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The key positive regulators of the maturation program are the LEC genes, probably assisted by several bZIP and MYB transcription
factors (Baud et al., 2008). All of these bind to the promoters of seed storage protein genes and genes involved in the synthesis of storage lipids
(Lara et al., 2003; Kagaya et al., 2005; Braybrook et al., 2006; Santos-Mendoza et al., 2008). We found that several of these genes were up-regulated in the dcl1-15 mutant: FUS3, LEC2, L1L, and several MYBs and bZIPs (Table I). In contrast, ABI3 was unaffected and LEC1 was down-regulated.
We observed that in the wild type, the FUS3 and LEC2 transcriptional reporter genes are excluded from the embryo proper until the early heart stage, just before the beginning
of maturation. In dcl1-15, they are expressed in the embryo proper at least by the early globular stage, coinciding with the onset of chlorophyll accumulation
in the mutant. Our analysis of lec2-1 dcl1-15 and fus3-3 dcl1-15 double mutants confirms that both proteins are required for the early maturation phenotype, further supporting their position
downstream of miRNAs.
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