Global expression dynamics and miRNA evolution profile govern floral/fiber architecture in the modern cotton (Gossypium)

Abstract

Majority of differentially expressed miRNAs with functional attributes have been recruited independently and parallelly during allopolyploidy followed by the millennia of human selection of both domesticated G. hirsutum and G. barbadense. The genus Gossypium is a marvelous evolutionary model for studying allopolyploidy and morpho-evolution of long-spinnable fibers from the ancestral wild-fuzz. Many genes, transcription factors, and notably, the regulatory miRNAs essentially govern such remarkable modern fiber phenotypes. To comprehend the impact of allopolyploidy on the evolutionary selection of transcriptional dynamicity of key miRNAs, comparative transcriptome profiling of vegetative and fiber tissues of domesticated diploid G. arboreum (A₂) and allopolyploid cotton species G. hirsutum (AD₁), and G. barbadense (AD₂) identified > 300 differentially expressed miRNAs (DEmiRs) within or between corresponding tissues of A₂, AD₁ and AD₂ species. Up to 49% and 32% DEmiRs were up- and down-regulated at fiber initiation stage of AD₁ and AD₂ species, respectively, whereas 50% and 18% DEmiRs were up- and down-regulated at fiber elongation stage of both the allopolyploid species. Interestingly, A-subgenome-specific DEmiRs exhibit expression dominance in the allopolyploid genetic backgrounds. Comparative spatio-temporal expression analyses of AD₁ and AD₂ species discovered that a majority of DEmiRs were recruited independently under millennia of human selection during domestication. Functional annotations of these DEmiRs revealed selection of associated molecular functions such as hormone-signaling, calcium-signaling and reactive oxygen species (ROS) signaling during fiber initiation and elongation. To validate the functional attributes of annotated DEmiRs, we demonstrated for the first time that the target-mimicry-based constitutive diminution of auxin-signaling associated miR167 directly affected the differentiation of floral and fiber tissues of transgenic cotton. These results strongly suggested that the evolutionarily favored DEmiRs including miR167 were involved in the transcriptional regulation of numerous genes during cotton evolution for enhanced fiber-associated agronomic traits.

Keywords: Cotton fiber; Domestication; Evolution; Polyploidy; miRNAs.