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Alpinia malaccensis (Burm.f.) Roscoe is a rare plant in Java, Indonesia, that produces essential oils. Its sustained decline causes great concern for future uses. Therefore, the study of its diversity in its natural habitat to predict future survival needs serious focus. The present study aims to determine the genetic diversity of A. malaccensis in Java based on ISSR markers. The sampling of a total of 11 populations yielded 33 accessions, which underwent amplifying using 12 ISSR primers. Using the molecular data analyzed their relationships, population structure, and genetic diversity. The UPGMA cluster, structure, and principal component analysis (PCA) demonstrated that the accessions divide in three groups, a result that correlates with their geography in Java. Group I consisted of var. malaccensis populations, while groups II and III comprised the var. nobilis populations, which proved truer among populations of var. nobilis. The genetic diversity category of A. malaccensis showed moderate based on Nei's genetic diversity (h = 0.2892) and Shannon's information index (I = 0.4438). The coefficient of genetic differentiation (GST) and molecular variance among the populations displayed higher within the individual population, which revealed a significant genetic variance among the 11 populations of A. malaccensis. The latest results confirm that ISSR markers can help distinguish the genotypes of A. malaccensis.

Drought tolerance in rice is controlled by several genes and is inherited quantitatively. Low genetic map density and the use of phenotypic traits that do not reflect the corresponding tolerance level have been obstacles in genetic analyses performed to identify genes that control drought-tolerant traits in rice. The current study aimed to construct a genetic map from high-density single-nucleotide polymorphism (SNP) markers generated from genome sequences of recombinant inbred lines (RILs), derived from IR64 × Hawara Bunar. Moreover, it sought to analyze the quantitative trait loci (QTL) and identify the drought tolerance candidate genes. A linkage map along 1980 cM on the 12 rice chromosomes was constructed employing 55,205 SNP markers resulting from the RIL genome sequences. A total of 175 morpho-physiological traits pertaining to drought stress were determined. A total of 41 QTLs were detected in 13 regions on rice chromosomes 1, 3, 6, 8, 9, and 12. Moreover, three hotspot QTL regions were found on chromosomes 6 and 8, along with two major QTL on chromosome 9. Differential gene expression for the loci within the QTL physical map intervals revealed many potential candidate genes. The markers tightly linked to the QTL and their candidate genes can potentially be used for pyramiding in marker-assisted breeding in order to achieve genetic improvement concerning the tolerance of rice to drought stress. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1007/s12298-021-01095-y.

There is a decrease in the land available for rice cultivation due to the rapid conversion to urban uses. Subsequently, acid soil could be an alternative land cultivating rice, but will require the use of aluminum (Al)-tolerant rice varieties. This Al tolerance trait is genetically controlled, and there is a need to discover more genes needed to develop Al-tolerant rice. Therefore, the objective of this study was to clone and characterize a novel Al tolerance gene isolated from a local cultivar of Indonesian rice. The gene cloning was conducted based on the rye/rice microsynteny relationship. In addition, the root growth and gene expression analyses were performed to verify the role of the gene on Al tolerance in gene-silenced rice and in overexpressed transgenic tobacco. The results showed an Al tolerance candidate gene, OsGERLP, was successfully cloned from rice cv. Hawara Bunar, with its gene encoding a protein similar to a bacterial ribosomal L32 protein. Additionally, the analysis showed that low gene expression caused the gene-silenced rice to be sensitive to Al, while high expression induced the Al tolerance in transgenic tobacco. Furthermore, it was discovered that the gene expression level in both plants was in line with the lower expression of the OsFRDL4 gene in the silenced rice and the high expression of the MATE gene in transgenic tobacco also with the higher citrate secretion from transgenic tobacco roots. In conclusion, the OsGERLP gene could act as a regulator for other Al tolerance genes, with the potential to develop Al-tolerant rice varieties.

