The SebHLH transcription factor mediates trans-activation of the SeFAD2 gene promoter through binding to E- and G-box elements

Abstract

Microsomal oleic acid desaturase (FAD2) catalyzes the first extra-plastidial desaturation in plants, converting oleic acid to linoleic acid, which is a major constituent in all cellular membranes as well as in seed storage oils. Seed-specific FAD2 (SeFAD2) produced 40% of linoleic acids in the total fatty acids of sesame (Sesamum indicum) seeds. The expression of SeFAD2 transcripts was spatially and temporally controlled during seed development. To investigate the regulatory mechanism controlling seed-specific SeFAD2 expression, we isolated a well-matched sequence homologous to the basic region/helix-loop-helix proteins by yeast one-hybrid screening and named it SebHLH. SebHLH transcripts were expressed in developing seeds and roots of sesame. SebHLH:GFP fusion protein localized in the nucleus. Recombinant SebHLH protein bound E-box (CANNTG) and G-box (CACGTG) elements in the region from -179 to -53 of the SeFAD2 gene promoter, and the external C and G nucleotides in the E- and G-box motifs were essential for SebHLH protein binding. The SebHLH gene, under the CaMV35S promoter, and the GUS reporter gene driven by E- and G-box motifs were co-expressed in developing sesame seeds and Arabidopsis transgenic leaves. This co-expression demonstrated that SebHLH protein mediates transactivation of the SeFAD2 gene promoter through binding to E- and G-box elements. E- or G-box elements frequently occur in the 5'-flanking region of genes that are involved in triacylglycerol biosynthesis and that exhibit seed-specific expression in Arabidopsis and other plants, suggesting that bHLH transcription factors play a key role in the transcriptional regulation of genes related to storage lipid biosynthesis and accumulation during seed development.

Genome Wide Analysis of Fatty Acid Desaturation and Its Response to Temperature

“…S6; Kim et al, 2006). Kim et al (2007) identified a basic region/helix-loop-helix transcription factor that transactivates FAD2 expression in sesame by binding both E box and G box elements in the promoter. Therefore, it is possible that a related transcription factor also enhances FAD2 expression in Arabidopsis by interacting with the E box situated near P1 and that this sequence variant might influence DNA binding.…”

In vitro binding of Sorghum bicolor transcription factors ABI4 and ABI5 to a conserved region of a GA 2-OXIDASE promoter: possible role of this interaction in the expression of seed dormancy

“…In order to broaden this analysis, and taking into account that many authors have reported the occurrence of plant transcription factors binding cis -elements located at 2kb or 3kb upstream from the ATG (Kim, 2007; Oh et al , 2007; Lee et al , 2012), a genomic sequence of 2kb, considered to be the putative 5′-regulatory region (promoter), was cloned and sequenced for both sprouting-resistant (IS9530) and sprouting-susceptible (RedlandB2) genotypes. To assess the possibility of a differential sequence composition in the regulatory region between the sprouting-resistant and sprouting-susceptible lines, both sequences were analysed in the PLACE database to identify cis -acting regulatory elements.…”

Overexpression of FAD2 promotes seed germination and hypocotyl elongation in Brassica napus

“…FAD2 is regulated by the SebHLH transcription factor through binding to the E-and G-box elements during sesame seed development, and the length of the hypocotyl has been proven to be associated with the light condition in plant photomorphogenesis (Wei and Deng 1996;Kim et al 2007). We therefore measured the length of the hypocotyl of seedlings grown under normal conditions.…”