Abstract
BackgroundCarotenoids 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.ResultsIn 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.ConclusionsWe 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.
Highlights
Carotenoids are isoprenoid pigments, essential for photosynthesis and photoprotection in plants
We report evidence that the wheat phytoene synthase (PSY) gene family consists of three paralogous genes and that PSY3 is characterized by a novel gene structure, consequence of intron loss events
PSY3 gene sequencing and mapping in bread wheat We recently reassessed the syntenic relationships within monocots and developed tools to identify precisely chromosometo-chromosome orthologous relationships and derived Conserved Orthologous Set (COS) markers, [27,28]
Summary
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. Carotenoids have several important functions, essential for plant development as: (i) they serve as accessory pigments to harvest light for photosynthesis and constitute the basic structural units of photosynthetic apparatus and (ii) they act as photoprotectors for plants to adapt to high light stress [2]. PSY is coded by a small gene family, which had been already shown to exist throughout the Grasses [5] and which consists of three paralogous genes that have been identified and characterized in rice, maize and sorghum. OsPSY3 plays a specialized role as it is not regulated by light but is strongly inducible in roots by high salt concentrations and/or drought
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