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The LAFL (i.e. LEC1, ABI3, FUS3, and LEC2) master transcriptional regulators interact to form different complexes that induce embryo development and maturation, and inhibit seed germination and vegetative growth in Arabidopsis. Orthologous genes involved in similar regulatory processes have been described in various angiosperms including important crop species. Consistent with a prominent role of the LAFL regulators in triggering and maintaining embryonic cell fate, their expression appears finely tuned in different tissues during seed development and tightly repressed in vegetative tissues by a surprisingly high number of genetic and epigenetic factors. Partial functional redundancies and intricate feedback regulations of the LAFL have hampered the elucidation of the underpinning molecular mechanisms. Nevertheless, genetic, genomic, cellular, molecular, and biochemical analyses implemented during the last years have greatly improved our knowledge of the LALF network. Here we summarize and discuss recent progress, together with current issues required to gain a comprehensive insight into the network, including the emerging function of LEC1 and possibly LEC2 as pioneer transcription factors.

A recombinant, site-directed mutant form of sorghum phosphoenolpyruvate carboxylase (PEPC), in which the phosphorylatable serine residue (Ser-8) was changed to cysteine (S8C), was chemically modified by iodoacetic acid and iodoacetamide for the purpose of testing the effect of introducing a negative charge at position 8. S-Carboxymethylation of the Cys-8 enzyme by iodoacetic acid decreased its sensitivity to L-malate from I_0.5 (50% inhibition) value of 0.12 to 0.35 mM at pH 7.3 when the active-site domain was protected during modification by the substrate phosphoenolpyruvate (PEP). In contrast, neither S-carboxymethylation of the wild-type enzyme nor modification of the mutant enzyme by iodoacetamide caused any change in the enzyme's sensitivity to L-malate. The modified, substrate-protected forms of the Ser-8 and S8C PEPCs had K_m(total PEP) and V_max values virtually identical to those of the unmodified control enzymes. Similar specific increases in the I_0.5 value of L-malate have been reported previously for in vitro phosphorylated leaf and recombinant Ser-8 PEPCs, the site-directed mutant Asp-8 enzyme, and C₄-leaf PEPC purified from light-adapted sorghum or maize (in vivo phospho-form). Therefore, these data from different but complementary experimental approaches provide convincing evidence that the effect of phosphorylation of Ser-8 on the L-malate sensitivity of sorghum C₄-PEPC is caused by the introduction of negative charge into this N-termninal regulatory domain.Copyright 1993, 1999 Academic Press