Characterization of a library from a single microdissected oat (Avena sativa L.) chromosome

Microdissection of the Ah01 chromosome in upland cotton and microcloning of resistance gene anologs from the single chromosome

BACKGROUND

Chromosome microdissection is one of the most important techniques in molecular cytogenetic research. Cotton (Gossypium Linnaeus, 1753) is the main natural fiber crop in the world. The resistance gene analog (RGA) cloning after its single chromosome microdissection can greatly promote cotton genome research and breeding.

RESULTS

Using the linker adaptor PCR (LA-PCR) with the primers of rice disease-resistance homologues, three nucleotide sequences PS016 (KU051681), PS054 (KU051682), and PS157 (KU051680) were obtained from the chromosome A_h01 of upland cotton (cv. TM-1). The Blast results showed that the three sequences are the nucleotide binding site-leucine rich repeat (NBS-LRR) type RGAs. Clustering results indicated that they are homologous to these published RGAs. Thus, the three RGAs can definitely be confirmed as NBS-LRR class of RGAs in upland cotton.

CONCLUSIONS

Using single chromosome microdissection technique, DNA libraries containing cotton RGAs were obtained. This technique can promote cotton gene cloning, marker development and even the improvement of cotton genome research and breeding.

Isolation and application of P genome-specific DNA sequences of Agropyron Gaertn. in Triticeae

Different types of P genome sequences and markers were developed, which could be used to analyze the evolution of P genome in Triticeae and identify precisely wheat- A. cristatum introgression lines. P genome of Agropyron Gaertn. plays an important role in Triticeae and could provide many desirable genes conferring high yield, disease resistance, and stress tolerance for wheat genetic improvement. Therefore, it is significant to develop specific sequences and functional markers of P genome. In this study, 126 sequences were isolated from the degenerate oligonucleotide primed-polymerase chain reaction (DOP-PCR) products of microdissected chromosome 6PS. Forty-eight sequences were identified as P genome-specific sequences by dot-blot hybridization and DNA sequences analysis. Among these sequences, 22 displayed the characteristics of retrotransposons, nine and one displayed the characteristics of DNA transposons and tandem repetitive sequence, respectively. Fourteen of 48 sequences were determined to distribute on different regions of P genome chromosomes by fluorescence in situ hybridization, and the distributing regions were as following: all over P genome chromosomes, centromeres, pericentromeric regions, distal regions, and terminal regions. We compared the P genome sequences with other genome sequences of Triticeae and found that the similar sequences of the P genome sequences were widespread in Triticeae, but differentiation occurred to various extents. Additionally, thirty-four molecular markers were developed from the P genome sequences, which could be used for analyzing the evolutionary relationship among 16 genomes of 18 species in Triticeae and identifying P genome chromatin in wheat-A. cristatum introgression lines. These results will not only facilitate the study of structure and evolution of P genome chromosomes, but also provide a rapid detecting tool for effective utilization of desirable genes of P genome in wheat improvement.

Use of laser microdissection for the construction of Humulusjaponicus Siebold et Zuccarini, 1846 (Cannabaceae) sex chromosome-specific DNA library and cytogenetics analysis

Dioecy is relatively rare among plant species, and distinguishable sex chromosomes have been reported in few dioecious species. The multiple sex chromosome system (XX/XY1Y2) of Humulusjaponicus Siebold et Zuccarini, 1846 differs from that of other members of the family Cannabaceae, in which the XX/XY chromosome system is present. Sex chromosomes of Humulusjaponicus were isolated from meiotic chromosome spreads of males by laser microdissection with the P.A.L.M. MicroLaser system. The chromosomal DNA was directly amplified by degenerate oligonucleotide primed polymerase chain reaction (DOP-PCR). Fast fluorescence in situ hybridization (FAST-FISH) using a labeled, chromosome-specific DOP-PCR product as a probe showed preferential hybridization to sex chromosomes. In addition, the DOP-PCR product was used to construct a short-insert, Humulusjaponicus sex chromosomes-specific DNA library. The randomly sequenced clones showed that about 12% of them have significant homology to Humuluslupulus and 88% to Cannabissativa Linnaeus, 1753 sequences from GenBank database. Forty-four percent of the sequences show homology to plant retroelements. It was concluded that laser microdissection is a useful tool for isolating the DNA of sex chromosomes of Humulusjaponicus and for the construction of chromosome-specific DNA libraries for the study of the structure and evolution of sex chromosomes. The results provide the potential for identifying unique or sex chromosome-specific sequence elements in Humulusjaponicus and could aid in the identification of sex chromosome-specific repeat and coding regions through chromosome isolation and genome complexity reduction.

