Production of multi-petaled Torenia fournieri flowers by functional disruption of two class-C MADS-box genes

Main conclusion Simultaneous knockdown or knockout of Torenia fournieri PLENA (TfPLE) and FALINELLI (TfFAR) genes with RNAi or genome-editing technologies generated a multi-petal phenotype in torenia. The MADS-box gene AGAMOUS (AG) is well known to play important roles in the development of stamens and carpels in Arabidopsis. Mutations in AG cause the morphological transformation of stamens and carpels into petaloid organs. In contrast, torenia (Torenia fournieri Lind.) has two types of class-C MADS-box genes, PLENA (PLE) and FALINELLI (FAR); however, their functions were previously undetermined. To examine the function of TfPLE and TfFAR in torenia, we used RNAi to knockdown expression of these two genes. TfPLE and TfFAR double-knockdown transgenic torenia plants had morphologically altered stamens and carpels that developed into petaloid organs. TfPLE knockdown transgenic plants also exhibited morphological transformations that included shortened styles, enlarged ovaries, and absent stigmata. Furthermore, simultaneous disruption of TfPLE and TfFAR genes by CRISPR/Cas9-mediated genome editing also resulted in the conversion of stamens and carpels into petaloid organs as was observed in the double-knockdown transgenic plants mediated by RNAi. In addition, the carpels of one TfPLE knockout mutant had the same morphological abnormalities as TfPLE knockdown transgenic plants. TfFAR knockdown genome-edited mutants had no morphological changes in their floral organs. These results clearly show that TfPLE and TfFAR cooperatively play important roles in the development of stamens and carpels. Simultaneous disruption of TfPLE and TfFAR functions caused a multi-petal phenotype, which is expected to be a highly valuable commercial floral trait in horticultural flowers.