This article presents the results of comparative studies of the frequency and distribution of chiasmata in pollen mother cells (PMCs) in five diploid tomato species, Solanum lycopersicum, S. pimpinellifolium, S. peruvianum, S. habrochaites, and S. neorickii, and one autotetraploid species, S. pimpinellifolium. It was established that under the same growing conditions, the total chiasma frequency in the cell depended on the species. At the same time, the green-fruited species S. peruvianum, S. neorickii, and S. habrochaites differed in distal chiasma frequency, while the red-fruited species S. lycopersicum and S. pimpinellifolium differed in interstitial chiasma frequency. It was shown that the total chiasma frequency in PMCs of plants of one species is a stable index of recombination potential that does not depend on the growing conditions. The redistribution between distal and interstitial chiasmata was found to be more variable, depending on the species, year, geographic growth conditions. In autotetraploid, the chiasma frequency per bivalent was lower than that in diploid S. pimpinellifolium plants, primarily due to interstitial chiasmata, the frequency of which remained at the level characteristic for diploid plants. It was concluded that the recombination plasticity of the tomato genomes was due to the redistribution of chiasmata along bivalents, and not to the change in their number in the cell.

In interspecific hybrids a decrease in genetic exchanges between chromosomes from different species and negative interactions between functionally incompatible loci limit genetic variation among the progeny. Earlier the fraction of crossover genotypes was increased in intraspecific hybrids of the cultivated tomato Solanum lycopersicum with the expression of the recA Escherichia coli gene. In this research transgenic hybrids between S. lycopersicum and some wild tomato species were obtained in order to study the effect of recA gene expression on the frequency of crossovers in the progeny of interspecific hybrids. Interspecific hybrids showed negative interactions between the loci of the cultivated tomato and the S. cheesmaniae, S. pimpinellifolium, and S. habrochaites species. In the latter case it resulted in semilethal necrosis. The recA gene expression in interspecific hybrids with S. cheesmaniae partially compensates among the F2 progeny the deficiency of recessive genotypes at the Wv:wv locus of chromosome 2. In general, the fractions of crossover genotypes in the F2 progeny were higher in transgenic interspecific hybrids than in control non-transgenic hybrids of the same combination of crossing, but lower than in intraspecific S. lycopersicum hybrids.

In cultivated tomato hybrids (Marglobe × Mo938), the anthocyanin-free gene shows linked inheritance with the d (dwarf) gene on chromosome 2, but with a recombination frequency approximately three times higher than that according to the genetic map and in other hybrids with the Marglobe line. Cytological analysis of the mother pollen cells of the hybrids (Marglobe × Mo938) revealed no abnormalities of meiotic division and segregation of chromosomes, as well as no decrease in fertility. By means of the functional allelism test, it was established that, unlike Mo500, Mo504, and Mo755 marker tomato lines, in Mo938 the anthocyanin-free trait is not determined by the aw (anthocyanin without) or aa (anthocyanin absent) genes of chromosome 2. Using the F2 progeny of interspecies hybrids (Mo938 × Solanum pimpinellifolium), independent inheritance of the anthocyanin-free gene relative to the wv (white virescent) and d marker genes, as well as to six SSR anchor markers distributed at different sites of chromosome 2, was established. Thus, the Mo938 tomato line carries the d and wv markers on chromosome 2, as well as the anthocyanin-free gene not belonging to chromosome 2.

To study and induce meiotic recombination in plants, we generated and analyzed transgenic tomato hybrids F1-RecA and F1-NLS-recA-LicBM3 expressing, respectively, the recA gene of Escherichia coli and the NLS-recA-licBM3 gene. It was found that the recA and NLS-recA-licBM3 genes are inherited through the maternal and paternal lineages, they have no selective influence on the pollen and are contained in tomato F1-RecA and F1-NLS-RecA-LicBM3 hybrids outside the second chromosome in the hemizygous state. The comparative analysis of the meiotic recombination frequency (rf) in the progenies of the transgenic and nontransgenic hybrids showed that only the expression of the recA gene of E. coli in cells of the F1-RecA plants produced a 1.2–1.5-fold increase in the frequency of recombination between some linked marker genes of the second chromosome of tomato.

Homologous DNA recombination in eukaryotes is necessary to maintain genome stability and integrity and for correct chromosome segregation and formation of new haplotypes in meiosis. At the same time, genetic determination and nonrandomness of meiotic recombination restrict the introgression of genes and generation of unique genotypes. As one of the approaches to study and induce meiotic recombination in plants, it is recommended to use the recA gene of Escherichia coli. It is shown that the recA and NLS-recA-licBM3 genes have maternal inheritance and are expressed in the progeny of transgenic tomato plants. Plants expressing recA or NLS-recA-licBM3 and containing one T-DNA insertion do not differ in pollen fertility from original nontransgenic forms and can therefore be used for comparative studies of the effect of bacterial recombinases on meiotic recombination between linked genes.

The experimental data are presented about effect of transgenes, maize Ds-element and R480 gene, on some stages of meiosis in F1 tomato plants and the frequency of meiotic recombination (rf) in their progeny. On the basis of own results and the data of literature the authors suggest and give prove the mechanism of transgenes local effect on crossingover between linked genes.

Taking into account current models of recombination in eucaryotes the authors make an attempt to use recA gene from E.coli, protein product of which participates in recombination in vivo, for induction of meiotic recombination in plants. The analysis was made of recA gene DNA sequence in silico, that was cloned and the chimeric genes were obtained in which the nucleotide sequences of recA reporter gene and sign of nuclear localization are fused in the frame. The complex molecular-biological analysis of expression of cloned genes in bacteria and functional analysis of properties of chimeric protein products were carry out. On the basis of obtained data the authors construct the native and chimeric genes under control of 35S CaMV promoter and agrobacterial strains for the plant transformation.

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An attempt has been made to study the nature of genetic differences in the crossing-over rate in marker segments of tomato chromosomes 4 and 11. To this end, an interspecific cross between the multimarker line Mo628 (Lycopersicum esculentum Mill.) and L. hursutum var. glabratum Mull. was made using a number of isoenzyme markers and the backross genetic analysis. The maximum reduction in the crossing-over rate in the segment ful-e (chromosome 4) has been revealed in the presence of heterozygosity for the locus Adn-1 (chromosome 4) (for +/+ - rf = 29.96 +/- 2.53%; for -/+ - rf = 23.41 +/- 1,38%) and in the segment h1-a (chromosome 11) with heterozygosity for the locus Aat-2 (chromosome 7) (for +/+ - rf = 19.28 +/- 1.47%; for -/+ - rf = 9.02 +/- 0.84%). Also, high degree of quasi-linkage between isoenzyme loci of the ''cultivated'' and ''wild'' types was found during chromosome segregation in meiosis of the F1 hybrids between L. esculentum and L. hirsutum var. glabratum. The possibility is discussed of the presence in tomato of some heretofore unknown genetic factors linked to the Adh-1, Aat-2 loci, significantly affecting crossing-over in the segments under study.