02702naa a2200277 a 450000100080000000500110000800800410001902200140006002400350007410000170010924501610012626000090028750001310029652017930042765000130222065000110223365300080224465300160225265300200226865300150228865300130230370000180231670000130233470000180234777300590236510507622019-10-09       2013    bl uuuu     u00u1 u    #d  a1614-29427 a10.1007/s11295-013-0635-72DOI1 aALQUEZAR, B.  aA comparative physiological and transcriptional study of carotenoid biosynthesis in white and red grapefruit (Citrus paradisi Macf.).h[electronic resource]  c2013  aArticle history: Received: 30 January 2013 / Revised: 26 March 2013 / Accepted: 15 April 2013 / Published online: 15 May 2013.  aABSTRACT.  Accumulation of lycopene in citrus fruits is an unusual feature restricted to selected mutants. Grapefruit (Citrus paradisi Macf.) is the Citrus specie with greater number of red-fleshed mutants, but the molecular bases of this alteration are not fully understood. To gain knowledge into the mechanisms implicated in this alteration, we conducted a comparative analysis of carotenoid profile and of the expression of genes related to carotenoid biosynthesis and catabolism in flavedo and pulp of two grapefruit cultivars with marked differences in colouration: the white Marsh and the red Star Ruby. Mature green fruit of Marsh accumulated chloroplastic carotenoids, while mature tissues lacked carotenoids. However, accumulation of downstream products such as abscisic acid (ABA) and expression of its biosynthetic genes, 9-cis-epoxycarotenoid dioxygenase (NCED1 and NCED2), increased after the onset of colouration. In contrast, red grapefruit accumulated lycopene, phytoene and phytofluene, while ABA content and NCED gene expression were lower than in Marsh, suggesting a blockage in the carotenoid biosynthetic pathway. Expression analysis of three genes of the isoprenoid pathway and nine of the carotenoid biosynthetic pathway revealed virtually no differences in flavedo and pulp between both genotypes, except for the chromoplast-specific lycopene cyclase 2 (β-LCY2) which was lower in the pulp of the red grapefruit. The proportion in the expression of the allele with high (β-LCY2a) and low (β-LCY2b) activity was also similar in the pulp of both genotypes. Therefore, results suggest that reduced expression of β-LCY2 appears to be responsible of lycopene accumulation in the red Star Ruby grapefruit.  © 2013 Springer-Verlag Berlin Heidelberg.  aCAROTENO  aCITRUS  aABA  aCAROTENOIDS  aGENE EXPRESSION  aGRAPEFRUIT  aLYCOPENE1 aRODRIGO, M.J.1 aLADO, J.1 aZACARÍAS, L.  tTree Genetics & Genomes, 2013gv.9, no.5, p.1257-1269.