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Genomics and Applied Biology, 2011, Vol.2 No.5
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Koshihikari as the base cultivar. This score indicates a
‘better than average’ rating, equaling that of Koshihikari.
The difference between Hikarishinseiki and Koshi-
hikari ranged from +0.25 to
-
0.64, and the average
was
-
0.06 when Ishikawa prefecture (2005:
-
0.64,
2007:
-
0.59), where stricter taste standards are applied,
was not included.
As shown above, although the characteristics of Hikari-
shinseiki as a dwarf variety of Koshihikari have now
been clarified, significant regional differences in yield
were revealed compared to Koshihikari. This may
give us clues as to how yield can be further increased.
2 Discussion
Although Koshihikari is a dominant variety of rice,
representing 40% of the rice cropping area in Japan,
problem arises as a result of lodging during heavy
rainstorms. In order to solve this problem, the dwarf
Koshihikari-type paddy rice variety ‘Hikarishinseiki’,
which shows stronger lodging resistance than that of
Koshihikari and has 99.8% or more of the Koshihikari
genome, was developed.
‘Koshihikari sd1’ was developed from first crossing
‘Jukkoku’ (
sd1sd1
) with ‘Kanto No.79’ (
Sd1Sd1
), an
early-maturing mutant of ‘Koshihikari’ (Tomita, 2009).
The pedigree method was conducted in breeding program
during the later generations of ‘Kanto 79’ × ‘Jikkoku’,
and then the dwarf
sd1
homozygous line (‘Jikkoku’-
type ‘Koshihikari’) whose heading date was the same
as ‘Koshihikari’, was selected and fixed in the F
4
generation. The flanking substituted region adjacent to
sd1
had been restricted by eight recurrent backcrossing
between the
Sd1sd1
descendants of ‘Jikkoku’-type
‘Koshihikari’ short line and ‘Koshihikari’ (
Sd1Sd1
)
as the recurrent parent. The semidwarf phenotype
(
sd1sd1
) was done by the BC
8
F
3
generation, therefore
in which ‘Koshihikari sd1’ line carried ≥99.8% of
‘Koshihikari’ background in their genome.
In this study, the two alleles at the
sd1/OsGA20ox2
locus on chromosome 1 of each line, Koshihikari and
Hikarishinseiki, were successfully distinguished by
RT-PCR amplification of the first exon followed by
digestion with
Pma
CI. RNA extracted from the root
was employed as the template then the 779 bp
fragment was clearly cleaved into the 613 bp and 166 bp
fragments by
Pma
CI digestion in Hikarishinseiki, but
not cleaved in Koshihkari. Therefore, it is concluded
that
sd1
gene derived from Jukkoku was transcribed in
Hikarishinseiki. This study would be a first evidence
of the transcription of
sd1
, a defective gene of
GA20ox
-
2
, which contributed to Green Revolution in rice.
Hikarishinseiki would be considered to be an alterna-
tive to Koshihikari, being resistant to typhoon damage
and easy to grow, and it was designated as a brand rice
description in the rice-producing districts in Okayama,
Tottori, Tokushima, Niigata, Kochi, Shiga, Mie, Kagawa,
Hyogo, Kyoto, Hiroshima, Tochigi, and Kumamoto
prefectures (by courtesy of Ministry of Agriculture,
Forestry and Fisheries of Japan). In this study, the
taste and quality of Hikarishinseiki were in line with
Koshihikari across Japan during two years, and it
would be practically valuable from the standpoint of
production and distribution. Nowadays, preliminary
tests to determine recommended cultivars have been
carried out extensively across Japan, with three prefectures,
Tottori, Wakayama, and Kanagawa, having proceeded
to main tests.
3 Methods
3.1 Transcription analysis of
sd1
Expression analysis of
sd1
was conducted by RT-PCR
assay using RNA extracted from the leaves of Hikari-
shinseiki and Koshihikari grown since June 2009 at
the farm of Tottori University and the roots of
Hikarishinseiki and Koshihikari germinated on a Petri
dish in the laboratory. After the reverse transcription
reaction using an RT primer (R6: TCAGCTGGCCGC
CTCGACCTGCGCCG) designed from the 3' end of
sd1
(Os01g0883800), RT-PCR was performed with 24
combinations of the following types of primers: four
upstream primers (F1: GGAGCCCAAGATCCCGGA
GCCATTCGTG, F2: CGACCTGAGGATGGAGCCC
AAGATCCCG, F3: GACTCCACCGCCGGCTCTGG
CATTGC, F4: CACGCCACCACAGCCGCACCAAC
CAC designed from the 1
st
exon of
sd1
) and six
downstream primers (R1: GAGGGTGCTGGAGAAG
TAGTCGGCGAC designed from the 1
st
exon of
sd1
,
R2: CACCCTCCCCATTGGCGCGAAGTCGG from
the range of the 1
st
to 2
nd
exon, R3: TACCATGAAG
GTGTCGCCGATGTTGATGACC from the 2
nd
exon,
R4: CGTTCGACAGCGCCATGAAGGTGTCGCC
from the range of the 2
nd
to 3
rd
exon, R5: TCAGCTG
GCCGCCTCGACCTG from the 3
rd
exon, and R6
mentioned above designed from the 3' end). Primer