Search

Summary: Greenbeards are selfish genetic elements that make their bearers behave either altruistically towards individuals bearing similar greenbeard copies or harmfully towards individuals bearing different copies. They were first proposed by W. D. Hamilton over 50 yr ago, to illustrate that kin selection may operate at the level of single genes. Examples of greenbeards have now been reported in a wide range of taxa, but they remain undocumented in plants. In this paper, we discuss the theoretical likelihood of greenbeard existence in plants. We then question why the greenbeard concept has never been applied to plants and speculate on how hypothetical greenbeards could affect plant–plant interactions. Finally, we point to different research directions to improve our knowledge of greenbeards in plants. [ABSTRACT FROM AUTHOR]

If metal tolerant plants, by virtue of their tolerance mechanism, are less efficient at the uptake, distribution or utilization of metals then essential micronutrient deficiency may occur at the low levels of metal supply found on non-mine soils. This argument forms the basis of the metal requirement hypothesis put forward to explain the lower fitness of tolerant individuals on uncontaminated soil, the so called 'cost of tolerance;. In this paper, copper balance was investigated in Mimulus guttatus Fischer ex. DC (the yellow monkey flower) for plants with or without the major tolerance gene which confers primary tolerance, and plants with few or many modifier genes which control degree of tolerance. No conclusive evidence to support an increased copper requirement in plants with the major tolerance gene, and/or may modifier genes was shown. Any differences in copper requirement found during vegetative growth were small, and were deemed insufficient to explain the apparent cost of tolerance. [ABSTRACT FROM AUTHOR]

Incompatibility is a common means of controlling breeding behaviour among plants, and has been an important factor in evolution. It acts to prevent self-fertilization, as well as to prevent sterilization of ovules by foreign pollen. Angiosperms have both inter- and intraspecific incompatibility, and these are controlled by the same S gene complex. Gymnosperms, however, have only interspecific incompatibility. Observations on incompatibility behaviour in flowering plants have suggested that interspecific incompatibility evolved first among gymnosperms or progymnosperms as a means of protecting their naked ovules from foreign pollen. Duplication and redifferentiation of this 'primary specificity' gene in angiosperm precursors subsequently gave rise to 'secondary specificity' controlling intraspecific incompatibility. Today there are three basic types of incompatibility found among the angiosperms: (i) inherently independent control--each allele independently expresses its individual specificity, shows allelic interaction in the pollen after S gene duplication; (ii) inherently complementary control--alleles of two or more incompatibility loci co-operate to produce a single specificity, shows no allelic interaction; and (iii) late complementary control--alleles of two or more incompatibility loci co-operate to produce a single specificity, shows allelic interaction. The pattern of distribution of these three types of control has given rise to a controversy over which represents the most primitive type of angiosperm incompatibility. The present paper examines the factors involved in secondary evolution of incompatibility, and concludes that independent control is in fact more primitive. Complementary control probably developed secondarily and independently several times during angiosperm evolution, the first occurrence. [ABSTRACT FROM AUTHOR]

Comparative mapping studies have revealed a great deal about the patterns of gene order and gene content evolution in plants. These findings have practical importance for leveraging genomic information from model to nonmodel plant species. However, there is much to be learned about the processes by which gene order and content evolve. The role of gene duplication and loss in the evolution of plant gene order, in particular, appears to be more important than commonly appreciated. An exciting area of current research is the study of gene order and content polymorphism within species. Some recent findings suggest that there may be a functional, and adaptive, relationship between gene order and phenotype that is mediated by the effects of gene order on transcriptional regulation. [ABSTRACT FROM AUTHOR]

Summary 1I. Introduction 2II. Fast and fascinating– thigmonasty and thigmotropism 2III. Subcellular touch-induced movements 10IV. Thigmomorphogenesis 10V. Discovery of theArabidopsis TCHgenes 12VI. Microarray identification of touch-inducible genes 12VII. Regulation ofTCHgene expression 13 Acknowledgements 14 References 14Perception and response to mechanical stimuli are likely essential at the cellular and organismal levels. Elaborate and impressive touch responses of plants capture the imagination as such behaviors are unexpected in otherwise often quiescent creatures. Touch responses can turn plants into aggressors against animals, trapping and devouring them, and enable flowers to be active in ensuring crosspollination and shoots to climb to sunlit heights. Morphogenesis is also influenced by mechanical perturbations, including both dynamic environmental stimuli, such as wind, and constant forces, such as gravity. Even individual cells must sense turgor and wall integrity, and subcellular organelles can translocate in response to mechanical perturbations. Signaling molecules and hormones, including intracellular calcium, reactive oxygen species, octadecanoids and ethylene, have been implicated in touch responses. Remarkably, touch-induced gene expression is widespread; more than 2.5% ofArabidopsisgenes are rapidly up-regulated in touch-stimulated plants. Many of these genes encode calcium-binding, cell wall modifying, defense, transcription factor and kinase proteins. With these genes as tools, molecular genetic methods may enable elucidation of mechanisms of touch perception, signal transduction and response regulation.New Phytologist(2004)doi: 10.1111/j.1469-8137.2004.01263.x© New Phytologist(2004) [ABSTRACT FROM AUTHOR]

Many recent studies have sought to identify targets of diversifying selection by testing the neutral expectation that all loci will show similar levels of population divergence ( Fst). Contrasts between quantitative traits ( Qst) and molecular markers ( Fst) suggest that quantitative traits typically diverge in response to local selection pressures more than do individual genes. Coalescence theory makes it possible to simulate the distribution of Fst and Qst expected under neutrality for many situations, including nonequilibrium conditions. Such simulations show that a very high variance of Fst and Qst are expected under neutrality, making it difficult to draw firm conclusions about the action of selection on individual loci or traits. Recent quantitative genetic theory shows that, under diversifying selection on quantitative traits, covariances (linkage disequilibrium) among allele frequencies at underlying additive loci contribute a substantial fraction of the among-population trait variance. Thus, adaptive trait divergence can be accomplished, with limited divergence of allele frequencies. However, the contribution of covariances among loci to the divergence of traits depends upon there being multiple loci underlying quantitative trait variation. [ABSTRACT FROM AUTHOR]

Leaf esterase polymorphism in eight populations of Poa annua L., from two habitat types (four opportunist and four semi-permanent populations), was demonstrated to be controlled by nine loci. Frequencies at five loci were studied. Locus Est l proved highly correlated with growth form: homozygotes AA were prostrate, whereas homozygotes BB were erect. All populations were polymorphic both for esterase isozymes and growth form. Mean frequencies of prostrate and erect plants were 12 and 88% respectively in opportunist populations, and 32 and 68% in semi-permanent populations. The outcrossing rate was strongly dependent upon plant density, but in both types of habitat, prostrate and erect plants appeared to be able to exchange genes. [ABSTRACT FROM AUTHOR]

The pattern of uptake of copper by plants of Mimulus guttatus that are either homozygous tolerant, homozygous non-tolerant, or heterozygous tolerant, was compared. Tolerant plants took up more copper, particularly into the roots, and root uptake by the homozygote tolerant was greater than the heterozygote. Plants of all three genotypes took up increasing quantities of copper to their roots until day 7, but no further increase was obtained by day 11. The physiological implication of these results is discussed. [ABSTRACT FROM AUTHOR]