SECURE PLANT FERTILITY IN A CHANGING CLIMATE

The megaspore mother cell (MMC) development is a crucial step for plant reproduction. MMC specification is regulated by hormones, and many genes are involved. SPOROCYTELESS/NOZZLE (SPL/NZZ) is considered the master regulator of this process since its mutant cannot specify the MMC. It encodes a transcriptional repressor protein, which is present in all land plants. Despite the importance of this gene, its role is not completely unveiled. Thanks to the work presented in this thesis, it is possible to propose a mechanism of action for SPL, which involves its interaction with MADS-domain transcription factors. In a complex with SEPALLATA3 (SEP3), SPL negatively regulates the expression of AINTEGUMENTA (ANT) in the nucellus. ANT is a repressor of the auxin transporter PIN1, in this way the ANT repression allows PIN1 expression in the nucellus. In this work, PIN1 is described to be fundamental for auxin transport at the tip of ovule primordia. Here, thanks to the ARF transcription factors, auxin promotes the differentiation of the MMC. The function of SPL seems to be conserved in plants. Indeed, preliminary data show that the protein encoded by the AtSPL homologous in Marchantia polymorpha, MpSPL, can rescue the MMC formation in Arabidopsis spl.1 mutant. The presented results show that the formation of the MMC is regulated by mechanism conserved in evolution and that, in Arabidopsis thaliana, it involves auxin transport and signalling, regulated by SPL and MADS-domain transcription factors.