Polyploidy and small RNA regulation of cotton fiber development.

Cotton is not only the most important source of renewal textile fibers, but also an excellent model for studying cell fate determination and polyploidy effects on gene expression and evolution of domestication traits. The combination of A and D-progenitor genomes into allotetraploid cotton induces intergenomic interactions and epigenetic effects, leading to the unequal expression of homoeologous genes. Small RNAs regulate the expression of transcription and signaling factors related to cellular growth, development and adaptation. An example is miRNA-mediated preferential degradation of homoeologous mRNAs encoding MYB-domain transcription factors that are required for the initiation of leaf trichomes in Arabidopsis and of seed fibers in cotton. This example of coevolution between small RNAs and their homoeologous targets could shape morphological traits such as fibers during the selection and domestication of polyploid crops.