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K. Bachmann - One of the best experts on this subject based on the ideXlab platform.
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The anthers of Senecio vulgaris (Asteraceae): saltatory evolution caught in the act
Plant Systematics and Evolution, 2003Co-Authors: Oliver Gailing, K. BachmannAbstract:Anthers of the common annual weed, Senecio vulgaris , show an incomplete development of the two adaxial pollen sacs (Microsporangia, MS). One or both adaxial MS can be missing, or they are replaced by sterile lobes. The reduction is stronger in the derived subspecies, S . vulgaris var. vulgaris than in the ancestral subspecies, S. vulgaris ssp. denticulatus . This character in S . vulgaris differs from the usual complete reduction of adaxial MS in other, independent instances of disporangiate anthers in the Asteraceae. It corresponds to the “transition phenotypes” associated with various recombinant genotypes derived from artificial crosses between tetrasporangiate (4 MS) and disporangiate (2 MS) species in the Asteracean genus Microseris . Senecio vulgaris could be a rare natural instance of homozygosity for a major gene permitting reduction of the adaxial MS in which the expression of the reduced phenotype is determined by different numbers of modifiers in the two subspecies.
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qtl mapping reveals a two step model for the evolutionary reduction of inner Microsporangia within the asteracean genus microseris
Theoretical and Applied Genetics, 2003Co-Authors: Oliver Gailing, K. BachmannAbstract: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.
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the evolutionary reduction of Microsporangia in microseris asteraceae transition genotypes and phenotypes
Plant Biology, 2000Co-Authors: Oliver Gailing, K. BachmannAbstract:: The loss of the two inner (adaxial) Microsporangia (MS) on the anthers is a shared, derived character for three species of the genus Microseris (Asteraceae). In a hybrid between M. douglasii (4 MS) and M. bigelovii (2 MS), one major gene and four modifier loci are responsible for the difference in MS number. The homozygous recessive (2 MS) genotype of the major gene is necessary but not sufficient for the reduction. In addition, at least five M. bigelovii (2 MS) alleles of the three major modifiers are needed for a stable 2-MS phenotype in all florets of a plant. One, two or three M. bigelovii alleles of the modifiers cause the random reduction or loss of some of the adaxial MS. When the major gene and two modifiers specify 2 MS and only one modifier is homozygous for the M. douglasii (4 MS) alleles, sister plants can have any phenotype from pure 2 MS to pure 4 MS. Here, we examine the phenotypic expression of these genotypes raised under the normal winter annual conditions and under long-day conditions. In all cases, the phenotypes vary among sister plants, but the range of variation (most notably under long-day conditions) depends on the specific modifier gene contributing the M. douglasii alleles. The phenotypic variance in one of the genotypes was decreased by a factor of ten in the depauperate heads produced in the long-day experiment. This effect is mediated by a dependence of the MS phenotype on the position of the floret relative to the edge of the flowering head (capitulum) and directly by the size of the capitulum. Genotypes specifying phenotypes with more or less precisely two or four MS in all florets show hardly any dependence on environmental or developmental factors. The significance of these observations lies in the non-linear, “canalized” relationship between phenotypic expression and gene dosage, which shows how a qualitative morphological change dependent on a single major gene mutation can pass through a potentially maladaptive intermediate stage.
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comparative developmental study of the evolutionary reduction of adaxial Microsporangia in microseris bigelovii asteraceae
Plant Biology, 1999Co-Authors: Oliver Gailing, K. BachmannAbstract:: About 10% of all angiosperm species have only 2 pollen sacs (Microsporangia) per anther in place of the normal 4. The reduction seems to have occurred independently in about 50 angiosperm families and is a prime example of the parallel evolution of a potentially diagnostic taxonomic character (homoplasy). In the genus Microseris reduction from 4 to 2 mi-croporangia (MS) is a synapomorphy for three of the diploid annual species. We have compared anther development in the tet-rasporangiate (4MS) M. douglasii with that in the disporangiate (2MS) M. bigelovii. In this case, the divergence between the developmental pathways becomes visible late in ontogeny, when the adaxial archesporial cells divide into primary parietal cells and sporogenous cells. In the disporangiate M. bigelovii this differentiation step is lacking so that no adaxial MS are formed. Anther development in a recombinant inbred derivative of a hybrid between M. douglasii and M. bigelovii resulted in the formation of sterile adaxial MS. This suggests a two-step evolution of the character: suppression of the differentiation of fertile cells in otherwise normal adaxial loculi followed by the suppression of the production of sterile precursors. Comparison with other cases of evolutionary reduction of Microsporangia suggests that there are (many) different ways to reach the same stable (“canalized”) phenotype. This may be generally true for homoplasy in complex developmental characters.
