Research Theme

Donkan Ryoku (Low temperature insensitivity) of rice

Rice is a plant of subtropical origin and cold disorder is a major problem in rice cultivation in Hokkaido. Rice is said to be the lowest temperature weakest in the booting stage, two weeks before flowering. Most studies find and introduce resistance genes from the idea that plants respond positively to various stresses to obtain resistance. We discovered an example different from the conventional way of thinking ‘Donkan Ryoku’ (low temperature insensitivity) which shows stress tolerance by not feeling low temperature stress. In addition, lower temperature disorders are effective not only for improving cold tolerance at the booting stage but also at low temperatures from late summer to autumn due to early birth. Therefore, we investigate the relation between photoperiod and temperature condition and growth rate and try to deepen the understanding of adjustment of heading period. (Y. Kurasawa, K. Yamamori, S. Sakaguchi, S. Kikuchi)

Fossil virus in rice genome

A lot of virus like sequences which are inserted in plant genome are reported and utilized for research. These sequences are called “Fossil virus”. We discovered endogenous rice tungro bacilliform virus-like sequence(ERTBVL) in rice genome. Asian rice has many ERTBVLs. However, African rice has less. The symptom of RTBV is milder in Asian rice than African rice. In this study, we believe that the ERTBVL sequence is involved in the viral immunity mechanism, and we are exploring the functions of the ERTBVL. (N. Saito, K. Utsu, H. Yoshizumi, K. Kitajima)

Analysis of transition control of Antirrhinum transposon Tam3

One phenomenon that is creating a genetic mutation that becomes important in breeding is the transition of a moving gene (transposon). When transposon (Tam3) transfers from a locus in Antirrhinum, which is an experimental material, pigment genes are expressed and flower color changes. This transition is promoted under low temperature conditions. In our laboratory, we analyze how the transposon is transferred on the genome using Antirrhinum. Ultimately, we are pursuing research with the aim of establishing a transposon as a form of new breeding. (K. Makiya, T. Ohigashi, I. Yuasa, S. Mitsui)

What’s anther culture?

Anther culture is a technique to regenerate plants via dedifferentiation and callus formation of microspores under the in vitro conditions. Plants derived from microspores can be feasible materials for studies on the reproduction and the differentiation of plants, because of their unique characteristics compared to those produced by seed propagation, e.g. albino (lack of chlorophyll) and polyploidy. (Y. Kanaoka, I. Masuda, Y. Kishi)

Mechanisms by which low temperature promotes the dedifferentiation of microspores.

The efficiency of callus formation is a crucial factor influencing the yield of the regenerated plants in anther culture. However, little is known about the mechanisms which induce the dedifferentiation of microspores triggered by the treatment with low temperature and exogenous phytohormone. We have studied the effect of the pretreatment on the cell plasticity of microspores.

Regenerated plants derived from anther culture of interspecific hybrids.

Interspecific hybrids F1 between Asian rice (O. sativa) and African rice (O. glaberrima) show complete spikelet sterility mainly because of the pollen sterility. We succeeded in producing regenerated plants derived from microspores of interspecific F1 by anther culture. Genetic analysis focused on their extraordinary genome constitution has proceeded so far.

Gene analysis using rice mutant

Mutants are important materials for genetic breeding studies, and we induce and select various mutants. In mutants, normal genes change to lose gene function or its function decreases. By examining this variant it will be possible to recognize and examine the gene for the first time.
Rice grass type and spikelet are important traits related to yield. Many genes are acting on these formations. To investigate the function of these genes is an important research subject as a basis for breeding, and we are conducting research using various mutants related to the morphology of rice. (T. Kawashima, C. Kawahara, E. Inada, S. Ikeda)

(A) A zebra mutant that causes lateral striped bleaching in leaves of rice seedlings. (B) Various malformation spikes in the cross between mutants that cause malformations in the spikelet structure of rice. (C) Test for mutants in which mutation is observed in seed size. (D) Cultivation and selection of mutants in paddy fields.

Understanding and overcoming reproductive barriers in rice

Reproductive barriers prevent gene flow between species. Such barriers are main obstacles for the inter-specific hybrid breeding. We are studying inter-specific hybrid sterility in rice, as a model case of reproductive barriers, to understand what molecular mechanisms are underlying, how they evolved, and how we can overcome them for the future breeding. (Y. Kitashima, M. Ogata)

Characterization of the genome constitution of rice resources in coastal region of the Mekong Delta and evaluation of salinity tolerance.

Rice is the largest food consumption for Asia people. Particularly in Vietnam, rice production contributes not only for Vietnamese but also for food security in the world. Nowadays, the Mekong Delta of Vietnam deal with the big issues as climate change which will be affected for rice production. Scientists are going to find the best solution for this problem. We are contributing for this work by evaluate the diversity of rice accessions that we conserve in the last decade.
The aim of this study is:
1. Evaluate the diversity of rice accessions from the Mekong Delta of Vietnam.
2. Getting rice accessions which can tolerant to saline condition.
(Tam N. T.)

Development of di-haploid rice lines between O. sativa indica and japonica sub-species through anther culture technique.

Access to improved and quality seeds by small holder farmers is one of the major constraints to increased rice production in Zambia. Development of new rice varieties using conventional breeding methods is not only cumbersome, but time consuming as well. Anther culture, if successfully conducted, provides a quicker method of producing homozygous in-bred lines that are ready for use by farmers, as well as for integration in other breeding programs. Through this research, we hope to come up with rice lines that can be used in Zambia. The parental lines used were selected for crossing due to their specific characteristics such as early heading, cold tolerance and aroma. (O. Malumbe)


Rice production in Hokkaido

Hokkaido is a major producer of rice, boasting Japan’s largest crop acreage and yield. Most rice grown in Japan is from the Japonica variety, which has a rounder pill-like shape and stickier texture compared to the Indica or Javanica varieties.

Rice cultivation in Hokkaido has developed over the years by overcoming the harsh climate that includes cold temperatures and heavy snowfall. Since the variety called Kirara 397 debuted in 1989, breeding has been used to develop other types of Hokkaido rice that taste better and withstand the cold climate better. The Nanatsuboshi and Yumepirika varieties are highly acclaimed for their glossy appearance, sticky texture and great balance of sweetness. Both have received the Toku-A ranking, the highest possible, in taste tests performed by the Japan Grain Inspection Association. Currently, Hokkaido is cultivating rice in a more safe and secure manner by taking advantage of its colder climate to use less agricultural chemicals.

Northern extensions of rice cultivation limit

Summer average temperature lines in Hokkaido (left)
Years of progress for rice varieties to north area in Hokkaido (Right)