Author: UMR5096
Last saved by: Saritas, Sevim
Company: IRD

Uncoupling Mid and Late Embryogenesis in Oilseeds by Partial Complementation of afl Mutants in Arabidopsis
Thomas Roscoe^1, Jocelyne Guilleminot^2, Jean-Jacques Bessoule^3, Frédéric Berger^4 and Martine Devic^1
^1CNRS-IRD ERL5300 Epigenetic Regulation and Seed Development Group, Institut de Recherche pour le Développement, Montpellier, FRANCE. 
^2Laboratoire Genome et Développement des Plantes, UMR 5096 CNRS-UPVD, Université de Perpignan, Perpignan, FRANCE. 
^3Laboratoire de Biogenèse Membranaire, Université de Bordeaux, CNRS UMR 5200, Villenave d'Ornon, FRANCE. 
^4Gregor Mendel Institute of Molecular Plant Biology, Vienna, AUSTRIA.

ABSCISIC ACID INSENSITIVE3 (ABI3), FUSCA3 (FUS3), and LEAFY COTYLEDON2 (LEC2), collectively AFL factors, are master regulators of seed maturation. We examined the role of the AFL B3 DNA binding domain in the production of seed reserves in Arabidopsis thaliana. Quantitation of seed reserves combined with cytological imaging of single, double and triple afl mutant embryos, revealed storage lipid and protein but not starch to be positively and spatially regulated by AFL factors. ABI3 and FUS3 contribute to carbon partitioning since the abi3 mutation reduces seed protein content to a greater extent than lipid content, whereas fus3 has a more severe effect on triacylglycerol content. Furthermore, FUS3 exerts a greater control over fatty acid desaturation mediated by both FAD2 and FAD3, whereas ABI3 exerts a greater control over fatty acid elongation. Although ABI3 influences reserve content throughout the embryo, LEC2 and FUS3 act in distinct territories, the cotyledon and embryonic axis respectively. By analysing the ability of an individual ectopically expressed AFL to genetically suppress afl mutations, we show that the conserved B3 DNA binding domain is necessary and sufficient for the initiation of synthesis and accumulation of triacylglycerol and for the initiation, but not maintenance of seed storage protein synthesis. We confirm functional redundancy among AFL factors and demonstrate the existence of a threshold for function in the AFL pool. No individual AFL factor is able to suppress precocious germination nor initiate dormancy and tolerance to desiccation. Thus, mid- and late-embryogenesis programmes are uncoupled, consequently, reserve accumulation is prematurely terminated concomitant with viviparous development. These findings have implications for the modulation of carbon partitioning in seeds and energy densification of plant biomass.