Investigating the Role of Laccases and Phenolic Compounds in Cotton Fiber Development

The single-celled cotton fibers, produced from seed coat epidermal cells are the largest natural source of textile fibers. The economic value of cotton fiber lies in its length and quality. The multifunctional laccase enzymes are involved in cell elongation, lignification and pigmentation in plants. The genome-wide analysis of cultivated allotetraploid (G. hirsutum) and its progenitor diploid (G. arboreum and G. raimondii) cotton species identified 84, 44 and 46 laccase genes, respectively. Analysis of chromosomal location, phylogeny, conserved domain and physical properties in three cotton species showed highly conserved nature of laccases across three cotton species. Gene expression, enzymatic activity and biochemical analysis of developing cotton fibers was performed using spinnable fiber producing G. arboretum species. Of the total 44, 40 laccases showed expression during different stages of fiber development. The higher enzymatic activity of laccases showed a perfect correlation with higher lignin content at 25 DPA (Days Post Anthesis). Further, analysis of cotton fiber phenolic compounds showed an overall decrease at 25 DPA indicating incorporation of these substrates into lignin polymer during secondary cell wall biosynthesis. Overall data indicate significant roles of laccases in cotton fiber development. As a follow up research, the Arabidopsis model system will be used for functional characterization of highly expressed laccase genes (GaLAC04_2, GaLAC04_3, GaLAC04_5, GaLAC11_2, GaLAC14_4 and GaLAC14_5). Further, the role of phenolic acids in cell elongation will be studied using arabidopsis root as a model system.