Genetic diversity and hierarchical population structure of a rare autotetraploid plant,Aster kantoensis (Asteraceae)

We sampled 17 populations of a rare autotetraploid Aster kantoensis (Asteraceae) from three river systems located in central Japan, and studied them for allelic variation at 22 enzyme loci. There was no significant correlation between the actual population size and three genetic diversity parameters, suggesting that the effective population size was very small even for the large populations, i.e., even large populations may still have a high probability of being of recent origin and remain influenced by the founder effect. Compared to other autotetraploid species, the total genetic variation of A. kantoensis is small. The number of alleles and gene diversity of a population were not significantly different among the river systems, although the percentage of polymorphic loci was different. Genetic differentiation among river systems was larger than between populations within the river systems, thereby indicating that gene flow between river systems is small, especially between the Kinu River system and Tama or Sagami River systems.     

Genetic variation in Drechslera teres populations as indicated by RAPD markers

Random amplified polymorphic DNA (RAPD) was used to assess genetic variation among 48 isolates of Drechslera teres originating from different sites in Finland. RAPD profiles were generated with five arbitrary 10-mer primers and revealed polymorphisms suitable for screening differentiation in this fungal population. Using UPGMA clustering analysis, a similarity coefficient of approximately 63% was observed between all D. teres isolates studied. The variation was, however, distributed on a small scale as different genotypes were found from the same plant. The isolates could not be grouped according to geographic origin, aggressiveness, growth rate or morphological features, indicating that the primers used in this study were neutral markers for these characters. The primers were, however, able to differentiate between isolates of Helminthosporium species (D. teres, Drechslera graminea and Bipolaris sorokiniana).     

Role ofDrosophila TRP in inositide-mediated Ca2+ entry

Inositol lipid signaling relies on an InsP₃-induced Ca²⁺ release from intracellular stores and on extracellular Ca²⁺ entry, which takes place when the Ca²⁺ stores become depleted of Ca²⁺. This interplay between Ca²⁺ release and Ca²⁺ entry has been termed capacitative Ca²⁺ entry and the inward current calcium release activated current (CRAC) to indicate gating of Ca²⁺ entry by Ca²⁺-store depletion. The signaling pathway and the gating mechanism of capacitative Ca²⁺ entry, however, are largely unknown and the molecular participants in this process have not been identified. In this article we review genetic, molecular, and functional studies of wild-type and mutantDrosophila photoreceptors, suggesting that thetransient receptor potential mutant (trp) is the first putative capacitative Ca²⁺ entry mutant. Furthermore, several lines of evidence suggest that thetrp gene product TRP is a candidate subunit of the plasma membrane channel that is activated by Ca²⁺ store depletion.     

Factors affecting gene delivery by particle bombardment ofDendrobium orchids

Summary Five parameters were examined for their effect on transformation ofDendrobium tissues by microprojectile bombardment. The superpromoter in pBI426 produced at least 1.5 times as many transient transformants as the single cauliflower mosaic virus 35S promoter in pBI121 (37 to 69% vs. 0 to 44%) with dark and frequent GUS (β-glucuronidase) staining. Tissue, genotype, and type of microparticle significantly affected transient GUS activity. Higher expression was seen in protocormlike bodies and in hybrid UH44 compared to etiolated shoots and protocorms and to hybrids M61 and K1329-39. Microparticles of 1.6-μm Bio-Rad gold were more effective than 1.0-μm ASI gold. Transient GUS activity did not differ among protocormlike bodies bombarded using helium propellant pressures of 650, 900, or 1100 psi. Transgenic plants were recovered fromDendrobium UH800 protocormlike bodies bombarded with pBI426-coated, 1.1-μm tungsten particles using an early-model gunpowder-driven apparatus with an estimated stable transformation rate of 11.7%. One transgenic plant ofDendrobium UH44 was recovered from etiolated shoot explants bombarded with pBI121-coated, 1.1-μm tungsten particles using the Dupont PDS-1000 with a stable transformation rate of 0.17%. Positive selection results showed 100 to 200 mg·liter⁻¹ kanamycin to be appropriate for regeneration of transgenic plants from protocormlike bodies, protocorms, and etiolated shoot explants over a 3- to 9.5-mo. period.     

Whisker-mediated plant transformation: An alternative technology

A number of different methods, involving direct DNA delivery are now available for plant transformation. Here we review the most recently developed technique which involves the mixing of silicon carbide whiskers with plant cells and plasmid DNA. Fertile transgenic plants have now been produced using whisker-mediated transformation, and this method can now be considered as a simple, inexpensive alternative for plant transformation. A brief review on transformation of animal cells andChlamydomonas using whiskers technology is also included.     

The extracellular nuclease of Serratia marcescens: studies on the activity in vitro and effect on transforming DNA in a groundwater aquifer microcosm

A quantitative endonuclease assay, which relies on the introduction of single and double strand breaks into supercoiled plasmid DNA, was used to study the activity of the extracellular nuclease of Serratia marcescens SM6 in buffer and in groundwater. The parallel enzyme concentration-dependent production of relaxed and linear plasmid molecules suggests that the nuclease produces single and double strand breaks in duplex DNA. Bovine serum albumin stimulated the nuclease activity towards DNA and RNA and increased the stability of the enzyme against thermal inactivation. The DNase activity at 4 °C and 50 °C was almost half of that at the optimum temperature (37 °C). The nuclease was active in groundwater, although the specific activity was lower than in buffer. In a groundwater aquifer microcosm, mineral-adsorbed transforming DNA was substantially less accessible to the nuclease than was dissolved DNA. The data suggest that the extracellular nuclease of Serratia marcescens may contribute to DNA turnover in the environment and that adsorption of DNA to minerals provides protection against the nuclease.Abbreviations GW groundwater GWA groundwater aquifer     

