In Chinese cabbage, rosette leaves expose their adaxial side to the light converting light energy into chemical energy, acting as a source for the growth of the leafy head. In the leafy head, the outer heading leaves expose their abaxial side to the light while the inner leaves are shielded from the light and have become a sink organ of the growing Chinese cabbage plant. Interestingly, variation in several ad/abaxial polarity genes is associated with the typical leafy head morphotype. The initiation of leaf primordia and the establishment of leaf ad/abaxial polarity are essential steps in the initiation of marginal meristem activity leading to leaf formation. Understanding the molecular genetic mechanisms of leaf primordia formation, polar differentiation, and leaf expansion is thus relevant to understand leafy head formation. As Brassica’s are mesa-hexaploids, many genes have multiple paralogues, complicating analysis of the genetic regulation of leaf development. In this study, we used laser dissection of Chinese cabbage leaf-primordia and the shoot apical meristem (SAM) to compare gene expression profiles between both adaxial and abaxial sides and the SAM aiming to capture transcriptome changes underlying leaf primordia development. We highlight genes with roles in hormone pathways and transcription factors. We also assessed gene expression gradients along expanded leaf blades from the same plants to analyze regulatory links between SAM, leaf primordia and the expanding rosette leaf. The catalogue of differentially expressed genes provides insights in gene expression patterns involved in leaf development and form a starting point to unravel leafy head formation.

中文翻译：

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转录组分析总结大白菜叶片萌生过程中发生的基因表达模式

在大白菜中，莲座叶将其正面暴露在光下，将光能转化为化学能，作为叶头生长的来源。在叶状头部，外部抽穗叶将其背面暴露在光线下，而内部叶子则遮光，成为生长中的大白菜植株的库器官。有趣的是，几个轴向/远轴极性基因的变异与典型的叶状头部形态类型相关。叶原基的起始和叶上/远轴极性的建立是导致叶形成的边缘分生组织活性启动的重要步骤。因此，了解叶原基形成、极性分化和叶片扩展的分子遗传机制与了解叶头的形成相关。由于芸苔属是台面六倍体，许多基因具有多个旁系同源物，使叶片发育的遗传调控分析变得复杂。在本研究中，我们利用激光解剖大白菜叶原基和茎尖分生组织（SAM）来比较近轴和远轴两侧的基因表达谱，SAM旨在捕获叶原基发育过程中转录组的变化。我们重点关注在激素途径和转录因子中发挥作用的基因。我们还评估了同一植物展开叶片的基因表达梯度，以分析 SAM、叶原基和展开莲座叶之间的调控联系。差异表达基因的目录提供了对叶片发育所涉及的基因表达模式的见解，并形成了解开叶头形成的起点。