MicroRNA 157-targeted SPL genes regulate floral organ size and ovule production in cotton

microRNAs (miRNAs) have been involved in regulation of diverse spectrum of plant development processes in many species. In cotton, few miRNAs have been well characterised in floral organ development. Floral organ, which should be finely tuned, is a crucial factor affecting the yield of cotton. Therefore, it is well worth revealing the function of miRNAs in regulation of floral organ development. Here, we report the role of miRNA156/157 in regulation of floral organ size in cotton.

Over-expression of the GhmiRNA157 precursor in cotton (Gossypium hirsutum) resulted in smaller floral organs, fewer ovules and decreased seed production due to suppression of cell proliferation and cell elongation. Five SQUAMOSA promoter-binding protein-like (SPL) genes were identified as targets of GhmiRNA157 using a RNA ligase-mediated rapid amplification of cDNA end approach, and the expression level of miR157-targeted GhSPLs decreased in the miR157 over-expression lines, indicating the presence of the miR157/SPL axis in cotton. Two MADS-box genes, orthologs of AtAGL6 and SITDR8, which are associated with floral organ development and reproductive production, were repressed in the miR157 over-expression lines. In addition, auxin-inducible genes were also down-regulated, and auxin signal visualized by a DR5::GUS reporter was attenuated in the miR157 over-expression lines.

Our results indicate that the miR157/SPL axis controls floral organ growth and ovule production by regulating MADS-box genes and auxin signal transduction. The work further elucidates the mechanism of floral organ development and provides helpful molecular basis for improvement of cotton yield.