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SUMMARY: Plant adaptation from aquatic to terrestrial environments required modifications to cell wall structure and function to provide tolerance to new abiotic and biotic stressors. Here, we investigate the nature and function of red auronidin pigment accumulation in the cell wall of the liverwort Marchantia polymorpha. Transgenic plants with auronidin production either constitutive or absent were analysed for their cell wall properties, including fractionation of polysaccharide and phenolic components. While small amounts of auronidin and other flavonoids were loosely associated with the cell wall, the majority of the pigments were tightly associated, similar to what is observed in angiosperms for polyphenolics such as lignin. No evidence of covalent binding to a polysaccharide component was found: we propose auronidin is present in the wall as a physically entrapped large molecular weight polymer. The results suggested auronidin is a dual function molecule that can both screen excess light and increase wall strength, hydrophobicity and resistance to enzymatic degradation by pathogens. Thus, liverworts have expanded the core phenylpropanoid toolkit that was present in the ancestor of all land plants, to deliver a lineage‐specific solution to some of the environmental stresses faced from a terrestrial lifestyle. [ABSTRACT FROM AUTHOR]

Objective: The aim of this study was to assess the ability of polyphenolic extracts from different kiwifruit genotypes to affect tyrosinase enzyme activity and determine potential relationships between tyrosinase inhibition and polyphenolic composition. To date, research on the tyrosinase inhibitory bioactivity of kiwifruit have focused on a single A. chinensis cultivar. Given the numerous genotypes of kiwifruit commercially grown have varying compositions, and a variety of polyphenolic compounds present within each of these cultivars, the full potential of the tyrosinase inhibitory of kiwifruit has not been fully evaluated. Methods: The polyphenolic composition of ethanol extracts from the cortical flesh of 10 kiwifruit genotypes was characterized using high-resolution accurate mass liquid chromatography mass spectrometry. The tyrosinase activity of each extract was measured spectrophotometrically in vitro. Multivariate analysis was subsequently conducted to identify kiwifruit compounds that may correlate with tyrosinase enzyme inhibition. Results: The kiwifruit extracts displayed a broad range of tyrosinase inhibitory activity with some extracts having minimal or no inhibitory effect while the most potent extract showed 33.54 ± 1.59% inhibition (P < 0.01) at a dose of 125 µg/mL. Multivariate analysis of polyphenolic and tyrosinase inhibition data identified that polymeric procyanidins likely explain the tyrosinase inhibitory ability and the differences between genotypes. This was confirmed by the high relative concentrations of these procyanidins in extracts that exhibited tyrosinase inhibitory properties, while being absent or at low concentrations in extracts that did not. Conclusion: Our findings demonstrate that some polyphenol kiwifruit extracts inhibit tyrosinase activity. The variability in the tyrosinase inhibitory activity of polyphenol extracts from 10 kiwifruit genotypes is attributed to the differences in the relative concentrations of polymeric procyanidins in these extracts. These results highlight that the tyrosinase inhibitory properties of kiwifruit genotypes could be examined further to support the development of kiwifruit-based cosmetic products. [ABSTRACT FROM AUTHOR]

