SSRM Academy of Sciences
Wx locus in maize plants carrying unstable macromutation Cg2
--L. G. Tumanova, N. A. Vikonskaya and N. V. Krivov
Maize plants with unstable mutation Cg2 show a high mutability at loci unlinked to Cg2. We observed genetic instability at the Wx locus of hybrid plants obtained by crossing marker line wx sh to line Cg2+143-206. The latter line carries the Cg2+ allele, which systematically mutates to Cg2. The proportion of corngrass phenotype plants resulting from such mutation events was 67.6% for the N206 family. Among the hybrid kernels of the F1 generation, the fraction of Wx variegated kernels ranged from 3.1% to 32.7% in various families.
Southern blot analysis of DNA from F1 plants was performed. As a Wx probe the 2.5kb EcoRI fragment of the pcWx16 plasmid containing cDNA of the Wx gene was used. The plasmid was kindly provided by A. Gierl. Plant DNA was digested with EcoRI. Among the fifteen plants examined, two samples (the 3219/7b and 3227/10a plants) whose hybridization patterns differed from others were found. The fifteen individuals all contained a 15kb EcoRI hybridizing fragment. A 3.6kb EcoRI additional fragment hybridizing to the Wx probe was observed in the 3219/7b plant and two fragments, 6.6kb and 2.4kb, in the 3227/10a plant (Fig. 1).
Figure 1. Southern blots on DNA from F1 plants hybridized with aWx cDNA probe. DNA samples were digested with EcoRI, electrophoresed on 1% agarose. Lanes: a) DNA sample from the 3219/7b plant; b) DNA sample from the 3227/3a plant; c) DNA sample from the 3227/10a plant.
An ear with 185 kernels was obtained on the selfed 3227/10a plant. The segregation ratio for Wx kernels did not significantly deviate from 3:1. There were 119 phenotypically normal kernels, 16 variegated and 50 mutant kernels in the ear. Variegated kernels were counted in the phenotypically normal Wx class.
Blot hybridization analysis of DNA of F2 plants grown from variegated kernels showed the same hybridization patterns as did the analysis of DNA from the 3227/10a plant.
Thus, among analyzed hybrids from a wx sh X Cg2+143-206 cross, two plants carrying the Wx gene with altered structure were discovered. The altered Wx gene is inherited in at least one of these plants. From the hypothesis about the existence of the Fpj mutable system responsible for Cg2 locus instability, one may suppose that Wx variegation is due to the effects of the mentioned system components.
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