. Epub 2012 Feb 13.
Columnar apple trees (Malus x domestica) provide several economic advantages due to their specific growth habit. The columnar phenotype is the result of the dominant allele of the gene Co and is characterized by thick stems with short internodes and reduced lateral branching. Co is located on chromosome 10 and often appears in a heterozygous state (Co/co). The molecular explanation of columnar growth is not well established. Therefore, we studied the transcriptomes of columnar and standard type apple trees using 454 and Illumina next generation sequencing (NGS) technologies. We analyzed the transcriptomes of shoot apical meristems (SAMs) because we expect that these organs are involved in forming the columnar growth phenotype. The results of the comparative transcriptome analysis show significant differences in expression levels of hundreds of genes. Many of the differentially expressed genes are associated with membrane and cell wall growth or modification and can be brought in line with the columnar phenotype. Additionally, earlier findings on the hormonal state of shoots of columnar apples could be affirmed. Our study resulted in a large number of genes differentially expressed in columnar vs. standard type apple tree SAMs. Although we have not unraveled the nature of the Co gene, we could show that the modified expression of these genes, most likely due to the presence of Co, can determine the columnar phenotype. Furthermore, the usefulness of NGS for the analysis of the molecular basis of complex phenotypes is discussed.
柱状苹果树（Malus x domestica）因其特殊的生长习性而具有许多经济优势。柱状表型是基因 Co 的显性等位基因的结果，其特征是茎粗、节间短、侧枝减少。Co 位于 10 号染色体上，通常以杂合状态（Co/co）出现。柱状生长的分子解释尚未得到很好的确立。因此，我们使用 454 和 Illumina 下一代测序（NGS）技术研究了柱状和标准型苹果树的转录组。我们分析了茎尖分生组织（SAM）的转录组，因为我们期望这些器官参与形成柱状生长表型。比较转录组分析的结果表明，数百个基因的表达水平存在显著差异。许多差异表达的基因与膜和细胞壁的生长或修饰有关，可以与柱状表型相一致。此外，还可以证实之前关于柱状苹果枝条激素状态的发现。我们的研究导致了大量在柱状与标准型苹果树 SAM 中差异表达的基因。尽管我们还没有揭示 Co 基因的性质，但我们可以表明，这些基因的修饰表达，很可能由于 Co 的存在，可以决定柱状表型。此外，还讨论了 NGS 在分析复杂表型的分子基础方面的有用性。
