Endonuclease Restriction Analysis of the Chloroplast Genome In Selected Gossypium Species

T.A. Wilkins and G.A. Galau


 
ABSTRACT

The potential nucleotide divergence in the chloroplast DNA of eight Gossypium species, including representative CMS aad restorer lines, was evaluated by electrophoretic analysis of restriction endonuclease-cleaved DNA fragments. Generation of unique restriction enzyme patterns of chloroplast DNA in each species allows an unambiguous identification of species-specific cytoplasms. Moreover, the chloroplast DNA of the G. harknessii progenitor of CMS lines was determined to be maternally inherited in both CMS and restorer lines without detectable rearrangement, nucleotide substitution, or addition/deletions. Thus, the CMS phenotype is not due to a possible cross-induced alteration in chloroplast DNA, nor can nuclear-encoded fertility restoration or restoration-enhancement of CMS be due to subsequent alterations in the chloroplast genome.

To put the alloplasmic CMS phenotype in better perspective, the differences in chloroplast DNAs of pertinent Gossypium species were quantitated by the Fragment Method as an index of cytoplasm divergence. Divergence was estimated by the extent of nucleotide substitution as determined by the proportion of restriction enzyme-cleaved DNA fragments shared between species. A direct correlation may exist between the relative magnitude of interspecific chloroplast DNA divergence and the expression of male Sterility in alloplasmic constructions in allotetraploid nuclear backgrounds. The relative divergence in nucleotide sequence among the chloroplast DNA of the eight species examined (G. harknessii G. raimondii, C. hirsutum, G. barbadense, G. arboreum G. herbaceum, G. longicalyx is consistent with the current understanding of Gossypium evolution. An A-genome-like progenitor was the maternal parent of the allotetraploids. However, the cytoplasms of the allotetraploids appear to have diverged relatively earlier than their nuclear DNAS, suggesting that introgressive hybridization may have occurred in the evolution of the allotetraplaids.



Reprinted from 1985 Proceedings: Beltwide Cotton Production Research Conferences pg. 73
©National Cotton Council, Memphis TN

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Document last modified Sunday, Dec 6 1998