Independent mutations in a single locus, the transcriptional factor MYB10, control natural variation in fruit color among Fragaria species

External and internal fruit color are important traits in strawberry (Fragaria spp.) breeding programs, where different preferences are sought depending on whether the fruits are produced for fresh consumption or processing. Therefore, there is a great interest in the development of predictive markers that effectively speed the development of new cultivars with increased consumer acceptance and/or which address processed fruit industry´s preferences. In order to identify loci controlling fruit color variation, two mapping populations were generated: one crossing diploid F. vesca parentals and another interspecific population between two octoploid species: the cultivated and the Chilean strawberry, F. x ananassa and F. chiloensis. Both populations allowed the detection of a QTL spanning a region of the F. vesca linkage group 1 (LG I) that includes the MYB10 gene, a known key regulator of anthocyanin biosynthesis. Mapping by sequencing in the F. vesca population revealed an LTR retrotransposon inserted in the third exon of FvMYB10, which produces a premature stop codon, and co-segregates with white fruits in the entire population. Genotyping by Sanger sequencing of additional white-fruited F. vesca accessions resulted in the identification of another three independent mutations in MYB10, two of them not previously described1. In octoploid strawberry, a mayor QTL on LG I-3 controls about 55% variation in internal flesh color and is associated with an insertion in the promoter region of FcMYB10. Similar insertions have been detected in other F. chiloensis accessions bearing white fruits. In all cases, transient over-expression of FvMYB10 restored anthocyanin biosynthesis and red color in fruit flesh and skin, indicating that lack of function of MYB10 was the underlying cause of white fruits in all analyzed cases

Allelic Variation of MYB10 Is the Major Force Controlling Natural Variation in Skin and Flesh Color in Strawberry (Fragaria spp.) Fruit

Independent mutations in the transcription factor MYB10 cause most of the anthocyanin variation observed in diploid woodland strawberry (Fragaria vesca) and octoploid cultivated strawberry (Fragaria x ananassa). The fruits of diploid and octoploid strawberry (Fragaria spp) show substantial natural variation in color due to distinct anthocyanin accumulation and distribution patterns. Anthocyanin biosynthesis is controlled by a clade of R2R3 MYB transcription factors, among which MYB10 is the main activator in strawberry fruit. Here, we show that mutations in MYB10 cause most of the variation in anthocyanin accumulation and distribution observed in diploid woodland strawberry (F. vesca) and octoploid cultivated strawberry (F. xananassa). Using a mapping-by-sequencing approach, we identified a gypsy-transposon in MYB10 that truncates the protein and knocks out anthocyanin biosynthesis in a white-fruited F. vesca ecotype. Two additional loss-of-function mutations in MYB10 were identified among geographically diverse white-fruited F. vesca ecotypes. Genetic and transcriptomic analyses of octoploid Fragaria spp revealed that FaMYB10-2, one of three MYB10 homoeologs identified, regulates anthocyanin biosynthesis in developing fruit. Furthermore, independent mutations in MYB10-2 are the underlying cause of natural variation in fruit skin and flesh color in octoploid strawberry. We identified a CACTA-like transposon (FaEnSpm-2) insertion in the MYB10-2 promoter of red-fleshed accessions that was associated with enhanced expression. Our findings suggest that cis-regulatory elements in FaEnSpm-2 are responsible for enhanced MYB10-2 expression and anthocyanin biosynthesis in strawberry fruit flesh.Peer reviewe

Allelic Variation of MYB10 is the Major Force Controlling Natural Variation of Skin and Flesh Color in Strawberry (Fragaria spp.) fruit

Anthocyanins are the principal color-producing compounds synthesized in developing fruits of strawberry (Fragaria spp.). Substantial natural variation in color have been observed in fruits of diploid and octoploid accessions, resulting from distinct accumulation and distribution of anthocyanins in fruits. Anthocyanin biosynthesis is controlled by a clade of R2R3 MYB transcription factors, among which MYB10 has been shown as the main activator in strawberry fruit. Here, we show that MYB10 mutations cause most of the anthocyanin variation observed in diploid woodland strawberry (F. vesca) and octoploid cultivated strawberry (F. ×ananassa). Using a mapping-by-sequencing approach, we identified a gypsytransposon insertion in MYB10 that truncates the protein and knocks out anthocyanin biosynthesis in a white-fruited F. vesca ecotype. Two additional lossof-function MYB10 mutations were identified among geographically diverse whitefruited F. vesca ecotypes. Genetic and transcriptomic analyses in octoploid Fragaria spp. revealed that FaMYB10-2, one of three MYB10 homoeologs identified, residing in the F. iinumae-derived subgenome, regulates the biosynthesis of anthocyanins in developing fruit. Furthermore, independent mutations in MYB10-2 are the underlying cause of natural variation in fruit skin and flesh color in octoploid strawberry. We identified a CACTA-like transposon (FaEnSpm-2) insertion in the MYB10-2 promoter of red-fleshed accessions that was associated with enhanced expression and anthocyanin accumulation. Our findings suggest that putative cis regulatory elements provided by FaEnSpm-2 are required for high and ectopic MYB10-2 expression and induction of anthocyanin biosynthesis in fruit flesh. We developed MYB10-2 (sub-genome) specific DNA markers for marker-assisted selection that accurately predicted anthocyanin phenotypes in octoploid segregating populations