Tissue-specific transcriptomics reveal functional differences in floral development. Zea mays cultivar:B73

Flowers are produced by floral meristems, groups of stem cells that give rise to floral organs. Grass flowers (florets) are contained in spikelets, which contain one to many florets depending on the species. Members of the Andropogoneae tribe, including maize, produce spikelets containing two florets; the upper and lower florets are usually dimorphic, with the lower floret greatly reduced compared to the upper floret. In maize, early development appears identical in both florets, although development of the lower floret is delayed relative to the upper floret. To gain insight into the functional differences between upper and lower floral meristems, we used laser capture microdissection coupled with RNA-seq to globally examine gene expression in floral meristems. Approximately 700 genes were differentially expressed between upper and lower floral meristems, including genes involved in hormone regulation, cell wall, sugar and energy homeostasis. Furthermore, cell wall modifications and sugar accumulation differed between the upper and lower florets. Finally, we identified a novel boundary domain between upper and lower florets, which we hypothesize is important for floral meristem activity. We propose a model in which growth is repressed in the lower floret by limiting sugar availability and upregulating genes involved in growth repression and suggest similar processes may also regulate meristem activity in other developmental contexts.

花由花分生组织（floral meristems）产生，后者是一类可分化为花器官的干细胞群。禾本科小花（florets）着生于小穗（spikelets）中，根据物种不同，每个小穗包含1至多枚小花。蜀黍族（Andropogoneae）的成员包括玉米（maize），其小穗通常包含两枚小花：上下小花通常呈二态性，相较于上位小花，下位小花显著退化。在玉米中，尽管下位小花的发育进程晚于上位小花，但二者的早期发育外观一致。为解析上下花分生组织的功能差异，我们采用激光捕获显微切割（laser capture microdissection）结合RNA-seq技术，全局分析了花分生组织的基因表达谱。上下花分生组织间共有约700个差异表达基因，涵盖激素调控、细胞壁、糖与能量稳态相关基因。此外，上下小花的细胞壁修饰与糖积累模式存在差异。最后，我们在上下小花间发现了一个全新的边界域，并推测其对花分生组织活性具有重要作用。我们提出了一个模型：通过限制糖分可用性并上调生长抑制相关基因，来抑制下位小花的生长，并提示类似过程可能在其他发育场景中调控分生组织活性。