Abstract

BackgroundRed colour in kiwifruit results from the presence of anthocyanin pigments. Their expression, however, is complex, and varies among genotypes, species, tissues and environments. An understanding of the biosynthesis, physiology and genetics of the anthocyanins involved, and the control of their expression in different tissues, is required. A complex, the MBW complex, consisting of R2R3-MYB and bHLH transcription factors together with a WD-repeat protein, activates anthocyanin 3-O-galactosyltransferase (F3GT1) to produce anthocyanins. We examined the expression and genetic control of anthocyanins in flowers of Actinidia hybrid families segregating for red and white petal colour.ResultsFour inter-related backcross families between Actinidia chinensis Planch. var. chinensis and Actinidia eriantha Benth. were identified that segregated 1:1 for red or white petal colour. Flower pigments consisted of five known anthocyanins (two delphinidin-based and three cyanidin-based) and three unknowns. Intensity and hue differed in red petals from pale pink to deep magenta, and while intensity of colour increased with total concentration of anthocyanin, no association was found between any particular anthocyanin data and hue. Real time qPCR demonstrated that an R2R3 MYB, MYB110a, was expressed at significant levels in red-petalled progeny, but not in individuals with white petals.A microsatellite marker was developed that identified alleles that segregated with red petal colour, but not with ovary, stamen filament, or fruit flesh colour in these families. The marker mapped to chromosome 10 in Actinidia.The white petal phenotype was complemented by syringing Agrobacterium tumefaciens carrying Actinidia 35S::MYB110a into the petal tissue. Red pigments developed in white petals both with, and without, co-transformation with Actinidia bHLH partners. MYB110a was shown to directly activate Actinidia F3GT1 in transient assays.ConclusionsThe transcription factor, MYB110a, regulates anthocyanin production in petals in this hybrid population, but not in other flower tissues or mature fruit. The identification of delphinidin-based anthocyanins in these flowers provides candidates for colour enhancement in novel fruits.

Highlights

  • Red colour in kiwifruit results from the presence of anthocyanin pigments

  • In all plants studied to date, activation of the anthocyanin pathway is through a 'MBW complex' consisting of R2R3-MYB and bHLH transcription factors (TFs) and a WD-repeat (WDR) protein that may facilitate protein-protein interactions [7,8,9]

  • In our study we found that both delphinidin compounds were present in the petals in a proportion of the progeny genotypes within three of the four families resulting from a backcross between A. eriantha and A. chinensis var. chinensis

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Summary

Introduction

Red colour in kiwifruit results from the presence of anthocyanin pigments Their expression, is complex, and varies among genotypes, species, tissues and environments. The anthocyanin pigments that are produced by a branch of the flavonoid pathway are important as insect and animal attractants, for pollination and seed dispersal. They are of increasing importance as quality traits in commercial fruit crops, for the colours they produce and for their potential human health benefits. In all plants studied to date, activation of the anthocyanin pathway is through a 'MBW complex' consisting of R2R3-MYB and bHLH TFs and a WD-repeat (WDR) protein that may facilitate protein-protein interactions [7,8,9]. In addition to the MYBs that are part of the activation complex, distinct R2R3- and R3-MYBs with a repressive action have been identified that may allow for feedback modulation of the amount of anthocyanin produced [10,11,12,13,14]

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