Plasmon analyses of Triticum (wheat) and Aegilops: PCR-single-strand conformational polymorphism (PCR-SSCP) analyses of organellar DNAs

Abstract

To investigate phylogenetic relationships among plasmons in Triticum and Aegilops, PCR-single-strand conformational polymorphism (PCR-SSCP) analyses were made of 14.0-kb chloroplast (ct) and 13. 7-kb mitochondrial (mt)DNA regions that were isolated from 46 alloplasmic wheat lines and one euplasmic line. These plasmons represent 31 species of the two genera. The ct and mtDNA regions included 10 and 9 structural genes, respectively. A total of 177 bands were detected, of which 40.6% were variable. The proportion of variable bands in ctDNA (51.1%) was higher than that of mtDNA (28. 9%). The phylogenetic trees of plasmons, derived by two different models, indicate a common picture of plasmon divergence in the two genera and suggest three major groups of plasmons (Einkorn, Triticum, and Aegilops). Because of uniparental plasmon transmission, the maternal parents of all but one polyploid species were identified. Only one Aegilops species, Ae. speltoides, was included in the Triticum group, suggesting that this species is the plasmon and B and G genome donor of all polyploid wheats. ctDNA variations were more intimately correlated with vegetative characters, whereas mtDNA variations were more closely correlated with reproductive characters. Plasmon divergence among the diploids of the two genera largely paralleled genome divergence. The relative times of origin of the polyploid species were inferred from genetic distances from their putative maternal parents.

Figure 1

PCR-SSCP autoradiogram. (A) The atpH-atpF region of ctDNA, and (B) the cox2 region of mtDNA, digested with HinfI. The code number of each line (top of the margin) is given in Table 1.

Figure 2

Phylogenetic trees for 46 Triticum and Aegilops plasmons based on SSCP variations detected in seven chloroplast and nine mitochondrial DNA regions. (A) A UPGMA tree based on genetic distances. (B) An NJ tree.

Figure 3

Plasmon and genome divergence at the diploid level in Triticum and Aegilops. (A) Plasmon relationships revealed by the present study. Number of lines connecting each pair (or group) of plasmons corresponds to their genetic distance (d) as follows: double, triple, quadruple, quintuple, and sextuple lines indicate d = 0.08–0.10, 0.06–0.08, 0.04–0.06, 0.02–0.04, and less than 0.02, respectively. Of 13 types and 4 subtypes of plasmon identified among the diploids, A type and three subtypes, C², S^l2, and T², are not shown in this figure, because A type was not studied, and the three subtypes are included in the respective main types, C, S^l, and T. (B) Genomic relationships. The number of lines connecting each pair of genomes corresponds to the modal number of bivalent chromosomes observed among the respective genomes (31, 32).