MAPPING OF THE REGIONS ASSOSCIATED WITH ZINC CONTENT IN THE GRAINS OF RICE
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Date
2008
Authors
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ACHARYA N.G. RANGA AGRICULTURAL UNIVERSITY, RAJENDRANAGAR, HYDERABAD
Abstract
Rice (Oryza sativa) is one of the most important crops in the world with over
154.3 million hectares under cultivation and production of over 634.5 million tons and
the productivity of 4.1 t/ha. Nutrient deficiency is a serious public health problem
concerning about 124 million children world wide. Among the mineral nutrient
deficiencies, zinc deficiency has a major impact on human health. The present study
was undertaken with the prime objectives of i) assessing the genetic diversity of rice
germplasm using microsatellite markers derived from the genomic regions associated
with Zinc metabolism and ii) identifying specific regions of the chromosomes
associated with zinc content in the grain.
A set of 83 rice genotypes with a wide variation in their zinc content in grain
was screened for genetic diversity using nineteen microsatellite markers, derived from
genomic regions associated with Zn metabolism. Among these only thirteen (68.42 %)
markers were observed to be polymorphic. The banding pattern obtained with only
three polymorphic markers viz., SC 116 marker based on zinc transport gene, SC 126
based on Yellow stripe like gene and SC 129 based on ZIP (Zrt/Irt related protein)
gene, was clear and scorable and hence used for cluster analysis. These markers had 7
alleles among the 83 rice accessions with a range of 2 to 3 alleles per each marker with
an average value of 2.3. The amount of polymorphism exhibited by SC 116 was found
to be high with the PIC value of 0.85, while the other two markers, SC 126 and SC 129
showed similar polymorphism by having the same PIC value of 0.73. Significant
grouping based on the data generated by the above three polymorphic markers could
not be obtained, since the trait of zinc accumulation in grains is controlled by multiple
genes and only three markers were used in the present investigation, which may not be
able to reveal sufficient polymorphism. More markers, preferably functional molecular
markers would elicit the genetic diversity of the characterized germplasm.
Of the forty five markers used for parental polymorphism studies between
Samba Mahsuri and Ranbir Basmati, only sixteen markers showed polymorphism, nine
markers showed monomorphism and twenty one were not amplified. Three
polymorphic markers which are associated with cation uptake viz., SC 129 marker
based on ZIP (Zrt/Irt related protein), SC 135 marker based on ZIP (Zrt/Irt related
protein) and SC 141 marker based on NRAMP (Natural Resistance –Associated
Macrophage Protein), were used to assay the 24 and 22 F2 individual plants
respectively showing high and low zinc content in grains, to identify specific regions of
the chromosome associated. The markers used for selective genotyping studies,
amplified Ranbir Basmati specific allele in homozygous condition in more F2 plants
having high zinc content and Samba Mahsuri specific allele was found in homozygous
condition in more F2 plants with low zinc content in rice grains. This situation was very
clearly noticed with respect to SC 135 marker. The linkage distance of these three
markers, SC 129, SC 135 and SC 141 with their respective genes OsZIP1, OsZIP8,
OsNRAMP7 on chromosomes 3, 5 and 12 were found to be 47.8 cM, 15.2 cM and 44.6
cM respectively. The association could be made more effective by analyzing more F2
population. The methodology of selective genotyping could successfully identify the
chromosomal regions associated with zinc content in grains.
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Keywords
MAPPING, REGIONS, ASSOSCIATED, ZINC, CONTENT, GRAINS, RICE