An Overview of Omics for Wheat Grain Quality Improvement - Crop Improvement: New Approaches and Modern Techniques - page 306

phytate competition is the major determinant of bioavailability of essential minerals
which is an important component of wheat grain quality. The recent discovery of
NAC gene transcription factor, TtNAM-B1 , role in enhancing grain mineral concen-
tration (Uauy et al. 2006b ) has opened new ways to efficiently utilize the genomic
approaches to harness quality related genes from wild relatives in order to get desir-
able products.
Some of the quality-encoding traits are polygenic, while the others are simply
inherited. The development and utilization of the functional markers for monogen-
ic quality traits like high molecular weight glutenins (HMW-GS), Low molecular
weight glutenins (LMW-GS), grain hardiness genes ( PINA and PINB ) and waxy
alleles have dramatically changed the selection of appropriate breeding material
having desirable genes. Similarly, efforts are underway to identify gene networks
underlying the quality traits through bi-parental quantitative trait and analysis
(QTL) and genome wide association studies (GWAS).
Genomics of Wheat Storage Proteins
The composition and amount of seed storage proteins play an important role in
determining wheat quality (Payne 1987 ). Beccari in 1745, first isolated the gluten
proteins and until now, the gluten proteins have been active area of investigation
at genomic and proteomic level over a period of 250 years, in order to determine
their structure and properties and to provide basis for manipulating and improving
end use quality (Shewry et al. 2002 ). At the beginning of the 20th century, Osborne
( 1907 ) developed a systematic way to classify wheat storage proteins based on their
graded extraction and differences in solubility. According to Osborne ( 1907 ) four
different protein groups can be recognized in wheat flour. These groups include al-
bumins (water soluble), globulins (water insoluble and soluble in saline solutions),
prolamins (soluble in 70-90 % ethanol) and glutens (soluble in dilute acid or alkali).
The most important protein, gluten, gives rise to two distinct groups based on their
solubility in 70 % ethanol, known as glutenins and gliadins (Wrigley et al. 1996 ).
Glutenins
High Molecular Weight Glutenin Subunits (HMW-GS)
HMW-GS reportedly account for 12 % of the total seed storage protein which corre-
spond to about 1-1.7 % of the flour dry weight (Halford et al. 1992 ). However much
of the work has been focused on functional and structural aspects of HMW-GS due
to their largest contribution in wheat end-use quality. HMW-GS are encoded at
Glu-1 loci present on the long arm of homeologous group 1 chromosomes (1AL,
1BL and 1DL), each locus contributing two gene subunits that differ in their prop-