Genetic redundancy in soybean photoresponses associated with duplication of the phytochrome A gene

Gene and genome duplications underlie the origins of evolutionary novelty in plants. Soybean, Glycine max, is considered to be a paleopolyploid species with a complex genome. We found multiple homologs of the phytochrome A gene (phyA) in the soybean genome and determined the DNA sequences of two paralogs designated GmphyA1 and GmphyA2. Analysis of the GmphyA2 gene from the lines carrying a recessive allele at a photoperiod insensitivity locus, E4, revealed that a Ty1/copia-like retrotransposon was inserted in exon 1 of the gene, which resulted in dysfunction of the gene. Mapping studies suggested that GmphyA2 is encoded by E4. The GmphyA1 gene was mapped to a region of linkage group O, which is homeologous to the region harboring E4 in linkage group I. Plants homozygous for the e4 allele were etiolated under continuous far red light, but the de-etiolation occurred partially, indicating that the mutation alone did not cause a complete loss of phyA function. The genetic redundancy suggests that the presence of duplicated copies of phyA genes accounts for the generation of photoperiod insensitivity, while protecting against the deleterious effects of mutation. Thus, this phenomenon provides a link between gene duplication and establishment of an adaptive response of plants to environments.

Speed of back-swimming of Lymnaea

The pond snail, Lymnaea stagnalis, can locomote on its back utilizing the surface tension of the water. We have called this form of movement 'back-swimming'. In order to perform this behavior, the snail must flip itself over on its back so that its foot is visible from above. Little is known about the mechanism of this back-swimming. As a first step for the elucidation of this mechanism, we measured the speed of back-swimming of Lymnaea at the different times of the day. They back-swam significantly faster in the morning than just before dark. These data are consistent with our earlier findings on circadian-timed activity pattern in Lymnaea. Lymnaea appear to secrete a thin membrane-like substance from their foot that may allow them to back-swim. To confirm the existence of this substance and to examine whether this substance is hydrophobic or hydrophilic, we applied a detergent onto the foot during back-swimming. A single drop of 1% Tween 20 drifted Lymnaea away that were still kept at the water surface. These results suggest that Lymnaea secrete a hydrophobic substance from their foot that floats to the water surface allowing Lymnaea to back-swim.

The evolution of sex-independent transmission ratio distortion involving multiple allelic interactions at a single locus in rice

Transmission ratio distortion (TRD) is frequently observed in inter- and intraspecific hybrids of plants, leading to a violation of Mendelian inheritance. Sex-independent TRD (siTRD) was detected in a hybrid between Asian cultivated rice and its wild ancestor. Here we examined how siTRD caused by an allelic interaction at a specific locus arose in Asian rice species. The siTRD is controlled by the S6 locus via a mechanism in which the S6 allele acts as a gamete eliminator, and both the male and female gametes possessing the opposite allele (S6a) are aborted only in heterozygotes (S6/S6a). Fine mapping revealed that the S6 locus is located near the centromere of chromosome 6. Testcross experiments using near-isogenic lines (NILs) carrying either the S6 or S6a alleles revealed that Asian rice strains frequently harbor an additional allele (S6n) the presence of which, in heterozygotic states (S6/S6n and S6a/S6n), does not result in siTRD. A prominent reduction in the nucleotide diversity of S6 or S6a carriers relative to that of S6n carriers was detected in the chromosomal region. These results suggest that the two incompatible alleles (S6 and S6a) arose independently from S6n and established genetically discontinuous relationships between limited constituents of the Asian rice population.

Sex-independent transmission ratio distortion system responsible for reproductive barriers between Asian and African rice species

* A sex-independent transmission ratio distortion (siTRD) system detected in the interspecific cross in rice was analyzed in order to understand its significance in reproductive barriers. The S(1) gene, derived from African rice Oryza glaberrima, induced preferential abortion of both male and female gametes possessing its allelic alternative (), from Asian rice O. sativa, only in the heterozygote. * The siTRD was characterized by resolving it into mTRD and fTRD occurring through male and female gametes, respectively, cytological analysis of gametophyte development, and mapping of the S(1) locus using near-isogenic lines. The allelic distribution of the S(1) locus in Asian and African rice species complexes was also analyzed. * The siTRD system involved at least two components affecting male and female gametogeneses, respectively, including a modifier(s) that enhances fTRD. The chromosomal location of the major component causing the mTRD was delimited within an approx. 40 kb region. The S(1) locus induced hybrid sterility in any pairwise combination between Asian and African rice species complexes. * The allelic state of the S(1) locus has diverged between Asian and African rice species complexes, suggesting that the TRD system has a significant role in the reproductive barriers in rice.

