A novel role of BPCs in the control of medial domain differentiation during gynoecium development in Arabidopsis thaliana.

The gynoecium, a highly specialized structure in flowering plants, ensures their high reproductive success through the control of different crucial steps spanning from ovule protection to fertilization and seed maturation and dispersion. Multiple bpc mutants show reduced vigor, small fruit size and height, a reduced number of seeds and problems in septum fusion and formation. BPCs are known to be involved in the regulation of key factors involved in plant development, and they are thought to function both as activators and repressors of target gene expression. Here we showed that gynoecium development is affected in different multiple mutants of the Basic PentaCysteine (BPC) genes, where the septum fails to develop properly, and that BPCs of class I and II regulate the expression of different genes involved in carpel development and phytohormonal pathways regulation. Considering the fundamental role of the gynoecium, which affects the reproductive success of the plants, we focused on understanding which genes could be putative direct targets of BPCs and thus involved in gynoecium development. We demonstrated that SPATULA and NO TRANSMITTING TRACT (NTT), which play pivotal roles in carpel and transmitting tract development, are downregulated. As a consequence, bpc multiple mutants fail to properly develop the septum and the transmitting tract. Interestingly, among the downregulated genes, we also found PIN-LIKES3, whose promoter can be directly bound by BPCs, which is an auxin efflux carrier that regulates and controls cytoplasmic availability of auxin and could also contribute to various growth processes.