New Roles of Transcriptional and Translational Regulation in Early Stages of Cotton Fiber Development

The fibers of cotton (Gossypium spp.) are a key agronomic resource. These fibers are made up of individual epidermal cells on the surface of the cotton seed which undergo a dramatic developmental shift, elongating into cells that are up to several centimeters long. Efforts to understand the causes of this shift has been hampered by the difficulty of isolating fiber cells from epidermal cells at the earliest stages of development. To address this issue, we characterized mRNA populations of early fiber and epidermal cells using laser capture microdissection (LCM) to isolate cell types with a high degree of specificity, and using RNA-seq, we were able to reveal key differences in the developmental programs between fibers and underlying epidermal cell layer. We were able to characterize cell type differences and temporal changes that occur in the earliest stages of fiber initiation and development at 0 and 2 Day Post Anthesis (DPA). We found differences in the expression of genes responsible for hormone activity, numerous transcription factor families, ribosomal activity, and cell cycle regulation, which leads the hypothesis that developmental changes leading to the arrest of the cell cycle in epidermal cells induces ribosome biosynthesis, leading to fiber cell initiation. Using chemical inhibitors of ribosome biosynthesis, Rbin-1, and cell cycle progression, Roscovitine, we were able to significantly affect the amount of fibers produced in cultured ovules, validating predictions made from our expression data. These results shed light on the early changes in gene activity controlling fiber development in cotton. Overall design: Examination of transcripts (mRNA) in cotton epidermal and fiber cells (ovule) at 0 and 2 DPA in TM-1 (G.hirsutum), 3-79 (G.barbadense), and fiberless mutant MD17

棉花（Gossypium spp.）纤维是一类关键的农艺资源。该类纤维由棉籽表面的单个表皮细胞发育而来，这些细胞会经历剧烈的发育转变，最终伸长至数厘米长度。此前，由于难以在发育早期从表皮细胞中分离出纤维细胞，解析这一转变成因的相关研究始终进展受阻。
为解决这一技术难题，本研究通过激光捕获显微切割（Laser Capture Microdissection, LCM）高特异性分离早期纤维细胞与表皮细胞，并借助RNA测序（RNA-seq）对二者的mRNA转录本群体进行了表征，进而揭示了纤维细胞与其下方表皮细胞层之间发育程序的核心差异。我们对开花后0天与2天（Day Post Anthesis, DPA）的纤维起始及发育早期阶段的细胞类型差异与时序变化进行了系统表征。
研究发现，激素活性相关基因、多个转录因子家族、核糖体活性及细胞周期调控相关基因的表达均存在显著差异，据此提出假说：表皮细胞周期停滞相关的发育变化会诱导核糖体生物合成，进而触发纤维细胞的起始过程。通过使用核糖体生物合成抑制剂Rbin-1与细胞周期进程抑制剂罗司维汀（Roscovitine），我们能够显著改变离体培养胚珠的纤维生成量，验证了基于转录组表达数据得出的预测结论。
上述研究结果阐明了调控棉花纤维发育的早期基因活性变化机制。整体实验设计：对陆地棉TM-1（G. hirsutum）、海岛棉3-79（G. barbadense）以及无纤维突变体MD17的开花后0天和2天的棉籽表皮细胞与纤维细胞（源自胚珠）中的转录本（mRNA）进行检测分析。