Coordinated expression of functionally diverse fructosyltransferase genes is associated with fructan accumulation in response to low temperature in perennial ryegrass

* Fructan is the major nonstructural carbohydrate reserve in temperate grasses. To understand regulatory mechanisms in fructan synthesis and adaptation to cold environments, the isolation, functional characterization and genetic mapping of fructosyltransferase (FT) genes in perennial ryegrass (Lolium perenne) are described. * Six cDNAs (prft1-prft6) encoding FTs were isolated from cold-treated ryegrass plants, and three were positioned on a perennial ryegrass linkage map. Recombinant proteins were produced in Pichia pastoris and enzymatic activity was characterized. Changes in carbohydrate levels and mRNA levels of FT genes during cold treatment were also analysed. * One gene encodes sucrose-sucrose 1-fructosyltransferase (1-SST), and two gene encode fructan-fructan 6G-fructosyltransferase (6G-FFT). Protein sequences for the other genes (prfts 1, 2 and 6) were similar to sucrose-fructan 6-fructosyltransferase (6-SFT). The 1-SST and prft1 genes were colocalized with an invertase gene on the ryegrass linkage map. The mRNA levels of prft1 and prft2 increased gradually during cold treatment, while those of the 1-SST and 6G-FFT genes first increased, but then decreased before increasing again during a longer period of cold treatment. * Thus at least two different patterns of gene expression have developed during the evolution of functionally diverse FT genes, which are associated in a coordinated way with fructan synthesis in a cold environment.

Sex-independent transmission ratio distortion system responsible for reproductive barriers between Asian and African rice species

* A sex-independent transmission ratio distortion (siTRD) system detected in the interspecific cross in rice was analyzed in order to understand its significance in reproductive barriers. The S(1) gene, derived from African rice Oryza glaberrima, induced preferential abortion of both male and female gametes possessing its allelic alternative (), from Asian rice O. sativa, only in the heterozygote. * The siTRD was characterized by resolving it into mTRD and fTRD occurring through male and female gametes, respectively, cytological analysis of gametophyte development, and mapping of the S(1) locus using near-isogenic lines. The allelic distribution of the S(1) locus in Asian and African rice species complexes was also analyzed. * The siTRD system involved at least two components affecting male and female gametogeneses, respectively, including a modifier(s) that enhances fTRD. The chromosomal location of the major component causing the mTRD was delimited within an approx. 40 kb region. The S(1) locus induced hybrid sterility in any pairwise combination between Asian and African rice species complexes. * The allelic state of the S(1) locus has diverged between Asian and African rice species complexes, suggesting that the TRD system has a significant role in the reproductive barriers in rice.

Functional analysis of soybean genes involved in flavonoid biosynthesis by virus-induced gene silencing

Virus-induced gene silencing (VIGS) is a powerful tool for functional analysis of genes in plants. A wide-host-range VIGS vector, which was developed based on the Cucumber mosaic virus (CMV), was tested for its ability to silence endogenous genes involved in flavonoid biosynthesis in soybean. Symptomless infection was established using a pseudorecombinant virus, which enabled detection of specific changes in metabolite content by VIGS. It has been demonstrated that the yellow seed coat phenotype of various cultivated soybean lines that lack anthocyanin pigmentation is induced by natural degradation of chalcone synthase (CHS) mRNA. When soybean plants with brown seed coats were infected with a virus that contains the CHS gene sequence, the colour of the seed coats changed to yellow, which indicates that the naturally occurring RNA silencing is reproduced by VIGS. In addition, CHS VIGS consequently led to a decrease in isoflavone content in seeds. VIGS was also tested on the putative flavonoid 3'-hydroxylase (F3'H) gene in the pathway. This experiment resulted in a decrease in the content of quercetin relative to kaempferol in the upper leaves after viral infection, which suggests that the putative gene actually encodes the F3'H protein. In both experiments, a marked decrease in the target mRNA and accumulation of short interfering RNAs were detected, indicating that sequence-specific mRNA degradation was induced. The present report is a successful demonstration of the application of VIGS for genes involved in flavonoid biosynthesis in plants; the CMV-based VIGS system provides an efficient tool for functional analysis of soybean genes.

