Identification of three tomato flower and fruit MADS-box proteins with a putative histone deacetylase binding domain

MADS-box transcription factors play crucial roles in organ and cell differentiation in organisms ranging from yeast to humans. Most of the work on plant MADS-box proteins focused on their roles in floral development whereas less information is available on their function in fruit maturation. We cloned three distinct tomato cDNAs using a RT-PCR approach, encoding LeMADS1, LeMADS5 and LeMADS6 factors and whose mRNAs mostly accumulate in tomato flowers and fruits. Phylogeny analysis indicates that LeMADS1, 5 and 6 belong to the MEF2-like family. When transiently expressed in tobacco leaves or in human cells, LeMADS1, 5 and 6 are targeted to the cell nucleus. As the endogenous target genes of these putative transcription factors are unknown, the transcriptional activity of these proteins was characterized in a heterologous system and we showed that, when fused to a Gal4-DNA-binding domain, they repress the transcription of heterologous reporter genes. Since histone deacetylases control MEF2 transcriptional activity and since a putative histone deacetylase binding site was present in LeMADS1, 5 and 6, we tested the potential interaction between these factors and HDAC5 deacetylase. Surprisingly, in this heterologous system, LeMADS1, 5 and 6 interacted with HDAC5 N-terminal region. Our data suggest that, like mammalian MEF2A, plant MADS-box transcriptional activity might be regulated by enzymes controlling chromatin acetylation.