An R2R3 MYB transcription factor determines red petal colour in an Actinidia (kiwifruit) hybrid population

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.

Genetics of Pigment Biosynthesis and Degradation

“…The possibility of a regulatory action underpinning the phenotype is supported by experiments using transient over-expression of MYB TFs in kiwifruit fruit or petals, as this results in development of red patches suggesting that the biosynthetic pathway is functional once activated (Montefiori et al 2011;Fraser et al 2013).…”

“…purpurea, delphinidin derivatives have been identified which have hydroxyl groups in the 3′ and 5′ positions of the B-ring, implying the activity of the F3′5′H (as well as the F3′H). Delphinidin derivatives have been identified in petals of A. eriantha, suggesting expression of these hydroxylases in flowers (Fraser et al 2013). …”

“…Anthocyanin-related MYBs are highly conserved within the R2R3 region of their MYB domains, while there is less conservation in the C-termini of the proteins where transcriptional activation or repression motifs are present (Feller et al 2011). In kiwifruit, two different anthocyanin-activating MYBs have been identified, MYB10 and MYB110, which are almost identical in the conserved MYB domain (95 % identity), but differ at the C-termini, mainly due to the presence of an indel of 23 amino acids (Fraser et al 2013). Both MYBs are functional and able to induce anthocyanin biosynthesis.…”

“…Both MYBs are functional and able to induce anthocyanin biosynthesis. MYB110 has been shown to determine red petal pigmentation in A. eriantha flowers (Fraser et al 2013) and cosegregates with red-fleshed fruit colour in an interspecific A. macrosperma x A. melanandra population. Individuals which have inherited a dominant allele of the MYB110 gene from the red parent (A. melanandra) have red-fleshed fruit (Fraser et al 2006).…”

Identification of Anthocyanins Compositions and Functional Analysis of An Anthocyanin Activator in <em>Solanum nigrum</em> Fruits

“…However, intense anthocyanins accumulation occurred when exogenous MYB was individually expressed in other plants. For example, kiwifruit AcMYB110 individually induced anthocyanins accumulation when ectopically expressed in tobacco leaves without ectopic expression of any other bHLH or WD40 as a partner [20]. Several MYB anthocyanins activators have also been identified in Solanaceae plants.…”