The binding of nuclear factors to the as-1 element in the CaMV 35S promoter is affected by cytosine methylation in vitro

Transcriptional gene silencing (TGS) is often associated with an increased level of cytosine methylation in the affected promoters. The effect of methylation of the cauliflower mosaic virus (CaMV) 35S promoter sequence on its binding to factors present in the nuclei was analyzed by electrophoretic mobility shift assays using extracts of petunia flowers. Specific DNA-protein interactions were detected in the region of the CaMV 35S promoter that contains the as-1 element and the region between - 345 and - 208. The binding of protein factor(s) to the as-1 element was influenced by cytosine methylation, whereas the binding to the region between - 345 and - 208 was unaffected. The results suggest that cytosine methylation of the as-1 element potentially affects the activity of the CaMV 35S promoter.

Epigenetic inactivation of chalcone synthase-A transgene transcription in petunia leads to a reversion of the post-transcriptional gene silencing phenotype

Petunia plants that exhibit a white-flowering phenotype as a consequence of chalcone synthase transgene-induced silencing occasionally give rise to revertant branches that produce flowers with wild-type pigmentation. Transcription run-on assays confirmed that the production of white flowers is caused by post-transcriptional gene silencing (PTGS), and indicated that transgene transcription is repressed in the revertant plants, providing evidence that induction of PTGS depends on the transcription rate. Transcriptional repression of the transgene was associated with cytosine methylation at CpG, CpNpG and CpNpN sites, and the expression was restored by treatment with either 5-azacytidine or trichostatin A. These results demonstrate that epigenetic changes occurred in the PTGS line, and these changes interfere with the initiation of transgene transcription, leading to a reversion of the PTGS phenotype.

The regulatory function of the upstream sequence of the beta-conglycinin alpha subunit gene in seed-specific transcription is associated with the presence of the RY sequence

beta-conglycinin, a major component of seed-storage proteins in soybean, comprises three subunits: alpha, alpha', and beta. Expression of these genes is spatially regulated in a stringent manner and occurs during seed development. To understand the mechanisms that control expression of the alpha subunit gene, we analyzed the nucleotide sequence of the 2.9-kb region upstream of the gene. The upstream sequence up to -1357 or a series of its 5'-deleted derivatives was fused to the beta-glucuronidase (GUS) gene. These reporter gene constructs were introduced into Arabidopsis thaliana plants via Agrobacterium-mediated gene transfer. Prominent GUS activity was detected in developing seeds of the T3 generation when 245 bp or longer sequences of the upstream region were fused to the GUS gene. We found a clear association of decreased GUS activity with a stepwise deletion of a region containing the RY sequence from the original construct. These results are consistent with the notion that multiple sequence elements including the RY sequences are involved in the seed-specific transcriptional activation of the beta-conglycinin alpha subunit gene in soybean.

Gene expression and genetic mapping analyses of a perennial ryegrass glycine-rich RNA-binding protein gene suggest a role in cold adaptation

A perennial ryegrass cDNA clone encoding a putative glycine-rich RNA binding protein (LpGRP1) was isolated from a cDNA library constructed from crown tissues of cold-treated plants. The deduced polypeptide sequence consists of 107 amino acids with a single N-terminal RNA recognition motif (RRM) and a single C-terminal glycine-rich domain. The sequence showed extensive homology to glycine-rich RNA binding proteins previously identified in other plant species. LpGRP1-specific genomic DNA sequence was isolated by an inverse PCR amplification. A single intron which shows conserved locations in plant genes was detected between the sequence motifs encoding RNP-1 and RNP-2 consensus protein domains. A significant increase in the mRNA level of LpGRP1 was detected in root, crown and leaf tissues during the treatment of plants at 4 degrees C, through which freezing tolerance is attained. The increase in the mRNA level was prominent at least 2 h after the commencement of the cold treatment, and persisted for at least 1 week. Changes in mRNA level induced by cold treatment were more obvious than those due to treatments with abscisic acid (ABA) and drought. The LpGRP1 protein was found to localise in the nucleus in onion epidermal cells, suggesting that it may be involved in pre-mRNA processing. The LpGRP1 gene locus was mapped to linkage group 2. Possible roles for the LpGRP1 protein in adaptation to cold environments are discussed.

The Star-type Color Pattern in Petunia hybrida ‘Red Star’ Flowers is Induced by Sequence-Specific Degradation of Chalcone Synthase RNA

Petunia hybrida 'Red Star' is a variety whose flowers exhibit a star-type red and white bicolor pattern. We analyzed the mRNA levels of six genes involved in anthocyanin biosynthesis. Only the level of chalcone synthase (CHS) mRNA was depressed in the unpigmented flower sectors. Both transcriptional activity and the accumulation of short interfering RNA of CHS in the unpigmented sectors were detected. Viral infection blocked the generation of CHS-silenced sectors. These results indicate that sequence-specific degradation of CHS RNA is the primary cause of the formation of white sectors in 'Red Star' flowers.

