VP16 fusion efficiently reveals the function of transcriptional repressors in Arabidopsis

Proper gene expression regulated by transcription factors is essential for plants to achieve proper growth and development. However, the biological functions of many transcription factors remain largely unknown. Furthermore, although there are transcription factors which possess a plant-specific repression domain(s), their biological functions and whether such transcription factors function as transcriptional repressors are unclear. Thus, aiming for searching clues to understand their functions, we generated transgenic plants in which a putative transcriptional repressor fused with a VP16 viral trans-activation domain was expressed constitutively. Several plants with strong morphological phenotypes such as leaf and flower development defects were isolated from those lines expressing potential transcriptional repressors with unknown functions, giving the clue to reveal the yet-to-be analyzed functions of each protein. Reversal of function of the well-known transcriptional and floral repressor SHORT VEGETATIVE PHASE by VP16 fusion was observed, exemplifying successful functional reversion by this system. Plants constitutively expressing VP16 fused WUSCHEL, which is known to function both as a transcriptional activator and repressor, showed both phenotypes reported in its overexpression and loss-of-function lines. Taken together, our data provide examples showing the efficacy of VP16 fusion to provide helpful information to uncover the unknown functions of potential transcriptional repressors. This technique could also be effective to produce "super plants" which obtained strong and useful traits for application by strongly activating genes which are usually silent.