New mitochondrial genome organization hybrids of Medicago sativa includingthe of substoichiometric mitochondrial DNA in three interspecific somatic parent-specific amplification units
F. Pupilli et al., New mitochondrial genome organization hybrids of Medicago sativa includingthe of substoichiometric mitochondrial DNA in three interspecific somatic parent-specific amplification units, THEOR A GEN, 103(6-7), 2001, pp. 972-978
Three somatic hybrid plants produced by protoplast fusion between Medicago
sativa and each of the three species Medicago coerulea, Medicago falcata an
d Medicago arborea have been analysed for the composition of their mitochon
drial DNA. Restriction fragment length polymorphism (RFLP) analysis of mito
chondrial genes in somatic hybrids and their parental lines showed various
degrees of rearrangement. The M. sativa+M. coerulea hybrid retained all of
the M. coerulea-specific bands but lost all the major M. sativa-specific ba
nds. The M. sativa+M. falcata hybrid showed only M. sativa-specific bands t
ogether with non-parental bands, and the M. sativa+M. arborea hybrid showed
a partial incorporation of bands from both parents together with non-paren
tal bands. The three different outcomes were attributed mainly to differenc
es in the genetic distance between the parents of each hybrid. Analysis of
the sexual progeny of the M. sativa+M. coerulea hybrid showed that a residu
al mitochondrial DNA subunit of M. sativa was retained in the hybrid cytopl
asm. This subunit was amplified and inherited in a mutually exclusive, alle
lic-like fashion with its M. coerulea homologous counterpart in the sexual
progeny of the hybrid. Possible mechanisms for the partitioning of mitochon
drial DNA in the generative lineage of the somatic hybrids are discussed in
relation to the creation of new nucleuscytoplasm assortments otherwise imp
ossible to obtain by a sexual cross in Medicago.