Writing in the Public Library of Science , researchers from Rome-based Casaccia Research Center and Germany-based Freiburg University report that using the mini-pathway of bacterial origin technique the beta-carotene content of potatoes could be increased 3600-fold.
"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)," wrote lead author Gainfranco Diretto "Assuming a beta-carotene to retinol conversion of 6:1, this is sufficient to provide 50% of the Recommended Daily Allowance of Vitamin A with 250 gms (fresh weight) of "golden" potatoes," he added in the Public Library of Science.
Vitamin A deficiency (VAD) is a public health problem in more than 50 per cent of all countries, especially in Africa and South-East Asia, according to the World Health Organisation, and causes blindness in up to 500,000 children each year.
The human body converts beta-carotene in the diet into vitamin A. Research into biofortication of plants continues to explore ways of increasing the vitamin A status and is being strongly supported by several humanitarian agencies like Harvest Plus, which is actively funding biofortified crop breeding in developing countries, and co-funded this new research.
Syngenta has been highly active in producing transgenic beta-carotene-rich rice, and announced in 2005 a new GM rice, called Syngenta Golden Rice II, that produces up to 23-times more provitamin A nutrients than the original beta-carotene-rich Golden Rice
This gives the rice a maximum carotenoid level of 37 micrograms per gram of rice and a preferential accumulation of beta-carotene.
The researchers used the genes phytoene synthase (CrtB), phytoene desaturase (CrtI) and lycopene beta-cyclase (CrtY) from Erwinia , and found that expression of all three genes, produced "golden" potatoes with caortenoid levels of 114 micrograms per gram dry weight and beta-carotene of 47 micrograms per gram dry weight.
"Thus, by introducing a bacterial mini-pathway for carotenoid biosynthesis, it is possible to increase potato tuber carotenoid content to levels much higher than what has been previously described, either in genetically engineered lines or in natural variants.," said Diretto.
The researchers also check the stability of the "golden tuber" trait found that after several different harvests only minor variations in carotenoid content were observed.
"We believe that the carotenoid and provitamin A content of potato can be further improved, with respect to the results shown here," said the researchers.
Diretto and co-workers suggested that future work should focus on the potential of the gene silencing technique to enhance the accumulation of specific carotenoids such as beta-carotene or zeaxanthin, and the potential of the cauliflower Or gene to increase total carotenoid and beta-carotene levels in tubers.
"Therefore, a combination of different approaches is very promising for the further improvement of potato carotenoid content, either for nutritional purposes, or for the production of high value-added compounds," concluded the researchers.
Source: Public Library of Science ( PloS) ONE Open-access on-line, Volume 2, e 350, doi: 10.1371/journal.pone.0000350 "Metabolic Engineering of Potato Carotenoid Content through Tuber-Specific Overexpression of a Bacterial Mini-Pathway" Authors: G. Diretto, S. Al-Babili, R. Tavazza, V. Papacchioli, P. Beyer, et al.