STRUCTURE AND FUNCTION OF THE CONSERVED LAFL GENE REGULATORY NETWORK THAT CONTROLS SEED DEVELOPMENT IN FLOWERING PLANTS
Lepiniec, L., Boulard, C., Barthole, G., Fatihi, A., Kelemen, Z., Marchive, C., Troncoso-Ponce, M.A., Thévenin, J., To, A., Miquel, M., Baud, S. and Dubreucq, B.
IJPB, INRA-AgroParisTech-CNRS, Université Paris-Saclay, France
Contact: Loïc Lepiniec, email@example.com
The LAFL genes, LEAFY COTYLEDON 1 (LEC1), LEC2, FUSCA3 (FUS3), and ABSCISIC INSENSITIVE 3 (ABI3) encode a homolog of the NF-YB protein and three transcriptional regulators of the “B3-domain” family, respectively. Genetic analyses demonstrated that they have complex pleiotropic, partially synergistic and overlapping function during seed maturation. They are differentially expressed and display some specific activities. For instance, we have shown that LEC2 directly induces the genes coding for seed storage proteins (e.g. At2S3) and proteins of the oil bodies (e.g. OLEOSIN1), as well as regulatory genes such as WRINKLED1 (WRI1) or two closely related MYB genes (MYB115 and 118). WRI1 is a member of the AP2 family that controls glycolytic and fatty acid biosynthetic genes and oil accumulation. MYB115 and 118 repress the maturation program during early endosperm development and induces two desaturase genes (AAD2 and AAD3) involved in omega7 monounsaturated fatty acids.
In order to unravel this complex network, we used the target OLEOSIN1 (OLE1) promoter as model in vitro, in moss protoplasts and in planta. We have confirmed that the three AFL-B3 proteins bind the core “RY” DNA elements (5’-CATG-3’), but with different flanking nucleotides. G-box cis-elements are also required for the proper activation of OLE1 promoter in vivo, suggesting that other regulatory proteins (e.g. bZIP) are involved. Moreover, LEC2, ABI3 and LEC1 have synergistic effects on the activation of the OLE1 promoter. Last, LEC1 and LEC2 proteins produced in Arabidopsis protoplasts can form a ternary complex with NF-YC2 in vitro in the presence of OLE1 promoter. Taken together, these results allow drawing a molecular model for the transcriptional regulation of seed genes by the AFL proteins.
Interestingly, the ectopic expression of LEC1 or LEC2 in vegetative tissues is sufficient to induce somatic embryogenesis. This developmental activity provides a possible explanation to the establishment of various genetic and epigenetic mechanisms that tightly repress their expression in vegetative tissues. Last, we are investigating the LAFL regulatory network in various plant species demonstrating its conservation in flowering plants. We are exploiting this knowledge to develop biotech strategies aimed at controlling oil and/or protein accumulation in crop seeds.