New sequence polymorphisms in the outer loops of the JC polyomavirus major capsid protein (VP1) possibly associated with progressive multifocal leukoencephalopathy

JC polyomavirus(JCPyV) causes progressive multifocal leukoencephalopathy (PML) in patients with decreased immune competence. To elucidate genetic changes in JCPyV associated with the pathogenesis of PML, multiple complete JCPyV DNA clones originating from the brains of three PML cases were established and sequenced. Although unique rearranged control regions occurred in all clones, a low level of nucleotide variation was also found in the coding region. In each case, a parental coding sequence was identified, from which variant coding sequences with nucleotide substitutions would have been generated. A comparison between the parental and variant coding sequences demonstrated that all 12 detected nucleotide substitutions gave rise to amino acid changes. Interestingly, seven of these changes were located in the surface loops of the major capsid protein (VP1). Finally, 16 reported VP1 sequences of PML-type JCPyV (i.e. derived from the brain or cerebrospinal fluid of PML patients) were compared with their genotypic prototypes, generated as consensus sequences of representative archetypal isolates belonging to the same genotypes; 13 VP1 proteins had amino acid changes in the surface loops. In contrast, VP1 proteins from isolates from the urine of immunocompetent and immunosuppressed patients rarely underwent mutations in the VP1 loops. The present findings suggest that PML-type JCPyV frequently undergoes amino acid substitutions in the VP1 loops. These polymorphisms should serve as a new marker for the identification of JCPyV isolates associated with PML. The biological significance of these mutations, however, remains unclear.

Single nucleotide polymorphisms in the gene encoding Krüppel-like factor 7 are associated with type 2 diabetes

AIMS/HYPOTHESIS

Although genetic susceptibility plays an important role in the pathogenesis of type 2 diabetes, most of the genes that influence susceptibility to type 2 diabetes have yet to be identified. Krüppel-like transcription factors are known to play important roles in development and cell differentiation, and have recently been implicated in the pathogenesis of type 2 diabetes. The present study aimed to examine the associations of single nucleotide polymorphisms (SNPs) in genes encoding members of the Krüppel-like-factor (KLF) family with type 2 diabetes in a large cohort of Japanese subjects.

METHODS

We genotyped 33 SNP loci found in 12 KLF genes in subjects with type 2 diabetes and in subjects from the general population using the PCR-Invader assay. We also examined the effects of the overexpression of KLF7 on adipogenesis in 3T3-L1 cells.

RESULTS

We identified a significant association between an SNP in KLF7 and type 2 diabetes (A vs C: p=0.004 after Bonferroni's correction, odds ratio=1.59, 95% CI 1.27-2.00). The expression of Klf7 decreased in response to the differentiation of 3T3-L1 adipocytes, and the overexpression of KLF7 resulted in significant inhibition of adipogenesis in 3T3-L1 cells.

CONCLUSIONS/INTERPRETATION

These results indicate that the gene encoding KLF7 is a novel candidate for conferring genetic susceptibility to type 2 diabetes.

Molecular analysis and physicochemical properties of electrophoretic variants of wild soybean Glycine soja storage proteins

Cultivated soybeans (Glycine max) are derived from wild soybeans (Glycine soja) and can be crossed with them to produce fertile offspring. The latter exhibit greater genetic variation than the former, suggesting a possibility that wild soybeans contain storage proteins with properties different from and better than those of cultivated soybeans. To identify a wild soybean suitable for breeding a new soybean cultivar, we analyzed seed proteins from 390 lines of wild soybeans by electrophoresis. We found some lines containing electrophoretic variants of glycinin and beta-conglycinin subunits: one line containing a small alpha' subunit of beta-conglycinin and two and five lines containing small A3 and large A4 polypeptides of glycinin, respectively. Beta-Conglycinin and glycinin containing such variant subunits exhibited solubility and emulsifying ability similar to those of the predominant types of wild and cultivated soybeans. Glycinins containing small A3 and large A4 gave a shoulder derived from the start of denaturation at a temperature 4 degrees C lower than that of glycinin from the predominant types of wild and cultivated soybeans, although their thermal denaturation midpoint temperatures were very similar to each other. Cloning and sequencing of the predominant and variant subunit cDNAs revealed that the small alpha' and the small A3 lacked 24 amino acid residues in the extension region and four amino acid residues in the hypervariable region, respectively, and that the large A4 did not have an insert corresponding to the difference in the electrophoretic mobility but Arg279 and Gln305 were replaced by glutamine and histidine, respectively, in the hypervariable region. These suggest that small differences even in the hypervariable region can affect the thermal stability, as well as the electrophoretic mobilities, of the proteins.

