International cooperation in rice genetics

Rice is the principal food of nearly half of mankind. Yet, until recently, our knowledge
of rice genetics lagged behind that of other food crops such as wheat, maize, barley, and
tomato. However, several developments that took place during the last decade have
resulted in rice becoming one of the best known crops genetically and a model plant
for molecular genetic studies:
• association of linkage groups with cytologically identifiable chromosomes in
• publication of the Rice genetics newsletter (RGN) annually, starting with
• publication of proposed rules for gene symbolization in rice and a list of

• initiation of an International Program on Rice Biotechnology by the
• holding of the First International Rice Genetics Symposium at IRRI in May
• establishment of the Rice Genetics Cooperative during the Symposium for
I shall briefly recount here some of the historical events that have led to the
1984
volume 1 in 1984
known genes with suggested gene symbols
Rockefeller Foundation in 1985
1985
promoting international cooperation in rice genetics
present high level of international cooperation in rice genetics.
Gene symbolization in rice
In the absence of any rules for assigning gene symbols, different symbols were
assigned to the same genes. As an example, symbols m, U, am, gl, and wx were all
assigned to the gene for glutinous endosperm (Kihara 1964). Similarly, the same gene
symbol was assigned to entirely different genes. Symbol gl, for example, was used to
designate glutinous endosperm as well as glabrous leaves. K. Ramiah of India was the
first geneticist to advocate the standardization of gene symbols in rice. Kadam and
Ramiah (1943) published a review of the use of gene symbols and suggested rules for
gene symbolization that adopted many conventions used in maize, cotton, and Drosophila.
The recommended symbols, along with those used by various authors and
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relevant references, were given. The recommendations were accepted by scientists in
some countries, but not in others.
Gene symbolization was discussed by the International Rice Commission (IRC)
Working Party on Rice Breeding at its Sixth Session in Penang, Malaysia, in 1955. The
Working Party suggested that unified system of gene nomenclature be developed, and
appointed a committee for this purpose, with N.E. Jodon of the U.S. as convenor and
S. Nagao of Japan and N. Parthasarathy of India as members.
In the meantime, the International Committee for Genetics Congress nominated a
small committee to draft rules for genetic symbols and nomenclature for all organisms.
The report of the International Committee was accepted by the Tenth International
Genetics Congress held in Montreal, Canada, in 1959. The report was timely, because
it provided the rice committee with guidelines in preparing rules for gene symbolization
in rice and listed suggested gene symbols. The report of the rice committee was
accepted by the IRC Working Party on Rice Production and Protection in 1959 and
published in the IRC newsletter (Anonymous 1959). The rules for gene nomenclature
and gene symbols were reviewed during the Symposium on Rice Genetics and
Cytogenetics held in 1963 at IRRI and were accepted by the participants. Unfortunately,
no mechanism existed for monitoring the use of symbols, and very few authors
followed the rules for symbolization.
To promote cooperation and adoption of uniform gene symbols for rice in Japan, an
Interim Committee of Japanese scientists was organized in 1979. The committee was
named the Japanese Committee on Rice Gene Nomenclature and Linkage Groups in
1981 and was renamed the Japanese Rice Genetics Information Committee in 1984.
The committee did significant groundwork in reviewing the IRC-recommended gene
symbols.
During 1981 and 1982, there was considerable correspondence between IRRI
scientists (M.S. Swaminathan and G.S. Khush) and officials of the Japanese Committee
on Rice Gene Nomenclature and Linkage Groups (H. I. Oka, T. Kinoshita, and Y.
Futsuhara) about the status of rice genetics. On the basis of this correspondence, the
decisions were made to publish the RGN annually for exchanging information among
rice geneticists and to hold an International Rice Genetics Symposium. The first
volume of the RGN was published in 1984; it contained proposed rules for gene
symbolization (RGN1:2-3) and a list of known genes with proposed gene symbols. The
First International Rice Genetics Symposium was held at IRRI in May 1985. On the
basis of discussions among participants it was decided to organize the Rice Genetics
Cooperative (RGC) to promote international cooperation in rice genetics and to publish
the RGN on an annual basis. One of the standing committees of the RGC coordinates
and monitors new gene symbols for adherence to the rules of gene nomenclature; the
new gene symbols are published annually in the RGN.
Chromosome numbering system
Various systems for numbering rice chromosomes have been proposed. Shastry et a1
(1960) studied the chromosome complement of rice at the pachytene stage of meiosis.
xx G. S. Khush
Chromosomes were numbered in decreasing order of length—the longest being
chromosome 1 and the shortest being chromosome 12. Nishimura (1961) assigned
numbers I to XII to the rice chromosomes involved in translocations, following the
order in which the translocations were discovered. Thus the two chromosomes
involved in the first translocation were numbered I and II, and the chromosomes
involved in the second translocation were numbered III and IV. Later on the Roman
numerals were changed to Arabic numerals. This system was arbitrary and was not
based on cytological identification of the chromosomes. Kurata and Omura (1978)
numbered the chromosomes on the basis of length at somatic prophase. The longest
was designated K1 and the shortest K12. However, somatic chromosomes are difficult
to identify because size differences are minor. During the First International Rice
Genetics Symposium, a committee under the chairmanship of C. M. Rick of the
University of California, Davis, California, USA, recommended that the chromosome
numbering system based on the length of pachytene chromosomes as proposed by
Shastry et al (1960) be followed. This recommendation was accepted by the RGC.
