title: Cloning and functional characterization of the maize carotenoid isomerase and β-carotene hydroxylase genes and their regulation during endosperm maturation.
abstract: In order to gain further insight into the partly-characterized carotenoid biosynthetic pathway in corn (Zea mays L.), we cloned cDNAs encoding the enzymes carotenoid isomerase (CRTISO) and β-carotene hydroxylase (BCH) using endosperm mRNA isolated from inbred line B73. For both enzymes, two distinct cDNAs were identified mapping to different chromosomes. The two crtiso cDNAs (Zmcrtiso1 and Zmcrtiso2) mapped to unlinked genes each containing 12 introns, a feature conserved among all crtiso genes studied thus far. ZmCRTISO1 was able to convert tetra-cis prolycopene to all-trans lycopene but could not isomerize the 15-cis double bond of 9,15,9'-tri-cis-ζ-carotene. ZmCRTISO2 is inactivated by a premature termination codon in B73 corn, but importantly the mutation is absent in other corn cultivars and the active enzyme showed the same activity as ZmCRTISO1. The two bch cDNAs (Zmbch1 and Zmbch2) mapped to unlinked genes each coding sequences containing five introns. ZmBCH1 was able to convert β-carotene into β-cryptoxanthin and zeaxanthin, but ZmBCH2 was able to form β-cryptoxanthin alone and had a lower overall activity than ZmBCH1. All four genes were expressed during endosperm development, with mRNA levels rising in line with carotenoid accumulation (especially zeaxanthin and lutein) until 25 DAP. Thereafter, expression declined for three of the genes, with only Zmcrtiso2 mRNA levels maintained by 30 DAP. We discuss the impact of paralogs with different expression profiles and functions on the regulation of carotenoid synthesis in corn.
authors.affiliation: School of Life Sciences, Northeast Normal University, 130024, Changchun, China.
authors.forename: Qunrui
authors.initials: Q
authors.lastname: Li
authors.forename: Gemma
authors.initials: G
authors.lastname: Farre
authors.forename: Shaista
authors.initials: S
authors.lastname: Naqvi
authors.forename: Jürgen
authors.initials: J
authors.lastname: Breitenbach
authors.forename: Georgina
authors.initials: G
authors.lastname: Sanahuja
authors.forename: Chao
authors.initials: C
authors.lastname: Bai
authors.forename: Gerhard
authors.initials: G
authors.lastname: Sandmann
authors.forename: Teresa
authors.initials: T
authors.lastname: Capell
authors.forename: Paul
authors.initials: P
authors.lastname: Christou
authors.forename: Changfu
authors.initials: C
authors.lastname: Zhu
mesh_terms: D000595:Amino Acid Sequence; D001483:Base Sequence; D002338:Carotenoids / Q000096:biosynthesis; D003001:Cloning, Molecular; D017931:DNA Primers / Q000235:genetics; D056625:Endosperm / Q000201:enzymology / Q000254:growth & development; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism; D020869:Gene Expression Profiling; D018507:Gene Expression Regulation, Developmental; D015971:Gene Expression Regulation, Enzymologic; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D006899:Mixed Function Oxygenases / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018749:RNA, Plant / Q000235:genetics / Q000378:metabolism; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D017386:Sequence Homology, Amino Acid; D003313:Zea mays / Q000201:enzymology* / Q000235:genetics* / Q000254:growth & development; D019745:cis-trans-Isomerases / Q000235:genetics* / Q000378:metabolism*
chemical_list: D017931:DNA Primers; D010940:Plant Proteins; D012333:RNA, Messenger; D018749:RNA, Plant; D011994:Recombinant Proteins; D002338:Carotenoids; D006899:Mixed Function Oxygenases; C079232:beta-carotene hydroxylase; D019745:cis-trans-Isomerases