Overexpression of Arabidopsis miR157b induces bushy architecture and delayed phase transition in Torenia fournieri.

miR156/157 is a small RNA molecule that is highly conserved among various plant species. Overexpression of miR156/157 has been reported to induce bushy architecture and delayed phase transition in several plant species. To investigate the effect of miR157 overexpression in a horticultural plant, and to explore the applicability of miRNA to molecular breeding, we introduced Arabidopsis MIR157b (AtMIR157b) into torenia (Torenia fournieri). The resulting 35S:AtMIR157b plants showed a high degree of branching along with small leaves, which resembled miR156/157-overexpressing plants of other species. We also isolated torenia SBP-box genes with target miR156/157 sequences and confirmed that their expression was selectively downregulated in 35S:AtMIR157b plants. The reduced accumulation of mRNA was probably due to sequence specificity. Moreover, expression of torenia homologs of the SBP-box protein-regulated genes TfLFY and TfMIR172 was also reduced by AtmiR157 overexpression. These findings suggest that the molecular mechanisms of miR156/157 regulation are conserved between Arabidopsis and torenia. The bushy architecture and small leaves of 35S:AtMIR157b torenia plants could be applied in molecular breeding of various horticultural plants as well as for increasing biomass and crop production.