Golden Rice 2: A Success of Transgenic Breeding

Sudhir Kumar1* & Mahesh Rao2

1. Scientist, ICAR RC for NEH Region Manipur Centre, Imphal-795004

2. Scientist, NRC Plant Biotechnology, New Delhi- 110012

*Author for correspondence e-mail: sudhiraaidu2006@gmail.com

Micronutrient and vitamins deficiency has affected the world population especially in

developing counties where daily calorie intake is dependent on consumption of staple food.

Vitamin-A deficiency is a serious health concern as it can lead to night blindness,

xerophthalmia, and to total blindness. Vitamin A deficiency is highly prevalent in children

and about 23% or higher is on risk of death as a result of measles, diarrhoea, or malaria

(UNICEF, 2009). Micronutrient and vitamin deficiency could be combat by dietary

diversification, fortification with pills or by biofortification. Biofortifiaation could be

achieved through either plant breeding or genetic engineering. Rice is the staple food crop

and providing energy for nearly half the world population. Rice grain biofortification has

emerged as a most sustainable and viable strategic in recent era for alleviation of

micronutrient deficiency (Bhullar and Gruissem, 2013). Plant breeding is relies on already

existing variability in the species and related genera. Rice endosperm (edible part) lack

vitamin A precursor and genetic variability for these traits is also not found in related species

and genera. Transgenic approaches could only the viable and sustainable strategies to develop

vitamin A precursor rich rice lines. The genetic engineering of rice for high production of b-

carotene, the precursor for vitamin A, constitutes a landmark achievement of transgenic

breeding. Golden Rice is the name coined to describe the genetically modified rice that

produces carotenoids in the endosperm of the grain, giving rise to a characteristic yellow

colour. Carotenoids are a group of plant pigments important in the human diet as the only

precursors of vitamin A. Pioneer work of golden rice has been started by Dr. Ingo Potrykus of

the Swiss Federal Institute of Technology and Dr. Peter Beyer of the University of Freiburg

in Germany and they engineered a beta-carotene pathway into Taipei 309, a japonica rice

variety. Wild-type rice has the biosynthetic capacity to produce geranylgeranyl-diphosphate

(GGPP), from an initial decarboxylation of pyruvate and condensation with glyceraldehyde-

3-phosphate catalyzed by 1-deoxy-Dxylulose- 5-phosphate synthase (DXS). To proceed

further for b-carotene formation (Vitamin A precursor), the plant enzymes phytoene synthase

(PSY), phytoene-desaturase (PDS), z-carotene-desaturase (ZDS) and carotene cis-trans-

isomerase (CRTISO) need to be supplemented. CRTISO is required to CRTISO is required to

convert the specific cis-carotene intermediates into the final all-trans form of lycopene that is

cyclized. The bacterial desaturase CRTI, expressed along with a plant enzyme phyoene

synthase (PSY), substitutes for the three plant enzymes by performing the complete

desaturation sequence with all-trans intermediates (Al-Babili and Beyer, 2005). Lycopene

cyclases (LCY) expressed in wild-type rice are sufficiently active to produce a- and b-

carotene. In this pioneer work, -carotene biosynthetic pathway was produced in very low

quantity (1.6 g/g) by using daffodil PSY gene along with multi-functional bacterial carotene

desaturase (crtI) gene and referred as Golden rice-1. (Burkhardt et al., 1997). The limiting

step in Golden Rice 1 was found to be the psy gene which resulted in to limited production of

carotene. Daffodil PSY protein was found at elevated levels in the Golden Rice endosperm

which suggests either that it is insufficiently active or that an alternative PSY functionality is

required in order to solve this hurdle. Pain et al., (2005) systematically tested psy cDNAs

from alternative plant sources, (maize, pepper, tomato, rice & daffodil) with the view of

increasing the carotenoid content of golden rice. The most effective was measured for maize

psy gene in the view of production carotenoids and b-carotenes. Enhancement of carotenoids

content and preferential b-carotene content by using maize PSY gene and bacterial CRT-1

gene leads to development of Golden rice-2. The Golden Rice 2 reported here has up to 37

mg/g carotenoid of which 31 mg/g is b-carotene. This increase in total carotenoid and

proportion of b-carotene over the original Golden Rice promises a greater impact on vitamin

A deficiency and related health issues. Datta et al. (2003) has developed golden rice version

in indica rice cultivars including IR64 by using antibiotic hph (hygromycin phosphor

transferase) selection system. Concerning over environment and biosafety aspect there is

need to develop alternative to antibiotic selection system. Marker free transgenic approach

could lead to effective in regard to wide scale adoption of genetically modified crops.

Baisakh et al. (2006) developed near-isogenic introgression lines (NIILs) of an elite indica

rice cultivar (IR64) through transfer of the genes for -carotene biosynthesis from dihaploid

(DH) golden rice (T309) using transgene-based marker-assisted backcross breeding.

Currently it urgent need of close collaboration of international research consortia with

national research system in order develop selectable marker free transgenic golden rice lines

in different version of indica, japonica and javanica rice to combat Vitamin A deficiency in

rice growing developing countries.

References:

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