Résumé
Auxin plays an essential role in many aspects of plant development, including growth and reproduction. Recently, we found that the auxin response repressor IAA30 of Paspalum notatum is down-regulated inovules of apomictic genotypes compared to sexual genotypes at the anthesis and early embryogenesis stages. Furthermore, differences in the spatio-temporal expression between reproductive modes were revealed by insitu hybridization experiments. These results suggest a contrasting regulation of auxin signalling during sexual and apomictic seed formation in this species. In order to analyze the biological function of IAA30 during plantreproduction, we decided to study IAA16, its predicted orthologue in Arabidopsis thaliana. RT-PCR experiments showed that IAA16 is expressed in siliques, leaves, seedlings and roots. These data will be further completedusing wild-type plants expressing the pIAA16:IAA16:Ruby construct. Cytoembryological analysis of two iaa16 mutant lines revealed the formation of multiple enlarged cells around the megaspore mother cell, the functionalmegaspore and the developing embryo sac, an observation reminiscent of aposporous initials. After pollination, both mutant lines showed defects in embryo patterning and one of them developed twin-embryos. Seedlingswith one cotyledon and seeds with double shoots (polyembryony) were also detected. To further investigate the defects, we crossed iaa16 with auxin patterning and cell identity marker lines. Analysis of iaa16 plantsexpressing the pWOX2-CENH3-GFP reporter construct confirmed abnormal symmetry patterns in the embryos. Fluorescence analysis for pDRN:GFP in iaa16 embryos suggested an altered auxin signal distribution. The resultsof this work indicate an essential role for IAA16 in the specification of female germline fate and embryogenesis in Arabidopsis.