The fungal cell wall is an essential structure which protects cells from various environmental stresses such as hyper- or hypo-osmosis, and endows them with specific morphology in response to their life or cell division cycle. In addition, the cell wall has a variety of enzymatic activities per se, which are required for nutritional uptake, secretion, and cell adhesion including mating processes. In addition to these cytological interests, clinical demands to clarify the regulatory mechanisms of cell wall synthesis have been increasing, since the cell wall is a unique and effective target of antifungal agents. However, the molecular mechanisms are poorly understood at present, although the role of several signal transduction pathways have recently been implicated in regulation. In this review, the author focuses on genes and their interactions which are involved in fission yeast cell wall biogenesis.
The chromosomes of the queen scallop Aequipecten opercularis were studied using conventional Giemsa staining, chromosome measurements, C-banding, silver staining, and fluorescent in situ hybridization (FISH) with 18S-28S rDNA and 5S rDNA probes. The karyotype (2n = 26) consists of large metacentric (pairs 1 and 2), telocentric (pairs 3, 4, 5, 6, 7, 8, and 9), and small metacentric chromosomes (pairs 10, 11, 12, and 13). The C-bands observed can be described as major and minor C-bands which are differentiated according to the intensity of the fluorescence and the frequency of the detection. Major C-bands were found on the long arm of the chromosome pairs 6, 7, 8, and 9 in an intercalary or subterminal position. Minor C-bands were located in the centromeric region in all chromosomes of the complement and also on one arm of pairs 12 and 13 in a terminal position. Silver spots were detected on the telomere of the long arms of one or two chromosomes of pair 7 in every case, although in two individuals up to four additional silver spots were detected. These were located on pairs 8 and 9 in the same position as the C-bands. 18S-28S ribosomal genes were found by FISH on the long arm of chromosome pair 7. 5S ribosomal genes were located subterminally on one arm of metacentric pair 1, but two sites were differentiated in the case of elongated chromosomes. The results obtained allow for the identification of at least six different chromosome pairs in A. opercularis and contribute to the construction of an idiogram that is suitable for gene mapping and establishing accurate interspecific comparisons in scallops.
The DNA sequences of the internal transcribed spacer (ITS) region of the rRNA gene were determined in 20 taxa of 12 species of Fagopyrum. By comparing the sequence data and constructing phylogenetic trees, the phylogenetic relationships among the Fagopyrum species were established. The sequences of ITS (ITS1 and ITS2) were about 3-7 times more variable than those of the 5.8S subunit of the rRNA gene. The classification of Fagopyrum species based on the DNA sequences of the rRNA gene almost coincides with the classification based on morphology, allozyme variability, and nucleotide sequences of the rbcL-accD region of the chloroplast DNA. A close relationship of F. lineare with the F. statice-F. leptopodum clade was suggested and this was strongly supported by a 68-bp gap in ITS1 found in these three species. A tetraploid F. cymosum from Kathi, India, has two distinct rRNA genes probably on homoeologous chromosomes, and was distinguished from the clade of other diploid/tetraploid F. cymosum with a high bootstrap value. This strengthened the hypothesis of the polyphyletic origin of the tetraploid F. cymosum.
The geographical variation of two genes, hwd1 and hwd2, controlling hybrid breakdown (F2 weakness) was surveyed in 239 Asian rice cultivars. The cultivars with the genotype Hwd1/Hwd1Hwd2/Hwd2 were predominant in South Asia and Southeast Asia, while those with the genotype Hwd1/Hwd1hwd2/hwd2 were predominant in Japan, the Philippines, and Yunnan province, China. Only one cultivar from Laos had the genotype hwd1/hwd1Hwd2/Hwd2. Preferential association was found between the presence or absence of hwd2 and the two major cultivar groups (indica and japonica) based on diagnostic RFLP markers. Dominant homozygotes were frequent in indica rice cultivars, while recessive homozygotes were frequent in japonica rice cultivars. This association was not clear for cultivars from the center of genetic diversity of rice, ranging from Vietnam to Bangladesh. Polymorphisms were surveyed for RFLP markers on chromosomes 10 and 7, harboring hwd1 and hwd2 loci, respectively. The region around hwd2 tended to be differentiated in allelic combination among cultivars into the indica and japonica rice groups. No such trend was found around the hwd1 region. These facts suggest the hybrid breakdown controlled by this genic system is a rare phenomenon and consequently did not contribute to cultivar differentiation of rice.
