New papers from the Schwab lab.
The Strawberry Pathogenesis-Related 10 (PR-10) Fra a proteins control flavonoid biosynthesis by binding to metabolic intermediates.
Ana Casanal, Ulrich Zander, Cristina Munoz, Florine Dupeux, Irene Luque, Miguel Angel Botella, Wilfried Schwab, Victoriano Valpuesta, Jose A. Marquez
Journal of Biological Chemistry
Pathogenesis-related 10 (PR-10) proteins are involved in many aspects of plant biology but their molecular function is still unclear. They are related by sequence and structural homology to mammalian lipid transport and plant abscisic acid receptor proteins, and are predicted to have cavities for ligand binding. Recently, three new members of the PR-10 family, the Fra a proteins, have been identified in strawberry, where they are required for the activity of the flavonoid biosynthesis pathway, which is essential for the development of color and flavor in fruits. Here we show that Fra a proteins bind natural flavonoids with different selectivity and affinities in the low ?M range. The structural analysis of Fra a 1 E and a Fra a 3-catechin complex indicates that loops L3, L5 and L7, surrounding the ligand-binding cavity show significant flexibility in the apo forms, but close over the ligand in the Fra a 3-catechin complex. Our findings provide mechanistic insight on the function of Fra a proteins and suggest that PR-10 proteins, which are widespread in plants may play a role in the control of secondary metabolic pathways by binding to metabolic intermediates.
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Metabolic interaction between anthoxyanin and lignin biosynthesis is associated with peroxidase FaPRX27 in strawberry fruit.
Ludwig Ring, Su-Ying Yeh, Stephanie Hücherig, Thomas Hoffmann, Rosario Blanco-Portales, Mathieu Fouche, Carmen Villatoro, Beatrice Denoyes, Amparo Monfort, José L. Caballero, Juan Munoz-Blanco, Jonathan Gershenson, Wilfried Schwab
Plant phenolics have drawn increasing attention due to their potential nutritional benefits. Although the basic reactions of the phenolics biosynthetic pathways in plants have been intensively analyzed, the regulation of their accumulation and flux through the pathway is not that well established. The aim of this study was to use a strawberry (Fragaria × ananassa) microarray to investigate gene expression patterns associated with the accumulation of phenylpropanoids, flavonoids, and anthocyanins in strawberry fruit. An examination of the transcriptome, coupled with metabolite profiling data from different commercial varieties, was undertaken to identify genes whose expression correlated with altered phenolics composition. Seventeen comparative microarray analyses revealed 15 genes that were differentially (more than 200-fold) expressed in phenolics-rich versus phenolics-poor varieties. The results were validated by heterologous expression of the peroxidase FaPRX27 gene, which showed the highest altered expression level (more than 900-fold). The encoded protein was functionally characterized and is assumed to be involved in lignin formation during strawberry fruit ripening. Quantitative trait locus analysis indicated that the genomic region of FaPRX27 is associated with the fruit color trait. Down-regulation of the CHALCONE SYNTHASE gene and concomitant induction of FaPRX27 expression diverted the flux from anthocyanins to lignin. The results highlight the competition of the different phenolics pathways for their common precursors. The list of the 15 candidates provides new genes that are likely to impact polyphenol accumulation in strawberry fruit and could be used to develop molecular markers to select phenolics-rich germplasm.
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Premature and ectopic anthocyanin formation by silencing of anthocyanidin reductase in strawberry (Fragaria x ananassa).
Thilo C. Fischer, Beate Mirbeth, Judith Rentsch, Corina Sutter, Ludwig Ring, Henryk Flachowsky, Ruth Habegger, Thomas Hoffmann, Magda-Viola Hanke, Wilfried Schwab
Strawberry (Fragaria × ananassa) is a fruit crop with a distinct biphasic flavonoid biosynthesis. Whereas, in the immature receptacle, high levels of proanthocyanidins accumulate, which are associated with herbivore deterrence and pathogen defense, the prominent color-giving anthocyanins are primarily produced in ripe ‘fruits’ helping to attract herbivores for seed dispersal.
Here, constitutive experimental down-regulation of one branch of proanthocyanidin biosynthesis was performed.
As a result, the proportion of epicatechin monomeric units within the proanthocyanidin polymer chains was reduced, but this was not the case for the epicatechin starter unit. Shortened chain lengths of proanthocyanidins were also observed. All enzymatic activities for the production of color-giving anthocyanins were already present in unripe fruits at levels allowing a striking red anthocyanin phenotype in unripe fruits of the RNAi silencing lines. An immediately recognizable phenotype was also observed for the stigmata of flowers, which is another epicatechin-forming tissue.
Thus, the down-regulation of anthocyanidin reductase (ANR) induced a redirection of the proanthocyanidin pathway, leading to premature and ectopic anthocyanin biosynthesis via enzymatic glycosylation as the alternative pathway. This redirection is also seen in flavonol biosynthesis, which is paralleled by higher pollen viability in silencing lines. ANRi transgenic lines of strawberry provide a versatile tool for the study of the biological functions of proanthocyanidins.
