title: The Phytoene synthase gene family of apple (Malus x domestica) and its role in controlling fruit carotenoid content.
abstract: BACKGROUND
  Carotenoid compounds play essential roles in plants such as protecting the photosynthetic apparatus and in hormone signalling. Coloured carotenoids provide yellow, orange and red colour to plant tissues, as well as offering nutritional benefit to humans and animals. The enzyme phytoene synthase (PSY) catalyses the first committed step of the carotenoid biosynthetic pathway and has been associated with control of pathway flux. We characterised four PSY genes found in the apple genome to further understand their involvement in fruit carotenoid accumulation.
  
  
  RESULTS
  The apple PSY gene family, containing six members, was predicted to have three functional members, PSY1, PSY2, and PSY4, based on translation of the predicted gene sequences and/or corresponding cDNAs. However, only PSY1 and PSY2 showed activity in a complementation assay. Protein localisation experiments revealed differential localization of the PSY proteins in chloroplasts; PSY1 and PSY2 localized to the thylakoid membranes, while PSY4 localized to plastoglobuli. Transcript levels in 'Granny Smith' and 'Royal Gala' apple cultivars showed PSY2 was most highly expressed in fruit and other vegetative tissues. We tested the transient activation of the apple PSY1 and PSY2 promoters and identified potential and differential regulation by AP2/ERF transcription factors, which suggested that the PSY genes are controlled by different transcriptional mechanisms.
  
  
  CONCLUSIONS
  The first committed carotenoid pathway step in apple is controlled by MdPSY1 and MdPSY2, while MdPSY4 play little or no role in this respect. This has implications for apple breeding programmes where carotenoid enhancement is a target and would allow co-segregation with phenotypes to be tested during the development of new cultivars.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 92169, Auckland, 1142, New Zealand. charles.dwamena@plantandfood.co.nz.
authors.forename: Charles
authors.initials: C
authors.lastname: Ampomah-Dwamena
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 92169, Auckland, 1142, New Zealand. n.driedonks@science.ru.nl.|Institute for Wetland and Water Research, Radboud University, Postbus 9010, 6500 GL, Nijmegen, Netherlands. n.driedonks@science.ru.nl.
authors.forename: Nicky
authors.initials: N
authors.lastname: Driedonks
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 11600, Palmerston North, 4442, New Zealand. david.lewis@plantandfood.co.nz.
authors.forename: David
authors.initials: D
authors.lastname: Lewis
authors.affiliation: Department of Biological Sciences, Lehman College, The City University of New York, 250 Bedford Park Blvd. West, Bronx, New York, NY, 10468, USA. mashum@gmail.com.
authors.forename: Maria
authors.initials: M
authors.lastname: Shumskaya
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 92169, Auckland, 1142, New Zealand. xiuyin.chen@plantandfood.co.nz.
authors.forename: Xiuyin
authors.initials: X
authors.lastname: Chen
authors.affiliation: Department of Biological Sciences, Lehman College, The City University of New York, 250 Bedford Park Blvd. West, Bronx, New York, NY, 10468, USA. eleanore.wurtzel@lehman.cuny.edu.|The Graduate School and University Center-CUNY, 365 Fifth Ave, New York, NY, 10016-4309, USA. eleanore.wurtzel@lehman.cuny.edu.
authors.forename: Eleanore T
authors.initials: ET
authors.lastname: Wurtzel
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 92169, Auckland, 1142, New Zealand. richard.espley@plantandfood.co.nz.
authors.forename: Richard V
authors.initials: RV
authors.lastname: Espley
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, Private Bag 92169, Auckland, 1142, New Zealand. andrew.allan@plantandfood.co.nz.
authors.forename: Andrew C
authors.initials: AC
authors.lastname: Allan
mesh_terms: D000595:Amino Acid Sequence; D002338:Carotenoids / Q000378:metabolism*; D005638:Fruit / Q000378:metabolism; D018506:Gene Expression Regulation, Plant; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase / Q000235:genetics* / Q000378:metabolism; D027845:Malus / Q000235:genetics* / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D010940:Plant Proteins; D002338:Carotenoids; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase