Unraveling Cotton Fiber Development Using Fiber Mutants in the Post‐Genomic Era

Cotton ( Gossypium spp.) fibers are unicellular trichomes that differentiate from ovule epidermal cells. Cotton fiber development is divided into four distinct yet overlapping stages: initiation, elongation, secondary cell wall (SCW) biosynthesis, and maturation. There are numerous naturally occurring and man‐made fiber mutants that display aberrant phenotypes ranging from fiberless to extremely short fiber, and to immature fiber. These mutants have provided cotton researchers an excellent model system to study fiber growth and development. During the past two decades, much advancement in the understanding of fiber development has been achieved through comparative analyses of fiber mutants and wild‐type cotton lines using a variety of technologies such as transcriptomic analysis and genetic mapping. The causative genes of five mutations related to fiber initiation, elongation, or SCW assembly have been identified. Lint and fuzz fiber initiations are regulated by MYBMIXTA‐like transcription factors along with many other genes. Cytoskeleton actins play a critical role in fiber elongation. Genes that are involved in biological processes such as transporting osmoticum or loosening cell walls are highly expressed during the elongation stage. Production of large amounts of cellulose at the SCW stage requires a sustainable supply of energy and carbohydrate precursors. Plant hormones affect fiber development. In this paper, we review progress in the elucidation of fiber development mechanisms based on analyzing fiber mutants and summarize genes and mechanisms that are critical to fiber development. We identify research gaps that should be future research priorities and provide a future perspective.