title: Carotenogenesis Is Regulated by 5'UTR-Mediated Translation of Phytoene Synthase Splice Variants.
abstract: Phytoene synthase (PSY) catalyzes the highly regulated, frequently rate-limiting synthesis of the first biosynthetically formed carotene. While PSY constitutes a small gene family in most plant taxa, the Brassicaceae, including Arabidopsis (Arabidopsis thaliana), predominantly possess a single PSY gene. This monogenic situation is compensated by the differential expression of two alternative splice variants (ASV), which differ in length and in the exon/intron retention of their 5'UTRs. ASV1 contains a long 5'UTR (untranslated region) and is involved in developmentally regulated carotenoid formation, such as during deetiolation. ASV2 contains a short 5'UTR and is preferentially induced when an immediate increase in the carotenoid pathway flux is required, such as under salt stress or upon sudden light intensity changes. We show that the long 5'UTR of ASV1 is capable of attenuating the translational activity in response to high carotenoid pathway fluxes. This function resides in a defined 5'UTR stretch with two predicted interconvertible RNA conformations, as known from riboswitches, which might act as a flux sensor. The translation-inhibitory structure is absent from the short 5'UTR of ASV2 allowing to bypass translational inhibition under conditions requiring rapidly increased pathway fluxes. The mechanism is not found in the rice (Oryza sativa) PSY1 5'UTR, consistent with the prevalence of transcriptional control mechanisms in taxa with multiple PSY genes. The translational control mechanism identified is interpreted in terms of flux adjustments needed in response to retrograde signals stemming from intermediates of the plastid-localized carotenoid biosynthesis pathway.
authors.affiliation: Faculty of Biology, Institute for Biology II (D.A., D.M., F.W., P.S., P.B., R.W.), Institute for Biology III (B.V.), University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Daniel
authors.identifier: 0000-0002-5930-2295
authors.initials: D
authors.lastname: Álvarez
authors.affiliation: Faculty of Biology, Institute for Biology II (D.A., D.M., F.W., P.S., P.B., R.W.), Institute for Biology III (B.V.), University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Björn
authors.initials: B
authors.lastname: Voß
authors.affiliation: Faculty of Biology, Institute for Biology II (D.A., D.M., F.W., P.S., P.B., R.W.), Institute for Biology III (B.V.), University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Dirk
authors.initials: D
authors.lastname: Maass
authors.affiliation: Faculty of Biology, Institute for Biology II (D.A., D.M., F.W., P.S., P.B., R.W.), Institute for Biology III (B.V.), University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Florian
authors.identifier: 0000-0002-9941-5550
authors.initials: F
authors.lastname: Wüst
authors.affiliation: Faculty of Biology, Institute for Biology II (D.A., D.M., F.W., P.S., P.B., R.W.), Institute for Biology III (B.V.), University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Patrick
authors.identifier: 0000-0002-8529-4161
authors.initials: P
authors.lastname: Schaub
authors.affiliation: Faculty of Biology, Institute for Biology II (D.A., D.M., F.W., P.S., P.B., R.W.), Institute for Biology III (B.V.), University of Freiburg, 79104 Freiburg, Germany.
authors.forename: Peter
authors.initials: P
authors.lastname: Beyer
authors.affiliation: Faculty of Biology, Institute for Biology II (D.A., D.M., F.W., P.S., P.B., R.W.), Institute for Biology III (B.V.), University of Freiburg, 79104 Freiburg, Germany ralf.welsch@biologie.uni-freiburg.de.
authors.forename: Ralf
authors.identifier: 0000-0002-2865-2743
authors.initials: R
authors.lastname: Welsch
mesh_terms: D020121:5' Untranslated Regions / Q000235:genetics*; D017398:Alternative Splicing / Q000235:genetics*; D017360:Arabidopsis / Q000201:enzymology* / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D002338:Carotenoids / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D019295:Computational Biology; D018506:Gene Expression Regulation, Plant; D017930:Genes, Reporter; D005966:Glucuronidase / Q000378:metabolism; D008954:Models, Biological; D009097:Multienzyme Complexes / Q000235:genetics* / Q000378:metabolism; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics; D014176:Protein Biosynthesis / Q000235:genetics*
chemical_list: D020121:5' Untranslated Regions; D029681:Arabidopsis Proteins; D009097:Multienzyme Complexes; C022434:prelycopersene pyrophosphate synthetase; D002338:Carotenoids; D005966:Glucuronidase