The characterization of the LEAFY COTYLEDON 2 activation domains reveals its conserved dual mode of action in flowering plants

Seed development in Arabidopsis thaliana is largely controlled by a set of transcription factors (TFs) called LAFL, including LEAFY COTYLEDON 2 (LEC2). In this study, we investigated the structure/function relationships of the protein LEC2 outside the well-described B3 DNA-binding domain. The results presented here unveil the presence of transcription activation domains (ADs) within the unstructured ends of the protein that are conserved in eudicots. Expression in both yeast and moss protoplasts of deleted and mutated versions of LEC2 confirmed the transcriptional activity of these ADs. Surprisingly, the expression of LEC2 variants lacking their ADs restored a wild-type seed phenotype in lec2 mutant, showing that these ADs are not essential for LEC2 function in seed development. Moreover, ZmAFL2/ZmABI19, a maize B3 factor related to LEC2 but deprived of N-ter AD, can also complement lec2 seed phenotype and induce abnormal vegetative development when overexpressed in Arabidopsis, supporting this observation. This work suggests that LEC2 can act both as a classical transcriptional activator or without transactivation activity, probably through its interaction with the pioneer factor LEC1. Taken together, the results provide important insights into the function of the LAFL master regulators during seed development, from cell differentiation to storage accumulation in seed.