Mir156b from Soybean CMS Line Modulates Floral Organ Development

The miR156 and plant specific transcription factor SQUAMOSA PROMOTER BINDING PROTEIN-LIKE (SPL) are known for their function regulating plant growth and development. In this study, we identified 20 GmSPLs which are targeted by gma-miR156b via plant small RNA target and degradome analysis. And we found high transcript levels of gma-miR156b and its targeted GmSPLs in the flower of soybean cytoplasmic male sterility (CMS) line and its maintainer. The gma-miR156b direct cleavage of GmSPL2b and GmSPL9b, and have opposite expression levels during early flower buds development. We observed a high expression level of GUS protein in the anthers of the line with pgma-MIR156b::GUS reporter. Over-expression of the gma-miR156b precursor in Arabidopsis inhibited floral organ development, including reduced anther size and the amount of pollen grains per anther etc. Like miR156-targeted SPL genes, non-targeted GmSPL8s were also down-regulated in early flower bud development of soybean CMS line compared with its maintainer line, which might act in concert with miR156-targeted SPL genes to participate in the floral organ development. Quantitative real time PCR (qRT-PCR) suggested that miR156/SPL modulates floral organ development by regulating the expression of LATERAL ORGAN BOUNDARIES DOMAIN22 (LBD22), LBD36, AGAMOUS-LIKE30 (AGL30) and AGL104. Our findings will facilitate understanding of the biological functions of miR156/SPL in floral organ development of soybean CMS.