title: Regulation of anthocyanin and proanthocyanidin biosynthesis by Medicago truncatula bHLH transcription factor MtTT8.
abstract: The MYB- basic helix-loop-helix (bHLH)-WD40 complexes regulating anthocyanin and proanthocyanidin (PA) biosynthesis in plants are not fully understood. Here Medicago truncatula bHLH MtTT8 was characterized as a central component of these ternary complexes that control anthocyanin and PA biosynthesis. Mttt8 mutant seeds have a transparent testa phenotype with reduced PAs and anthocyanins. MtTT8 restores PA and anthocyanin productions in Arabidopsis tt8 mutant. Ectopic expression of MtTT8 restores anthocyanins and PAs in mttt8 plant and hairy roots and further enhances both productions in wild-type hairy roots. Transcriptomic analyses and metabolite profiling of mttt8 mutant seeds and M. truncatula hairy roots (mttt8 mutant, mttt8 mutant complemented with MtTT8, or MtTT8 overexpression lines) indicate that MtTT8 regulates a subset of genes involved in PA and anthocyanin biosynthesis. MtTT8 is genetically regulated by MtLAP1, MtPAR and MtWD40-1. Combinations of MtPAR, MtLAP1, MtTT8 and MtWD40-1 activate MtTT8 promoter in yeast assay. MtTT8 interacts with these transcription factors to form regulatory complexes. MtTT8, MtWD40-1 and an MYB factor, MtPAR or MtLAP1, interacted and activated promoters of anthocyanidin reductase and anthocyanidin synthase to regulate PA and anthocyanin biosynthesis, respectively. Our results provide new insights into the complex regulation of PA and anthocyanin biosynthesis in M. truncatula.
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430075, China.
authors.forename: Penghui
authors.initials: P
authors.lastname: Li
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430075, China.
authors.forename: Beibei
authors.initials: B
authors.lastname: Chen
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430075, China.
authors.forename: Gaoyang
authors.initials: G
authors.lastname: Zhang
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430075, China.
authors.forename: Longxiang
authors.initials: L
authors.lastname: Chen
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430075, China.
authors.forename: Qiang
authors.initials: Q
authors.lastname: Dong
authors.affiliation: Plant Biology Division, the Samuel Roberts Noble Foundation, Ardmore, OK, 73401, USA.
authors.forename: Jiangqi
authors.initials: J
authors.lastname: Wen
authors.affiliation: Plant Biology Division, the Samuel Roberts Noble Foundation, Ardmore, OK, 73401, USA.
authors.forename: Kirankumar S
authors.initials: KS
authors.lastname: Mysore
authors.affiliation: National Key Laboratory of Crop Genetic Improvement, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, 430075, China.|Plant Biology Division, the Samuel Roberts Noble Foundation, Ardmore, OK, 73401, USA.
authors.forename: Jian
authors.initials: J
authors.lastname: Zhao
mesh_terms: D000872:Anthocyanins / Q000096:biosynthesis*; D017360:Arabidopsis / Q000235:genetics; D051792:Basic Helix-Loop-Helix Proteins / Q000235:genetics / Q000378:metabolism*; D053898:Biosynthetic Pathways / Q000235:genetics; D015536:Down-Regulation / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D005816:Genetic Complementation Test; D046913:Medicago truncatula / Q000235:genetics / Q000378:metabolism*; D055432:Metabolomics; D009154:Mutation / Q000235:genetics; D010641:Phenotype; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D018517:Plant Roots / Q000235:genetics; D030821:Plants, Genetically Modified; D044945:Proanthocyanidins / Q000096:biosynthesis*; D011401:Promoter Regions, Genetic; D011485:Protein Binding
chemical_list: D000872:Anthocyanins; D051792:Basic Helix-Loop-Helix Proteins; D010940:Plant Proteins; D044945:Proanthocyanidins
keywords: Medicago; anthocyanin; basic helix-loop-helix (bHLH) transcription factor; proanthocyanidin; protein interaction; regulatory complex; transparent testa