Cytogenetic characterization and fae1 gene variation in progenies from asymmetric somatic hybrids between Brassica napus and Crambe abyssinica

Progress of chromosome engineering mediated by asymmetric somatic hybridization

Plant somatic hybridization has progressed steadily over the past 35 years. Many hybrid plants have been generated from fusion combinations of different phylogenetic species, some of which have been utilized in crop breeding programs. Among them, asymmetric hybrid, which usually contains a fraction of alien genome, has received more attention because of its importance in crop improvement. However, few studies have dealt with the heredity of the genome of somatic hybrid for a long time, which has limited the progress of this approach. Over recent ten years, along with the development of an effective cytogenetical tool "in situ hybridization (ISH)", asymmetric fusion of common wheat (Triticum aestivum L.) with different grasses or cereals has been greatly developed. Genetics, genomes, functional genes and agricultural traits of wheat asymmetric hybrids have been subject to systematic investigations using gene cloning, genomic in situ hybridization (GISH) and molecular makers. The future goal is to fully elucidate the functional relationships among improved agronomic traits, the genes and underlying molecular mechanisms, and the genome dynamics of somatic introgression lines. This will accelerate the development of elite germplasms via somatic hybridization and the application of these materials in the molecular improvement of crop plants.

The use of cytogenetic tools for studies in the crop-to-wild gene transfer scenario

Interspecific hybridization in plants is an important evolutionary phenomenon involved in the dynamics of speciation that receives increasing interest in the context of possible gene escapes from transgenic crop varieties. Crops are able to cross-pollinate with a number of wild related species and exchange chromosome segments through homoeologous recombination. In this paper, we review a set of cytogenetic techniques that are appropriate to document the different steps required for the stable introgression of a chromosome segment from a donor species (i.e., the crop) into a recipient species (i.e., the wild). Several examples in hybrids and derivatives are given to illustrate how these approaches may be used to evaluate the potential for gene transfer between crops and wild relatives. Different techniques, from classical chromosome staining methods to recent developments in molecular cytogenetics, can be used to differentiate genomes and identify the chromosome regions eventually involved in genetic exchanges. Some clues are also given for the study of fertility restoration in the interspecific hybrid forms.

Production and characterization of intertribal somatic hybrids of Raphanus sativus and Brassica rapa with dye and medicinal plant Isatis indigotica

Intertribal somatic hybrids of Raphanus sativus (2n = 18, RR) and Brassica rapa spp. chinensis (2n = 20, AA) with the dye and medicinal plant Isatis indigotica (2n = 14, I I) were firstly obtained by polyethylene glycol-induced symmetric fusions of mesophyll protoplasts. One mature hybrid with R. sativus established in field had intermediate morphology but was totally sterile. It had the expected chromosome number (2n = 32, RRI I) and parental chromosomes were distinguished by genomic in situ hybridization (GISH) analysis, and these chromosomes were paired as 16 bivalents in pollen mother cells (PMCs) at diakinesis and mainly segregated equally as 16:16 at anaphase I (A I), but the meiotic disturbance in second division was obvious. Five mature hybrids with B. rapa established in field were morphologically intermediate but showed some differences in phenotypic traits and fertility, two were partially fertile. Cytological and GISH investigations revealed that these hybrids had 2n = 48 with AAIIII complement and their PMCs showed normal pairing of 24 bivalents and mainly equal segregation 24:24, but meiotic abnormalities of lagging chromosomes and micronuclei appeared frequently during second divisions. AFLP analysis showed that all of these hybrids had mainly the DNA banding pattern from the addition of two parents plus some alterations. Some hybrids should be used for the genetic improvement of crops and the dye and medicinal plant.

GISH and AFLP analyses of novel Brassica napus lines derived from one hybrid between B. napus and Orychophragmus violaceus

New Brassica napus inbred lines with different petal colors and with canola quality and increased levels of oleic (approximately 70%, 10% higher than that of B. napus parent) and linoleic (28%) acids have been developed in the progenies of one B. napus cv. Oro x Orychophragmus violaceus F5 hybrid plant (2n = 31). Their genetic constituents were analyzed by using the methods of genomic in situ hybridization (GISH) and amplified fragments length polymorphism (AFLP). No intact chromosomes of O. violaceus origin were detected by GISH in their somatic cells of ovaries and root tips (2n = 38) and pollen mother cells (PMCs) with normal chromosome pairing (19 bivalents) and segregation (19:19), though signals of variable sizes and intensities were located mainly at terminal and centromeric parts of some mitotic chromosomes and meiotic bivalents at diakinesis or chromosomes in anaphase I groups and one large patch of chromatin was intensively labeled and separated spatially in some telophase I nuclei and metaphase II PMCs. AFLP analysis revealed that substantial genomic changes have occurred in these lines and O. violaceus-specific bands, deleted bands in 'Oro' and novel bands for two parents were detected. The possible mechanisms for these results were discussed.

GISH analysis of disomic Brassica napus-Crambe abyssinica chromosome addition lines produced by microspore culture from monosomic addition lines

Two Brassica napus-Crambe abyssinica monosomic addition lines (2n=39, AACC plus a single chromosome from C. abyssinca) were obtained from the F(2) progeny of the asymmetric somatic hybrid. The alien chromosome from C. abyssinca in the addition line was clearly distinguished by genomic in situ hybridization (GISH). Twenty-seven microspore-derived plants from the addition lines were obtained. Fourteen seedlings were determined to be diploid plants (2n=38) arising from spontaneous chromosome doubling, while 13 seedlings were confirmed as haploid plants. Doubled haploid plants produced after treatment with colchicine and two disomic chromosome addition lines (2n=40, AACC plus a single pair of homologous chromosomes from C. abyssinca) could again be identified by GISH analysis. The lines are potentially useful for molecular genetic analysis of novel C. abyssinica genes or alleles contributing to traits relevant for oilseed rape (B. napus) breeding.

Behaviour of Sinapis alba chromosomes in a Brassica napus background revealed by genomic in-situ hybridization

Genomic in-situ hybridization (GISH) was applied to study the behaviour of addition chromosomes in first and second backcross (BC) progenies of hybrids between Brassica napus ssp. napus L. (AACC, 2n = 38) and Sinapis alba L. (SS, 2n = 24) produced by electrofusion. With GISH using genomic DNA of S. alba was used as probe it was possible to clearly distinguish both of the parental genomes and effectively monitor the fate of S. alba chromosomes in the BC(1) and BC(2) progenies. GISH analysis confirmed the sesquidiploid genome composition (AACCS) of the BC(1) progenies, which contained 38 chromosomes from B. napus and 12 chromosomes from S. alba. Genome painting in the pollen mother cells (PMCs) of the BC(1) plants revealed intergenomic association between B. napus and S. alba chromosomes, whereby a maximum of 4 trivalents between AC and S chromosomes were identified at metaphase I. In the BC(2) progenies, aneuploids with different numbers of additional chromosomes from S. alba, ranging from 1 to 7, were confirmed. Three putative monosomic alien addition lines were characterized, and the results are discussed with respect to the potential for intergenomic chromosome recombination.