The origin of saffron. Part 2: The role of polyploidy for saffron secondary metabolites
Evolution and Systematics of Plants and Fungi
Final Report Abstract
Crocus sativus, a triploid flowering plant, is known as the main source of saffron, the world's most expensive spice. Saffron consists of dried stigmas, which possess a unique aroma, bitter flavor, and deep golden-yellow color. This characteristic is due to the plant's metabolites such as crocetin and its glucosyl esters (crocins), and picrocrocin and its aglycone safranal. Historically, saffron was not exclusively associated with C. sativus. Ancient records indicate that various Aegean and eastern Mediterranean civilizations also utilized initially C. cartwrightianus, a species from the Aegean islands commonly known as wild saffron. Based on our studies, C. cartwrightianus was identified as progenitor of the saffron crocus and the wild populations from Attica were shown to have the highest similarity to C. sativus. Both species share the long dark-red stigmas and resemblances in taste and aroma. However, we found significant genetic diversity within the Attic C. cartwrightianus populations, including the presence of saffron-specific traits and alleles, distributed in diverse combinations among different individuals of the wild species. The autotriploid origin of the saffron crocus resulted from the combination of different genotypes of C. cartwrightianus from Attica. High genetic diversity in C. cartwrightianus together with obligate outbreeding and genomic recombination led to constant reshuffling of the alleles since the origin of the saffron crocus, and are the reason that today probably not a single individual exists carrying the exact parental allele combinations of C. sativus. In saffron crocus, however, the allelic status is ‘frozen’ due to the triploid and sterile nature of this species. All worldwide cultivated C. sativus goes back to a single polyploidization event. Screening of natural C. cartwrightianus populations in Attica found only diploid individuals, while attempts to artificially create polyploids resulted at best in endopolyploidy, which after a short growing time reverted to the diploid state. We conclude that polyploidization is rare in the species. We used transcriptome and metabolome analyses to compare wild saffron with the triploid cultivars. We found that the wild individuals from Attica were most similar to saffron in their metabolic profiles while C. cartwrightianus populations from Aegean islands were rather different. Surprisingly we found more diverse carotenoids in the wild progenitor than in the cultivars. We interpret this result as indication that in wild saffron metabolic intermediates prevail, while in saffron they are metabolized into the typical secondary compounds of the spice. Comparative transcriptome analysis between both species revealed differences in the genes involved in the downstream parts of the apocarotenoid metabolism. Of particular future interest are several differentially expressed UDP-glycosyltransferases (UGTs), underscoring the key role of these enzymes in saffron biosynthesis.
Publications
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Phylogeny of the saffron-crocus species group, Crocus series Crocus (Iridaceae). Molecular Phylogenetics and Evolution, 127, 891-897.
Nemati, Zahra; Blattner, Frank R.; Kerndorff, Helmut; Erol, Osman & Harpke, Dörte
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Saffron (Crocus sativus) is an autotriploid that evolved in Attica (Greece) from wild Crocus cartwrightianus. Molecular Phylogenetics and Evolution, 136, 14-20.
Nemati, Zahra; Harpke, Dörte; Gemicioglu, Almila; Kerndorff, Helmut & Blattner, Frank R.
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Ancient Artworks and Crocus Genetics Both Support Saffron’s Origin in Early Greece. Frontiers in Plant Science, 13.
Kazemi-Shahandashti, Seyyedeh-Sanam; Mann, Ludwig; El-nagish, Abdullah; Harpke, Dörte; Nemati, Zahra; Usadel, Björn & Heitkam, Tony
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Metabolomic and transcriptomic analyses of yellow-flowered crocuses to infer alternative sources of saffron metabolites. BMC Plant Biology, 24(1).
Nemati, Zahra; Kazemi-Shahandashti, Seyyedeh-Sanam; Garibay-Hernández, Adriana; Mock, Hans-Peter; Schmidt, Maximilian H.-W.; Usadel, Björn & Blattner, Frank R.
