Systematically and Comprehensively Understanding the Regulation of Cotton Fiber Initiation: A Review

Abstract

Cotton fibers provide an important source of raw materials for the textile industry worldwide. Cotton fiber is a kind of single cell that differentiates from the epidermis of the ovule and provides a perfect research model for the differentiation and elongation of plant cells. Cotton fiber initiation is the first stage throughout the entire developmental process. The number of fiber cell initials on the seed ovule epidermis decides the final fiber yield. Thus, it is of great significance to clarify the mechanism underlying cotton fiber initiation. Fiber cell initiation is controlled by complex and interrelated regulatory networks. Plant phytohormones, transcription factors, sugar signals, small signal molecules, functional genes, non-coding RNAs, and histone modification play important roles during this process. Here, we not only summarize the different kinds of factors involved in fiber cell initiation but also discuss the mechanisms of these factors that act together to regulate cotton fiber initiation. Our aim is to synthesize a systematic and comprehensive review of different factors during fiber initiation that will provide the basics for further illustrating these mechanisms and offer theoretical guidance for improving fiber yield in future molecular breeding work.

Keywords: cotton; fiber initiation; molecular mechanism; phytohormones; transcription factors.

Figure 1

Cotton fiber phenotypes in cotton fiber in TM-1, n₂NSM, Li₁, and XZ142FLM. (a) Phenotypes of four representative varieties during the period of boll opening. Among them, white fibers with no black seeds are observed in TM-1, n₂NSM, and Li₁. Only black seeds are observed in XZ142FLM. Scale bars, 1.0 cm. (b) Examination of seed phenotype after fiber combing. TM-1 seeds have long lint and short fuzz fibers, n₂NSM seeds only have long lint, Li₁ seeds have short lint and fuzz fibers, and XZ142FLM seeds have no fibers attached. Scale bars, 1.0 cm.

Figure 2

A schematic model of phytohormones of regulation of cotton fiber initiation by phytohormones. The arrows indicate the promotional effects and bars represent the inhibitory effects. Red five-pointed star represents fiber initiation; Yellow ovals indicate the auxin-signaling pathway; orange ovals represent the GA-signaling pathway; green ovals indicate the BR-signaling pathway; and brown ovals represent the JA-signaling pathway.

Figure 3

Diagram summarizing the roles of transcription factors, sugar signaling, small signaling molecules, and non-coding RNAs in cotton fiber initiation. The arrows indicate the promotional effects and bars represent the inhibitory effects. Red font represents MYB transcription factors; dark blue font indicates HD-ZIP transcription factors; purple font represents WRKY transcription factors; orange font indicates TCP transcription factors; dark green font represents sugar-signaling-related genes; brown font indicates small signaling molecules-related genes; light green font represents non-coding RNAs; light blue font indicates other functional genes.