UNRAVELING THE ROLE OF BPC PROTEINS IN INFLORESCENCE AND FLOWER DEVELOPMENT IN A. THALIANA

BPC proteins belong to a small plant specific family of transcription factors and they share functional similarities with the GAGA ASSOCIATED FACTOR (GAF) of Drosophila melanogaster. In Arabidopsis thaliana, there are seven BPs genes, although BPC5 is considered a pseudogene. Except BPC5, BPC genes are ubiquitously expressed in all plant tissues throughout development and this overlap in expression could suggest that BPCs act redundantly. The C-terminal domain of BPC proteins facilitates binding to DNA at GA-rich sequences and for BPC1, a consensus binding site has been proposed. However, little is known about their function in gene regulation and INNER NO OUTER, SEEDSTICK and LEAFY COTYLEDON2 are the only BPC target genes identified until now. To study BPC function in vivo, we have now constructed bpc1 bpc2 bpc3 triple mutants, which develop inflorescences comprising more flowers than wild-type plants, their phyllotaxis is altered and flowers develop extra floral organs. These features could be linked to meristem size and activity: it is well known that plants with bigger and/or more active meristems produce higher number of flowers and floral organs respect to wild-type. An involvement of BPC regulators in meristem maintenance has not been uncovered yet, however the BBR factor (the BPC homolog in barley) binds and regulates the BKN3 gene, the barley homolog of Arabidopsis SHOOTMERISTEMLESS (STM). In Arabidopsis, STM is involved in meristem maintenance and activity and it is also involved in the cytokinin pathway, a class of plant hormones able to promote shoot meristem growth and maintenance. These data made it interesting to investigate the involvement of BPCs and their role in the cytokinin pathway.