Microdissection and painting of the Y chromosome in spinach (Spinacia oleracea)

Spinach has long been used as a model for genetic and physiological studies of sex determination and expression. Although trisomic analysis from a cross between diploid and triploid plants identified the XY chromosome as the largest chromosome, no direct evidence has been provided to support this at the molecular level. In this study, the largest chromosomes of spinach from mitotic metaphase spreads were microdissected using glass needles. Degenerate oligonucleotide primed polymerase chain reaction was used to amplify the dissected chromosomes. The amplified products from the Y chromosome were identified using the male-specific marker T11A. For the first time, the largest spinach chromosome was confirmed to be a sex chromosome at the molecular level. PCR products from the isolated chromosomes were used in an in situ probe mixture for painting the Y chromosome. The fluorescence signals were mainly distributed on all chromosomes and four pair of weaker punctate fluorescence signal sites were observed on the terminal region of two pair of autosomes. These findings provide a foundation for the study of sex chromosome evolution in spinach.

Characterization of chromosome-specific genomic DNA from hexaploid oat

We have sequenced, assembled, and characterized a set of complexity-reduced genomic clones derived from a chromosome 18D-specific library from hexaploid oat ( Avena sativa L.). Sequences from 314 clones were assembled into 99 contigs of identical or nearly identical sequence. The Censor tool was used to identify similarity to known and characterized repeat sequences in RepBase. Eight repeat classes were scattered throughout 50 contigs, with most repeats belonging to seven transposon and retrotransposon classes. After accounting for known repeats, additional matches to orthologous genes from other species were identified in 24 regions of 22 contigs, and an additional 47 regions matched genomic sequences from oat and other related species. These results provide information about the types and density of transposable elements in the oat genome, as well as the potential for identifying unique or chromosome-specific sequence elements in oat. Overall, these results predict a low success rate in identifying chromosome-specific coding regions in oat through chromosome isolation and genome complexity reduction.

The development of chromosome microdissection and microcloning technique and its applications in genomic research

The technique of chromosome microdissection and microcloning has been developed for more than 20 years. As a bridge between cytogenetics and molecular genetics, it leads to a number of applications: chromosome painting probe isolation, genetic linkage map and physical map construction, and expressed sequence tags generation. During those 20 years, this technique has not only been benefited from other technological advances but also cross-fertilized with other techniques. Today, it becomes a practicality with extensive uses. The purpose of this article is to review the development of this technique and its application in the field of genomic research. Moreover, a new method of generating ESTs of specific chromosomes developed by our lab is introduced. By using this method, the technique of chromosome microdissection and microcloning would be more valuable in the advancement of genomic research.

[Construction and identification of the chromosome specific DNA library.]

The objective of the present study was to construct a human chromosome 21 specific DNA library for further use in research of genetic disease. Human chromosome 21 microdissected from the peripheral blood cells were subjected to repeatedly incubation in gradient temperature bath to release DNA. The library of chromosome 21 was constructed using the DNA fragment of 100-500 bp and 500-2 000 bp recovered from the products of DOP-PCR. Florescence in situ hy-bridization (FISH) and dot blotting analyses were carried out to assess the chromosome 21 specificity of the DNA library. The results indicated that DNA of chromosome 21 was released easily after repeatedly incubation in gradient temperature bath. Recovery of DNA fragments from DOP-PCR in different size ranges improved the efficiency of cloning of large fragments. Both FISH and dot blotting analyses revealed that the DNA library constructed in this study was chromosome 21-specific. This DNA library facilitates identification and investigation of the chromosome 21 related abnormality.

