| Research Abstract |
The aim of the present investigation is to provide the molecular basis for polyploid evolution in plants. For this, various species, diploid and polyploid, of twogenera, Triticum(wheat)and Aegilops, have been employed, and four problems, as described below, have been investigated. The main results obtained in a fouryear term are as follows :
A)Basic studies---A library of the genomic DNA clones of a common wheat cultivar Chinese Spring was constructed. Using these clones, RFLP between Chinese Spring and other common wheat accessions was tested. Among them, a spelta wheat revealed the largest RFLP to Chinese Spring, and their F_2 population (actually a population of F_3 lines)was raised. Linkage relationships were tested among all RFLP loci, leading to successful construction of the world-first 21 linkage groups of RFLP loci in common wheat.
B)Studies at the genome level---Using the DNA clones as probes which showed RFLP between Chinese Spring and Spelta, RFLP among a large number of acce
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ssions of de-, tetra- and hexaploid wheats as well as those of all Aegilops Sitopsis species, and Ae, squarrosa was investigated. The interspecific variation was much larger than the interspecific variation. T.urartu appeared to be the A genome donor to polyploid wheats. Emmer and Timopheevi groups of wheat were found to have originated diphyletically, the latter being of much recent origin than the former group. Common wheat revealed very high genetic homogeneity, and close relation to Emmer wheat, indicating recent oriin from Emmer wheat as a parent.
C)Studies at the chromosome level---RFLP loci were mapped on individual chromosomes and chromosome arms by nulli-tetrasomic and telosomic analysis, respectively. Homoeologous chromosomes and chromosome arms showed little homology as to the distibution of the RFLP loci probed with the same clones. This fact indicated high evolutionary change of the genomic DNA sequences probed with the present DNA clones.
D)Studies at the gene level---Nuclear genes for histones and for histone gene-binding proteins, chloroplast genes, rbcL, atpA and atpE, and mitochondrial genes, cox3 and atp6, were studied. The histone and histone gene-binding protein genes are mostly located on all three homoeologous loci in A,B and Dgenomes of common wheat. Apparently, those genes are evolutionary very conservative. The organellar genes also showed high evolutionary conservatism, although mitochondrial genome underwent great structural change. Less
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