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Life Science Research and Sustainable Development ISBN: 978-98-84663-33-9

domestication. The identified quantitative trait locus (QTL) Ghd7, isolated from an elite rice
hybrid and encoding a CCT domain protein, has major effects on an array of traits in rice,
including number of grains per panicle, plant height and heading date. Enhanced expression of
Ghd7 under long-day conditions delays heading and increases plant height and panicle size.
Natural mutants with reduced function enable rice to be cultivated in temperate and cooler
regions. Thus, Ghd7 has played crucial roles for increasing productivity and adaptability of rice
globally. To precisely map the Ghd7 locus, theyassayed 1,082 plants showing the
recessivephenotype for all the three traits (short,early heading and small panicle) from
population1 with two simple sequence repeatmarkers, RM5451 and RM1135, bracketingthe
Ghd7-containing region. By further genotypingof the recombinant plants using markersRM3859,
RM5436, C39 and RM7110, they localized the Ghd7 locus to the intervalbetween RM3859 and
C39, cosegregatingwith RM5436. Ghd7 haspleiotropiceffect similar to those of Ghd8.GRAIN
WIDTH 5 (GW5) has been identified as a major QTL for Seed Width on chromosome 5 (qSW5)
for the determination of rice grain width and weight (Shomuraet al., 2008; Wan et al.,2008
andWenget al., 2008). A survey of GW5/qSW5 polymorphisms in various rice landraces has
revealed that deletions in this gene may have played an important role in the selection of
increased grain size from artificial and natural crossings during rice domestication (Shomuraet
al., 2008). The GW5/qSW5 gene encodes a nuclear protein of 144 amino acids with an arginine-
rich domain. Because GW5/qSW5 physically interacts with polyubiquitin, it is likely to act as a
regulator in the ubiquitin– proteasome pathway and regulates cell division of the outer glume of
the rice spikelet.
In particular, researcher mapped a major QTL for grain width, GW2, with the WY3 allele
at GW2 contributingto increased grain width. Previous studies have mapped two QTLsfor grain
width near the GW2 region on the short arm of chromosome2 (Fan et al., 2009) suggesting they
may be the same QTL and thatthe GW2 locus may contribute to increased grain width in the
various rice varieties. Map-based cloning of the GW2 QTLby using two parental varieties that
showed highly significant differencesin grain size to more easily identify the QTL. The crossed of
Japonicavariety, WY3, with a very large grain (1,000-grain weight, 41.9 g ±1.3 g) and a high-
quality elite indica variety, Fengaizhan-1 (FAZ1),with a small grain (1,000-grain weight, 17.9 ± 0.7
g) toproduce an F2 population. GW2 was initially detected from a cross between a large-grain
japonica rice variety, WY3, and a small-grain indica rice variety, Fengaizhan-1 (FAZ1). A 1-bp
deletion in the GW2 gene in WY3 results in the introduction of a premature stop codon in its exon
4, causing the large-grain phenotype in WY3. GW2 negatively regulates cell division by targeting
its substrates to proteasomes for regulated proteolysis; loss of GW2 function results in an increase
in cell number in the spikelet hull and acceleration of the grain-milk filling rate, thus enhancing
grain width, weight, and yield. There are two homologs of the rice GW2 in maize, referred to as
ZmGW2-CHR4 and ZmGW2-CHR5, both of which contribute to the phenotypic variation in
kernel size and weight (Li et al., 2010).
The another group of cloned genes associated with grain shape and weight includes the
SMALL AND ROUND SEED (SRS) loci identified in the japonica rice subspecies. Mutations in
SRS1 result in reduction in both cell length and cell numbers in the longitudinal direction, and
elongation of the cells in the lateral direction of the lemma of rice flowers. Deletions of 38 bp in
srs1-1 and 31 bp in srs1-4 disrupt the coding region. Other srs1 mutant alleles are caused by
alterations in the stop codon and mRNA splicing sites (Abe et al., 2010). The SRS1 mRNA and
proteins are abundant in young leaves, internodes, and panicles. SRS1 encodes a protein of 1365
amino acids with no known functional domains (Abe et al., 2010). The small and round seed

https://jesjalna.org/Zoology-Publications/index.html 42 Department of Zoology, J. E. S. College, Jalna