Abstract Background The polyphenolic products of the phenylpropanoid pathway, including proanthocyanidins, anthocyanins and flavonols, possess antioxidant properties that may provide health benefits. To investigate the genetic architecture of control of their biosynthesis in apple fruit, various polyphenolic compounds were quantified in progeny from a 'Royal Gala' × 'Braeburn' apple population segregating for antioxidant content, using ultra high performance liquid chromatography of extracts derived from fruit cortex and skin. Results Construction of genetic maps for 'Royal Gala' and 'Braeburn' enabled detection of 79 quantitative trait loci (QTL) for content of 17 fruit polyphenolic compounds. Seven QTL clusters were stable across two years of harvest and included QTLs for content of flavanols, flavonols, anthocyanins and hydroxycinnamic acids. Alignment of the parental genetic maps with the apple whole genome sequence in silico enabled screening for co-segregation with the QTLs of a range of candidate genes coding for enzymes in the polyphenolic biosynthetic pathway. This co-location was confirmed by genetic mapping of markers derived from the gene sequences. Leucoanthocyanidin reductase (LAR1) co-located with a QTL cluster for the fruit flavanols catechin, epicatechin, procyanidin dimer and five unknown procyanidin oligomers identified near the top of linkage group (LG) 16, while hydroxy cinnamate/quinate transferase (HCT/HQT) co-located with a QTL for chlorogenic acid concentration mapping near the bottom of LG 17. Conclusion We conclude that LAR1 and HCT/HQT are likely to influence the concentration of these compounds in apple fruit and provide useful allele-specific markers for marker assisted selection of trees bearing fruit with healthy attributes.

Abstract Background The control of plant anthocyanin accumulation is via transcriptional regulation of the genes encoding the biosynthetic enzymes. A key activator appears to be an R2R3 MYB transcription factor. In apple fruit, skin anthocyanin levels are controlled by a gene called MYBA or MYB1, while the gene determining fruit flesh and foliage anthocyanin has been termed MYB10. In order to further understand tissue-specific anthocyanin regulation we have isolated orthologous MYB genes from all the commercially important rosaceous species. Results We use gene specific primers to show that the three MYB activators of apple anthocyanin (MYB10/MYB1/MYBA) are likely alleles of each other. MYB transcription factors, with high sequence identity to the apple gene were isolated from across the rosaceous family (e.g. apples, pears, plums, cherries, peaches, raspberries, rose, strawberry). Key identifying amino acid residues were found in both the DNA-binding and C-terminal domains of these MYBs. The expression of these MYB10 genes correlates with fruit and flower anthocyanin levels. Their function was tested in tobacco and strawberry. In tobacco, these MYBs were shown to induce the anthocyanin pathway when co-expressed with bHLHs, while over-expression of strawberry and apple genes in the crop of origin elevates anthocyanins. Conclusions This family-wide study of rosaceous R2R3 MYBs provides insight into the evolution of this plant trait. It has implications for the development of new coloured fruit and flowers, as well as aiding the understanding of temporal-spatial colour change.

Kiwifruit (Actinidia spp.) is a recently domesticated fruit crop with several novel‐coloured cultivars being developed. Achieving uniform fruit flesh pigmentation in red genotypes is challenging. To investigate the cause of colour variation between fruits, we focused on a red‐fleshed Actinidia chinensis var. chinensis genotype. It was hypothesized that carbohydrate supply could be responsible for this variation. Early in fruit development, we imposed high or low (carbon starvation) carbohydrate supplies treatments; carbohydrate import or redistribution was controlled by applying a girdle at the shoot base. Carbon starvation affected fruit development as well as anthocyanin and carbohydrate metabolite concentrations, including the signalling molecule trehalose 6‐phosphate. RNA‐Seq analysis showed down‐regulation of both gene‐encoding enzymes in the anthocyanin and carbohydrate biosynthetic pathways. The catalytic trehalose 6‐phosphate synthase gene TPS1.1a was down‐regulated, whereas putative regulatory TPS7 and TPS11 were strongly up‐regulated. Unexpectedly, under carbon starvation MYB10, the anthocyanin pathway regulatory activator was slightly up‐regulated, whereas MYB27 was also up‐regulated and acts as a repressor. To link these two metabolic pathways, we propose a model where trehalose 6‐phosphate and the active repressor MYB27 are involved in sensing the carbon starvation status. This signals the plant to save resources and reduce the production of anthocyanin in fruits. In carbon‐starved red‐fleshed kiwifruit, both carbohydrate and anthocyanin concentrations were greatly reduced. Our model suggests that anthocyanin biosynthesis was actively repressed by MYB27 via trehalose 6‐phosphate signalling to conserve carbon. [ABSTRACT FROM AUTHOR]