Microisolation of the chicken Z chromosome and construction off microclone libraries

A simple method was used to adapt a standard light microscope for the collection of chicken Z chromosomes from mitotic-metaphase spreads. The DNA of the collected chromosomes was enzymatically amplified using a partially degenerate primer. The resulting sequences, within a size range of 200-800 bp, were cloned to produce a Z chromosome DNA library, using blunt-end ligation into a SmaI-digested pUC18 plasmid (the SureClone system; Pharmacia, U.S.A.). The microcloning experiments produced 1250 clones; the size range of the cloned inserts was 250-800 bp, with an average of 480 bp (176 clones examined). Using male chicken genomic DNA as a probe, 10 out of 17 randomly selected clones showed strong positive signals on Southern blots, confirming the origin of the inserts as chicken DNA. In addition, the Z-chromosome origin of a selected microclone was verified in a semiquantitative Southern blot hybridization that showed positive signals with intensities that were approximately twice as strong for male (ZZ) as for female (ZW) chicken genomic DNA when the clone was used as a probe. The value of these libraries in further analysis of the chicken Z chromosome is discussed.

Rapid EST isolation from chromosome 1R of rye

BACKGROUND

To obtain important expressed sequence tags (ESTs) located on specific chromosomes is currently difficult. Construction of single-chromosome EST library could be an efficient strategy to isolate important ESTs located on specific chromosomes. In this research we developed a method to rapidly isolate ESTs from chromosome 1R of rye by combining the techniques of chromosome microdissection with hybrid specific amplification (HSA).

RESULTS

Chromosome 1R was isolated by a glass needle and digested with proteinase K (PK). The DNA of chromosome 1R was amplified by two rounds of PCR using a degenerated oligonucleotide 6-MW sequence with a Sau3AI digestion site as the primer. The PCR product was digested with Sau3AI and linked with adaptor HSA1, then hybridized with the Sau3AI digested cDNA with adaptor HSA2 of rye leaves with and without salicylic acid (SA) treatment, respectively. The hybridized DNA fragments were recovered by the HSA method and cloned into pMD18-T vector. The cloned inserts were released by PCR using the partial sequences in HSA1 and HSA2 as the primers and then sequenced. Of the 94 ESTs obtained and analyzed, 6 were known sequences located on rye chromosome 1R or on homologous group 1 chromosomes of wheat; all of them were highly homologous with ESTs of wheat, barley and/or other plants in Gramineae, some of which were induced by abiotic or biotic stresses. Isolated in this research were 22 ESTs with unknown functions, probably representing some new genes on rye chromosome 1R.

CONCLUSION

We developed a new method to rapidly clone chromosome-specific ESTs from chromosome 1R of rye. The information reported here should be useful for cloning and investigating the new genes found on chromosome 1R.

Laser Microdissection‐Based Analysis of Plant Sex Chromosomes

A recent progress in plant molecular biology has led to enormous available data of DNA sequences, including complete nuclear genomes of Arabidopsis, rice, and poplar. On the other hand, in plant species with more complex genomes, containing widespread repetitive sequences, it is important to establish genomic resources that help us to focus on particular part of genomes. Laser technology enables to handle with specific subcellular structures or even individual chromosomes. Here we present a comprehensive protocol to isolate and characterize DNA sequences derived from the sex chromosomes of white campion (Silene latifolia). This dioecious plant has become the most favorite model to study the structure, function, and evolution of plant sex chromosomes due to a large and distinguishable size of both the X and Y chromosomes. The protocol includes a versatile technique to prepare metaphase chromosomes from either germinating seeds or in vitro cultured hairy roots. Such slides can be used for laser chromosome microdissection, fluorescence in situ-hybridization mapping, and immunostaining. Here we also demonstrate some applications of the laser-dissected chromosome template, especially a modified FAST-FISH technique to paint individual chromosomes, and construction and screening of chromosome-specific DNA libraries.