Using the scutellar tissue of rice mature embryos as a target tissue, a selectable marker gene, bar, and an unselectable gene, fatty acid desaturase gene from tobacco (NtFAD3), on separate plasmids, were introduced by particle bombardment. Co-integration, co-expression and inheritance of these genes were analyzed as well as seed fertility of the transgenic plants. Twenty-three out of 32 bialaphos-resistant plants integrated the NtFAD3 gene, which was confirmed by Southern-blot analysis of R0 plants, and showed one to more than 20 hybridizing bands of exogenous DNA, indicating a 72% (23/32) co-integration frequency. However, the frequency of the transgenic plants containing the 1.4-kb fragment of NtFAD3 gene was 34% (11/32). Northern-blot analysis revealed that seven out of ten fertile transgenic rice plants which had a 1.4-kb fragment of NtFAD3 cDNA expressed NtFAD3 mRNA. The NtFAD3 gene under the control of CaMV35S promoter stably expressed in the transgenic rice plants and modified the proportions of linoleic acid (18:2) and linolenic acid (18:3) in fatty acids; the content of 18:2 decreased and that of 18:3 increased. Fourteen out of 32 (44%) transgenic plants set seeds and 18 (56%) showed low fertility or sterility. Molecular analysis of the selfed progeny indicated that all copies in almost all R0 plants were inherited as a single dominant hemizygous locus.
Restriction site variation in 18-kb region including the Gpdh (sn-glycerol-3-phosphate dehydrogenase) locus has been assessed in 27 isofemale lines, 12 lines from the Chounan population and 15 lines from the Pusan population in Korea. Of the 25 restriction sites that were scored, 5 sites were polymorphic (20.0%): PstI (-2.35), XbaI (-1.7), HindIII (0.0), HindIII (+0.25), and PstI (+5.7). Two insertions (I) and three deletions (D) were detected. All the restriction sites and length polymorphisms were located in introns and outside regions of the Gpdh structure gene, the area from -7.0 site to -5.5 site. The proportion of segregating nucleotides, p, for all 27 lines was 0.019 and the estimated heterozygosity per nucleotide pair, was 0.013. Sixteen kinds of restriction map haplotypes of all lines analyzed were detected. Few lines were identical at the restriction map level. The estimated haplotype diversity, h, was 0.968. The haplotype diversity (0.997) of GpdhFF bearing chromosomes was slightly higher than that (0.982) of GpdhSS chromosomes. Analysis for a linkage disequilibria between the polymorphism also showed that HindIII (+0.25) vs. I (a) and PstI (-2.35) vs. D (a) have relatively high level of the linkage disequilibria. There were no significant relationship between restriction site polymorphism and GPDH activity in 27 second-chromosome lines; however, there was an apparent difference in the effect of length variation on GPDH activity. The activity of deletion-bearing lines was lower than that of deletion-free lines, while there was no effect of insertion on activity. Duplication of Gpdh was observed in about one-third of the 27 isofemale lines. The duplication-bearing lines in both populations had higher levels of GPDH activity and GPDH CRM than duplication-free lines. In a further investigation of the duplication structure, the duplication of Korean populations was shown to have a similar structure to other populations investigated (Symonds and Gibson, 1992; Takano et al., 1989).