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qtl mapping reveals specific genes for the evolutionary reduction of Microsporangia in microseris asteraceae
Plant Biology, 1999Co-Authors: Oliver Gailing, E J Hombergen, K. BachmannAbstract:: Where closely related plant species with basic and derived characters can be crossed and produce fertile offspring, the genetics of character evolution can be inferred from the segregation patterns in hybrid offspring. Three species of Micro-seris (Compositae) share a reduction from the usual 4 to 2 pollen sacs per anther by the suppression of the adaxial rnicrosporan-gia (MS), as a common derived character. These species can be crossed with a species with 4 MS. The segregation of MS numbers from such a hybrid was analysed by co-segregation with genetically mapped molecular markers (AFLPs). Five loci specifically affecting the MS number were found. The homozygous recessive genotype for a main gene is necessary but not sufficient to reduce MS numbers. Three of the four modifiers interact only in this homozygous recessive background to reduce the number to 2. This suggests that mutation of the main gene was followed by selection of the modifiers to stabilize the new phenotype. Since the plants are nearly completely self-fertilisirig in nature, the loss of two MS will not reduce reproductive success. The selection pressure needed to assemble such a complicated system for the complete absence of the two adaxial MS needs to be explained.
Oliver Gailing - One of the best experts on this subject based on the ideXlab platform.
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The anthers of Senecio vulgaris (Asteraceae): saltatory evolution caught in the act
Plant Systematics and Evolution, 2003Co-Authors: Oliver Gailing, K. BachmannAbstract:Anthers of the common annual weed, Senecio vulgaris , show an incomplete development of the two adaxial pollen sacs (Microsporangia, MS). One or both adaxial MS can be missing, or they are replaced by sterile lobes. The reduction is stronger in the derived subspecies, S . vulgaris var. vulgaris than in the ancestral subspecies, S. vulgaris ssp. denticulatus . This character in S . vulgaris differs from the usual complete reduction of adaxial MS in other, independent instances of disporangiate anthers in the Asteraceae. It corresponds to the “transition phenotypes” associated with various recombinant genotypes derived from artificial crosses between tetrasporangiate (4 MS) and disporangiate (2 MS) species in the Asteracean genus Microseris . Senecio vulgaris could be a rare natural instance of homozygosity for a major gene permitting reduction of the adaxial MS in which the expression of the reduced phenotype is determined by different numbers of modifiers in the two subspecies.
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qtl mapping reveals a two step model for the evolutionary reduction of inner Microsporangia within the asteracean genus microseris
Theoretical and Applied Genetics, 2003Co-Authors: Oliver Gailing, K. BachmannAbstract: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.
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the evolutionary reduction of Microsporangia in microseris asteraceae transition genotypes and phenotypes
Plant Biology, 2000Co-Authors: Oliver Gailing, K. BachmannAbstract:: The loss of the two inner (adaxial) Microsporangia (MS) on the anthers is a shared, derived character for three species of the genus Microseris (Asteraceae). In a hybrid between M. douglasii (4 MS) and M. bigelovii (2 MS), one major gene and four modifier loci are responsible for the difference in MS number. The homozygous recessive (2 MS) genotype of the major gene is necessary but not sufficient for the reduction. In addition, at least five M. bigelovii (2 MS) alleles of the three major modifiers are needed for a stable 2-MS phenotype in all florets of a plant. One, two or three M. bigelovii alleles of the modifiers cause the random reduction or loss of some of the adaxial MS. When the major gene and two modifiers specify 2 MS and only one modifier is homozygous for the M. douglasii (4 MS) alleles, sister plants can have any phenotype from pure 2 MS to pure 4 MS. Here, we examine the phenotypic expression of these genotypes raised under the normal winter annual conditions and under long-day conditions. In all cases, the phenotypes vary among sister plants, but the range of variation (most notably under long-day conditions) depends on the specific modifier gene contributing the M. douglasii alleles. The phenotypic variance in one of the genotypes was decreased by a factor of ten in the depauperate heads produced in the long-day experiment. This effect is mediated by a dependence of the MS phenotype on the position of the floret relative to the edge of the flowering head (capitulum) and directly by the size of the capitulum. Genotypes specifying phenotypes with more or less precisely two or four MS in all florets show hardly any dependence on environmental or developmental factors. The significance of these observations lies in the non-linear, “canalized” relationship between phenotypic expression and gene dosage, which shows how a qualitative morphological change dependent on a single major gene mutation can pass through a potentially maladaptive intermediate stage.
