Molecular analysis of a sunflower gene encoding an homologous of the B subunit of a CAAT binding factor

A genomic DNA fragment containing the entire LEAFY COTYLEDON1-LIKE (HaL1L) gene was obtained by the Chromosome walking technique and it was confirmed and elongated by the screening of a sunflower genomic DNA BAC Library. HaL1L encodes a NF-YB of a CCAAT box-binding factor (NFY) involved in the genus Helianthus in early stages of zygotic and somatic embryogenesis. In the HaL1L 5'-flanking region, elements peculiar to a putative TATA-box promoter and two "CG isles" were identified. An investigation on the methylation status of the CG rich DNA regions showed that differentially methylated cytosines were recognizable in DNA of embryos at the fifth day from pollination in comparison to the leaf DNA. These data suggested epigenetic regulation of HaL1L transcription carried out by methylation of cytosine residues during plant development. The nucleotide sequences were also analyzed to individuate cis-regulatory elements involved in the HaL1L regulation by other transcription factors (TFs). One of the most intriguing motifs is WUSATA. It represent the target sequence for the TF WUSCHEL, which could be involved in the complex regulation system controlling embryo development. Noteworthy, the presence of auxin (ARE) and abscisic acid (ABRE) responsive motifs in the HaL1L promoter region suggested an hormonal involvement in the expression control of this gene. Finally, a control at translational level by a temporary unavailability of pre-synthesized HaL1L mRNA could be also supposed for the presence of a cytoplasmic polyadenylation signal identified in the 3'-downstream region.