Cotton fiber as a model for understanding shifts in cell development under domestication

Abstract

Cotton fiber provides the predominant plant textile in the world, and it is also a model for plant cell wall biosynthesis. The development of the single-celled cotton fiber takes place across several overlapping but discrete stages, including fiber initiation, elongation, the transition from elongation to secondary cell wall formation, cell wall thickening, and maturation and cell death. During each stage, the developing fiber undergoes a complex restructuring of genome-wide gene expression change and physiological/biosynthetic processes, which ultimately generate a strikingly elongated and nearly pure cellulose product that forms the basis of the global cotton industry. Here, we provide an overview of this developmental process focusing both on its temporal as well as evolutionary dimensions. We suggest potential avenues for further improvement of cotton as a crop plant.

Keywords: cotton fiber; fiber development; fiber elongation; fiber evolution; fiber initiation.

Figure 1

Evolutionary model for allopolyploid Gossypium. Approximately 5-10 mya, the cotton underwent diversification resulting in separate evolutionary trajectories for the now-extinct A-(maternal) and D-(paternal) progenitors of the allopolyploid clade. Subsequently, (~ 1 mya) these lineages hybridized and underwent genome doubling, resulting in the allotetraploid AD clade. This clade diversified into seven polyploid species, two of which underwent domestication and improvement, i.e., G. hirsutum and G. barbadense.

Figure 2

A depiction of fiber development showing both macro- (A) and microscopic (B) views of G. hirsutum fiber at several important timepoints, described in C. At 0 DPA, fiber initials are present on the surface of the ovule. From 1-2 DPA, fiber tips are refined and elongation begins. By 7 DPA, all fibers are undergoing elongation. Elongation continues and subsequently begins to taper in the transition stage (~14 DPA, depending on species and/or accession) as secondary wall synthesis begins. By 30 DPA, elongation has ceased and the fiber is actively engaged in secondary cell wall deposition. The fruit finally matures at around 50 DPA, at which point the mature fibers have died and the boll dehisced. Scale bars for the scanning electron images is 5mm; all other scale bars are 1cm. The original picture is from Lee et al. (2007), reprinted with permission.