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comparative developmental study of the evolutionary reduction of adaxial Microsporangia in microseris bigelovii asteraceae
Plant Biology, 1999Co-Authors: Oliver Gailing, K. BachmannAbstract:: About 10% of all angiosperm species have only 2 pollen sacs (Microsporangia) per anther in place of the normal 4. The reduction seems to have occurred independently in about 50 angiosperm families and is a prime example of the parallel evolution of a potentially diagnostic taxonomic character (homoplasy). In the genus Microseris reduction from 4 to 2 mi-croporangia (MS) is a synapomorphy for three of the diploid annual species. We have compared anther development in the tet-rasporangiate (4MS) M. douglasii with that in the disporangiate (2MS) M. bigelovii. In this case, the divergence between the developmental pathways becomes visible late in ontogeny, when the adaxial archesporial cells divide into primary parietal cells and sporogenous cells. In the disporangiate M. bigelovii this differentiation step is lacking so that no adaxial MS are formed. Anther development in a recombinant inbred derivative of a hybrid between M. douglasii and M. bigelovii resulted in the formation of sterile adaxial MS. This suggests a two-step evolution of the character: suppression of the differentiation of fertile cells in otherwise normal adaxial loculi followed by the suppression of the production of sterile precursors. Comparison with other cases of evolutionary reduction of Microsporangia suggests that there are (many) different ways to reach the same stable (“canalized”) phenotype. This may be generally true for homoplasy in complex developmental characters.
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qtl mapping reveals specific genes for the evolutionary reduction of Microsporangia in microseris asteraceae
Plant Biology, 1999Co-Authors: Oliver Gailing, E J Hombergen, K. BachmannAbstract:: Where closely related plant species with basic and derived characters can be crossed and produce fertile offspring, the genetics of character evolution can be inferred from the segregation patterns in hybrid offspring. Three species of Micro-seris (Compositae) share a reduction from the usual 4 to 2 pollen sacs per anther by the suppression of the adaxial rnicrosporan-gia (MS), as a common derived character. These species can be crossed with a species with 4 MS. The segregation of MS numbers from such a hybrid was analysed by co-segregation with genetically mapped molecular markers (AFLPs). Five loci specifically affecting the MS number were found. The homozygous recessive genotype for a main gene is necessary but not sufficient to reduce MS numbers. Three of the four modifiers interact only in this homozygous recessive background to reduce the number to 2. This suggests that mutation of the main gene was followed by selection of the modifiers to stabilize the new phenotype. Since the plants are nearly completely self-fertilisirig in nature, the loss of two MS will not reduce reproductive success. The selection pressure needed to assemble such a complicated system for the complete absence of the two adaxial MS needs to be explained.
E. N. Muratova - One of the best experts on this subject based on the ideXlab platform.
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Microsporogenesis and pollen formation in Scotch pine (Pinus sylvestris L.) under modern climatic conditions of Siberia
Biology Bulletin, 2009Co-Authors: N. E. Noskova, I. N. Tretyakova, E. N. MuratovaAbstract:The prolongation of the warm season during autumn, which has become typical for Siberia in the past 5–6 years, has caused changes in the terms of reproductive processes in Microsporangia of Scotch pine in the Krasnoyarsk region. Meiosis has started to begin in the autumn of the year preceding pollination, and then come to an end the next spring, whereas usually this process has occurred in the spring of the year of pollination. Under such conditions the division of microsporocytes is accompanied by different abnormalities, causing various anomalies and the incomplete development of pollen grains.
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Microsporogenesis and pollen formation in Scotch pine (Pinus sylvestris L.)