Recurrence Rate and Transplantability After Liver Resection in Patients With Hepatocellular Carcinoma Who Initially Met Transplantation Criteria

To understand the recurrence rate and transplantability after liver resection (LR), which are essential factors to predict the prognosis of initial resection and salvage transplantation for hepatocellular carcinoma (HCC), we reviewed the clinical records of 279 consecutive HCC patients who met the Milan criteria and underwent LR between 1990 and 2000. Recurrence-free survival rates after 1, 2, 3, 5, and 10 years following LR were 84%, 62%, 49%, 29%, and 17%, respectively. Multivariate analysis using clinical factors such as age, sex, histological differentiation, serum levels of alpha-fetoprotein and 7S domain of type IV collagen (7S collagen), platelet counts, indocyanin green retention test after 15 minutes, and type of LR (resection of one or more segments, or less than one segment) revealed 7S collagen to be a independent factor that significantly affects recurrence-free survival. Yearly recurrence rates up to 5 years after resection ranged from 14% to 27%, averaging 20%. Concerning 169 patients who underwent tests for 7S collagen, the average yearly recurrence rate (27%) in patients with 7S collagen levels 8.0 ng/mL or higher was remarkably greater than that in the patients with levels less than 8.0 ng/mL (16%). The transplantability rate at the time of recurrence meeting the Milan criteria was roughly 60%. There were no pre-LR factors that significantly predicted transplantability. This result indicates that patients with lower 7S collagen levels are more eligible for initial LR and then salvage LT rather than primary LT.

[A 65-year-old man with rigid-bradykinetic parkinsonism, vertical gaze palsy, difficulty of eye-lid opening, and marked pseudo-bulbar palsy]

We report a 65-year-old man with rigid-bradykinetic parkinsonism, vertical gaze palsy, difficulty in eye-lid opening, and marked pseudo-bulbar palsy. He felt difficulty of it, hand movement at 59 years old. When he was 60 years old, monotonous speech and slowness of movement appeared. He visited a neurologist who noted vertical gaze palsy, neck rigidity, and bradykinesia. He was diagnosed as progressive supranuclear palsy (PSP) and given 300 mg L-Dopa/Benserazide by the neurologist. This medication improved his rigidity and bradykinesia. At 62 years of the age, his eye-lids closed involuntary and it was difficult to open. In addition, he began to complain of wearing-off, autonomic symptoms, and dysphagia. Anti-parkinsonian drugs were increased, but his bradykinesia progressed. At 64 years of the age, he was admitted to the Neurology Service of Juntendo Hospital. On admission, he was alert and not demented. No aphasia, apraxia, or agnosia was noted. In the cranial nerves, upward and downward gaze were markedly restricted. His face was hypomimic and seborrhoic. It was difficult to swallow liquid or solid for him. No weakness was noted, but he walked in small steps with freezing and falling tendency to backward. Rigidity was noted on his extremities and stronger on his left side than right. Tremor was absent. Bradykinesia of his body and extremities was marked. No cerebellar ataxia was noted. Deep tendon reflexes were within normal range. Planter response was flexor bilaterally. Myerson's sign was noted. Sensory and autonomic function were normal. He was treated with L-Dopa, Pergolide, and Bromocriptine. However, these medications improved his bradykinesia and gait disturbance only slightly, dysphagia became progressively worse. He developed aspiration pneumonia when he was 65 years old and admitted to Juntendo Hospital. A large amount of sputum was aspirated from his trachea. Two days after from admission, he was found dead on his bed. He was discussed in a neurological CPC and the chief discussant arrived at a conclusion that the patient had progressive supranuclear palsy (PSP). Other differential diagnoses included Parkinson's disease, pallido-nigroluysian atrophy (PNLA), multiple system atrophy (MSA), and corticobasal degeneration(CBD). Many participants considered that PSP or PNLA was most likely. Post-mortem exmination revealed marked nigral neuronal loss and gliosis. The globus pallidus and the luysian body changed mildly. However, the frontal cortex was relatively spared, there were many ballooned neurons in the cortical layer. Other parts were spared. With sliver (Bodian and Gallyas-Braak) and anti-phsphorylated tau stain, abundant astrocytic plaques, neurofibrillary tangles, and argyrophilic threads on the frontal cortex, striatum, and substantia nigra were seen. There was no tufted astrocyte which was hallmark of diagnosis of PSP. In addition, several Lewy bodies were seen in the brainstem. Because astrocyte plaque was considered specific for pathology of CBD, the pathologist revealed that the pathological diagnosis of this patient was CBD. Nevertheless, discussion was focused on the relatively mild degeneration of the frontal cortex for CBD.

[The cognitive dysfunction in Parkinson's disease]

Parkinson's disease (PD) is a slowly progressive disorder which begins with motor symptoms. Several cognitive deficits can be observed in nondemented patients with PD during their history. The core symptom in the cognitive deficits in PD is the executive dysfunction. Neuropsychological tests such as Wisconsin Card Sorting Test, Trail Making Test are used to measure the degree of this dysfunction. Executive dysfunction is thought related to abnormalities in the dorsolateral prefrontal circuit which largely passes through the caudate nucleus. The dysfunction emerges as the pathology spreads to the nigrocaudate project corresponding to Hoehn & Yahr stage II-III. Effective therapy for cognitive dysfunction in PD remains elusive, however donepezil, Attention Process Training, Music therapy and Transcranial magnetic stimulation have been reported to have partial efficacy.

High frequency Agrobacterium-mediated transformation and plant regeneration via direct shoot formation from leaf explants in Beta vulgaris and Beta maritima

We have developed a new procedure for Agrobacterium-mediated transformation of plants in the genus Beta using shoot-base as the material for Agrobacterium infection. The frequency of regeneration from shoot bases was analyzed in seven accessions of sugarbeet ( Beta vulgaris) and two accessions of B. maritima to select materials suitable for obtaining transformed plants. The frequency of transformation of the chosen accessions using Agrobacterium strain LBA4404 and selection on 150-mg/l kanamycin was found to be higher than that in previously published methods. Genomic DNA analysis and beta-glucuronidase reporter assays showed that the transgene was inherited and expressed in subsequent generations. In our method, shoot bases are prepared by a simple procedure, and transformation does not involve the callus phase, thus minimizing the occurrence of somaclonal variations.

Choledocholithiasis caused by migration of a surgical clip into the biliary tract following laparoscopic cholecystectomy

As experience with laparoscopic cholecystectomy (LC) has increased, so have the number and variety of complications. We report a case of choledocholithiasis caused by migration of a surgical clip applied during LC. A 57-year-old Japanese man who had undergone LC 6 years previously was referred to our hospital with pruritus and jaundice. Magnetic resonance cholangiopancreatography and ultrasonography revealed a solid mass in the common hepatic duct and dilatation of the intrahepatic bile ducts. Abdominal arteriography demonstrated interruption of the right hepatic artery by surgical clips. Five days after a biopsy of the mass was performed through a percutaneous transhepatic biliary drainage tube, the mass moved to the terminus of the common bile duct along with one of the surgical clips. A basket catheter was used to remove the mass via endoscopy. Despite the fact that other clips in the common hepatic duct were partially exposed, the patient has been well for 2 years with no additional interventions.

Soybean germplasm pools in Asia revealed by nuclear SSRs

Soybean was domesticated in East Asia, where various kinds of landraces have been established as a result of adaptation to different environments and the diversification of food cultures. Asia is thus an important germplasm pool of soybean. In order to evaluate the genetic structure of the Asian soybean population, we analyzed allelic profiles at 20 simple-sequence repeat (SSR) loci of 131 accessions introduced from 14 Asian countries. The SSR loci produced an average of 11.9 alleles and a mean gene diversity of 0.782 in the accessions tested. Quantification theory III analysis and cluster analysis with the UPGMA method clearly separated the Japanese from the Chinese accessions, suggesting that the Japanese and Chinese populations formed different germplasm pools. The Korean accessions were involved in both germplasm pools, whereas most of the accessions from southeast and south/central Asia were derived from the Chinese pool. Relatively high genetic diversity and the absence of region-specific clusters in the southeast and south/central Asian populations suggest that soybean in these areas has been introduced repeatedly and independently from the diverse Chinese germplasm pool. The present study indicates that the two germplasm pools can be used as exotic genetic resources to enlarge the genetic bases of the respective Asian soybean populations.