BIOFORTIFICATION IN MAIZE V G SHOBHANA Dr N
BIOFORTIFICATION IN MAIZE V G SHOBHANA Dr. N SENTHIL KALPANA K. Dr. P NAGARAJAN Dr. M RAVEENDRAN Dr. P BALASUBRAMANIAN CENTRE FOR PLANT MOLECULAR BIOLOGY TAMIL NADU AGRICULTURAL UNIVERSITY COIMBATORE – 641 003
BIOFORTIFICATION Fortification x Biofortification Methods: Selective Breeding Genetic modification The Big Difference!! Developing world – Vitamin A, Zinc, Iodine and Iron Developed world – Selenium, prostrate cancer The Orange Ribbon Symbol of Malnutrition
Importance Two billion people - currently micronutrient malnourished - increased morbidity and mortality rates, lower worker productivity and high healthcare costs. Nutritional deficiencies (iron, zinc, vitamin A) - almost two-thirds of the childhood death worldwide. Major food crops can be enriched (‘biofortified’) with micronutrients using plant breeding and transgenic strategies. Micronutrient enrichment traits exist within their genomes. Micronutrient element enrichment of seeds can increase crop yields when sowed to micronutrient-poor soils, assuring their adoption by farmers.
The Golden Rice Story
Percentage of population affected by under-nutrition by country, according to United Nations statistics
PHYTIC ACID (PHYTIN OR PHYTATE) Myo-inositol-1, 2, 3, 4, 5, 6 -hexakisphosphate or Ins P 6. Is the most abundant myo-inositol phosphate in plant cells, but its biosynthesis is poorly understood. Also uncertain is the role of myo-inositol as a precursor of phytic acid biosynthesis. MW : 660. 03 Formula : C 6 H 18 O 24 P 6 BIOSYNTHETIC PATHWAY
PHYTIC ACID Myo-inositol 1, 2, 3, 4, 5, 6 -hexakisphosphate, is abundant component of plant seeds. Deposited in protein bodies as a mixed salt of mineral cations such as K+, Mg 2+, Ca 2+, Zn 2+, and Fe 3+ (50% to 80% of the phosphorus in seeds). Phytic acid serves as a major storage form for myo-inositol, phosphorus, and mineral cations for use during seedling growth. Other known role of phytic acid - control of inorganic phosphate (Pi) levels in both developing seeds and seedlings. In maize kernels, nearly 90% is accumulated in embryo and 10% in aleurone layers (also in rice and barley). Maize endosperm contains only trace amount of phytic acid.
Importance Monogastric animals digest phytic acid poorly. Undigested phytic acid is eliminated and is a leading phosphorus pollution source. Low-phytic acid grain and legume in feed - reduces phosphorus pollution to environment and reduce amount of phosphorus supplementation required in animal feeds (Ertl et al. , 1998). Such grain would also offer more available Fe and Zn for human nutrition (Mendoza et al. , 1998).
Variability of phytate P in crop plants
BIOSYNTHETIC PATHWAYS OF PHYTATE IN PLANTS Two types of pathway * Lipid -dependent (hydrolysis of PI(4, 5)P 2 by phospholipase) * Lipid -independent (sequential phosphorylation of I(3)P or inositol) Paulik et al. , (2005)
Phytic acid – Wheeler and Ferrel, 1971 430 genotypes were screened for their phytate content Low and high maize inbreds were identified Crossing of low inbred with high inbreds evolved in 50 hybrids Iron and Zinc – major minerals – screened by Atomic Absorption Spectrophotometer
The following strategies were adopted to reduce the phytate o Plants can be transformed for increased phytase production in the seeds. o o The transgenic approach will, in the long run, prove to be most versatile and cost-effective. Mutation breeding for impaired phytic acid biosynthesis has proved to be useful in maize, barley and rice ( Raboy, 2000). o Available low phytate mutant lines can be crossed with locally adopted cultivars and will result in low phytate maize with desired agronomic backgrounds.
GENETICS Maize has 10 chromosomes (n=10). The combined length of the chromosomes is 1500 c. M. "Chromosomal knobs". They are highly repetitive heterochromatic domains that stain darkly. Barbara Mc. Clintock used these knob markers to prove her transposon theory of "jumping genes". Composition Figures in grams (g) or milligrams (mg) per 100 g of food. Seed (Fresh weight) 361 Calories per 100 g Water: 10. 6% Protein: 9. 4 g Fat: 4. 3 g Carbohydrate: 74. 4 g Fiber: 1. 8 g Ash: 1. 3 g Minerals Calcium: 9 mg Phosphorus: 290 mg Iron: 2. 5 mg Vitamins Vit A: 140 mg Thiamine (B 1): 0. 43 mg Riboflavin (B 2): 0. 1 mg Niacin: 1. 9 mg
Pollen treated M 2 progenies - developed by Dr. Raboy – yielded two maize mutants. lpa 1 and lpa 2 with 60% reduction in the seed phytate levels were produced. These mutants were widely used in most of the breeding programmes in US. lpa 1 – 1. 1 (mg/g) phytate P in 4. 7 (mg/g) total P lpa 1 – 2. 6 (mg/g) phytate P in 4. 6 (mg/g) total P Indian corns have 2. 0 – 2. 5 (mg/g) phytate P in 4. 0 - 4. 5 (mg/g) of total P.
METHODOLOGY Low phytic acid donors with lpa 1 and lpa 2 genes will be used from Victor Raboy, USDA and will be used to develop low phytate maize. Local inbred lines will be used as recurrent parents. Identification of closely linked DNA markers with phytate in maize using already available linked markers like umc 157 with lpa 1 and umc 167 with lpa 2. Develop backcross population and marker backcross selection for low phytate maize lines. assisted
EXPECTED OUTPUT Identification of low phytate genotypes of maize which could be potential donors in breeding for micronutrients. Molecular markers linked to low phytate will assist in identifying target genes involved in adsorption, transport and unloading of micronutrients in the grain. Low phytate versions of high yielding maize hybrids in cultivation in India with increased iron and zinc bioavailability and reduced phosphorus pollution in the environment.
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