Metabolic engineering of potato carotenoid content through tuber-specific overexpression of a bacterial mini-pathway.
BACKGROUND
Since the creation of "Golden Rice", biofortification of plant-derived foods is a promising strategy for the alleviation of nutritional deficiencies. Potato is the most important staple food for mankind after the cereals rice, wheat and maize, and is extremely poor in provitamin A carotenoids.


METHODS
We transformed potato with a mini-pathway of bacterial origin, driving the synthesis of beta-carotene (Provitamin A) from geranylgeranyl diphosphate. Three genes, encoding phytoene synthase (CrtB), phytoene desaturase (CrtI) and lycopene beta-cyclase (CrtY) from Erwinia, under tuber-specific or constitutive promoter control, were used. 86 independent transgenic lines, containing six different promoter/gene combinations, were produced and analyzed. Extensive regulatory effects on the expression of endogenous genes for carotenoid biosynthesis are observed in transgenic lines. Constitutive expression of the CrtY and/or CrtI genes interferes with the establishment of transgenosis and with the accumulation of leaf carotenoids. Expression of all three genes, under tuber-specific promoter control, results in tubers with a deep yellow ("golden") phenotype without any adverse leaf phenotypes. In these tubers, carotenoids increase approx. 20-fold, to 114 mcg/g dry weight and beta-carotene 3600-fold, to 47 mcg/g dry weight.


CONCLUSIONS
This is the highest carotenoid and beta-carotene content reported for biofortified potato as well as for any of the four major staple foods (the next best event being "Golden Rice 2", with 31 mcg/g dry weight beta-carotene). Assuming a beta-carotene to retinol conversion of 6ratio1, this is sufficient to provide 50% of the Recommended Daily Allowance of Vitamin A with 250 gms (fresh weight) of "golden" potatoes.
Diretto
Gianfranco
G
Ente per le Nuove Tecnologie, l'Energia e l'Ambiente (ENEA), Casaccia Research Center, Roma, Italy.
Al-Babili
Salim
S
Tavazza
Raffaela
R
Papacchioli
Velia
V
Beyer
Peter
P
Giuliano
Giovanni
G
D019883:Alkyl and Aryl Transferases / Q000235:genetics; D002338:Carotenoids / Q000378:metabolism*; D005798:Genes, Bacterial; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D019753:Intramolecular Lyases / Q000235:genetics; D010088:Oxidoreductases / Q000235:genetics; D030821:Plants, Genetically Modified; D011198:Solanum tuberosum / Q000235:genetics / Q000378:metabolism*; D014169:Transformation, Bacterial
D002338:Carotenoids; D010088:Oxidoreductases; C022398:phytoene dehydrogenase; D019883:Alkyl and Aryl Transferases; D051232:Geranylgeranyl-Diphosphate Geranylgeranyltransferase; D019753:Intramolecular Lyases; C070925:lycopene cyclase-isomerase