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