Extraction and genetic control of two new water-soluble proteins of mature barley seed

This paper describes the genetic control of two new water-soluble proteins in barley. Water-soluble proteins (WSPs) of mature barley seed form part of the albumin/globulin class of seed proteins. They can be extracted from hand-milled grain with water, though some WSPs are more efficiently extracted with a solution of 10 mM dithiothreitol. Polymorphisms for WSPs were detected in isoelectric focusing gels incorporating various ampholine combinations. Two new controlling genes (Wsp4 andWsp5) have been identified and located using wheat/barley chromosome addition lines and barley doubled haploids.Wsp4 is located on chromosome 2 (2H), andWsp5 was found to be tightly linked toWsp2 on the long arm of chromosome 7 (5HL). Segregation of a sixth gene (Wsp6) is also described, but this has not been mapped. The results are discussed with respect to other previously mappedWsp loci.This work was funed by the Scottish Office of Agriculture and Fisheries Department and the Agricultural and Food Research Council.     

Trade-offs in responses to host plants within a population of a generalist herbivore,Christoneura rosaceana

Evolutionary constraints on the ability of herbivores to efficiently use a set of phytochemically similar hosts, while maintaining a high performance on phytochemically different hosts, are central in explaining the predominance of host specialization in phytophagous insects. Such feeding trade-offs could be manifested within insect populations as negative genetic correlations in fitness on different host species. We tested the hypothesis that feeding trade-offs were present within a population of the obliquebanded leafroller,Choristoneura rosaceana (Harris). Components of fitness were measured in families originating from an apple orchard that were fed on four host-plant species in the laboratory. Under the conditions of this experiment, all across-host genetic correlations were strongly positive, suggesting that this population comprised true generalists. With the exception of diapausing propensity, the heritability of the fitness components tended to be lower in caterpillars fed on apple leaves than in insects fed other hosts. This suggests a constraint on the selective response of the fitness components in the orchard environment.     

GENETIC AND MORPHOLOGICAL DIVERGENCE AMONG MORPHOTYPES OF THE ISOPOD EXCIROLANA ON THE TWO SIDES OF THE ISTHMUS OF PANAMA

Excirolana braziliensis is a dioecious marine isopod that lives in the high intertidal zone of sandy beaches on both sides of Central and South America. It possesses no larval stage and has only limited means of adult dispersal. Indirect estimates of gene flow have indicated that populations from each beach exchange less than one propagule per generation. Multivariate morphometrics have discovered three morphs of this species in Panama, two of them closely related and found on opposite sides of Central America (“C morph” in the Caribbean and “C′ morph” in the eastern Pacific), the third found predominantly in the eastern Pacific (“P morph”). Though the P and C′ morphs are seldom found on the same beach, they have overlapping latitudinal ranges in the eastern Pacific. A related species, Excirolana chamensis, has been described from the Pacific coast of Panama. Each beach contains populations that remain morphologically and genetically stable, but a single drastic change in both isozymes and morphology has been documented. We studied isozymes and multivariate morphology of 10 populations of E. braziliensis and of one population of E. chamensis. Our objective was to assess the degree of genetic and morphological variation, the correlation of divergence on these two levels of integration, the phylogenetic relationships between morphs, and the possible contributions of low vagility, low gene flow, and occasional extinction and recolonization to the genetic structuring of populations. Genetic distance between the P morph, on one hand, and the other two morphotypes of E. braziliensis, on the other, was as high as the distance between E. braziliensis and E. chamensis. Several lines of evidence agree that E. chamensis and the P morph had diverged from other morphs of E. braziliensis before the rise of the Panama Isthmus separated the C and C′ forms, and that the P morph constitutes a different species. A high degree of genetic differentiation also exists between populations of the same morph. On the isozyme level, every population can be differentiated from every other on the basis of at least one diagnostically different locus, regardless of geographical distance or morphological affiliation. Morphological and genetic distances between populations are highly correlated. However, despite the high degree of local variation, evolution of E. braziliensis as a whole has not been particularly rapid; divergence between the C and C′ morphs isolated for 3 million yr by the Isthmus of Panama is not high by the standard of within-morph differentiation or by comparison with other organisms similarly separated. Alleles that are common in one population may be absent from another of the same morph, yet they appear in a different morph in a separate ocean. The high degree of local differentiation, the exclusive occupation of a beach by one genotype with rare arrival of foreign individuals that cannot interbreed freely with the residents, the genetic stability of populations with infrequent complete replacement by another genetic population, and the sharing by morphs of polymorphisms that are not shared by local populations, all suggest a mode of evolution concentrated in rare episodes of extinction and recolonization, possibly coupled with exceptional events of gene flow that help preserve ancestral variability in both oceans.     

Genic diversity in Red River pupfish Cyprinodon rubrofluviatilis (Atheriniformes: Cyprinodontidae) and its implications for the conservation genetics of the species

Starch gel electrophoresis of proteins was used to study geographic variation at 26 gene loci in the Red River pupfish ( Cyprinodon rubrofluviatílís ), a species restricted to west Texas and Oklahoma. Marked differences were detected between populations in the Red and Brazos river drainages, with fixed or nearly fixed differences occurring at five gene loci. In addition, mean heterozygosity was uniformly high for the Red River form ( = 0·076–0·101) while samples of the Brazos River form were genetically depauperate ( =0·00–0·017). Introduced populations in the South Canadian and Colorado river drainages appear to have been derived from the Red River drainage. The presence of alleles diagnostic of the Red and Brazos river forms supports the suggestion from previous work that they may represent cryptic species. Regardless of taxonomy, however, the presence of two genetically distinct forms must be taken into consideration by those concerned with maintenance of biotic diversity.