Regulation of carotenoid biosynthesis during tomato fruit development: expression of the gene for lycopene epsilon-cyclase is down-regulated during ripening and is elevated in the mutantDelta

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Summary

The red colour of tomato (Lycopersicon esculentum) fruits is provided by the carotenoid pigment lycopene whose concentration increases dramatically during the ripening process. A single dominant gene,Del, in the tomato mutantDeltachanges the fruit colour to orange as a result of accumulation of δ-carotene at the expense of lycopene. The cDNA for lycopene ε-cyclase (CrtL-e), which converts lycopene to δ-carotene, was cloned from tomato. The primary structure of CRTL-E is 71% identical to the homologous polypeptide fromArabidopsisand 36% identical to the tomato lycopene β-cyclase, CRTL-B. TheCrtL-egene was mapped to a single locus on chromosome 12 of the tomato linkage map. This locus co-segregated with theDelgene. In the wild-type tomato, the transcript level ofCrtL-edecreases at the ‘breaker' stage of ripening to a non-detectable level in the ripe fruit. In contrast, it increases approximatley 30-fold during fruit ripening in theDeltaplants. TheDeltamutation does not affect carotenoid composition nor the mRNA level ofCrtL-ein leaves and flowers. These results strongly suggest that the mutationDelis an allele of the gene for ε-cyclase. Together with previous data, our results indicate that the primary mechanism that controls lycopene accumulation in tomato fruits is based on the differential regulation of expression of carotenoid biosynthesis genes. During fruit development, the mRNA levels for the lycopene-producing enzymes phytoene synthase (PSY) and phytoene desaturase (PDS) increase, while the mRNA levels of the genes for the lycopene β- and ε-cyclases, which convert lycopene to either β- or δ-carotene, respectively, decline and completely disappear.

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