title: The Onion (Allium cepaL.)R2R3-MYBGeneMYB1Regulates Anthocyanin Biosynthesis.
abstract: Bulb color is an important consumer trait for onion (Allium cepaL., Allioideae, Asparagales). The bulbs accumulate a range of flavonoid compounds, including anthocyanins (red), flavonols (pale yellow), and chalcones (bright yellow). Flavonoid regulation is poorly characterized in onion and in other plants belonging to the Asparagales, despite being a major plant order containing many important crop and ornamental species. R2R3-MYB transcription factors associated with the regulation of distinct branches of the flavonoid pathway were isolated from onion. These belonged to sub-groups (SGs) that commonly activate anthocyanin (SG6, MYB1) or flavonol (SG7, MYB29) production, or repress phenylpropanoid/flavonoid synthesis (SG4, MYB4, MYB5).MYB1was demonstrated to be a positive regulator of anthocyanin biosynthesis by the induction of anthocyanin production in onion tissue when transiently overexpressed and by reduction of pigmentation when transiently repressed via RNAi. Furthermore, ectopic red pigmentation was observed in garlic (Allium sativumL.) plants stably transformed with a construct for co-overexpression ofMYB1and abHLHpartner.MYB1also was able to complement the acyanic petal phenotype of a definedR2R3-MYBanthocyanin mutant inAntirrhinum majus of the asterid clade of eudicots. The availability of sequence information for flavonoid-related MYBs from onion enabled phylogenetic groupings to be determined across monocotyledonous and dicotyledonous species, including the identification of characteristic amino acid motifs. This analysis suggests that divergent evolution of the R2R3-MYB family has occurred between Poaceae/Orchidaceae and Allioideae species. The DNA sequences identified will be valuable for future analysis of classical flavonoid genetic loci inAlliumcrops and will assist the breeding of these important crop species.
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Palmerston North, New Zealand.
authors.forename: Kathy E
authors.initials: KE
authors.lastname: Schwinn
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Palmerston North, New Zealand.
authors.forename: Hanh
authors.initials: H
authors.lastname: Ngo
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Christchurch, New Zealand.
authors.forename: Fernand
authors.initials: F
authors.lastname: Kenel
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Palmerston North, New Zealand.
authors.forename: David A
authors.initials: DA
authors.lastname: Brummell
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Palmerston North, New Zealand.
authors.forename: Nick W
authors.initials: NW
authors.lastname: Albert
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Christchurch, New Zealand.
authors.forename: John A
authors.initials: JA
authors.lastname: McCallum
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Christchurch, New Zealand.
authors.forename: Meeghan
authors.initials: M
authors.lastname: Pither-Joyce
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Auckland, New Zealand.
authors.forename: Ross N
authors.initials: RN
authors.lastname: Crowhurst
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Christchurch, New Zealand.
authors.forename: Colin
authors.initials: C
authors.lastname: Eady
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited Palmerston North, New Zealand.
authors.forename: Kevin M
authors.initials: KM
authors.lastname: Davies
keywords: Asparagales; R2R3-MYB; anthocyanin; garlic; onion; regulation; transgenic