Molecular basis of the genetic diversity of the cytoplasm in triticum and Aegilops. I. Diversity of the chloroplast genome and its lineage revealed by the restriction pattern of ct-DNAs.

Abstract

Intact chloroplast DNAs were isolated from 34 self-fertile alloplasmic as well as from four euplasmic lines of wheats. The restriction patterns of these ct-DNAs were studied using four enzymes, Sal I, Pst I, Eco RI and Bam HI. Ct-DNAs from the 38 cytoplasms could be classified into three, four, four, and ten types, based on the Sal I, Pst I, Eco RI and Bam HI restriction patterns, respectively. In total, ten chloroplast genome types (Types 1 to 10) could be identified. The physical maps of ct-DNAs of common wheat (including emmer wheats and Ae. Longissima), Ae. Squarrosa (including its relatives, Ae. cylindrica and Ae. Ventricosa), and Ae. Uniaristata appeared to be about 0.2-0.5kbp smaller than that of most other species. Significantly the restriction patterns of ct-DNAs of Ae. caudata and an amphidiploid between Ae. caudata (_??_) and Ae, umbellulata (_??_) that had been produced 40 years ago were identical. No restriction pattern differences were found among three cultivars of common wheat (T. aestivum and T. spelta), two species of emmer wheat, two varieties of Ae. Biuncialis, three varieties of Ae. triaristata (one 4x and two 6x forms), and two strains of Ae. crassa (a 4x and 6x form). In many cases, a diploid and its polyploid relatives, which were previously assumed by Tsunewaki and his coworkers (ref. Tsunewaki 1980) to have received a nuclear genome and cytoplasm from the diploid, showed identical restriction patterns; one typical example is Ae. umbellulata (2x) and its relatives, Ae. triuncialis (4x), Ae. biuncialis (4x), Ae. columnaris (4x), and Ae. triaristata (4x and 6x). All these facts indicate a conservatism of chloroplast genomes during speciation. In all but two cases, each of the chloroplast genome types corresponded to one of the specific plasma types (or subtypes) established by Tsunewaki and his coworkers. One exceptional case is the chloroplast genome type 1 that included five distinctly different plasma types, A, D², S^b, S¹ and S^v Other exceptions are chloroplast genome types 7 and 8, both of which corresponded to the same plasma type, S. Since their differences appear on four restriction fragments, the plasma type corresponding to chloroplast genome type 7 (Ae. longissima, wild, and cultivated emmers and common wheat) has been renamed, B. Based on the number of restriction fragments differing between all pairs of the plasma types, a phylogenetic tree for 14 plasma types was constructed. Several characteristic genetic properties of the plasma types, such as large subunit types of Fraction I protein, induction of weakness, variegation, and male sterility, were localized in certain branches of the tree. However, none of them could be assigned to any specific change in the restriction fragments. Finally, the maternal lineages of most polyploid species were deduced from the restriction patterns of ct-DNAs: emmer and common wheats to Ae. longissima, 4x and 6x timopheevi wheats to Ae. aucheri, most 4x and 6x species of Polyeides section (Ae. triuncialis, Ae, biuncialis, Ae. columnaris, and 4x and 6x Ae. triaristata) to Ae. umbellulata, one strain of Ae. triuncialis to Ae. caudata, and Ae. cylindrica and Ae. ventricosa to Ae. squarrosa.