An Overview of Omics for Wheat Grain Quality Improvement - Crop Improvement: New Approaches and Modern Techniques - page 329

Likewise HMW-GSs, many genes encoding LMW-GS have been isolated and
analyzed in cultivated and wild species of the family Triticeae . The genes coding
LMW-GS have been studied in the genera Elytrigia (Gupta and Shephard, 1990 )
Elymus (Obukhova et al. 1997 ), Dasypyrum (Blanco et al. 1991 ) and Hordeum
(Atienza et al. 2002 ). Ae. tauschii (DD) has been an important source for genetic
studies of LMW-GS (Gianibelli et al. 2000, 2002a ; Hsam et al. 2001 ; Pfluger et al.
2001 ; Vensel et al. 1997 ; Zhao et al. 2008) and exhibited greater variation in the
coding sequence of LMW-GS (Masci et al. 1991 ; Lafiandra et al. 2000 ). Similarly,
the other speices that have been analyzed for LMW-GS include T. monococcum,
T. urartu (Tranquilli et al. 2002 ; Lee et al. 1999 ), T. turgidum var. dicoccoides
(AABB) (Ciaffi et al. 1993 ), T. dicoccum (AABB) (Galterio et al. 2001 ), T. poloni-
cum (AABB) (Liu and Shepherd, 1996 ), T. macha (Xiong et al. 2010 ), Ae. bellulata ,
Ae. comosa , Ae. markgrafii and Ae. speltoides (Li et al. 2010 ), hexaploid obsolete
cultivars and landraces (Ovesna et al. 2001 ). The variability found for LMW-GS
in wheat wild relatives indicates the valuable potential is available to improve the
properties demanded to make variable products. The advancements have been re-
ported on the molecular characterization of Glu-3 genes from different Triticeae
species. For example nucleotide sequences are available from several species of
Aegilops spp. (Jiang et al. 2008 ; Li et al. 2008 ), Agropyron elongatum (Luo et al.
2005 ), Secale sylvestre (Shang et al. 2005 ), Crithopsis delileana (Guo et al. 2008 ),
Hordeum chilense , and H. brevisubulatum (Piston et al. 2005 ). The nucleotide di-
versity of LMW-GS in these wild species indicated the allelic rich of Glu-3 loci in
Triticeae . The comparative analysis of nucleotide sequences of LMW-GS revealed
some important differences among species. For example, Hordeum chilense and
A. elongatum lacks the N-terminal regions in the predicted mature proteins (Piston
et al. 2005 ). However, further efforts need to be continued to study the evolution-
ary pattern and structure of LMW-GS gene in Triticeae which will further facilitate
their utilization for wheat quality improvement.
A wide survey to isolate hundreds of Pina, Pinb and GSP genes from wild ac-
cessions of T. aestivum, T. turgidum, T. urartu, T. monococcum, T. timopheevii, T.
zhukovskyi, Ae. tauschii, Ae. speltoides, Secale and Hordeum have been conducted
(Morris 2002 ). The wild ancestors are known to have very soft texture as compared
to domesticated derivatives (Morris 2002 ) however the exact variability for tex-
ture is not well established in diploid species. Diploid and hexaploid accessions
of wild species had starch-associated friabilin which are generally absent in tetra-
ploid species. However puroindoline genes are present in accessions of diploid T.
urartu , T. monococcum , Ae. tauschii and Ae. speltoides (Lillemo et al. 2002 ). SKCS
based characterization of 67 accessions of T. monococcum revealed the soft texture
(Pogna et al. 2002 ). Similarly, scanning electron microscopy based characteriza-
tion of texture revealed that Aegilops accessions of different genomes and ploidy
were usually soft (Chen et al. 2005 ) with exception of a single Ae. Sharonensis
accession. The species which lack Pina sequences include S-genome species Ae.
bicornis and Ae. longissima which was contradictory to the findings of Simeone
et al. ( 2006 ). They analyzed many combinations of 13 and 24 variable amino acids
in the seven new haplotypes of Pina and Pinb , respectively . A null allele at PINA