A dominant allele at the D locus (also known as I in diploid potato) is required for the synthesis of red and purple anthocyanin pigments in tuber skin. It has previously been reported that D maps to a region of chromosome 10 that harbors one or more homologs of Petuniaan2, an R2R3 MYB transcription factor that coordinately regulates the expression of multiple anthocyanin biosynthetic genes in the floral limb. To test whether D acts similarly in tuber skin, RT-PCR was used to evaluate the expression of flavanone 3-hydroxylase (f3h), dihydroflavonol 4-reductase (dfr) and flavonoid 3′,5′-hydroxylase (f3′5′h). All three genes were expressed in the periderm of red- and purple-skinned clones, while dfr and f3′5′h were not expressed, and f3h was only weakly expressed, in white-skinned clones. A potato cDNA clone with similarity to an2 was isolated from an expression library prepared from red tuber skin, and an assay developed to distinguish the two alleles of this gene in a diploid potato clone known to be heterozygous Dd. One allele was observed to cosegregate with pigmented skin in an F1 population of 136 individuals. This allele was expressed in tuber skin of red- and purple-colored progeny, but not in white tubers, while other parental alleles were not expressed in white or colored tubers. The allele was placed under the control of a doubled 35S promoter and transformed into the light red-colored cultivar Désirée, the white-skinned cultivar Bintje, and two white diploid clones known to lack the functional allele of D. Transformants accumulated pigment in tuber skin, as well as in other tissues, including young foliage, flower petals, and tuber flesh.

The potato P locus is required for the production of blue/purple anthocyanin pigments in any tissue of the potato plant such as tubers, flowers, or stems. We have previously reported, based on RFLP mapping in tomato, that the gene coding for the anthocyanin biosynthetic enzyme flavonoid 3',5'-hydroxylase (f3'5'h) maps to the same region of the tomato genome as P maps in potato. To further evaluate this association a Petunia f3'5'h gene was used to screen a potato cDNA library prepared from purple-colored flowers and stems. Six positively hybridizing cDNA clones were sequenced and all appeared to be derived from a single gene that shares 85% sequence identity at the amino acid level with Petunia f3'5'h. The potato gene cosegregated with purple tuber color in a diploid F1 sub-population of 37 purple and 25 red individuals and was found to be expressed in tuber skin only in the presence of the anthocyanin regulatory locus I. A potato f3'5'h cDNA clone was placed under the control of a doubled CaMV 35S promoter and introduced into the red-skinned cultivar 'Desiree'. Tuber and stem tissues that are colored red in Desiree were purple in nine of 17 independently transformed lines.

Interest in anthocyanin-pigmented potato tuber Xesh is increasing. To genetically map and characterize loci that inXuence this trait, diploid potato clone 10618-01, which has partially pigmented Xesh, was crossed with diploid 320-02, which has white Xesh. Almost all progeny exhibited purple coloration in the Xesh, with some clones having only a small percentage of tissue pigmented, other clones having most tissue pigmented, and the majority of clones showing intermediate color phenotypes. The two parents and 228 progeny were genotyped with 493 AFLP, 8 CAPS, and 13 SSR markers. QTLs inXuencing extent of Xesh pigmentation were detected on chromosomes 5, 8, and 9. The potato homolog of Petunia an1, a basic helix-loophelix (bHLH) transcriptional regulator of anthocyanin biosynthesis, was found to co-localize with the QTL on chromosome 9. A CAPS marker based on this gene was used to evaluate a collection of 21 tetraploid potato clones with highly or fully pigmented red or purple Xesh, as well as 53 cultivars with white or yellow Xesh. All 21 pigmentedXesh clones shared a marker allele that was present in only 21 of the 53 white and yellow clones, suggesting that a common bHLH allele contributes toward, although it is clearly not suYcient for, highly or fully pigmented tuber Xesh in cultivated potato.

No abstract

Figure 5, on page 273, was not reproduced correctly. The correct version is printed below. RT-PCR expression analysis of the f3¢5¢h transgene. Total RNA was isolated from leaves of De´sire´e and of De´sire´e transformed with f3¢5¢h. RNA was treated with DNase to eliminate genomic DNA, converted into cDNA, and then subjected to PCR with primers 4F and 4R (Fig. 2a). Amplification products were separated on a 2% agarose gel. Transformed De´sire´e plants included those with a purple tuber phenotype, as well as those indistinguishable from wild type (not purple)The online version of the original article can be found at http:// dx