Färberreben (Teinturiers) sowie rote Farbmutanten weißer Qualitätsrebsorten entstanden durch <em>VvmybA</em>-bedingte Mutationen am Beerenfarblokus

Abstract

In this work, the color mutations of seven red clones of famous grapevine varieties from the German-speaking area were identified by analyzing the transcription factor genes located at the berry color locus (Chr 2, ca. 14,2 Mb) VvmybA1, VvmybA2 and VvmybA3. Both, `Silvaner Rot´ and `Müller-Thurgau Rot´ showed the most commonly found allele MybA1b, whereas the other color mutations were not described in literature so far. The color-related mutations in `Elbling Rot´ (VvmybA313, homologous recombination of VvmybA3 and VvmybA1) as `Räuschling Rot´ and `Kernling´ (VvmybA232a / VvmybA232b, both homologous recombination of VvmybA2 and VvmybA3) most likely arose via the conservative synthesis-dependant strand annealing mechanism (SDSA) that uses a homologous region as template for the repair of a double strand break (DSB). In contrast, `Riesling Rot´ and `Silvaner Blau´ showed the same functional gene variant (VvmybA31) that putatively arose by means of the non-conservative single-strand annealing mechanism (SSA) analogous to the MybA1b allele. Whereas in the case of the MybA1b allele the retrotransposon Gret1 and one LTR are just missing, `Riesling Rot´ and `Silvaner Blau´ both show a deletion of the complete area (ca. 70 kb) between VvmybA1 and VvmybA3. Based on the SSR-marker analysis of the homozygous selfed lines, the specific mutations could be linked to the haplophases inherited by their respective parents. Hence, it was possible to show that for all analyzed color mutants, expect `Räuschling Rot´, a white ancestor inherited the mutation-bearing haplophase and therefore the mutation had to have arisen in the white clones. Additionally, byanalyzing the anthocyanin composition in ripe berries and by evaluating the coloration of autumn leaves, two unique characteristics linked to specific mutations could be identified. All cultivars bearing the MybA1b allele exclusively showed red coloration of the autumn leaves whereas the color mutants with the VvmybA2-related mutations (`Räuschling Rot´ and `Kernling´) possessed a 95% proportion of cyanidin- 3-O-glucoside in ripe berry skins. Furthermore, the molecular origin of the teinturier grapes could be identified and the effects of the mutation on the phenotype were evaluated. A 408 bp repeat (2x, 3x and 5x possible) in the promoter region of VvmybA1 is putatively leading to the autoregulation of the locus and therefore to ectopic formation of anthocyanins independently of ripening. The origin of the mutation goes back to the variety `Teinturier´ (a periclinal chimera) and was then passed on to the next generation. In a putative model, the MYBA1 protein can bind on its own promoter due to additional MYB binding sites in the repeat and is therefore leading to an enhanced VvmybA1 expression. Additionally, by analyzing the leaf samples of `Teinturier´ clones and berry samples of the direct progeny, it was possible to show that the repeat number is strongly correlating with an increase of the anthocyanin concentration. Presumably due to the retrotransposon Gret1 and further repetitive DNA elements, the berry color locus of Vitis vinifera displays a hotspot for homologous recombinations which can lead to plenty functional VvmybA variants and drive therefore the evolution of the berry color continuously forward.