title: Distinct expression and function of carotenoid metabolic genes and homoeologs in developing wheat grains.
abstract: β-carotene, the most active provitamin A molecule produced by plants, plays important roles in human nutrition and health. β-carotene does not usually accumulate in the endosperm (i.e. flour) of mature wheat grains, which is a major food source of calories for humans. Therefore, enriching β-carotene accumulation in wheat grain endosperm will enable a sustainable dietary supplementation of provitamin A. Several metabolic genes affecting β-carotene accumulation have already been isolated from wheat, including phytoene synthase 1 (PSY1), lycopene ε-cyclase (LCYe) and carotenoid β-ring hydroxylase1/2 (HYD1/2).
  
  
  
  In this work, we cloned and biochemically characterized two carotenoid cleavage dioxygenases (CCDs), CCD1 and CCD4, from wheat. While CCD1 homoeologs cleaved β-apo-8'-carotenal, β-carotene, lutein and zeaxanthin into apocarotenoid products, CCD4 homoeologs were inactive towards these substrates in in vitro assays. When analyzed by real-time qPCR, PSY1, LCYe, HYD1/2 and CCD1/4 homoeologs showed distinct expression patterns in vegetative tissues and sections of developing tetraploid and hexaploid wheat grains, suggesting that carotenoid metabolic genes and homoeologs are differentially regulated at the transcriptional level in wheat.
  
  
  
  The CCD1/4 enzyme activity and the spatial-temporal gene expression data provide critical insights into the specific carotenoid metabolic gene homoeologs that control β-carotene accumulation in wheat grain endosperm, thus establishing the knowledge base for generation of wheat varieties with enhanced β-carotene in the endosperm through breeding and genome editing approaches.
authors.affiliation: Department of Plant Sciences, Mail Stop 3, University of California, Davis, CA, 95616, USA.
authors.forename: Xiaoqiong
authors.initials: X
authors.lastname: Qin
authors.affiliation: Department of Plant Sciences, Mail Stop 3, University of California, Davis, CA, 95616, USA.|Quantitative and Systems Biology Program, University of California, Merced, CA, 95343, USA.
authors.forename: Kathryn
authors.initials: K
authors.lastname: Fischer
authors.affiliation: Department of Plant Sciences, Mail Stop 3, University of California, Davis, CA, 95616, USA.
authors.forename: Shu
authors.initials: S
authors.lastname: Yu
authors.affiliation: Department of Plant Sciences, Mail Stop 3, University of California, Davis, CA, 95616, USA.|Howard Hughes Medical Institute, Chevy Chase, MD, 20815, USA.
authors.forename: Jorge
authors.initials: J
authors.lastname: Dubcovsky
authors.affiliation: Department of Plant Sciences, Mail Stop 3, University of California, Davis, CA, 95616, USA. ltian@ucdavis.edu.|Shanghai Key Laboratory of Plant Functional Genomics and Resources, Shanghai Chenshan Botanical Garden, Shanghai, 201602, China. ltian@ucdavis.edu.|Shanghai Chenshan Plant Science Research Center, Chinese Academy of Sciences, Shanghai, 201602, China. ltian@ucdavis.edu.
authors.forename: Li
authors.identifier: 0000-0001-6461-6072
authors.initials: L
authors.lastname: Tian
mesh_terms: D002338:Carotenoids / Q000378:metabolism*; D049308:Dioxygenases / Q000235:genetics / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase / Q000235:genetics / Q000378:metabolism; D019753:Intramolecular Lyases / Q000235:genetics / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D012639:Seeds / Q000201:enzymology / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism; D014908:Triticum / Q000201:enzymology / Q000235:genetics / Q000254:growth & development / Q000378:metabolism*
chemical_list: D010940:Plant Proteins; D002338:Carotenoids; D049308:Dioxygenases; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase
keywords: Carotenoid; Carotenoid cleavage dioxygenase; Endosperm; Grain; Provitamin A; Spatial expression; Wheat; β-carotene