Biology Bulletin, 2009Co-Authors: N. E. Noskova, Tret'iakova In, E. N. MuratovaAbstract:: The prolongation of a warm season during autumn, typical for the Siberia in recent 5-6 years, caused changes in the terms of reproductive processes in Microsporangia of Scotch pine in the Krasnoyarsk region. The meiosis started in the autumn of the year, preceding the pollination, and comes to the end in next spring, whereas usually this process occurs in the spring of the year of pollination. In such conditions the division of microsporocytes accompanied with different abnormalities, causing various anomalies and the incomplete development of pollen grains.
Nels R Lersten - One of the best experts on this subject based on the ideXlab platform.
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systematic significance of pollen arrangement in Microsporangia of poaceae and cyperaceaei review and observations on representative tax a
American Journal of Botany, 1996Co-Authors: Christine C Kirpes, Lynn G Clark, Nels R LerstenAbstract:An anatomical survey of anthers of the Poaceae and Cyperaceae and two related families, the Restionaceae and Flagellariaceae, was conducted to determine the taxonomic distribution and possible phylogenetic significance of pollen arrangement. An unusual pollen arrangement was known from a small number of taxa in the Poaceae and Cyperaceae, in which a single, uniseriate cylinder of pollen grains is arranged in the anther locule such that each grain is in contact with the tapetum (termed here "peripheral" pollen). This contrasts with the prevailing arrangement in other angiosperms in which the locule contains a relatively large number of pollen grains in no special configuration, with many interior grains that never touch the tapetum (termed here "central" pollen). A total of 48 species in these four families was examined in this study, and observations on pollen arrangement for numerous additional species in these families were gleaned from the literature. We confirm that the peripheral arrangement is predominant in Poaceae and Cyperaceae, although both families also include species with central pollen, whereas only central pollen is found in Restionaceae and Flagellariaceae. In the peripheral arrangement, the pore of the pollen grain or pseudomonad, when observed, is in contact with the tapetum, but it has not been definitively demonstrated that this is always the case. Peripheral pollen in the Poaceae and Cyperaceae is nonhomologous because of the presence of pseudomonads in the latter family. It remains unexplained why peripherally arranged pollen or pseudomonads, with the attendant reduction in the number of pollen grains, should be associated with anemophily in these two families.
Bjorn Walles - One of the best experts on this subject based on the ideXlab platform.
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cell differentiation in Microsporangia of pinus sylvestris ii early pachytene
Nordic Journal of Botany, 2008Co-Authors: John R Rowley, Bjorn WallesAbstract:Tapetal cells of Pinus sylvesiris L. underwent one hypersecretory cycle during early pachytene and entered a second cycle by the time of mid pachytene in microspore mother cells. Initially in each cycle tapetal cells became papillaform then dome-shaped and thereafter, in conjunction with radial narrowing of the cells, dilation of the ER system was intensive throughout the cytoplasm. Recovery from hyperactivity culminated with the presence of plasmodesma-like connections between tapetal cells and a period of mitosis in tapetal cells. The differentiation of tapetal cells occurred asynchronously within a microsporangium and their dedifferentiation began nonuni-formly, becoming synchronous coincidental with the presence of “plasmodesmata”. Microsporangia increased in size and tapetal cells were laterally wide before “plasmodesmata” receded and tapetal cells again differentiated asynchronously.
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cell differentiation in Microsporangia of pinus sylvestris v diakinesis to tetrad formation
Nordic Journal of Botany, 1993Co-Authors: John R Rowley, Bjorn WallesAbstract:Following the diffuse stage, the progression of meiosis in Pinus sylvestris unlike that earlier in meiosis, was conspicuously asynchronous. During the diffuse stage of meiosis tapetal cells dedifferentiated. Plasmodesmata were formed, the cells developed a uniform, meristematic appearance and the nuclei underwent mitosis. Throughout the stages covered by this report tapetal cells redifferentiated, again becoming hypersecretory cells, and Ubisch bodies (orbicules) formed. In angio-sperms Ubisch bodies apparently form only once whereas in Pinus they are produced several or many times with a different and characteristic form each time. The future Ubisch bodies are filled from connections with cisternae of the endoplasmic reticu-lum, then coated by plasma membrane and its glycocalyx. The plasma membrane and glycocalyx coating are likely to be responsible for the specific exine form of Ubisch bodies. Cytokinesis after meiosis was typical of plant cells, but no cell wall formed. Thus deep invasions of callose between microspores give an appearance of furrowing, as was often suggested in classical literature.