Morphological and Molecular Diversity of Cassava (Manihot esculenta Crantz) Resulted from In Vitro PropagationIn vitro propagation of cassava (Manihot esculenta Crantz) on medium containing plant growth regulator (PGR) may induce morphological variation. This study aimed to analyze the morphological and genetic diversity of 13 genotypes of cassava resulted from in vitro propagation and stem cuttings based on 11 vegetative characters and 7 ISSR markers. Morphological and genetic characters were scored and used for clustering using NTSYS-pc 2.11a. Roti control and Adira 4 control genotypes that were in vitro propagated without PGR addition showed different morphological characters with Roti variant and FEC-25 genotypes that were in vitro propagated with the addition of PGR. Morphological and molecular characters of 13 genotypes showed high diversity. Clustering analysis based on morphological characters classified the in vitro propagated and control plants into four groups at 45.6% similarity. Clustering analysis based on molecular characters classified the plants into three groups at 66.0% similarity.Keywords: cassava; diversity; in vitro; ISSR; morphologyABSTRAKPerbanyakan tanaman ubi kayu (Manihot esculenta Crantz) secara in vitro menggunakan zat pengatur tumbuh (ZPT) diyakini dapat menginduksi variasi morfologi. Tujuan dari penelitian ini adalah untuk menganalisis keragaman morfologi dan molekuler dari 13 genotipe ubi kayu hasil perbanyakan in vitro dan perbanyakan dengan stek batang berdasarkan 11 karakter vegetatif dan 7 penanda ISSR. Karakter morfologi dan molekuler diskor untuk analisis kelompok menggunakan program NTSYS-pc 2.11a. Genotipe Roti kontrol dan Adira 4 kontrol yang merupakan hasil perbanyakan in vitro tanpa penambahan ZPT menunjukkan perbedaan variasi morfologi dengan genotipe Roti varian dan FEC-25 yang merupakan tanaman hasil perbanyakan dengan penambahan ZPT. Hasil analisis pada 13 genotipe menunjukkan adanya keragaman yang tinggi. Hasil analisis kelompok berdasarkan penanda morfologi memisahkan antara genotipe hasil perbanyakan secara in vitro yang ditambah ZPT dengan tanaman kontrolnya ke dalam 4 kelompok dengan nilai koefisen similaritas 45,6%. Hasil analisis kelompok berdasarkan penanda molekuler memisahkan antara genotipe hasil perbanyakan secara in vitro yang ditambah ZPT dengan tanaman kontrolnya ke dalam 3 kelompok dengan nilai koefisen similaritas 66,0%.

Iron (Fe) toxicity is one of the limiting factors that can lead to the decrease of rice yield in paddy fields. Association studies to identify potential alleles or markers linked to iron toxicity tolerant trait can be carried out using high throughput single nucleotide polymorphisms (SNPs). We conducted an association study for Fe toxicity tolerance characters, using Forty-five double haploid lines derived from reciprocal double-crossing, i.e. IR54 / Parekaligolara // Bio110 / Markuti in high Fe wetland rice field. Genome-wide association study was carried out using 384 SNP-plex markers distributed on 12 rice chromosomes. A total of 77 SNPs were significantly associated with the Fe toxicity tolerance-related traits. Functional annotation allowed us to shortlist four SNP markers associated with Fe toxicity tolerance trait, i.e.: TBGI204006, TBGI310247, id9006377, and id10000498. The research suggests that association studies followed by functional annotation can effectively detect potential alleles and candidate genes for the trait. The identified QTL and genes provided valuable sources for future genetic improvement of Fe tolerant rice lines.

Amplified fragment length polymorphism markers were evaluated to determine the genetic diversity and relationships among cultivated and weedy ryes (Secale cereale L.) using a large global set of accessions. On the basis of 395 polymorphic bands resulted from nine PstI-MseI primer combinations, cultivated rye exhibited higher average genetic diversity (Ht = 0.34) than that of the weedy rye (Ht = 0.27), however, it had lower genetic differentiation (Fst = 0.16). The average genetic diversity of cultivated rye varied from region to region ranging from 0.21 to 0.31. As expected, all cultivated accessions clustered together both in dendrogram and principal coordinate diagram indicating common breeding program selection criteria based on similar value-added agronomic characteristics. A clustering of cultivated rye accessions into groups based strictly on geographical origin was not found. The relationships among cultivated, weedy and wild ryes were discussed.

To gain insights into the structure and function of the wheat (Triticum aestivum L.) genomes, we identified 278 ESTs related to abiotic stress (cold, heat, drought, salinity, and aluminum) from 7671 ESTs previously mapped to wheat chromosomes. Of the 278 abiotic stress related ESTs, 259 (811 loci) were assigned to chromosome deletion bins and analyzed for their distribution pattern among the 7 homoeologous chromosome groups. Distribution of abiotic stress related EST loci were not uniform throughout the different regions of the chromosomes of the 3 wheat genomes. Both the short and long arms of group 4 chromosomes showed a higher number of loci in their distal regions compared with proximal regions. Of the 811 loci, the number of mapped loci on the A, B, and D genomes were 258, 281, and 272, respectively. The highest number of abiotic stress related loci were found in homoeologous chromosome group 2 (142 loci) and the lowest number were found in group 6 (94 loci). When considering the genome-specific ESTs, the B genome showed the highest number of unique ESTs (7 loci), while none were found in the D genome. Similarly, considering homoeologous group-specific ESTs, group 2 showed the highest number with 16 unique ESTs (58 loci), followed by group 4 with 9 unique ESTs (33 loci). Many of the classified proteins fell into the biological process categories associated with metabolism, cell growth, and cell maintenance. Most of the mapped ESTs fell into the category of enzyme activity (28%), followed by binding activity (27%). Enzymes related to abiotic stress such as β-galactosidase, peroxidase, glutathione reductase, and trehalose-6-phosphate synthase were identified. The comparison of stress-responsive ESTs with genomic sequences of rice (Oryza sativa L.) chromosomes revealed the complexities of colinearity. This bin map provides insight into the structural and functional details of wheat genomic regions in relation to abiotic stress.

Characterization and manipulation of aluminum (Al) tolerance genes offers a solution to Al toxicity problems in crop cultivation on acid soil, which composes approximately 40% of all arable land. By exploiting the rice (Oryza sativa L.)/rye (Secale cereale L.) syntenic relationship, the potential for map-based cloning of genes controlling Al tolerance in rye (the most Al-tolerant cereal) was explored. An attempt to clone an Al tolerance gene (Alt3) from rye was initiated by using DNA markers flanking the rye Alt3 gene, from many cereals. Two rice-derived, PCR-based markers flanking the Alt3 gene, B1 and B4, were used to screen 1,123 plants of a rye F2 population segregating for Alt3. Fifteen recombinant plants were identified. Four additional RFLP markers developed from rice genes/putative genes, spanning 10 kb of a 160-kb rice BAC, were mapped to the Alt3 region. Two rice markers flanked the Alt3 locus at a distance of 0.05 cM, while two others co-segregated with it. The rice/rye micro-colinearity worked very well to delineate and map the Alt3 gene region in rye. A rye fragment suspected to be part of the Alt3 candidate gene was identified, but at this level, the rye/rice microsynteny relationship broke down. Because of sequence differences between rice and rye and the complexity of the rye sequence, we have been unable to clone a full-length candidate gene in rye. Further attempts to clone a full-length rye Alt3 candidate gene will necessitate the creation of a rye large-insert library.

This report describes the rationale, approaches, organization, and resource development leading to a large-scale deletion bin map of the hexaploid (2n = 6x = 42) wheat genome (Triticum aestivum L.). Accompanying reports in this issue detail results from chromosome bin-mapping of expressed sequence tags (ESTs) representing genes onto the seven homoeologous chromosome groups and a global analysis of the entire mapped wheat EST data set. Among the resources developed were the first extensive public wheat EST collection (113,220 ESTs). Described are protocols for sequencing, sequence processing, EST nomenclature, and the assembly of ESTs into contigs. These contigs plus singletons (unassembled ESTs) were used for selection of distinct sequence motif unigenes. Selected ESTs were rearrayed, validated by 5′ and 3′ sequencing, and amplified for probing a series of wheat aneuploid and deletion stocks. Images and data for all Southern hybridizations were deposited in databases and were used by the coordinators for each of the seven homoeologous chromosome groups to validate the mapping results. Results from this project have established the foundation for future developments in wheat genomics.

Because of the huge size of the common wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD) genome of 17,300 Mb, sequencing and mapping of the expressed portion is a logical first step for gene discovery. Here we report mapping of 7104 expressed sequence tag (EST) unigenes by Southern hybridization into a chromosome bin map using a set of wheat aneuploids and deletion stocks. Each EST detected a mean of 4.8 restriction fragments and 2.8 loci. More loci were mapped in the B genome (5774) than in the A (5173) or D (5146) genomes. The EST density was significantly higher for the D genome than for the A or B. In general, EST density increased relative to the physical distance from the centromere. The majority of EST-dense regions are in the distal parts of chromosomes. Most of the agronomically important genes are located in EST-dense regions. The chromosome bin map of ESTs is a unique resource for SNP analysis, comparative mapping, structural and functional analysis, and polyploid evolution, as well as providing a framework for constructing a sequence-ready, BAC-contig map of the wheat genome.

A total of 1918 loci, detected by the hybridization of 938 expressed sequence tag unigenes (ESTs) from 26 Triticeae cDNA libraries, were mapped to wheat (Triticum aestivum L.) homoeologous group 4 chromosomes using a set of deletion, ditelosomic, and nulli-tetrasomic lines. The 1918 EST loci were not distributed uniformly among the three group 4 chromosomes; 41, 28, and 31% mapped to chromosomes 4A, 4B, and 4D, respectively. This pattern is in contrast to the cumulative results of EST mapping in all homoeologous groups, as reported elsewhere, that found the highest proportion of loci mapped to the B genome. Sixty-five percent of these 1918 loci mapped to the long arms of homoeologous group 4 chromosomes, while 35% mapped to the short arms. The distal regions of chromosome arms showed higher numbers of loci than the proximal regions, with the exception of 4DL. This study confirmed the complex structure of chromosome 4A that contains two reciprocal translocations and two inversions, previously identified. An additional inversion in the centromeric region of 4A was revealed. A consensus map for homoeologous group 4 was developed from 119 ESTs unique to group 4. Forty-nine percent of these ESTs were found to be homoologous to sequences on rice chromosome 3, 12% had matches with sequences on other rice chromosomes, and 39% had no matches with rice sequences at all. Limited homology (only 26 of the 119 consensus ESTs) was found between wheat ESTs on homoeologous group 4 and the Arabidopsis genome. Forty-two percent of the homoeologous group 4 ESTs could be classified into functional categories on the basis of blastX searches against all protein databases.

The focus of this study was to analyze the content, distribution, and comparative genome relationships of 996 chromosome bin-mapped expressed sequence tags (ESTs) accounting for 2266 restriction fragments (loci) on the homoeologous group 3 chromosomes of hexaploid wheat (Triticum aestivum L.). Of these loci, 634, 884, and 748 were mapped on chromosomes 3A, 3B, and 3D, respectively. The individual chromosome bin maps revealed bins with a high density of mapped ESTs in the distal region and bins of low density in the proximal region of the chromosome arms, with the exception of 3DS and 3DL. These distributions were more localized on the higher-resolution group 3 consensus map with intermediate regions of high-mapped-EST density on both chromosome arms. Gene ontology (GO) classification of mapped ESTs was not significantly different for homoeologous group 3 chromosomes compared to the other groups. A combined analysis of the individual bin maps using 537 of the mapped ESTs revealed rearrangements between the group 3 chromosomes. Approximately 232 (44%) of the consensus mapped ESTs matched sequences on rice chromosome 1 and revealed large- and small-scale differences in gene order. Of the group 3 mapped EST unigenes ∼21 and 32% matched the Arabidopsis coding regions and proteins, respectively, but no chromosome-level gene order conservation was detected.

To localize wheat (Triticum aestivum L.) ESTs on chromosomes, 882 homoeologous group 6-specific ESTs were identified by physically mapping 7965 singletons from 37 cDNA libraries on 146 chromosome, arm, and sub-arm aneuploid and deletion stocks. The 882 ESTs were physically mapped to 25 regions (bins) flanked by 23 deletion breakpoints. Of the 5154 restriction fragments detected by 882 ESTs, 2043 (loci) were localized to group 6 chromosomes and 806 were mapped on other chromosome groups. The number of loci mapped was greatest on chromosome 6B and least on 6D. The 264 ESTs that detected orthologous loci on all three homoeologs using one restriction enzyme were used to construct a consensus physical map. The physical distribution of ESTs was uneven on chromosomes with a tendency toward higher densities in the distal halves of chromosome arms. About 43% of the wheat group 6 ESTs identified rice homologs upon comparisons of genome sequences. Fifty-eight percent of these ESTs were present on rice chromosome 2 and the remaining were on other rice chromosomes. Even within the group 6 bins, rice chromosomal blocks identified by 1–6 wheat ESTs were homologous to up to 11 rice chromosomes. These rice-block contigs were used to resolve the order of wheat ESTs within each bin.

Rye (Secale cereale L.) is considered to be the most aluminum (Al)-tolerant species among the Triticeae. It has been suggested that aluminum tolerance in rye is controlled by three major genes (Alt genes) located on rye chromosome arms 3RL, 4RL, and 6RS, respectively. Screening of an F6 rye recombinant inbred line (RIL) population derived from the cross between an Al-tolerant rye (M39A-1–6) and an Al-sensitive rye (M77A-1) showed that a single gene controls aluminum tolerance in the population analyzed. In order to identify molecular markers tightly linked to the gene, we used a combination of amplified fragment length polymorphism (AFLP) and bulked segregant analysis techniques to evaluate the F6 rye RIL population. We analyzed approximately 22,500 selectively amplified DNA fragments using 204 primer combinations and identified three AFLP markers tightly linked to the Alt gene. Two of these markers flanked the Alt locus at distance of 0.4 and 0.7 cM. Chromosomal localization using cloned AFLP and a restriction fragment length polymorphism (RFLP) marker indicated that the gene was on the long arm of rye chromosome 4R. The RFLP marker (BCD1230) co-segregated with the Alt gene. Since the gene is on chromosome 4R, the gene was designated as Alt3. These markers are being used as a starting point in the construction of a high resolution map of the Alt3 region in rye.

A total of 944 expressed sequence tags (ESTs) generated 2212 EST loci mapped to homoeologous group 1 chromosomes in hexaploid wheat (Triticum aestivum L.). EST deletion maps and the consensus map of group 1 chromosomes were constructed to show EST distribution. EST loci were unevenly distributed among chromosomes 1A, 1B, and 1D with 660, 826, and 726, respectively. The number of EST loci was greater on the long arms than on the short arms for all three chromosomes. The distribution of ESTs along chromosome arms was nonrandom with EST clusters occurring in the distal regions of short arms and middle regions of long arms. Duplications of group 1 ESTs in other homoeologous groups occurred at a rate of 35.5%. Seventy-five percent of wheat chromosome 1 ESTs had significant matches with rice sequences (E ≤ e−10), where large regions of conservation occurred between wheat consensus chromosome 1 and rice chromosome 5 and between the proximal portion of the long arm of wheat consensus chromosome 1 and rice chromosome 10. Only 9.5% of group 1 ESTs showed significant matches to Arabidopsis genome sequences. The results presented are useful for gene mapping and evolutionary and comparative genomics of grasses.

The complex hexaploid wheat genome offers many challenges for genomics research. Expressed sequence tags facilitate the analysis of gene-coding regions and provide a rich source of molecular markers for mapping and comparison with model organisms. The objectives of this study were to construct a high-density EST chromosome bin map of wheat homoeologous group 2 chromosomes to determine the distribution of ESTs, construct a consensus map of group 2 ESTs, investigate synteny, examine patterns of duplication, and assess the colinearity with rice of ESTs assigned to the group 2 consensus bin map. A total of 2600 loci generated from 1110 ESTs were mapped to group 2 chromosomes by Southern hybridization onto wheat aneuploid chromosome and deletion stocks. A consensus map was constructed of 552 ESTs mapping to more than one group 2 chromosome. Regions of high gene density in distal bins and low gene density in proximal bins were found. Two interstitial gene-rich islands flanked by relatively gene-poor regions on both the short and long arms and having good synteny with rice were discovered. The map locations of two ESTs indicated the possible presence of a small pericentric inversion on chromosome 2B. Wheat chromosome group 2 was shown to share syntenous blocks with rice chromosomes 4 and 7.

We constructed high-density deletion bin maps of wheat chromosomes 5A, 5B, and 5D, including 2338 loci mapped with 1052 EST probes and 217 previously mapped loci (total 2555 loci). This information was combined to construct a consensus chromosome bin map of group 5 including 24 bins. A relatively higher number of loci were mapped on chromosome 5B (38%) compared to 5A (34%) and 5D (28%). Differences in the levels of polymorphism among the three chromosomes were partially responsible for these differences. A higher number of duplicated loci was found on chromosome 5B (42%). Three times more loci were mapped on the long arms than on the short arms, and a significantly higher number of probes, loci, and duplicated loci were mapped on the distal halves than on the proximal halves of the chromosome arms. Good overall colinearity was observed among the three homoeologous group 5 chromosomes, except for the previously known 5AL/4AL translocation and a putative small pericentric inversion in chromosome 5A. Statistically significant colinearity was observed between low-copy-number ESTs from wheat homoeologous group 5 and rice chromosomes 12 (88 ESTs), 9 (72 ESTs), and 3 (84 ESTs).

The objectives of this study were to develop a high-density chromosome bin map of homoeologous group 7 in hexaploid wheat (Triticum aestivum L.), to identify gene distribution in these chromosomes, and to perform comparative studies of wheat with rice and barley. We mapped 2148 loci from 919 EST clones onto group 7 chromosomes of wheat. In the majority of cases the numbers of loci were significantly lower in the centromeric regions and tended to increase in the distal regions. The level of duplicated loci in this group was 24% with most of these loci being localized toward the distal regions. One hundred nineteen EST probes that hybridized to three fragments and mapped to the three group 7 chromosomes were designated landmark probes and were used to construct a consensus homoeologous group 7 map. An additional 49 probes that mapped to 7AS, 7DS, and the ancestral translocated segment involving 7BS also were designated landmarks. Landmark probe orders and comparative maps of wheat, rice, and barley were produced on the basis of corresponding rice BAC/PAC and genetic markers that mapped on chromosomes 6 and 8 of rice. Identification of landmark ESTs and development of consensus maps may provide a framework of conserved coding regions predating the evolution of wheat genomes.

This report describes the rationale, approaches, organization, and resource development leading to a large-scale deletion bin map of the hexaploid (2n = 6x = 42) wheat genome (Triticum aestivum L.). Accompanying reports in this issue detail results from chromosome bin-mapping of expressed sequence tags (ESTs) representing genes onto the seven homoeologous chromosome groups and a global analysis of the entire mapped wheat EST data set. Among the resources developed were the first extensive public wheat EST collection (113,220 ESTs). Described are protocols for sequencing, sequence processing, EST nomenclature, and the assembly of ESTs into contigs. These contigs plus singletons (unassembled ESTs) were used for selection of distinct sequence motif unigenes. Selected ESTs were rearrayed, validated by 5′ and 3′ sequencing, and amplified for probing a series of wheat aneuploid and deletion stocks. Images and data for all Southern hybridizations were deposited in databases and were used by the coordinators for each of the seven homoeologous chromosome groups to validate the mapping results. Results from this project have established the foundation for future developments in wheat genomics.

Aluminum (Al) toxicity is considered to be a major problem for crop growth and production on acid soils. The ability of crops to overcome Al toxicity varies among crop species and cultivars. Rye (Secale cereale L.) is the most Al-tolerant species among the Triticeae. Our previous study showed that Al tolerance in a rye F6 recombinant inbred line (RIL) population was controlled by a single gene designated as the aluminum tolerance (Alt3) gene on chromosome 4RL. Based on the DNA sequence of a rice (Oryza sativa L.) BAC clone suspected to be syntenic to the Alt3 gene region, we developed two PCR-based codominant markers flanking the gene. These two markers, a sequence-tagged site (STS) marker and a cleaved amplified polymorphic sequence (CAPS) marker, each flanked the Alt3 gene at an approximate distance of 0.4 cM and can be used to facilitate high-resolution mapping of the gene. The markers might also be used for marker-assisted selection in rye or wheat (Triticum aestivum L.) breeding programs to obtain Al-tolerant lines and (or) cultivars.Key words: rye, aluminum tolerance, CAPS, STS, flanking marker, rice BAC, synteny.

Genes detected by wheat expressed sequence tags (ESTs) were mapped into chromosome bins delineated by breakpoints of 159 overlapping deletions. These data were used to assess the organizational and evolutionary aspects of wheat genomes. Relative gene density and recombination rate increased with the relative distance of a bin from the centromere. Single-gene loci present once in the wheat genomes were found predominantly in the proximal, low-recombination regions, while multigene loci tended to be more frequent in distal, high-recombination regions. One-quarter of all gene motifs within wheat genomes were represented by two or more duplicated loci (paralogous sets). For 40 such sets, ancestral loci and loci derived from them by duplication were identified. Loci derived by duplication were most frequently located in distal, high-recombination chromosome regions whereas ancestral loci were most frequently located proximal to them. It is suggested that recombination has played a central role in the evolution of wheat genome structure and that gradients of recombination rates along chromosome arms promote more rapid rates of genome evolution in distal, high-recombination regions than in proximal, low-recombination regions.

Mapping expressed sequence tags (ESTs) to hexaploid wheat is aimed to reveal the structure and function of the hexaploid wheat genome. Sixty eight ESTs representing 26 genes were mapped into all seven homologous chromosome groups of wheat (Triticum aestivum L) using a polymerase chain reaction technique. The majority of the ESTs were mapped to homologous chromosome group 2, and the least were mapped to homologous chromosome group 6. Comparative analysisbetween the EST map from this study and the EST map based on RFLPs showed 14 genes that have been mapped by both approaches were mapped to the same arm of the same homologous chromosome, which indicated that using PCRbasedESTs was a reliable approach in mapping ESTs in hexaploid wheat.Key words: wheat, EST, PCR, homologous.

Loci detected by Southern blot hybridization of 3,977 expressed sequence tag unigenes were mapped into 159 chromosome bins delineated by breakpoints of a series of overlapping deletions. These data were used to assess synteny levels along homoeologous chromosomes of the wheat A, B, and D genomes, in relation to both bin position on the centromere-telomere axis and the gradient of recombination rates along chromosome arms. Synteny level decreased with the distance of a chromosome region from the centromere. It also decreased with an increase in recombination rates along the average chromosome arm. There were twice as many unique loci in the B genome than in the A and D genomes, and synteny levels between the B genome chromosomes and the A and D genome homoeologues were lower than those between the A and D genome homoeologues. These differences among the wheat genomes were attributed to differences in the mating systems of wheat diploid ancestors. Synteny perturbations were characterized in 31 paralogous sets of loci with perturbed synteny. Both insertions and deletions of loci were detected and both preferentially occurred in high recombination regions of chromosomes.

The use of DNA sequence-based comparative genomics for evolutionary studies and for transferring information from model species to crop species has revolutionized molecular genetics and crop improvement strategies. This study compared 4485 expressed sequence tags (ESTs) that were physically mapped in wheat chromosome bins, to the public rice genome sequence data from 2251 ordered BAC/PAC clones using BLAST. A rice genome view of homologous wheat genome locations based on comparative sequence analysis revealed numerous chromosomal rearrangements that will significantly complicate the use of rice as a model for cross-species transfer of information in nonconserved regions.