A recessive mutation in muscadine grapes causes berry color-loss without influencing anthocyanin pathway

Transcriptome profiling and mutational analysis suggest a potential deficiency in anthocyanin transport by glutathione S-transferases and/or degradation mechanisms that might cause unpigmented berries. Anthocyanins, a major class of flavonoids, are important pigments of grape berries. Despite the recent discovery of the genetic cause underlying the loss of color, the metabolomic and molecular responses are unknown. Anthocyanin quantification among diverse berry color muscadines suggests that all genotypes could produce adequate anthocyanin quantities, irrespective of berry color. Transcriptome profiling of contrasting color muscadine genotypes proposes a potential deficiency that occurs within the anthocyanin transport and/or degradation mechanisms and might cause unpigmented berries. Genome-wide association studies highlighted a region on chromosome-4, comprising several genes encoding glutathione S-transferases involved in anthocyanin transport. Sequence comparison among genotypes reveals the presence of two GST4b alleles that differ by substituting the conserved amino acid residue Pro(171)-to-Leu. Molecular dynamics simulations demonstrate that GST4b2-Leu(171) encodes an inactive protein due to modifications within the H-binding site. Population genotyping suggests the recessive inheritance of the unpigmented trait with a GST4b2/2 homozygous. A model defining colorless muscadines' response to the mutation stimulus, avoiding the impact of trapped anthocyanins within the cytoplasm is established.

Automated summary

Transcriptome profiling and mutational analysis suggest a potential deficiency in anthocyanin transport and degradation mechanisms that may cause unpigmented berries. Genome-wide association studies highlight a region on chromosome-4 and its relationship with genes encoding glutathione S-transferases. The presence of GST4b2/2 alleles is associated with the unpigmented trait.