In the silkworm, Bombyx mori, nonsusceptibility to B. mori densonucleosis virus type-1 (BmDNV-1) is controlled by a recessive gene, nsd-1 (nonsusceptibility to DNV-1), located on the twenty-first chromosome. We investigated genetic linkage between five random amplified polymorphic DNA (RAPD) markers and the +nsd-1 gene. Initially, we constructed the CSD-1 strain (nsd-1/+) which is congenic to strain C137 (nsd-1/ nsd-1) for the twenty-first chromosome, starting with a female of C137 and a male of strain J137 (+nsd-1/+nsd-1). For the crossing over experiment, a female of C137 was crossed with a male (nsd-1/+) of CSD-1. Segregation analysis showed that the most closely linked RAPD marker mapped 3.0 cM distant from +nsd-1. A more specific marker for +nsd-1 was made by converting this RAPD band into a sequence characterized amplified region (SCAR) using a series of newly designed primer pairs based on its DNA sequence.
Genomic DNAs were compared between males and females of the domesticated silkworm, Bombyx mori, strains C108, C137, J137, p50, and WILD-W (constructed by crossing a wild silkworm, B. mandarina, female with a male of strain C108) by polymerase chain reaction (PCR) with 700 arbitrary 10-mer primers. Four female-specific RAPDs (W-Kabuki, W-Samurai, W-Kamikaze, and W-Yamato) were found. The sex chromosome formulas of B. mori and B. mandarina are ZW (XY) for the female and ZZ (XX) for the male. The four female-specific RAPDs are assumed to be derived from the W chromosome because the other chromosomes are shared by both sexes. A computer search for deduced amino acid sequences of these four RAPDs revealed that all of them showed homology to previously reported amino acid sequences encoded in known retrotransposable elements from various organisms.
Restriction fragment length polymorphisms (RFLPs) of mitochondrial DNA (mtDNA) of wild and cultivated soybeans were analyzed to study their phylogenetic relationships. The observed number of differences in hybridization profiles greatly varied (1 - 17 patterns) with both the mtDNA probes and the restriction enzymes that were used. A cladistic analysis was conducted based on the RFLP data. In the parsimonious tree, four distinct groups appeared among 20 accessions of the subgenus Soja representing 20 mitochondrial genome types. Common features with regard to geographic distributions in natural populations in East Asia were observed among the mitochondrial genome types of wild soybean that belonged to the same group: one clade consisted of genome types IIg and VIIg that are detected with very low frequencies; another clade consisted of genome types Ic, Id, Ie, and Ik whose distributions are highly biased mainly in Japan. The genome types that are widely distributed in East Asia such as IVa, IVb, and Va were not grouped into the same clade. The mitochondrial genome types IIIb, IVb, and IVc, in which two different chloroplast genome types exist, belonged to the same clade. Possible changes in mitochondrial genomes during the expansion of the distribution of wild soybeans in East Asia were discussed.
Intraspecific variation in the effects of mating on the emigration response behavior and fecundity of Drosophila melanogaster was investigated using isofemale lines of the Himeji population in Japan. The emigration activities of the mated and unmated females were examined with Sakai's population system. The isofemale lines were classified into two groups with respect to the effect of mating on emigration activity; 1) copulation decreased the emigration activity in 26 out of 28 isofemale lines, and 2) higher emigration activity was noted in the mated than in the unmated females in two lines. The percentage of expressed genotypic variance on emigration activity was higher in the unmated females than in the mated ones. Gregarious oviposition did not seem to be related to the decrease of emigration activity in the mated females.
We found a repetition of CA dinucleotides on the second intron of mouse polymeric immunoglobulin receptor (PIgR) gene. This repetition is genetically polymorphic among mouse strains and was used as a simple sequence length polymorphism marker to map the PIgR gene. Alleles of this and other SSLP markers were determined with PCR for progenies from a back cross between C57BL/6J mice and F1 heterozygotes of AKR/J and C57BL/6J. This mapping located the pIgR gene between D1Mit200 and D1Mit218 of the mouse chromosome 1.