Deciphering the genomic structure, function and evolution of carotenogenesis related phytoene synthases in grasses.
BACKGROUND
Carotenoids are isoprenoid pigments, essential for photosynthesis and photoprotection in plants. The enzyme phytoene synthase (PSY) plays an essential role in mediating condensation of two geranylgeranyl diphosphate molecules, the first committed step in carotenogenesis. PSY are nuclear enzymes encoded by a small gene family consisting of three paralogous genes (PSY1-3) that have been widely characterized in rice, maize and sorghum.


RESULTS
In wheat, for which yellow pigment content is extremely important for flour colour, only PSY1 has been extensively studied because of its association with QTLs reported for yellow pigment whereas PSY2 has been partially characterized. Here, we report the isolation of bread wheat PSY3 genes from a Renan BAC library using Brachypodium as a model genome for the Triticeae to develop Conserved Orthologous Set markers prior to gene cloning and sequencing. Wheat PSY3 homoeologous genes were sequenced and annotated, unravelling their novel structure associated with intron-loss events and consequent exonic fusions. A wheat PSY3 promoter region was also investigated for the presence of cis-acting elements involved in the response to abscisic acid (ABA), since carotenoids also play an important role as precursors of signalling molecules devoted to plant development and biotic/abiotic stress responses. Expression of wheat PSYs in leaves and roots was investigated during ABA treatment to confirm the up-regulation of PSY3 during abiotic stress.


CONCLUSIONS
We investigated the structural and functional determinisms of PSY genes in wheat. More generally, among eudicots and monocots, the PSY gene family was found to be associated with differences in gene copy numbers, allowing us to propose an evolutionary model for the entire PSY gene family in Grasses.
INRA-UMR 1095 Génétique Diversité Ecophysiologie des Céréales (GDEC), Clermont-Ferrand, France.
Bianca
B
Dibari
Florent
F
Murat
Audrey
A
Chosson
Véronique
V
Gautier
Charles
C
Poncet
Philippe
P
Lecomte
Ingrid
I
Mercier
Hélène
H
Bergès
Caroline
C
Pont
Antonio
A
Blanco
Jérôme
J
Salse
D000040:Abscisic Acid / Q000494:pharmacology; D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism; D002338:Carotenoids / Q000378:metabolism*; D019143:Evolution, Molecular; D005091:Exons; D018745:Genome, Plant; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D007438:Introns; D018515:Plant Leaves / Q000201:enzymology / Q000235:genetics; D010940:Plant Proteins / Q000235:genetics* / Q000378:metabolism; D018517:Plant Roots / Q000201:enzymology / Q000235:genetics; D011401:Promoter Regions, Genetic; D040641:Quantitative Trait Loci; D014908:Triticum / Q000201:enzymology / Q000235:genetics*; D015854:Up-Regulation / Q000187:drug effects
D010940:Plant Proteins; D002338:Carotenoids; D000040:Abscisic Acid; D019883:Alkyl and Aryl Transferases; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase