title: Comparative analysis of carotenoid accumulation in two goji (Lycium barbarum L. and L. ruthenicum Murr.) fruits.
abstract: BACKGROUND
  The traditional Chinese medicinal plants Lycium barbarum L. and L. ruthenicum Murr. are valued for the abundance of bioactive carotenoids and anthocyanins in their fruits, respectively. However, the cellular and molecular mechanisms contributing to their species-specific bioactive profiles remain poorly understood.
  
  
  RESULTS
  In this study, the red fruit (RF) of L. barbarum was found to accumulate high levels of carotenoids (primarily zeaxanthin), while they were undetectable in the black fruit (BF) of L. ruthenicum. Cytological and gene transcriptional analyses revealed that the chromoplast differentiation that occurs in the chloroplast during fruit ripening only occurs in RF, indicating that the lack of chromoplast biogenesis in BF leads to no sink for carotenoid storage and the failure to synthesize carotenoids. Similar enzyme activities of phytoene synthase 1 (PSY1), chromoplast-specific lycopene β-cyclase (CYC-B) and β-carotene hydroxylase 2 (CRTR-B2) were observed in both L. ruthenicum and L. barbarum, suggesting that the undetectable carotenoid levels in BF were not due to the inactivation of carotenoid biosynthetic enzymes. The transcript levels of the carotenoid biosynthetic genes, particularly PSY1, phytoene desaturase (PDS), ζ-carotene desaturase (ZDS), CYC-B and CRTR-B2, were greatly increased during RF ripening, indicating increased zeaxanthin biosynthesis. Additionally, carotenoid cleavage dioxygenase 4 (CCD4) was expressed at much higher levels in BF than in RF, suggesting continuous carotenoid degradation in BF.
  
  
  CONCLUSIONS
  The failure of the chromoplast development in BF causes low carotenoid biosynthesis levels and continuous carotenoid degradation, which ultimately leads to undetectable carotenoid levels in ripe BF. In contrast, the successful chromoplast biogenesis in RF furnishes the sink necessary for carotenoid storage. Based on this observation, the abundant zeaxanthin accumulation in RF is primarily determined via both the large carotenoid biosynthesis levels and the lack of carotenoid degradation, which are regulated at the transcriptional level.
authors.forename: Yongliang
authors.initials: Y
authors.lastname: Liu
authors.forename: Shaohua
authors.initials: S
authors.lastname: Zeng
authors.forename: Wei
authors.initials: W
authors.lastname: Sun
authors.forename: Min
authors.initials: M
authors.lastname: Wu
authors.forename: Weiming
authors.initials: W
authors.lastname: Hu
authors.forename: Xiaofei
authors.initials: X
authors.lastname: Shen
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics / Q000378:metabolism; D000872:Anthocyanins / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism*; D005638:Fruit / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D019753:Intramolecular Lyases / Q000235:genetics / Q000378:metabolism; D032305:Lycium / Q000737:chemistry* / Q000201:enzymology / Q000235:genetics; D006899:Mixed Function Oxygenases / Q000235:genetics / Q000378:metabolism; D010088:Oxidoreductases / Q000235:genetics / Q000378:metabolism; D018515:Plant Leaves / Q000737:chemistry / Q000201:enzymology / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D010946:Plants, Medicinal; D018087:Plastids / Q000378:metabolism; D013045:Species Specificity
chemical_list: D000872:Anthocyanins; D010940:Plant Proteins; D002338:Carotenoids; C100185:(all-E) phytoene; D006899:Mixed Function Oxygenases; D010088:Oxidoreductases; C079232:beta-carotene hydroxylase; C022398:phytoene dehydrogenase; C099215:zeta-carotene desaturase; D019883:Alkyl and Aryl Transferases; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase