Genetic determination of pappus part number in the annual hybridMicroseris B 87 (Asteraceae—Lactuceae)

The ChileanMicroseris pygmaea has a ten-part paleaceous pappus while the CalifornianM. bigelovii has five pappus parts on each achene. Hybrids between the two species have between five and ten pappus parts with averages below 7.5. Hybrid B 87 has an F 1 average value of 6.7 pappus parts. 140 F 2 plants were raised from this hybrid, and 12 F 3 families were obtained by selfing from F 2 plants. One larger F 4 family has been raised. Pappus part number in all of these is still canalized between 5 and 10. Variation within these limits is genetically determined by a quantitatively acting polygenic system. Modeling of this system suggests that a minimum of four, but probably not many more, genes are involved. This opens the possibility of a complete genetic analysis of the system.     

Single-gene heterozygotes derived from the polygenic pappus part system ofMicroseris hybrid C34 (Asteraceae—Lactuceae)

Microseris strain C34 is a hybrid between the Chilean speciesM. pygmaea (10 pappus parts) and the CalifornianM. bigelovii (5 pappus parts). The plants are propagated by selfing from the original hybrid specimen. Each plant has from 5 to 10 pappus parts per achene with an average value that is additively determined by four unlinked quantitatively acting genes. Single-gene heterozygote sublines have been obtained for two of these,pp-1 (shown to be linked to a modifier of acid phosphatase-1) andpp-4. Sublines homozygous for all four additive genes show residual genetic variation influencing pappus part number. At least one additional gene can be demonstrated by its linkage with leucine aminopeptidase-1. Lines for the further characterization of these hypostatic genes are selected.     

A second marker enzyme in the genetics of pappus part numbers inMicroseris hybrid B87 (Asteraceae,Lactuceae)

CrossingMicroseris pygmaea (10 pappus parts) withM. bigelovii (5 pappus parts) results in hybrids with variable pappus part numbers between 5 and 10. Previous work has shown that a system of four additively acting genes determines the average pappus part numbers of these hybrids. In hybrid B87 two genes have a 10-determining and a 5-determining allele each, two others a 5-determining and a null (inactive or missing) allele. Genetic linkage of one of the latter with the enzyme geneEsterase-1 and the leaf shape genespatulate leaves has been demonstrated. Here we demonstrate linkage between one of the two 10-determining genes and the enzyme locusEsterase- Y/B. The genotypes in the pappus part system of many specimens can now be fully determined. This is a major advance for the analysis of the evolution of this additive polygenic system.Genetics of Pappus Part Numbers inMicroseris Hybrid B87, II.—Part I:Bachmann & al. 1981.     

Pappus part number in annual species ofMicroseris (Compositae,Cichoriaceae)

All North American annual species of the genusMicroseris have a five-part pappus, the one South American annual,M. pygmaea, has ten pappus parts. The pappus develops over a constant number of ten provascular bundles with or without inhibition between alternate sites of pappus development. Each natural population contains a predictable proportion of achenes with aberrant pappus part numbers. Hybridization betweenM. bigelovii (5 parts) andM. pygmaea results in F 1 and F 2 plants with many aberrant achenes. In each plant either five or ten can be shown to be the basic number with aberrant numbers following a Poisson distribution for numbers added to 5 or deleted from 10. Occasional plants show no basic number but have a random distribution of numbers about an intermediate mean. The evolutionary genetics of this character is discussed.     

Genetic components of heterocarpy inMicroseris hybrid B87 (Asteraceae,Lactuceae)

Microseris B87 is derived from a single hybrid specimen betweenM. pygmaea with few, weakly hairy peripheral achenes and aM. bigelovii with many, strongly hairy peripheral achenes. Offspring through the F4 and F5 generations obtained by spontaneous selfing were analyzed for the segregation of quantitative and qualitative characters relating to achene dimorphism. The phenotypic effects of two previously identified unlinked genes determining the relative number of outer achenes are characterized in partially and completely homozygous sublines. We show that two morphological markers genetically linked to one of these genes are themselves regulated by the system inducing heterocarpy. Not more than two more unlinked genes are involved in the genetic basis of the heterocarpic response. The interaction of these genes in determining the heterocarpy phenotypes is discussed in the framework of a model postulating genes for a morphogen gradient across the capitulum and genes responding to this gradient.     

Variability of the inflorescence ofMicroseris laciniata (Compositae: Cichorieae)

Quantitative characters of the flowering head of a garden population ofMicroseris laciniata were scored during the second, third, and fourth season of growth. Number of achenes per head, number of phyllaries per head and the average number of pappus parts per achene in single heads show significant plant to plant variation. Achenes per head and pappus parts per achene were scored in identical plants in two subsequent seasons. The number of pappus parts per achene varies freely between five and ten. This contrasts with annual species ofMicroseris in which either five or ten pappus parts are found, depending on the species. In spite of a clear plant-specific average of pappus parts, both high and low pappus part determination can be demonstrated in all specimens. The number of pappus parts depends on the position of an achene on the receptacle, marginal achenes usually having fewer pappus parts than central ones. This gradient is not closely correlated with the position of an achene on the genetic spiral.     

The karyotypes ofMicroseris bigelovii,M. douglasii,andM. pygmaea (Asteraceae)

The karyotypes of the three annuals,Microseris bigelovii, M. douglasii andM. pygmaea, consist of 2n = 18, small, submetacentric chromosomes. Length, centromere position, C-banding pattern, silver staining of NOR's, and the use of base specific fluorochromes, allow the identification of four of the nine chromosome pairs. The banding pattern ofM. bigelovii andM. pygmaea is identical, but intraspecific differences are found between strains ofM. douglasii.     

QTL mapping reveals a two-step model for the evolutionary reduction of inner microsporangia within the asteracean genus <Emphasis Type="Italic">Microseris</Emphasis>

The reduction of inner (adaxial) pollen sacs (microsporangia, MS) as a diagnostic character for the three asteracean species, Microseris bigelovii, Microseris elegans and Microseris pygmaea, was analysed in an interspecific cross between Microseris douglasii and Microseris bigelovii with 4 MS and 2 MS, respectively, using the average number of MS per plant as a quantitative character. A previous QTL (Quantitative Trait Locus) analysis had revealed one major QTL (3B) and three modifier QTLs (3A, 4A, 7A) with epistatic effects only on the homozygous recessive 2 MS genotype of QTL 3B. Here we performed a bulked segregant analysis on four 2 MS and four 4 MS DNA-bulks with 407 EcoRI/MseI AFLP-primer combinations each. In this way additional AFLP markers were mapped close to QTL 3B and QTL 3A. Three of them were converted to SCAR (Sequence Characterized Amplified region) markers. All markers were tested in natural populations of the disporangiate (2 MS) species M. bigelovii, M. elegans and M. pygmaea, and in different populations of tetrasporangiate (4 MS) M. douglasii. The marker distribution suggests that locus 3B mutated in a progenitor of the disporangiate species. QTL 3A has evolved in the 2 MS background of the major gene in the disporangiate species. Since M. pygmaea and M. bigelovii are the sister group to M. elegans, the 4 MS genotype for (markers of) QTL 3A in M. pygmaea populations is most likely due to a back mutation to the 4 MS state and could explain the slight instability of the 2 MS phenotype in this species.Communicated by O. Savolainen     

Comparison of chloroplast and nuclear phylogeny in the autogamous annualMicroseris douglasii (Asteraceae: Lactuceae)

Morphology suggests that the Californian annualMicroseris douglasii is a monophyletic sister group to the other three diploid annuals ofMicroseris. Phylogenetic analysis of 44 inbred strains ofM. douglasii derived from 23 populations with 72 RAPD markers in the nuclear DNA strongly supports this phylogeny. However, 13 chloroplast RFLPs divideM. douglasii into four distinct groups. Two of these each share one or more cpRFLPs withM. bigelovii andM. pygmaea. Several hypotheses can explain the incongruence between nuclear and chloroplast phylogeny: (1) random sorting out of chloroplasts during phylogeny from a polymorphic pool, (2) cytoplasmic introgression from the related annualM. bigelovii intoM. douglasii after hybridization followed by elimination of theM. bigelovii nuclear genome. We suggest cytoplasmic introgression as the most likely origin. Possible remnants of nuclear introgression have been found in two populations ofM. douglasii that are polymorphic for chloroplast types. In these populationsM. bigelovii type chloroplast DNA seems to be accompanied by nuclear genes for flower color and leaf shape.     

Sequence variation at theSec-1 locus of rye,Secale cereale (Poaceae)

This paper describes the structure of a 9.2-kb repeat unit of DNA, which represents one-secalin gene and spacer sequence located at theSec-1 locus on the short arm of chromosome 1 of rye. The gene units at theSec-1 locus comprise 1.1 kb representing the gene and 8.1 kb of spacer sequence separating the genes. A sequence comparison of nine genes and their promoter regions from theSec-1 locus, reveals that there is greater variation within the coding sequence than there is within the promoter regions. The gene sequence variation is discussed in terms of the size variation seen for the-secalin proteins in rye species. The results include a comparison of promoter sequences from members of the Triticeae to examine the degree of conservation between other seed storage protein genes.     

Artiodactyl emergence is accompanied by the birth of an extensive pool of diverse germline TRDV1 genes

Molecular cloning of cDNA from / T cells has shown that in sheep, the variable domain of the chain is chiefly determined by the expression of the TRDV1 subgroup, apparently composed of a large number of genes. There are three other TRDV subgroups, but these include only one gene each. To evaluate the extent and the complexity of the genomic TRDV repertoire, we screened a sheep liver genomic library from a single individual of the Altamurana breed and sheep fibroblast genomic DNA from a single individual of the Gentile di Puglia breed. We identified a total of 22 TRDV1 genes and the TRDV4 gene. A sequence comparison between germline and the rearranged genes indicates that, in sheep, the TRDV repertoire is generated by the VDJ rearrangement of at least 40 distinct TRDV1 genes. All germline TRDV1 genes present a high degree of similarity in their coding as well as in 5 and 3 flanking regions. However, a systematic analysis of the translation products reveals that these genes present a broadly different and specific repertoire in the complementarity-determining regions or recognition loops, allowing us to organize the TRDV genes into sets. We assume that selection processes operating at the level of ligand recognition have shaped the sheep TRDV germline repertoire. A phylogenetic study based on a sequence analysis of the TRDV genes from different mammalian species shows that the diversification level of these genes is higher in artiodactyl species compared to humans and mice.     

Evolution of thedec-1 eggshell locus inDrosophila. I. Restriction site mapping and limited sequence comparison in themelanogaster species subgroup

Summary We have analyzed 18 kb of DNA in and upstream of thedefective chorion-1 (dec-1) locus of the eight known species of themelanogaster species subgroup ofDrosophila. The restriction maps ofD. simulans, D. mauritiana, D. sechellia, D. erecta, andD. orena are shown to have basically the restriction map ofD. melanogaster, whereas the maps ofD. teissieri andD. yakuba were more difficult to align. However, the basic amount of DNA and sequence arrangement appear to have been conserved in these species. A small deletion of varying length (65–200 bp) is found in a repeated sequence of the central transcribed region ofD. melanogaster, D. simulans, andD. erecta. Restriction site mapping indicated that thedec-1 gene is highly conserved in themelanogaster species subgroup. However, sequence comparison revealed that the amount of nucleotide and amino acid substitution in the repeated region is much larger than in the 5 translated region. The 5 flanking region showed noticeable restriction site polymorphisms between species. Based on calculations from the restriction maps a dendrogram was derived that supports earlier published phylogenetic relationships within themelanogaster species subgroup except that theerecta-orena pair is placed closer to themelanogaster complex than toD. teissieri andD. yakuba.     

Isolation of virus-like (VL30) elements from theQ10 andD regions of the major histocompatibility complex

Previous studies from our laboratory have described two endogenous provirus-like sequences in a series of cosmids spanning theTL region of the major histocompatibility complex (MHC) of normal C57BL/10 mice. At least one of these viruses shares similarities withVL30 elements. To determine if additionalVL30-like retroviral elements are integrated in the MHC, we constructed a cosmid library using DNA from a radiation leukemia virus (RadLV)-transformed cell line derived from C57BL/6 mice. The library was first screened using theH-2III (5) probe, which detects Class I genes of theH-2 complex. In the primary screening 163H-2III positives were isolated. TheH-2III-positive isolates were then hybridized with an AKR-derived virus probe,EcoB/S, which contains sequences from both thepol and theenv genes of the virus. Nine virus-positive isolates were detected. Localization of these cosmid isolates containing viral sequences within theH-2 complex was done utilizing low-copy probes and confirmed using previously mapped cosmid isolates from other laboratories. We report here the isolation and characterization ofVL30-like elements from theQa andD regions of theMHC of several inbred mouse strains.     

RAPD mapping of three QTLs determining trichome formation in Microseris hybrid H27 (Asteraceae:Lactuceae)

Segregation for 289 random amplified polymorphic DNA markers (RAPDs) has been determined in 106 F₂ plants of an interspecific hybrid (H27) between Microseris douglasii (strain B14) and M. bigelovii (C94). Multicelluar trichomes (type D, specific for Microseris) occur on the leaf teeth of early vegetative rosettes of the B14 parent and on the leaf blades of later rosettes in both parents. Trichomes on the leaf blades appear earlier and eventually more densely in B14. Segregation for trichome appearance is quantitative and strongly transgressive in the F₂ hybrid. Cosegregation between RAPDs and trichome phenotypes combined with linkage data have revealed a main gene (quantitative trait locus A, QTL-A) with a pleiotropic effect on all trichome characters and two unlinked additive modifiers (QTL-B, QTL-C). Alleles of both modifiers reduce the main gene effect in each parent. Their recombination explains the occurrence of plants with transgressive phenotypes in the hybrid offspring. Additional QTLs affecting trichomes are at and below the level of statistical significance.     

Different mechanisms generating sequence variability are revealed in distinct regions of the hydroxyproline-rich glycoprotein gene from maize and related specie*

Summary The sequences of the genes coding for a hydroxyproline-rich glycoprotein from two varieties of maize (Zea mays, Ac1503 and W22), a teosinte (Zea diploperennis) and sorghum (Sorghum vulgare) have been obtained and compared. Distinct patterns of variability have been observed along their sequences. The 500 by region immediately upstream of the TATA box is highly conserved in theZea species and contains stretches of sequences also found in the sorghum gene. Further upstream, significant rearrangements are observed, even between the two maize varieties. These observations allow definition of a 5 region, which is common to the four genes and is probably essential for their expression. The 3 end shows variability, mostly due to small duplications and single nucleotide substitutions. There is an intron present in this region showing a high degree of sequence conservation among the four genes analyzed. The coding region is the most divergent, but variability arises from duplications of fragments coding for similar protein blocks and from single nucleotide substitutions. These results indicate that a number of distinct mechanisms (probably point mutation, transposon insertion and excision, homologous recombination and unequal crossing-over) are active in the production of sequence variability in maize and related species. They are revealed in different parts of the gene, probably as the result of the different types of functional constraints acting on them, and of the specific nature of the sequence in each region.The sequences reported in this paper have been deposited in the EMBL/GenBank Database (Bolt, Beranek, and Newman Laboratories, Cambridge, Mass., and EMBL, Heidelberg), accession nos. M36635 (maize Ac1503), X63134 (maize W22), X64173 (teosinte) and X56010 (sorghum)     

The R1 gene conferring race-specific resistance to Phytophthora infestans in potato is located on potato chromosome V.

Summary Late blight in potato is caused by the fungusPhytophthora infestans and can inflict severe damage on the potato crop. Resistance toP. infestans is either based on major dominantR genes conferring vertical, race-specific resistance or on minor genes inducing horizontal, unspecific resistance. A dihaploid potato line was identified which carried theR1 gene, conferring vertical resistance to allP. infestans races, with the exception of those homozygous for the recessive virulence allele of the locusV1. The F₁ progeny of a cross between this resistant parent P(R1) and P(r), a line susceptible to all races, was analysed for segregation ofR1 and of restriction fragment length polymorphism (RFLP) markers distributed on the potato RFLP map comprising more than 300 loci. TheR1 locus was mapped to chromosome V in the interval between RFLP markers GP21 and GP179. The map position ofR1 was found to be very similar to the one ofRx2, a dominant locus inducing extreme resistance to potato virus X.     

Fungal catabolic gene regulation: Molecular genetic analysis of theamdS gene ofAspergillus nidulans

Aspergillus nidulans is an excellent experimental organism for the study of gene regulation. Genetic and molecular analyses oftrans-acting andcis-acting mutations have revealed a complex pattern of regulation involving multiple independent controls. Expression of theamdS gene is regulated by thefacB andamdA genes which encode positively acting regulatory proteins mediating a major and a minor form of acetate induction respectively. The product of theamdR gene mediates omega amino acid induction ofamdS. The binding sites for each of these proteins have been localised throughamdS cis-acting mutations which specifically affect the interaction with the regulatory protein. The global controls of nitrogen metabolite repression and carbon catabolite repression regulate the expression of many catabolic genes, includingamdS. Nitrogen control is exerted through the positively actingareA gene product and carbon control is dependent on thecreA gene product. Each of the characterized regulatory genes encodes a DNA-binding protein which recognises particular sequences in theamdS promoter to activate or repress gene expression. In addition, there is evidence for other genetically uncharacterised proteins, including a CCAAT-binding complex, which interact with the 5 region of theamdS gene.     

Callus induction and plantlet regeneration in ornamental Alocasia micholitziana

Callus induction from petiole explants has been achieved in Alocasia micholitziana `Green Velvet'. The highest percentage (71%) of explants inducing callus was obtained on MS medium supplemented with 0.5 M 2,4-D and 0.5 M kinetin in the dark after 4 months of culture. Shoots were regenerated at the highest frequency of 33.3% under light condition when 0.5 M BA was added to MS medium with the average of 7.8±2.3 shoots per callus explant. The callus-derived shoots rooted on hormone free MS medium and within 4 weeks the plantlets were ready for acclimatization. The regenerated plants appeared morphologically similar to mother plants.     

The bacterial phleomycin resistance geneble as a dominant selectable marker inChlamydomonas

A chimeric gene composed of the coding sequence of theble gene fromStreptoalloteichus hindustanus fused to the 5 and 3 untranslated regions of theChlamydomonas reinhardtii nuclear geneRBCS2 has been constructed. Introduction of this chimeric gene into the nuclear genome ofC. reinhardtii by co-transformation with theARG7 marker yields Arg⁺ transformants of which approximately 80% possess theble gene. Of these co-transformants, approximately 3% display a phleomycin-resistant (Pm^R) phenotype. Western blot analysis using antibodies against theble gene product confirms the presence of the protein in the Pm^R transformants and genetic analysis demonstrates the co-segregation of theble gene with the phenotype in progeny arising from the mating of a Pm^R transformant to wild-type strains. Direct selection of Pm^R transformants was achieved by allowing an 18-h period for recovery and growth of transformed cells prior to selection. This work represents the first demonstration of stable expression and inheritance of a foreign gene in the nuclear genome ofC. reinhardtii and provides a useful dominant marker for nuclear transformation.     

Fertile somatic hybrids between transgenicNicotiana tabacum and transgenicN. debneyi selected by dual-antibiotic resistance

Summary A simple, yet effective selection system was used to produce fertile somatic hybrids betweenNicotiana tabacum andN. debneyi. This approach utilized transgenic antibiotic-resistantN. tabacum andN. Debneyi as donor plants for mesophyll protoplast fusions. Thirteen somatic hybrid plants were regenerated from calli capable of growth on medium containing both antibiotics. The majority of the hybrids displayed a range of leaf and floral morphologies and growth habits that were intermediate to those of the parental species, and had chromosome numbers varying from amphidiploid (2n = 96) to hypoaneuploid (2n = 60). Isoenzyme and RFLP analysis demonstrated the presence and expression of nuclear genes from both parents in all of the hybrids. Most plants are fully fertile. Thus, these plants differ from the malesterile tobacco cybrids and alloplasmic lines produced by transferring theN. debneyi cytoplasm to tobacco. A nonrandom pattern of cytoplasmic segregation in the fusion products occurred with a bias towards the presence ofN. debneyi cp and mtDNA. Evidence for the presence of rearranged or recombinant cp and mtDNA in some of the hybrids was obtained. The somatic hybrids were successfully backcrossed to theN. tabacum parent and are now being tested for immunity to black root rot, a trait specific toN. debneyi, but not existent in theN. tabacum parental line.