The SebHLH transcription factor mediates trans-activation of the SeFAD2 gene promoter through binding to E- and G-box elements.
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.
Kim
Mi Jung
MJ
School of Life Sciences and Biotechnology, Korea University, Seoul, 136-701, Korea.
Kim
Jeong-Kook
JK
Shin
Jeong Sheop
JS
Suh
Mi Chung
MC
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000235:genetics; D024721:E-Box Elements; D044943:Fatty Acid Desaturases / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D051790:G-Box Binding Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D049452:Green Fluorescent Proteins / Q000032:analysis; D018257:Helix-Loop-Helix Motifs; D008969:Molecular Sequence Data; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D018517:Plant Roots / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011993:Recombinant Fusion Proteins / Q000032:analysis; D012639:Seeds / Q000235:genetics / Q000254:growth & development / Q000378:metabolism; D016415:Sequence Alignment; D031685:Sesamum / Q000235:genetics* / Q000378:metabolism; D015534:Trans-Activators / Q000737:chemistry / Q000378:metabolism / Q000502:physiology*; D015533:Transcriptional Activation
D051790:G-Box Binding Factors; D010940:Plant Proteins; D011993:Recombinant Fusion Proteins; D015534:Trans-Activators; D049452:Green Fluorescent Proteins; D044943:Fatty Acid Desaturases; C040448:delta-12 fatty acid desaturase