Microdissection and microcloning of plant chromosomes

Cytogenetic and molecular tools play an increasingly important role in plant genome research. A number of interesting applications that involve chromosome painting, the relationship between specific chromosomes and specific linkage groups, the relationships between physical and genetic distances on linkage maps, and the isolation of genes of interest, have been the subjects of recently published research. The aim of this paper is to review the different techniques available for chromosome microdissection and microcloning, and their use for the study of plant genomes. The quality of chromosomal DNA obtained is considered, and some recent results from our laboratory are presented.

Cloning of resistance gene analogs located on the alien chromosome in an addition line of wheat-Thinopyrum intermedium

Homology-based gene/gene-analog cloning method has been extensively applied in isolation of RGAs (resistance gene analogs) in various plant species. However, serious interference of sequences on homoeologous chromosomes in polyploidy species usually occurred when cloning RGAs in a specific chromosome. In this research, the techniques of chromosome microdissection combined with homology-based cloning were used to clone RGAs from a specific chromosome of Wheat-Thinopyrum alien addition line TAi-27, which was derived from common wheat and Thinopyrum intermedium with a pair of chromosomes from Th. intermedium. The alien chromosomes carry genes for resistance to BYDV. The alien chromosome in TAi-27 was isolated by a glass needle and digested with proteinase K. The DNA of the alien chromosome was amplified by two rounds of Sau3A linker adaptor-mediated PCR. RGAs were amplified by PCR with the degenerated primers designed based on conserved domains of published resistance genes (R genes) by using the alien chromosome DNA, genomic DNA and cDNA of Th. intermedium, TAi-27 and 3B-2 (a parent of TAi-27) as templates. A total of seven RGAs were obtained and sequenced. Of which, a constitutively expressed single-copy NBS-LRR type RGA ACR 3 was amplified from the dissected alien chromosome of TAi-27, TcDR 2 and TcDR 3 were from cDNA of Th. intermedium, AcDR 3 was from cDNA of TAi-27, FcDR 2 was from cDNA of 3B-2, AR 2 was from genomic DNA of TAi-27 and TR 2 was from genomic DNA of Th. intermedium. Sequence homology analyses showed that the above RGAs were highly homologous with known resistance genes or resistance gene analogs and belonged to NBS-LRR type of R genes. ACR 3 was recovered by PCR from genomic DNA and cDNA of Th. intermedium and TAi-27, but not from 3B-2. Southern hybridization using the digested genomic DNA of Th. intermedium, TAi-27 and 3B-2 as the template and ACR 3 as the probe showed that there is only one copy of ACR 3 in the genome of Th. intermedium and TAi-27, but it is absent in 3B-2. The ACR 3 could be used as a specific probe of the R gene on the alien chromosome of TAi-27. Results of Northern hybridization suggested that ACR 3 was constitutively expressed in Th. intermedium and TAi-27, but not 3B-2, and expressed higher in leaves than in roots. This research demonstrated a new way to clone RGAs located on a specific chromosome. The information reported here should be useful to understand the resistance mechanism of, and to clone resistant genes from, the alien chromosome in TAi-27.

Screening and analysis of differentially expressed genes from an alien addition line of wheat Thinopyrum intermedium induced by barley yellow dwarf virus infection

