title: Induction of anthocyanin in the inner epidermis of red onion leaves by environmental stimuli and transient expression of transcription factors.
abstract: Novel imaging approaches have allowed measurements of the anthocyanin induction in onion epidermal cells that can be induced through water stress or transient expression of exogenous transcription factors. Environmental and genetic mechanisms that allow the normally colourless inner epidermal cells of red onion (Allium cepa) bulbs to accumulate anthocyanin were quantified by both absorbance ratios and fluorescence. We observed that water-stressing excised leaf segments induced anthocyanin formation, and fluorescence indicated that this anthocyanin was spectrally similar to the anthocyanin in the outer epidermal cells. This environmental induction may require a signal emanating from the leaf mesophyll, as induction did not occur in detached epidermal peels. Exogenous transcription factors that successfully drive anthocyanin biosynthesis in other species were also tested through transient gene expression using particle bombardment. Although the petunia R2R3-MYB factor AN2 induced anthocyanin in both excised leaves and epidermal peels, several transcription factors including maize C1 and Lc inhibited normal anthocyanin development in excised leaves. This inhibition may be due to moderate levels of conservation between the exogenous transcription factors and endogenous Allium transcription factors. The over-expressed exogenous transcription factors cannot drive anthocyanin biosynthesis themselves, but bind to the endogenous transcription factors and prevent them from driving anthocyanin biosynthesis.
authors.affiliation: School of Biological Sciences, The University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand.
authors.forename: Elizabeth J
authors.initials: EJ
authors.lastname: Wiltshire
authors.affiliation: The New Zealand Institute for Plant & Food Research Limited, PO Box 4704, Christchurch, 8140, New Zealand.|New Zealand Agriseeds, 2547 Old West Coast Road, RD1, Christchurch, 7671, New Zealand.
authors.forename: Colin C
authors.initials: CC
authors.lastname: Eady
authors.affiliation: School of Biological Sciences, The University of Canterbury, Private Bag 4800, Christchurch, 8140, New Zealand. david.collings@newcastle.edu.au.|School of Environmental and Life Sciences, The University of Newcastle, Callaghan, NSW, 2308, Australia. david.collings@newcastle.edu.au.
authors.forename: David A
authors.identifier: http://orcid.org/0000-0003-3863-5979
authors.initials: DA
authors.lastname: Collings
mesh_terms: D000872:Anthocyanins / Q000378:metabolism*; D018506:Gene Expression Regulation, Plant / Q000235:genetics / Q000502:physiology; D019697:Onions / Q000235:genetics / Q000378:metabolism*; D018515:Plant Leaves / Q000235:genetics / Q000378:metabolism*; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism*; D030821:Plants, Genetically Modified / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*
chemical_list: D000872:Anthocyanins; D010940:Plant Proteins; D014157:Transcription Factors
keywords: Allium cepa; Anthocyanin induction, epidermal peel, particle bombardment; Transcription factor; Transient gene expression