Hot topics

Y. Matsuoka (Fukui Pref Univ)
Maize domestication - when, where, and how many times? (A recent view from plant genetics)

There exists extraordinary morphological and genetic diversity among the maize (Zea mays ssp. mays) landraces developed by pre-Columbian cultivators. To explain this high level of diversity in maize, several authors have proposed that maize landraces were the products of multiple independent domestications of a wild relative of maize, teosinte. Contrary to the view, a series of genetic studies by John Doebly and his colleagues strongly suggest that the high level of diversity of maize can be explained by a single domestication and subsequent diversification. Recently, comprehensive microsatellite-based phylogenetic analyses of maize and its progenitor, teosinte, have been reported, which successfully distinguish between these two models regarding the origin of maize and indicate that all existent maize arose from a single domestication event in southern Mexico about 9,000 years ago. It is also indicated that the oldest surviving maize types appear to be those of the Mexican highlands with maize spreading from this region over the Americas along two major paths. I will discuss the implications of this work in the light of other genetic and archaeological evidence.

O-1 K. Tsunewaki (Fukui Pref Univ)
Aneuploid analysis of albino genes in tetraploid wheats

Although occurrence of albinos in hybrid offspring between cultivars or strains of polypIoid wheat is not uncommon, no loci have been identified for albinism (McIntosh et al. 1998). It is due to lethality of albino, that makes maintenance of fixed albino stocks impossible. I succeeded to identify two types of homozygotes, abn1 /abn1 +/+ and +/+ abn2 /abn2, for two complementary (or duplicated) recessive albino genes, abn1 and abn2. To identify their chromosomal locations, I carried out aneuploid analysis of those genes, using a set of disomic D-genome chromosome substitution (abbrev. DS) lines of T. durum cv Langdon 16 (abbrev. Ldn) (Joppa and Williams 1988). Ldn and Line 183 were selected to represent the genotypes, abn1/abn1 +/+ and +/+ abn2/abn2, respectively. Crosses were made between 14 DS lines and normal Ldn as female and Line 183. The F₁ hybrids were self-pollinated, and the F₂ seeds were sown to observe segregation of albinos. The F₂ population of the cross, DS 2D(2A) x Line 183, did not segregate any albinos, indicating that chromosome 2A of Ldn carries the abn1 gene and chromosome 2D of DS 2D(2A) has its normal homoeoallele. All other F₂ population segregated albinos in the same frequencies as the control F₂ population. These results suggest that chromosome 2B of Line 183 carries the abn2 gene, because, if not, the F₂ population of DS 2D(2B) should give much higher albino frequency than those of normal Ldn or other DS lines. The present conclusion explains well the results of Nishikawa (1986).

O-2 Y. Mukai¹, G. Suzuki¹, A. Nakano¹ and M. Yamamoto² (¹Osaka Kyoiku Univ, ²Kansai Women's Col)
Molecular breeding by genome fusion in rice. I. Introduction of wheat genome into rice

The most important task for plant breeding research is to introduce a set of agronomically useful genes of a certain crop into another distant crop beyond the barrier of reproductive isolation. For the revolutionary improvement of a crop, a new system which can transform a number of genes controlling many functions to plants is indispensable. Therefore, it is of urgent necessity for practical use of plant genomics to establish the transformation system that introduces large fragments of plant genome to other crops. In order to expand genetic variability in rice, we are trying to introduce the large genomic DNA fragments containing agronomically important genes of wheat into rice. We are doing research that breeds rice with wheat genome by successive introduction of the huge DNA fragments such as BAC clones. We call this method "genome fusion". In the first step of our research, we aim to develop the system which can introduce a mass wheat genome efficiently and the simple method of detecting the introduced genome or gene in transgenics. Our goal is to make bread and udon noodles from rice powder in the future by giving bread making nature and the noodle aptitude to rice. It is useful also to environmental preservation by not only contributing to consumption expansion of rice by aiming at conversion into the rice from wheat flour, but maintaining a paddy field by rice cultivation.

O-3 M. Yamamoto¹, T. Ohta² and Y. Mukai² (¹Kansai Women's Col, ²Osaka Kyoiku Univ)
Application of molecular combing to wheat research

Wheat has the large-sized genome including a large amount of repetitive DNA. The presence of such junk DNA stands in the way of plant genome analysis. When bacterial artificial chromosome (BAC) clones were used as probes in fluorescence in situ hybridization (FISH) experiments, hybridization signals were detected on the almost chromosomes and extended DNA fibers of wheat. Genome organization of agronomically important genes m wheat has been analyzed by southern blots and sequencing using lambda or BAC clones. Molecular combing is a new technique to directly map target DNA sequences onto individually stretched DNA molecules. This technique can give the visual information on the structure of BAC before its molecular biological analysis. This information results in saving time and labor in analysis and provides us with a useful finding for the construction of BAC contig. The orientation of the seed storage protein genes and the grain-hardness genes was analyzed on wheat BAC DNA molecules (circular and linear types). Furthermore, application of molecular combing FISH includes determining the structure of the clone, the copy number of genes, and the order of genes and specific sequences.