The alien addition line TAI-27 contains a pair of chromosomes of Thinopyrum intermedium that carry resistance against barley yellow dwarf virus (BYDV). A subtractive library was constructed using the leaves of TAI-27, which were infected by Schizaphis graminum carrying the GAV strain of BYDV, and the control at the three-leaf stage. Nine differentially expressed genes were identified from 100 randomly picked clones and sequenced. Two of the nine clones were highly homologous with known genes. Of the remaining seven cDNA clones, five clones matched with known expressed sequence tag (EST) sequences from wheat and (or) barley whereas the other two clones were unknown. Five of the nine differentially expressed sequences (WTJ9, WTJ11, WTJ15, WTJ19, and WTJ32) were highly homologous (identities >94%) with ESTs from wheat or barley challenged with pathogens. These five sequences and another one (WTJ18) were also highly homologous (identities >86%) with abiotic stress induced ESTs in wheat or barley. Reverse Northern hybridization showed that seven of the nine differentially expressed cDNA sequences hybridized with cDNA of T. intermedium infected by BYDV. Three of these also hybridized with cDNA of line 3B-2 (a parent of TAI-27) infected by BYDV. The alien chromosome in TAI-27 was microdissected. The second round linker adaptor mediated PCR products of the alien chromosomal DNA were labeled with digoxygenin and used as the probe to hybridize with the nine differentially expressed genes. The analysis showed that seven differentially expressed genes were homologous with the alien chromosome of TAI-27. These seven differentially expressed sequences could be used as ESTs of the alien chromosome of TAI-27. This research laid the foundation for screening and cloning of new specific functional genes conferring resistance to BYDV and probably other pathogens.

Microdissection and molecular manipulation of single chromosomes in woody fruit trees with small chromosomes using pomelo (Citrus grandis) as a model. II. Cloning of resistance gene analogs from single chromosomes

Amplification of resistance gene analogs (RGAs) is both a useful method for acquiring DNA markers closely linked to disease resistance (R) genes and a potential approach for the rapid cloning of R genes in plants. However, the screening of target sequences from among the numerous amplified RGAs can be very laborious. The amplification of RGAs from specific chromosomes could greatly reduce the number of RGAs to be screened and, consequently, speed up the identification of target RGAs. We have developed two methods for amplifying RGAs from single chromosomes. Method 1 uses products of Sau3A linker adaptor-mediated PCR (LAM-PCR) from a single chromosome as the templates for RGA amplification, while Method 2 directly uses a single chromosomal DNA molecule as the template. Using a pair of degenerate primers designed on the basis of the conserved nucleotide-binding-site motifs in many R genes, RGAs were successfully amplified from single chromosomes of pomelo using both these methods. Sequencing and cluster analysis of RGA clones obtained from single chromosomes revealed the number, type and organization of R-gene clusters on the chromosomes. We suggest that Method 1 is suitable for analyzing chromosomes that are unidentifiable under a microscope, while Method 2 is more appropriate when chromosomes can be clearly identified.

Microdissection and molecular manipulation of single chromosomes in woody fruit trees with small chromosomes using pomelo (Citrus grandis) as a model. I. Construction of single chromosomal DNA libraries

Construction of single chromosomal DNA libraries by means of chromosome microdissection and microcloning will be useful for genomic research, especially for those species that have not been extensively studied genetically. Application of the technology of microdissection and microcloning to woody fruit plants has not been reported hitherto, largely due to the generally small sizes of metaphase chromosomes and the difficulty of chromosome preparation. The present study was performed to establish a method for single chromosome microdissection and microcloning in woody fruit species using pomelo as a model. The standard karyotype of a pomelo cultivar ( Citrus grandis cv. Guanxi) was established based on 20 prometaphase photomicrographs. According to the standard karyotype, chromosome 1 was identified and isolated with fine glass microneedles controlled by a micromanipulator. DNA fragments ranging from 0.3 kb to 2 kb were acquired from the isolated single chromosome 1 via two rounds of PCR mediated by Sau3A linker adaptors and then cloned into T-easy vectors to generate a DNA library of chromosome 1. Approximately 30,000 recombinant clones were obtained. Evaluation based on 108 randomly selected clones showed that the sizes of the cloned inserts varied from 0.5 kb to 1.5 kb with an average of 860 bp. Our research suggests that microdissection and microcloning of single small chromosomes in woody plants is feasible.