Linkage map of rice
The first report of linkage in rice was by Parnell et al (1917). Morinaga and Nagamatsu
(1942) and Ramiah and Rao (1953) reported additional linkages between genes. Jodon
(1956) proposed 7 linkage groups, and Nagao and Takahashi (1963) postulated 12 (IXII).
When the independence of these linkage groups was tested by Iwata and Omura
(1975,1976) through trisomic tests, the 12 linkage groups were reduced to 9. However,
3 additional linkage groups were soon discovered; by 1980, 12 independent linkage
groups had been established.
Associating linkage groups with chromosomes
Several workers have established primary trisomic series of rice. However, only two
of the trisomic series have been used in associating linkage groups with respective
chromosomes. Primary trisomics of rice variety Nipponbare were utilized for associating
linkage groups with chromosomes at Kyushu University, Japan, by N. Iwata and
associates (Iwata et al 1984). Similarly, primary trisomics of IR36 rice were produced
and used by G.S. Khush and associates at IRRI, Philippines (Khush et al 1984). The
extra chromosomes of trisomics of Nipponbare were identified at somatic prophase,
and those of IR36 at the pachytene stage of meiosis. When the chromosome-linkage
group associations found in these independently conducted studies were compared, the
results did not agree.
Toward a unified system of numbering rice chromosomes and linkage groups
To remove the discrepancies between the results of Iwata et al (1984) and Khush et al
(1984), it was decided to reexamine the extra chromosomes of trisomics of IR36 at
pachytene. Consequently, R.J. Singh (representing the IRRI group) and N. Kurata
(representing the Kyushu University group) met in June 1986 at IRRI and examined
the extra chromosomes of IR36 trisomics. Identifications of extra chromosomes of six
International cooperation in rice genetics xxi
trisomics were confirmed. The remaining six trisomics were examined by N. Kurata
and H.K. Wu of Taiwan. On the basis of these results and discussions during several
meetings, a tentative agreement has been reached to change the designations of four
trisomics of IR36. It is planned to change the designation of triplo-4 to triplo-3, triplo-
3 to triplo-6, triplo-6 to triplo-12, and triplo-12 to triplo-4. These recommendations will
be reviewed by a committee appointed by RGC, and the results of discussions will be
presented to the general body on the last day of this symposium. It is hoped that an
acceptable system of numbering rice chromosomes and linkage group will emerge as
an outcome of the symposium.
Rice genetics newsletter
The RGC has assumed responsibility for the publication of the RGN on an annual basis.
To date, six issues have been published. The RGN is an excellent medium for
exchanging information on the latest findings in rice genetics. We need your cooperation
and contributions to future issues of the RGN.
Rice genetics symposia
As mentioned earlier, the First International Rice Genetics Symposium was held at
IRRI in May 1985. We are assembled here today to participate in the Second
International Rice Genetics Symposium. Major advances in rice molecular and cellular
genetics have taken place during the five intervening years. I am sure much new
information will be presented during this symposium and that the participants will have
the opportunity to have informal discussions with other colleagues and explore areas
for research collaboration. I am grateful to the members of the organizing committee
for their full support in preparing for the symposium. This is the largest of all the
symposia and conferences held at IRRI to date, and many colleagues at IRRI have given
their support to make this a successful event. The Third International Rice Genetics
Symposium will be held in 1995, and we hope future symposia will continue to be held
at regular intervals.
Rockefeller Foundation’s International Program on Rice Biotechnology
This is a unique network that supports upstream research on molecular and cellular
biology for solving downstream problems of rice production. Through carefully
identified laboratories in developed countries, the Rockefeller Foundation is supporting
research that should eventually lead to the production of transgenic rices with novel
genes.
During less than five years of the existence of the network, protocols for transformation
of rice have been developed, useful genes for transformation have been
identified. a restriction fragment length polymorphism (RFLP) map of 320 markers has
been prepared, and efforts are under way for tagging genes of economic importance
with RFLP markers. Thanks to the advances in molecular and cellular biology under
the Rockefeller Foundation Program, rice has become model cereal crop for further
research on fundamental and applied genetics.
xxii G. S. Khush
Establishment of the Rice Genetics Cooperative
One of the important outcomes of the First International Rice Genetics Symposium was
the birth of the RGC for enhancing international collaboration in rice genetics. The
RGC has played a key role in monitoring gene symbols, publishing the RGN, and
sponsoring discussions aimed at evolving a unified system for numbering rice
chromosomes and linkage groups. The RGC has also established two genetic stock
centers for collecting, conserving, and distributing seeds of genetic markers and
chromosomal aberrations. We hope the RGC will continue to serve the cause of rice
genetics for years to come.
With this brief introduction to the history of international collaboration in rice
genetics, I add my words of warm welcome to those already expressed by our Director
General, Klaus Lampe. I hope you will have fruitful discussions during the symposium
and an enjoyable stay at IRRI. We at IRRI are looking forward to your inputs to the
symposium and to enhanced collaboration in rice genetics.