EMBRYONIC SURFACE FORMATION WITHIN THE DEVELOPING SEED: NEW STRUCTURES AND NEW MOLECULAR PLAYERS
Moussu, S.1, Creff A.1, Doll, N.1, Brocard, L.2,3, Chamot, S.1, Fourquin, C.1, Widiez, T.1, Nimchuck, Z.4, Joubès, J.3, Domergue, F.3 and Ingram, G.1
1Laboratoire Reproduction et Développement des Plantes, Université de Lyon, CNRS, INRA , UCB Lyon 1, Ecole Normale Supérieure de Lyon, F-69342 Lyon, France
2CNRS/ University of Bordeaux, Plant Imaging Platform of Bordeaux Imaging Center, UMS 3420, F-33000 Bordeaux, France
3Université de Bordeaux/CNRS, Laboratoire de Biogenèse Membranaire, UMR5200, F-33000 Bordeaux, France
4Department of Biology/ Curriculum in Genetics and Molecular Biology, University of North Carolina at Chapel Hill, Chapel Hill, NC, USA
Contact: Gwyneth Ingram, Gwyneth.Ingram@ens-lyon.fr
Arabidopsis seed development involves the concomitant development of two zygotic compartments, the embryo and the endosperm. Post-fertilization the endosperm expands as a coenocyte and then cellularises. Subsequently, the embryo grows invasively through the endosperm, which breaks down. How interactions between the growing embryo and the degenerating endosperm are regulated, and how the physical separation between these two compartments is achieved and maintained, remain poorly understood. Here we investigate signaling pathways involved in this separation process, and in the formation of the embryonic cuticle. We describe a novel structure, the embryo sheath, which forms on the surface of the embryo as it starts to elongate. The sheath is deposited outside the embryonic cuticle, and incorporates endosperm-derived material rich in extensin-like epitopes. Sheath production is dependent upon the activity of ZHOUPI, an endosperm-specific transcription factor necessary for endosperm degradation, embryo growth, embryo-endosperm separation and normal embryo cuticle formation. We show that a cysteine-rich peptide, KERBEROS, whose expression is ZOU dependent, is necessary both for the formation of a normal embryo sheath, and for embryo-endosperm separation. Finally, we investigate the interaction between KERBEROS function and the function of two Receptor-Like Kinases, GSO1 and GSO2, which are also necessary for the formation of a normal embryonic surface. Our results reveal a complex dialogue between the embryo and the endosperm during early seed development.