title: Isolation and functional characterisation of banana phytoene               synthase genes as potential cisgenes.
abstract: Carotenoids occur in all photosynthetic organisms where they protect photosystems from auto-oxidation, participate in photosynthetic energy transfer and are secondary metabolites. Of the more than 600 known plant carotenoids, few can be converted into vitamin A by humans and so these pro-vitamin A carotenoids (pVAC) are important in human nutrition. Phytoene synthase (PSY) is a key enzyme in the biosynthetic pathway of pVACs and plays a central role in regulating pVAC accumulation in the edible portion of crop plants. Banana is a major commercial crop and serves as a staple crop for more than 30 million people. There is natural variation in fruit pVAC content across different banana cultivars, but this is not well understood. Therefore, we isolated PSY genes from banana cultivars with relatively high (cv. Asupina) and low (cv. Cavendish) pVAC content. We provide evidence that PSY in banana is encoded by two paralogs (PSY1 and PSY2), each with a similar gene structure to homologous genes in other monocots. Further, we demonstrate that PSY2 is more highly expressed in fruit pulp compared to leaf. Functional analysis of PSY1 and PSY2 in rice callus and E. coli demonstrates that both genes encode functional enzymes, and that Asupina PSYs have approximately twice the enzymatic activity of the corresponding Cavendish PSYs. These results suggest that differences in PSY enzyme activity contribute significantly to the differences in Asupina and Cavendish fruit pVAC content. Importantly, Asupina PSY genes could potentially be used to generate new cisgenic or intragenic banana cultivars with enhanced pVAC content.
authors: Centre for Tropical Crops and Biocommodities, Queensland University of Technology, 2 George Street, Brisbane, QLD, 4001, Australia. b.mlalazi@qut.edu.au
authors: Bulukani
authors: B
authors: Mlalazi
authors: Ralf
authors: R
authors: Welsch
authors: Priver
authors: P
authors: Namanya
authors: Harjeet
authors: H
authors: Khanna
authors: R Jason
authors: RJ
authors: Geijskes
authors: Mark D
authors: MD
authors: Harrison
authors: Rob
authors: R
authors: Harding
authors: James L
authors: JL
authors: Dale
authors: Marion
authors: M
authors: Bateson
mesh_terms: D019883:Alkyl and Aryl Transferases / Q000235:genetics* / Q000378:metabolism*; D002338:Carotenoids / Q000378:metabolism; D003001:Cloning, Molecular; D004926:Escherichia coli / Q000235:genetics; D018506:Gene Expression Regulation, Plant; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D028521:Musa / Q000235:genetics*; D009928:Organ Specificity; D012275:Oryza / Q000235:genetics / Q000378:metabolism; D010802:Phylogeny; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified
chemical_list: D010940:Plant Proteins; D002338:Carotenoids; D019883:Alkyl and Aryl Transferases; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase