Wild Ancestral Species Research Articles

Enrichment and Diversification of the Wheat Genome via Alien Introgression

Wheat, including durum and common wheat, respectively, is an allopolyploid with two or three homoeologous subgenomes originating from diploid wild ancestral species. The wheat genome’s polyploid origin consisting of just three diploid ancestors has constrained its genetic variation, which has bottlenecked improvement. However, wheat has a large number of relatives, including cultivated crop species (e.g., barley and rye), wild grass species, and ancestral species. Moreover, each ancestor and relative has many other related subspecies that have evolved to inhabit specific geographic areas. Cumulatively, they represent an invaluable source of genetic diversity and variation available to enrich and diversify the wheat genome. The ancestral species share one or more homologous genomes with wheat, which can be utilized in breeding efforts through typical meiotic homologous recombination. Additionally, genome introgressions of distant relatives can be moved into wheat using chromosome engineering-based approaches that feature induced meiotic homoeologous recombination. Recent advances in genomics have dramatically improved the efficacy and throughput of chromosome engineering for alien introgressions, which has served to boost the genetic potential of the wheat genome in breeding efforts. Here, we report research strategies and progress made using alien introgressions toward the enrichment and diversification of the wheat genome in the genomics era.

Visualizing and Inferring Chromosome Segregation in the Pedigree of an Improved Banana Cultivar (Gold Finger) with Genome Ancestry Mosaic Painting

Banana breeding faces numerous challenges, such as sterility and low seed viability. Enhancing our understanding of banana genetics, notably through next-generation sequencing, can help mitigate these challenges. The genotyping datasets currently available from genebanks were used to decipher cultivated bananas’ genetic makeup of natural cultivars using genome ancestry mosaic painting. This article presents the application of this method to breeding materials by analyzing the chromosome segregation at the origin of ‘Gold Finger’ (FHIA-01), a successful improved tetraploid variety that was developed in the 1980s. First, the method enabled us to clarify the variety’s intricate genetic composition from ancestral wild species. Second, it enabled us to infer the parental gametes responsible for the formation of this hybrid. It thus revealed 16 recombinations in the haploid male gamete and 10 in the unreduced triploid female gamete. Finally, we could deduce the meiotic mechanism lying behind the transmission of unreduced gametes (i.e., FDR). While we show that the method is a powerful tool for the visualization and inference of gametic contribution in hybrids, we also discuss its advantages and limitations to advance our comprehension of banana genetics in a breeding context.

Exploring Pan-Genomes: An Overview of Resources and Tools for Unraveling Structure, Function, and Evolution of Crop Genes and Genomes.

The availability of multiple sequenced genomes from a single species made it possible to explore intra- and inter-specific genomic comparisons at higher resolution and build clade-specific pan-genomes of several crops. The pan-genomes of crops constructed from various cultivars, accessions, landraces, and wild ancestral species represent a compendium of genes and structural variations and allow researchers to search for the novel genes and alleles that were inadvertently lost in domesticated crops during the historical process of crop domestication or in the process of extensive plant breeding. Fortunately, many valuable genes and alleles associated with desirable traits like disease resistance, abiotic stress tolerance, plant architecture, and nutrition qualities exist in landraces, ancestral species, and crop wild relatives. The novel genes from the wild ancestors and landraces can be introduced back to high-yielding varieties of modern crops by implementing classical plant breeding, genomic selection, and transgenic/gene editing approaches. Thus, pan-genomic represents a great leap in plant research and offers new avenues for targeted breeding to mitigate the impact of global climate change. Here, we summarize the tools used for pan-genome assembly and annotations, web-portals hosting plant pan-genomes, etc. Furthermore, we highlight a few discoveries made in crops using the pan-genomic approach and future potential of this emerging field of study.

Regulator of Awn Elongation 3, an E3 ubiquitin ligase, is responsible for loss of awns during African rice domestication

Two species of rice have been independently domesticated from different ancestral wild species in Asia and Africa. Comparison of mutations that underlie phenotypic and physiological alterations associated with domestication traits in these species gives insights into the domestication history of rice in both regions. Asian cultivated rice, Oryza sativa, and African cultivated rice, Oryza glaberrima, have been modified and improved for common traits beneficial for humans, including erect plant architecture, nonshattering seeds, nonpigmented pericarp, and lack of awns. Independent mutations in orthologous genes associated with these traits have been documented in the two cultivated species. Contrary to this prevailing model, selection for awnlessness targeted different genes in O. sativa and O. glaberrima. We identify Regulator of Awn Elongation 3 (RAE3) a gene that encodes an E3 ubiquitin ligase and is responsible for the awnless phenotype only in O. glaberrima. A 48-bp deletion may disrupt the substrate recognition domain in RAE3 and diminish awn elongation. Sequencing analysis demonstrated low nucleotide diversity in a ~600-kb region around the derived rae3 allele on chromosome 6 in O. glaberrima compared with its wild progenitor. Identification of RAE3 sheds light on the molecular mechanism underlying awn development and provides an example of how selection on different genes can confer the same domestication phenotype in Asian and African rice.

Transgenerational changes in pod maturation phenology and seed traits of Glycine soja infested by the bean bug Riptortus pedestris.

Land plants have diverse defenses against herbivores. In some cases, plant response to insect herbivory may be chronological and even transgenerational. Feeding by various stink bugs, such as the bean bug Riptortus pedestris (Hemiptera: Alydidae), induce physiological changes in soybean, called as green stem syndrome, which are characterized by delayed senescence in stems, leaves, and pods. To investigate the plant response to the bean bug feeding in the infested generation and its offspring, we studied the effects of R. pedestris infestation on Glycine soja, the ancestral wild species of soybean. Field surveys revealed that the occurrence of the autumn R. pedestris generation coincided with G. soja pod maturation in both lowland and mountainous sites. Following infestation by R. pedestris, pod maturation was significantly delayed in G. soja. When G. soja seeds obtained from infested and non-infested plants were cultivated, the progeny of infested plants exhibited much earlier pod maturation and larger-sized seed production than that of control plants, indicating that R. pedestris feeding induced transgenerational changes. Because earlier seed maturity results in asynchrony with occurrence of R. pedestris, the transgenerational changes in plant phenology are considered to be an adaptive transgenerational and chronological defense for the plant against feeding by the stink bug.

Whole-genome sequence analysis unveils different origins of European and Asiatic mouflon and domestication-related genes in sheep

The domestication and subsequent development of sheep are crucial events in the history of human civilization and the agricultural revolution. However, the impact of interspecific introgression on the genomic regions under domestication and subsequent selection remains unclear. Here, we analyze the whole genomes of domestic sheep and their wild relative species. We found introgression from wild sheep such as the snow sheep and its American relatives (bighorn and thinhorn sheep) into urial, Asiatic and European mouflons. We observed independent events of adaptive introgression from wild sheep into the Asiatic and European mouflons, as well as shared introgressed regions from both snow sheep and argali into Asiatic mouflon before or during the domestication process. We revealed European mouflons might arise through hybridization events between a now extinct sheep in Europe and feral domesticated sheep around 6000–5000 years BP. We also unveiled later introgressions from wild sheep to their sympatric domestic sheep after domestication. Several of the introgression events contain loci with candidate domestication genes (e.g., PAPPA2, NR6A1, SH3GL3, RFX3 and CAMK4), associated with morphological, immune, reproduction or production traits (wool/meat/milk). We also detected introgression events that introduced genes related to nervous response (NEURL1), neurogenesis (PRUNE2), hearing ability (USH2A), and placental viability (PAG11 and PAG3) into domestic sheep and their ancestral wild species from other wild species.

Chromosome karyotype and stability of new synthetic hexaploid wheat.

Synthetic hexaploid wheat offers breeders ready access to potentially novel genetic variation in wild ancestral species. In this study, we crossed MY3478 (2n = 4x = 28, AABB) as the maternal parent with the stripe rust-resistant SY41 (2n = 2x = 14, DD) as the paternal parent to construct the new hexaploid wheat line NA0928 through natural allopolyploidization. Agronomic traits and the cytology of the S8-S9 generations of NA0928 were analyzed. Abundant variation in agronomic traits was observed among each strain of NA0928 in the S8 generation. Agronomic traits were superior in strains resistant to stripe rust compared with those of highly susceptible strains. The rank order of the coefficients of variation were tiller number (55.3%) > spike length (15.3%) > number of spikelets (13.9%) > plant height (8.7). Number of tillers and spike length are important traits in wheat breeding to improve yield. Cytological observation and fluorescence in situ hybridization showed that the chromosome number and configuration showed rich variation among NA0928 strains in the S9 generation. Chromosome number ranged from 36 to 44. Variation in chromosome karyotype was detected in the A and B subgenomes. Meiotic chromosome behavior in pollen mother cells and multicolor genomic in situ hybridization revealed that two new synthetic hexaploid wheat strains showed genetic stability; one strain was resistant to stripe rust and developed multiple tillers, and the other strain was susceptible to stripe rust, but both showed improved thousand-kernel weight (TKW) weight and produced multiple tillers. The two strains will be valuable germplasm resources for use in wheat breeding.

Temminck's Gallus giganteus; a gigantic obstacle to Darwin's theory of domesticated fowl origin?

In 1813, based on the single foot of a large chicken, Temminck named a ‘new' species of junglefowl, Gallus giganteus. He considered this ‘species’ the ancestor of several large domesticated chicken breeds and believed it was one of six wild ancestral species of domestic fowl. Temminck's hypothesis was rejected by Blyth who thought Red Junglefowl G. gallus was the sole ancestor. The arrival into Britain of several very large Asian chicken breeds in the mid-19th century led to speculation that Temminck's G. giganteus may have been their wild ancestor. Darwin, who had initially agreed with Blyth, noted several peculiarities in the Cochin, a large Asian breed, which he concluded might not have been achieved by selective breeding, and questioned whether G. giganteus was involved in their ancestry. Temminck's giant junglefowl appeared to be a significant hurdle for Darwin in his effort to prove a single ancestral origin for domestic chickens.‘My very decided opinion, that we may seek in vain for wild types of G. giganteus' (letter from Blyth to Darwin, 1856).‘We have not such good evidence with fowls as with pigeons, of all breeds having descended from a single primitive stock' (Darwin 1868: 239).

The sequence and de novo assembly of the wild yak genome

Vulnerable populations of wild yak (Bos mutus), the wild ancestral species of domestic yak, survive in extremely cold, harsh and oxygen-poor regions of the Qinghai-Tibetan Plateau (QTP) and adjacent high-altitude regions. In this study, we sequenced and assembled its genome de novo. In total, six different insert-size libraries were sequenced, and 662 Gb of clean data were generated. The assembled wild yak genome is 2.83 Gb in length, with an N50 contig size of 63.2 kb and a scaffold size of 16.3 Mb. BUSCO assessment indicated that 93.8% of the highly conserved mammal genes were completely present in the genome assembly. Annotation of the wild yak genome assembly identified 1.41 Gb (49.65%) of repetitive sequences and a total of 22,910 protein-coding genes, including 20,660 (90.18%) annotated with functional terms. This first construction of the wild yak genome provides a variable genetic resource that will facilitate further study of the genetic diversity of bovine species and accelerate yak breeding efforts.

BRS 425: the first runner peanut cultivar related to wild ancestral species

Abstract BRS 425 is a high-oleic runner peanut cultivar related to wild ancestral parents, partially resistant to early and late leaf spot and spotted wilt. It is large-seeded and contains 46% oil. BRS 425 is adapted to the main peanut-producing regions of Brazil.

Hybrid seedling inviability locus (HIs1) mapped on linkage group 4 of the Japanese flowering cherry, Cerasus × yedoensis ‘Somei-yoshino’

Cerasus × yedoensis ‘Somei-yoshino’ (2n = 16), one of the most popular cultivars of Japanese flowering cherry, is considered a hybrid between Cerasus spachiana and Cerasus speciosa. In the present study, we observed segregation of the trait for seedling growth in F1 progenies of Somei-yoshino. In all three families crossed with ancestral wild species, C. spachiana, approximately half of the seedlings showed growth failure. To identify loci involved in seedling inviability, we constructed a genetic linkage map of Somei-yoshino. Both normal growth (N = 77) and growth failure seedlings (N = 101) of an F1 progenies crossed between Somei-yoshino (CY) and C. spachiana (E750) were used for map construction. In accordance to pseudo-testcross strategy, female (CY) and male (E750) linkage maps were constructed. The CY map consists of eight linkage groups with 59 simple sequence repeat (SSR) and 17 amplified fragment length polymorphism (AFLP) markers. The map length is 574.9 cM. In contrast, the E750 map reached 196.8 cM and included 17 SSRs. Subsequently, we explored positions of loci associated to seedling inviability along with linkage maps. Results of segregation distortion of markers, association analysis, and interval mapping consistently showed that an inviability gene was located between two SSR markers, EMPaS13 and BPPCT005 in the fourth linkage group (LG4) of the Somei-yoshino map with 99.6 % explanations for the inviability trait but not present in LG4 of the E750 map. From the genotypes and expressions of seedling inviability, we named the locus Hybrid Inviability of seedlings 1 (HIs1). Finally, HIs1 was mapped to LG4 as Mendelian trait loci and was completely linked with an SSR, EMPaS13. Although the mechanisms of seedling inviability cannot be explained by only one locus model of HIs1, one of the candidate genes involved in hybrid incompatibility between Somei-yoshino and C. spachiana is certainly located on LG4 of the CY map.

동아시아 및 동남아시아에서 수집한 들깨, 차조기 작물과 잡초형 계통들의 형태적 변이

ABSTRACT To better understand the morphological variation of the Perilla crop and their weedy types in East and Southeast Asia, we studied the morphological variation of 90 accessions by examining 10 morphological characteristics, such as flowering time, seed size, seed hardness, seed color, color of surface leaf, color of reverse side leaf etc. As a result, morphological variation determined that between cultivated var. frutescens and var. crispa, and between cultivated var. frutescens and its weedy type showed significant morphological differences in terms of seed size and seed hardness, whenever cultivated var. crispa and its weedy type could not showed significant differences in most morphological characters. In PCAs (principal component analysis), among 10 morphological characteristics, flower color (QL6), color of surface leaf (QL3), seed size (QN2), seed hardness (QL1), seed color (QL2), stem color (QL7), and color of reverse side leaf (QL4) contributed in negative direction on the first axis, while flowering time (QN1), leaf shape (QL5), and degree of pubescence (QL8) contributed in positive direction on the first axis. Among these morphological characters, particularly flower color (QL6), color of surface leaf (QL3), seed size (QN2), seed hardness (QL1), and degree of pubescence (QL8) were useful characters for discrimination between cultivated var. frutescens and weedy var. crispa, and between cultivated var. frutescens and its weedy type. However, most accession of cultivated and weedy types of var. crispa was not clearly discriminated by PCA analyses. Although the wild ancestral species of var. frutescens and of var. crispa are still unknown in East and Southeast Asia, the weedy types of Perilla crop may be the key taxon for our understanding of the origin of cultivated types of var. frutescens and var. crispa.Keywords : Perilla crop, cultivated and weedy types, geographic differentiation, morphological variation, principal component analysis

Identification of rice sheath blight and blast quantitative trait loci in two different O. sativa/O. nivara advanced backcross populations

Two accessions of Oryza nivara, a wild ancestral species of rice (O. sativa) identified as being moderately resistant to sheath blight and leaf blast disease, were used as donor parents to develop two advanced backcross populations with the US rice cultivar, Bengal, as the recurrent parent. The O. nivara donor parent for Wild-1 (252 BC2F1 lines) was acc. IRGC100898 and for Wild-2 (253 BC2F1 lines) was acc. IRGC104705. Both populations were genotyped with 131 simple sequence repeat markers and the linkage maps covered 1,567.5 cM (Wild-1) and 1,312.2 cM (Wild-2). Sheath blight (ShB) disease was evaluated in both inoculated greenhouse and field conditions. Days to heading (DH), plant height (PH), and plant type (PT), confounding factors for sheath blight disease under field conditions, were recorded. Leaf blast disease was rated under inoculated greenhouse conditions. Multiple interval mapping identified qShB6 with resistance to sheath blight disease attributed to the O. nivara parent in the greenhouse. In the field, qShB6 also was the most significant ShB quantitative trait locus (QTL) in all trials, with resistance attributed to O. nivara. In addition, qShB1 and qShB3 were identified in all trials but were not always attributed to the same parent. The qShB6 QTL is in the same region as the DH-QTL, qDH6, and qShB1 is in the same region as the major PH-QTL, qPH1, suggesting that these ShB-QTL may be confounded by other traits. Although qShB3 did not have as large an effect as other loci, it was not confounded by either DH or PH. For leaf blast, qBLAST8-1 was found in both populations providing resistance to races IB1 and IB49, whereas qBLAST12 providing resistance to both races, was only found in Wild-2. Resistance was attributed to O. nivara for both QTL, and blast resistance genes have been previously reported in these regions.

Molecular Adaptation of Peanut Metabolic Pathways to Wide Variations of Mineral Ion Composition and Concentration

Plant evolution, nutritional genomics, and mineral nutrition have been well documented but no studies have focused on the molecular adaptation of crop metabolism to wide variations of mineral ion composition and concentration. Diversification of peanut species from primary centers of domestication in South America depended on metabolic adaptation to the mineral ion conditions of the newer habitats. Understanding the diversification molecular biology of peanut metabolic pathways will permit the synthesis of the best mineral ion combinations for doubling CO2 assimilation. Valencia and Virginia cultivars belong to different subspecies of the tetraploid Arachis hypogaea. They were planted in the absence and presence of up to 99 mM (equivalent to 166 moles per hectare) of different mineral ions. Molecular properties of the primary metabolic pathways were studied by Northern analyses using Valencia GDH-synthesized RNAs as probes for Virginia mRNA and GDH-synthesized RNAs. Messenger RNAs are silenced by homologous RNAs synthesized by GDH. Peanut cellulose was analyzed by gravimetry; and fatty acids by HPLC. Complementary DNA probes made from Valencia GDH-synthesized RNAs hybridized perfectly to Virginia mRNAs and GDH-synthesized RNAs. Wide variations in mineral ion compositions and concentrations induced the GDHs of Valencia and Virginia to synthesize RNAs that differentially down-regulated the mRNAs encoding phosphate translocator, granule-bound starch synthase, phosphoglucomutase, glucosyltransferase, acetyl CoA carboxylase, nitrate reductase, and NADH-glutamate synthase so that the percent weights of oil (41.53 ± 8.75) and cellulose (30.29 ± 3.12) were similar in the control and mineral-treated peanuts. Therefore, RNA sequences that defined the molecular adaptation of mRNAs encoding the enzymes of primary metabolism were the same in the varietal types of A. hypogaea, in agreement with genetic data suggesting that tetraploid Arachis evolved relatively recently from the wild diploid ancestral species. Another molecular adaptation was to phosphate with or without K+ ion, and it prevented the silencing by GDH-synthesized RNAs of the mRNA encoding phosphate translocator resulting to doubling of cellulosic biomass yield (41323 kg/ha) compared with the N + P + K + S-treated positive control peanut (19428 kg/ha). Molecular adaptation of primary metabolic pathways at the mRNA level to SO42- ion with or without SO42- ion did not increase cellulosic biomass yields (27057 kg/ha) compared with negative control peanut because the mRNAs encoding granule-bound starch synthase, and NADH-glutamate synthase were not silenced by GDH-synthesized RNA in the N + S, SO42-, and N + P + K + S-treated peanuts. These results could contribute towards further modeling at the mRNA level for improved mineral nutrient management of peanut production for fuel, fiber, feed, and food.

Genetic diversity of cultivated and wild radish and phylogenetic relationships among Raphanus and Brassica species revealed by the analysis of trnK/matK sequence

Nucleotide sequence variations of the trnK/matK region were investigated in cultivated and wild radish species and related Brassica species. Two insertions/deletions and 9 substitutions were detected among the Raphanus accessions. The value of the nucleotide diversity (π) was found to be higher in cultivated radish (0.00184) than in the wild species (0.00134). Based on the nucleotide diversity, the phylogenetic relationships of Raphanus and its related species were inferred by constructing a Neighbor-Joining tree. Raphanus species and Brassica barrelieri formed a sister clade located between the Rapa/Oleracea group and the Nigra group of Brassica. These results were in complete agreement with those obtained by Warwick and Black. The placement of Raphanus species at this position showed the existence of a paraphyletic relationship among the Brassica species. Each of the three varieties of cultivated radish, R. sativus var. sativus (European small radish), var. hortensis (East Asian big radish) and var. niger (black radish), belonged to a different cluster of the phylogenetic tree, suggesting the existence of independent multiple origins of these varieties. Based on the phylogenetic tree, problems related to the identification of the wild ancestral species of cultivated radish and original birthplaces of cultivated radish varieties were discussed.

Chloroplast DNA Variation in the Most Primitive Cultivated Diploid Potato Species Solanum stenotomum Juz. et Buk. and its Putative Wild Ancestral Species using High-Resolution Markers

Solanum stenotomum Juz. et Buk. (2n = 2x = 24) is considered to be the most primitive diploid cultivated species from which all the other Andean cultivated potatoes were originated (Hawkes 1990). To disclose chloroplast DNA (ctDNA) variability and the maternal origin of S. stenotomum, 36 accessions of S. stenotomum and 86 accessions of putative wild ancestral species were determined for ctDNA types and analyzed by high-resolution markers (seven ctDNA microsatellites and an H3 marker). High-resolution markers discriminated 57 different ctDNAs (haplotypes), which were classified into the W-type ctDNA group and C-, S- and A-type ctDNA group, and within the latter group S- and A-type ctDNAs were distinct from each other among many different haplotypes mostly having C-type ctDNA. This ctDNA relationship supported our previous findings obtained for mostly Andean cultivated species (Sukhotu et al. 2004). Compared with other putative ancestral wild species, S. stenotomum showed somewhat limited ctDNA diversity, having two major haplotypes 1 and 2 also found in different wild species in different places. Therefore, the ctDNA in S. stenotomum was of at least dual origins either by successive domestication from different species or else by introgression after initial S. stenotomum arose.

Variation in coxII intron in the wild ancestral species of wheat.

To study the maternal lineage and evolution of polyploid species of wheat, variation in mitochondrial DNA was investigated in Triticum and Aegilops by PCR-aided RFLP analysis. A 1.3 kb region containing the intron of coxII was studied using 20 accessions from five species of Sitopsis section of Aegilops, one species of Einkorn wheat, four species of tetraploid wheat, and one species of common wheat. Only three restriction site changes and a single deletion/insertion were found among 884 restriction fragments surveyed. This fact suggests the highly conserved nature of this region within Triticum and Aegilops. Four haplo-types were recognized in coxII intron. A parsimonious relationship indicated that three haplo-types were independently derived from one prototype which was found in wild Einkorn and Aegilops species except for Ae. speltoides. All but one accession of Ae. speltoides possessed a derivative haplo-type, common in Timopheevi wheat. The result supported the hypothesis that Ae. speltoides donated the G genome to Timopheevi wheat; however did not agree with that Ae. speltoides was the B genome donor to the Emmer and common wheat.

Species-specific accumulation of interspersed sequences in genus Saccharum

The genus Saccharum consists of two wild and four cultivated species. Novel interspersed sequences were isolated from cultivated sugar cane S. officinarum. These sequences were accumulated in all four cultivated species and their wild ancestral species S. robustum, but were not detected in the other wild species S. spontaneum and the relative Erianthus arundinaceus. The species-specific accumulation of interspersed sequences would correlate to the domestication of sugar canes.

Disruption of GSTZ1 Gene by Large Genetic Alteration in Oryza glaberrima

After the completion of the genome sequencing project of common rice (Oryza sativa L.), comparative genomic studies between rice and related species became important to reveal the function of each gene. The rice genome contains two copies of the gene encoding zeta class glutathione S-transferase (GSTZ) that is reported to be the enzyme in the catabolic pathway of tyrosine and phenylalanine. Two GSTZ genes of O. sativa, OsGSTZ1 and OsGSTZ2, display a tandem arrangement. Upstream OsGSTZ1 gene is constitutively expressed, whereas the downstream OsGSTZ2 gene is inducible by stresses. We analyzed the expression of the GSTZ gene in the African cultivated species O. glaberrima and wild species O. longistaminata by using RT-PCR. The results showed that both GSTZ1 and GSTZ2 genes were expressed in O. longistaminata, whereas only the cDNA fragment of downstream GSTZ2 was detected in O. glaberrima. Thus, the genomic sequence of the GSTZ1 locus of O. glaberrima was determined by PCR genomic walking. Sequence comparison between O. sativa and O. glaberrima revealed that the genomic sequence upstream from the eighth intron of the OgGSTZ1 gene was highly homologous, in inverted orientation, to a BAC clone, over 1-Mb apart from the OsGSTZ1 gene in O. sativa. This result suggested that the OgGSTZ1 gene was disrupted by a large rearrangement or inversion. The genetic alteration was also observed in several lines of O. glaberrima and its ancestral wild species O. barthii. The loss of the OgGSTZ1 gene in O. glaberrima is important, as the expression of the gene is 12-fold higher than that of OsGSTZ2 in O. sativa and since O. sativa and O. glaberrima differ in several such as seed yield and annual/perennial habitat that might be related to the translocation of nitrogen metabolites from leaves to seeds.

Molecular Characterization of a 313-kb Genomic Region Containing the Self-incompatibility Locus of Ipomoea trifida, a Diploid Relative of Sweet Potato

Diploid Ipomoea trifida is an ancestral wild species of the cultivated hexaploid sweet potato, and displays a sporophytic self-incompatibility (SI) that is controlled by a single multiallelic S-locus. To characterize the genomic region of the S-locus using a map-based cloning method, a BAC library consisting of approximately 40,000 clones was constructed from genomic DNA of S1-homozygote, and screened using S-linked DNA markers which were mapped in our previous study. We constructed a contig covering the S-locus region with additional screening of fosmid and λ phase libraries. RFLP analysis of recombinant plants using terminal end sequences of the BAC clones as probes indicated that the S-locus region was delimited within a map distance of 0.57 cM, spanning approximately 300 kb in physical distance. Remarkable suppression of genetic recombination was detected in the S-locus region. From sequence analysis of the 313-kp region, 43 ORFs, many repetitive sequences and 5 transposable elements were predicted. None of the ORFs, however, showed a high homology with the SI genes reported to date at the S-locus of other plant families, suggesting that a unique molecular mechanism is involved in the SI system of the Convolvulaceae family.