TY - JOUR
T1 - A chromoplast-specific carotenoid biosynthesis pathway is revealed by cloning of the tomato white-flower locus
AU - Galpaz, Navot
AU - Ronen, Gil
AU - Khalfa, Zehava
AU - Zamir, Dani
AU - Hirschberg, Joseph
PY - 2006/8
Y1 - 2006/8
N2 - Carotenoids and their oxygenated derivatives xanthophylls play essential roles in the pigmentation of flowers and fruits. Wild-type tomato (Solanum lycopersicum) flowers are intensely yellow due to accumulation of the xanthophylls neoxanthin and violaxanthin. To study the regulation of xanthophyll biosynthesis, we analyzed the mutant white-flower (wf). It was found that the recessive wf phenotype is caused by mutations in a flower-specific β-ring carotene hyroxylase gene (CrtR-b2). Two deletions and one exon-skipping mutation in different CrtR-b2 wf alleles abolish carotenoid biosynthesis in flowers but not leaves, where the homologous CrtR-b1 is constitutively expressed. A second β-carotene hydroxylase enzyme as well as flower- and fruit-specific geranylgeranyl diphosphate synthase, phytoene synthase, and lycopene β-cyclase together define a carotenoid biosynthesis pathway active in chroinoplasts only, underscoring the crucial role of gene duplication in specialized plant metabolic pathways. We hypothesize that this pathway in tomato was initially selected during evolution to enhance flower coloration and only later recruited to enhance fruit pigmentation. The elimination of β-carotene hydroxylation in wf petals results in an 80% reduction in total carotenoid concentration, possibly caused by the inability of petals to store high concentrations of carotenoids other than xanthophylls and by degradation of β-carotene, which accumulates as a result of the wf mutation but is not due to altered expression of genes in the biosynthetic pathway.
AB - Carotenoids and their oxygenated derivatives xanthophylls play essential roles in the pigmentation of flowers and fruits. Wild-type tomato (Solanum lycopersicum) flowers are intensely yellow due to accumulation of the xanthophylls neoxanthin and violaxanthin. To study the regulation of xanthophyll biosynthesis, we analyzed the mutant white-flower (wf). It was found that the recessive wf phenotype is caused by mutations in a flower-specific β-ring carotene hyroxylase gene (CrtR-b2). Two deletions and one exon-skipping mutation in different CrtR-b2 wf alleles abolish carotenoid biosynthesis in flowers but not leaves, where the homologous CrtR-b1 is constitutively expressed. A second β-carotene hydroxylase enzyme as well as flower- and fruit-specific geranylgeranyl diphosphate synthase, phytoene synthase, and lycopene β-cyclase together define a carotenoid biosynthesis pathway active in chroinoplasts only, underscoring the crucial role of gene duplication in specialized plant metabolic pathways. We hypothesize that this pathway in tomato was initially selected during evolution to enhance flower coloration and only later recruited to enhance fruit pigmentation. The elimination of β-carotene hydroxylation in wf petals results in an 80% reduction in total carotenoid concentration, possibly caused by the inability of petals to store high concentrations of carotenoids other than xanthophylls and by degradation of β-carotene, which accumulates as a result of the wf mutation but is not due to altered expression of genes in the biosynthetic pathway.
UR - http://www.scopus.com/inward/record.url?scp=33747472599&partnerID=8YFLogxK
U2 - 10.1105/tpc.105.039966
DO - 10.1105/tpc.105.039966
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C2 - 16816137
AN - SCOPUS:33747472599
SN - 1040-4651
VL - 18
SP - 1947
EP - 1960
JO - Plant Cell
JF - Plant Cell
IS - 8
ER -