Isolation of A/D and C genome specific dispersed and clustered repetitive DNA sequences from Avena sativa

DNA gel-blot and in situ hybridization with genome-specific repeated sequences have proven to be valuable tools in analyzing genome structure and relationships in species with complex allopolyploid genomes such as hexaploid oat (Avena sativa L., 2n = 6x = 42; AACCDD genome). In this report, we describe a systematic approach for isolating genome-, chromosome-, and region-specific repeated and low-copy DNA sequences from oat that can presumably be applied to any complex genome species. Genome-specific DNA sequences were first identified in a random set of A. sativa genomic DNA cosmid clones by gel-blot hybridization using labeled genomic DNA from different Avena species. Because no repetitive sequences were identified that could distinguish between the A and D gneomes, sequences specific to these two genomes are refereed to as A/D genome specific. A/D or C genome specific DNA subfragments were used as screening probes to identify additional genome-specific cosmid clones in the A. sativa genomic library. We identified clustered and dispersed repetitive DNA elements for the A/D and C genomes that could be used as cytogenetic markers for discrimination of the various oat chromosomes. Some analyzed cosmids appeared to be composed entirely of genome-specific elements, whereas others represented regions with genome- and non-specific repeated sequences with interspersed low-copy DNA sequences. Thus, genome-specific hybridization analysis of restriction digests of random and selected A. sativa cosmids also provides insight into the sequence organization of the oat genome.

Genetic and physical mapping of Lrk10-like receptor kinase sequences in hexaploid oat (Avena sativa L.)

Oat receptor-like kinase gene sequences, homologous to the Lrk10 gene from wheat (Triticum aestivum L.), were mapped in oat (Avena sativa L.). PCR primers designed from the wheat Lrk10 were used to produce ALrk10 from oat. Two DNA sequences, ALrk1A1 and ALrk4A5, were produced from primers designed from coding and noncoding regions of ALrk10. Their use as RFLP probes indicated that the kinase genes mapped to four loci on different hexaploid oat 'Kanota' x 'Ogle' linkage groups (4_12, 5, 6, and 13) and to a fifth locus unlinked to other markers. Three of these linkage groups contain a region homologous to the short arm of chromosome I of wheat and the fourth contains a region homologous to chromosome 3 of wheat. Analysis with several nullisomics of oat indicated that two of the map locations are on satellite chromosomes. RFLP mapping in a 'Dumont' x 'OT328' population indicated that one map location is closely linked to Pg9, a resistance gene to oat stem rust (Puccinia graminis subsp. avenae). Comparative mapping indicates this to be the region of a presumed cluster of crown rust (Puccinia coronata subsp. avenae) and stem rust resistance genes (Pg3, Pg9, Pc44, Pc46, Pc50, Pc68, Pc95, and PcX). The map position of several RGAs located on KO6 and KO3_38 with respect to Lrk10 and storage protein genes are also reported.

Development and applications of a complete set of rice telotrisomics

We previously isolated a complete set of primary trisomics along with many other aneuploids from triploid plants derived from an indica rice variety "Zhongxian 3037." About 30,000 progeny from these trisomic and aneuploid plants were grown each year from 1994 to 1999. The variants that differed morphologically from both the diploids and the original primary trisomics were collected for cytological identification. From these variants, a complete set of telotrisomics covering all 24 rice chromosome arms was obtained. The identities of the extra chromosomes were further confirmed by dosage analysis of the RFLP markers on extra chromosome arms. The telocentric nature of the extra chromosomes in these stocks was verified by fluorescence in situ hybridization (FISH) using a rice centromeric BAC clone as a marker probe. In general, the shorter the extra chromosome arm of a telotrisomic, the stronger the resemblance it bears to the diploid; the longer the extra chromosome arm, the stronger the resemblance to the corresponding primary trisomic. We demonstrated that DNA clones can be rapidly assigned to specific chromosome arms by dosage analysis with the telotrisomics. We also showed that telotrisomics are valuable tools for chromosome microdissection and for developing chromosome-specific DNA markers.

