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The Journal of Heredity 1996:87(5):385-389
© 1996 The American Genetic Association 87:385-389
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Mutator-Induced Cytoplasmic Mutants in Barley: Genetic Evidence of Activation of a Putative Chloroplast Transposon
Instituto de Genética "Ewald A. Favret" CICA, INTA, CC 25, 1712 Castelar, Argentina
Corresponding Editor: James L. Hamrick
Abstract
The four mutants described here were visually selected among the selfed progeny of a chloroplast mutator (cpm/cpm) genotype. Due to their mode of inheritance they were designated as cytoplasmic lines (CLs). One of them, CL3 was a homogeneous viridis (light-green) type, while the other three presented diverse positional patterns of variegation and also had different expression depending on the stage of growth. They showed different levels of additional variation, observed as longitudinal streaks, either lighter or darker than the color of each mutant background. By crossing CL plants as female with normal-green and genetically stable plants, it was possible to obtain, in subsequent generations, mutant families with the general characteristics of the corresponding CL but, in a stable state, free of additional variation. This was mainly evident for CL4, which in the progenies from selfing showed a much higher level of additional variation than the other CLs analyzed, having most of the variation of the normal-green type. Backcrosses of pure and stable CL4 plants as female with a mutator genotype, showed seedlings with normal-green streaks, after one generation of selfing, indicating they were not a consequence of a delayed chloroplast sorting. The high rate of reversion, several times higher than that of forward mutations, suggests the origin of CL4 was the insertion of a putative transposable element in the corresponding mutant gene of the chloroplast. It is hypothesized that the Cpm/cpm gene is involved in cpDNA repair, while transposon activation is explained based on the genome stress hypothesis, in which a RecA-like protein is postulated to play a central role.
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