title: Expression profiles of key phenylpropanoid genes during Vanilla planifolia pod development reveal a positive correlation between PAL gene expression and vanillin biosynthesis.
abstract: In Vanilla planifolia pods, development of flavor precursors is dependent on the phenylpropanoid pathway. The distinctive vanilla aroma is produced by numerous phenolic compounds of which vanillin is the most important. Because of the economic importance of vanilla, vanillin biosynthetic pathways have been extensively studied but agreement has not yet been reached on the processes leading to its accumulation. In order to explore the transcriptional control exerted on these pathways, five key phenylpropanoid genes expressed during pod development were identified and their mRNA accumulation profiles were evaluated during pod development and maturation using quantitative real-time PCR. As a prerequisite for expression analysis using qRT-PCR, five potential reference genes were tested, and two genes encoding Actin and EF1 were shown to be the most stable reference genes for accurate normalization during pod development. For the first time, genes encoding a phenylalanine ammonia-lyase (VpPAL1) and a cinnamate 4-hydroxylase (VpC4H1) were identified in vanilla pods and studied during maturation. Among phenylpropanoid genes, differential regulation was observed from 3 to 8 months after pollination. VpPAL1 was gradually up-regulated, reaching the maximum expression level at maturity. In contrast, genes encoding 4HBS, C4H, OMT2 and OMT3 did not show significant increase in expression levels after the fourth month post-pollination. Expression profiling of these key phenylpropanoid genes is also discussed in light of accumulation patterns for key phenolic compounds. Interestingly, VpPAL1 gene expression was shown to be positively correlated to maturation and vanillin accumulation.
authors.affiliation: Université de la Réunion, UMR Peuplements Végétaux et Bioagresseurs en Milieu Tropical (PVBMT), Pôle de Protection des Plantes, 7, Chemin de l'IRAT, Ligne Paradis, 97410 Saint Pierre, France. Electronic address: isabelle.fock@univ-reunion.fr.
authors.forename: Isabelle
authors.initials: I
authors.lastname: Fock-Bastide
authors.affiliation: Université de la Réunion, UMR Peuplements Végétaux et Bioagresseurs en Milieu Tropical (PVBMT), Pôle de Protection des Plantes, 7, Chemin de l'IRAT, Ligne Paradis, 97410 Saint Pierre, France.
authors.forename: Tony Lionel
authors.initials: TL
authors.lastname: Palama
authors.affiliation: Université de la Réunion, UMR Peuplements Végétaux et Bioagresseurs en Milieu Tropical (PVBMT), Pôle de Protection des Plantes, 7, Chemin de l'IRAT, Ligne Paradis, 97410 Saint Pierre, France.
authors.forename: Séverine
authors.initials: S
authors.lastname: Bory
authors.affiliation: IRD, UMR Peuplements Végétaux et Bioagresseurs en Milieu Tropical (PVBMT), Pôle de Protection des Plantes, 7, Chemin de l'IRAT, Ligne Paradis, 97410 Saint Pierre, France.
authors.forename: Aurélie
authors.initials: A
authors.lastname: Lécolier
authors.affiliation: IRD, UMR Peuplements Végétaux et Bioagresseurs en Milieu Tropical (PVBMT), Pôle de Protection des Plantes, 7, Chemin de l'IRAT, Ligne Paradis, 97410 Saint Pierre, France.
authors.forename: Michel
authors.initials: M
authors.lastname: Noirot
authors.affiliation: IRD, UMR Diversité, Adaptation et Développement des Plantes (DIADE), 911 Avenue Agropolis, BP64501, 34394 Montpellier, France.
authors.forename: Thierry
authors.initials: T
authors.lastname: Joët
mesh_terms: D001483:Base Sequence; D001547:Benzaldehydes / Q000378:metabolism*; D017931:DNA Primers; D020869:Gene Expression Profiling; D017343:Genes, Plant; D010650:Phenylalanine Ammonia-Lyase / Q000235:genetics*; D010666:Phenylpropionates / Q000378:metabolism*; D010802:Phylogeny; D060888:Real-Time Polymerase Chain Reaction; D031669:Vanilla / Q000201:enzymology / Q000235:genetics* / Q000254:growth & development
chemical_list: D001547:Benzaldehydes; D017931:DNA Primers; D010666:Phenylpropionates; C100058:vanillin; D010650:Phenylalanine Ammonia-Lyase
keywords: 4-hydroxybenzaldehyde synthase; 4HBS; C4H; Cinnamate 4-hydroxylase; Fruit maturation; HBAc; HBAlc; HBAld; MAP; O-methyltransferases; OMT; PAL; PCAld; Phenolic compounds; Phenylalanine ammonia-lyase; Real-time quantitative PCR; Reference genes; Van; VanAc; VanAlc; Vanilla planifolia; cinnamate 4-hydroxylase; months after pollination; p-hydroxybenzaldehyde; p-hydroxybenzoic acid; p-hydroxybenzyl alcohol; phenylalanine ammonia-lyase; protocatechualdehyde; vanillic acid; vanillin; vanillyl alcohol