Molecular aids for integration of alien chromatin through wide crosses

Wide crosses in wheat have now been performed for over 100 years. In that time, approximately 100 genes have been transferred for numerous traits, including biotic and abiotic stresses and value-added traits. Resistance genes from alien sources do become defeated with time, so the search for additional variability must continue. Recent screening of alien species has identified accessions with multiple pest resistance plus combinations of pest resistance and value-added traits. The majority of existing induced recombinants are of a noncompensating type with considerable linkage drag, so sequential useage of Ph mutants is recommended to produce smaller interstitial recombinants. Molecular methods, including GISH, RAPD, RFLP, AFLP, and microsatellites, are being widely used to identify integrated alien chromosomes, chromosome segments, and genes.Key words: Triticum aestivium, molecular markers, disease resistance, gene introgression, interspecific hybrids.

Laser isolation of plant sex chromosomes: studies on the DNA composition of the X and Y sex chromosomes of Silene latifolia

X and Y sex chromosomes from the dioecious plant Silene latifolia (white campion) were isolated from mitotic metaphase chromosome preparations on polyester membranes. Autosomes were ablated using an argon ion laser microbeam and isolated sex chromosomes were then recovered on excised fragments of polyester membrane. Sex chromosome associated DNA sequences were amplified using the degenerate oligonucleotide primed polymerase chain reaction (DOP-PCR) and pools of DOP-PCR products were used to investigate the genomic organization of the S. latifolia sex chromosomes. The chromosomal locations of cloned sex chromosome repeat sequences were analysed by fluorescence in situ hybridization and data complementary to laser ablation studies were obtained by genomic in situ hybridization. In combination, these studies demonstrate that the X and Y sex chromosomes of S. latifolia are of very similar DNA composition and also that they share a significant repetitive DNA content with the autosomes. The evolution of sex chromosomes in Silene is discussed and compared with that in another dioecious species, Rumex acetosa.

Microprotoplast-mediated transfer of single specific chromosomes between sexually incompatible plants

Microprotoplast-mediated chromosome transfer (MMCT) through fusion of small (subdiploid) microprotoplasts of a transgenic triploid potato (Solanum tuberosum) cell line with leaf protoplasts of tobacco (Nicotiana tabacum) and the wild tomato species Lycopersicon peruvianum is reported. The microprotoplasts contained one or a few chromosomes. Monosomic addition plants were produced from the fusion products. We employed mass-scale induction of micronuclei in donor suspension cells of potato using the microtubule inhibitor Cremart. Protoplasts were isolated from micronucleated cells after incubation in a cell wall digesting enzyme mixture. The microprotoplasts were isolated from the micronucleated protoplasts by high-speed centrifugation. By using sequential filtration, small microprotoplasts containing one or few chromosomes were separated from the bigger subdiploid microprotoplasts. These small microprotoplasts were fused with recipient protoplasts of tobacco or tomato using polyethylene glycol. The selectable marker kanamycin resistance (KanR) and the reporter gene β-glucuronidase (gus), carried by the donor potato chromosome, were used for the selection of fusion products and the isolation of hybrid calli. Several monosomic addition plants were obtained within the short period of 3–4 months after fusion. These contained one potato chromosome carrying a single copy of gus and one or two copies of the neomycin phosphotransferase (nptII) gene conferring KanR, and the complete set of chromosomes of tobacco or tomato, as revealed by genomic in situ hybridization and Southern blot hybridization. The alien genes, gus and nptII, were stably expressed in both the tobacco and tomato backgrounds. They were transmitted to the progeny after backcrossing to tomato. Monosomic and disomic additions, and some introgression plants showing integration of gus and nptII in the tomato genome, were recovered in the first backcross progeny. The potential value of MMCT for the transfer of economically important traits, genome analysis, and gene expression is discussed. Key words : chromosome transfer, microprotoplast fusion, monosomic–disomic additions, sexual transmission, DNA integration, alien gene expression.