Zinc (Zn) is an essential component of thousands of proteins in plants, although it is toxic in excess. In this review, the dominant fluxes of Zn in the soil-root-shoot continuum are described, including Zn inputs to soils, the plant availability of soluble Zn(2+) at the root surface, and plant uptake and accumulation of Zn. Knowledge of these fluxes can inform agronomic and genetic strategies to address the widespread problem of Zn-limited crop growth. Substantial within-species genetic variation in Zn composition is being used to alleviate human dietary Zn deficiencies through biofortification. Intriguingly, a meta-analysis of data from an extensive literature survey indicates that a small proportion of the genetic variation in shoot Zn concentration can be attributed to evolutionary processes whose effects manifest above the family level. Remarkable insights into the evolutionary potential of plants to respond to elevated soil Zn have recently been made through detailed anatomical, physiological, chemical, genetic and molecular characterizations of the brassicaceous Zn hyperaccumulators Thlaspi caerulescens and Arabidopsis halleri.

Zinc in plants

▪ Abstract The study of natural plant populations has provided some of the strongest and most convincing cases of the operation of natural selection currently known, partly because of amenability to reciprocal transplant experiments, common garden work, and long-term in situ manipulation. Genetic differentiation among plant populations over small scales (a few cm to a few hundred cm) has been documented and is reviewed here, in herbaceous annuals and perennials, woody perennials, aquatics, terrestrials, narrow endemics, and widely distributed species. Character differentiation has been documented for most important features of plant structure and function. Examples are known for seed characters, leaf traits, phenology, physiological and biochemical activities, heavy metal tolerance, herbicide resistance, parasite resistance, competitive ability, organellar characters, breeding systems, and life history. Among the forces that have shaped these patterns of differentiation are toxic soils, fertilizers, mowin...

Evolutionary significance of local genetic differentiation in plants

Over the last three decades, mitochondrial DNA has been the most popular marker of molecular diversity, for a combination of technical ease-of-use considerations, and supposed biological and evolutionary properties of clonality, near-neutrality and clock-like nature of its substitution rate. Reviewing recent literature on the subject, we argue that mitochondrial DNA is not always clonal, far from neutrally evolving and certainly not clock-like, questioning its relevance as a witness of recent species and population history. We critically evaluate the usage of mitochondrial DNA for species delineation and identification. Finally, we note the great potential of accumulating mtDNA data for evolutionary and functional analysis of the mitochondrial genome.

https://onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-294X.2009.04380.x

Mitochondrial DNA as a marker of molecular diversity: a reappraisal

Sexual reproduction is an ancient feature of life on earth, and the familiar X and Y chromo- somes in humans and other model species have led to the impression that sex determination mecha- nisms are old and conserved. In fact, males and females are deter- mined by diverse mechanisms that evolve rapidly in many taxa. Yet this diversity in primary sex-deter- mining signals is coupled with conserved molecular pathways that trigger male or female develop- ment. Conflicting selection on dif- ferent parts of the genome and on the two sexes may drive many of these transitions, but few systems with rapid turnover of sex determi- nation mechanisms have been rig- orously studied. Here we survey our current understanding of how and why sex determination evolves in animals and plants and identify important gaps in our knowledge that present exciting research op- portunities to characterize the evo- lutionary forces and molecular pathways underlying the evolution of sex determination.

/pdf/sex-determination-why-so-many-ways-of-doing-it-ivb1ovfz8c.pdf

Sex Determination: Why So Many Ways of Doing It?

Most ecological processes now show responses to anthropogenic climate change. In terrestrial, freshwater, and marine ecosystems, species are changing genetically, physiologically, morphologically, and phenologically and are shifting their distributions, which affects food webs and results in new interactions. Disruptions scale from the gene to the ecosystem and have documented consequences for people, including unpredictable fisheries and crop yields, loss of genetic diversity in wild crop varieties, and increasing impacts of pests and diseases. In addition to the more easily observed changes, such as shifts in flowering phenology, we argue that many hidden dynamics, such as genetic changes, are also taking place. Understanding shifts in ecological processes can guide human adaptation strategies. In addition to reducing greenhouse gases, climate action and policy must therefore focus equally on strategies that safeguard biodiversity and ecosystems.

https://science.sciencemag.org/content/sci/354/6313/aaf7671.full.pdf

The broad footprint of climate change from genes to biomes to people

A much-debated issue in plant evolutionary biology concerns the maintenance of a high frequency of male sterility in natural populations. For the past decade, a theoretical framework has been provided by the concept of nucleocytoplasmic conflict. Recent molecular studies on cytoplasmic male sterility indicate that novel chimeric genes, resulting from duplications and rearrangements of mitochondrial DNA sequences, are involved In its control. Thus, male sterility, which is phenotypically the loss of the male function, is encoded by a new mitochondrial function at the molecular level. Molecular data are in agreement with theoretical models that consider cytoplasmic male sterility as a stage in the coevolution between nucleus and mitochondria, and not simply as a deleterious mitochondrial mutation.

Cytoplasmic male sterility in plants: molecular evidence and the nucleocytoplasmic conflict.

We examined how population age affects the relative importance of clonal propagation and sexual reproduction in the aquatic macrophyte Sparganium errectum. Plants were collected from two newly established populations and four successionally mature populations. The comparison of life history traits associated with sexual reproduction and clonal multiplication was carried out in a controlled environment experiment. We found that several physiological trade-offs occurred between sexual reproduction and clonal propagation. Moreover, we found a higher investment in sexual reproduction in newly established populations than in older populations. These results suggest that clonal propagation is favoured at the population level while, because seeds produced by sexual reproduction are the only means for long distance dispersal, selection will favour sexual reproduction at the metapopulation level. This discrepancy between selective pressures at different spatial scales could favour the maintenance of a mixed sexual-asexual reproductive system in Sparganium erectum.

Variation in sexual and asexual reproduction among young and old populations of the perennial macrophyte Sparganium erectum

The conditions for maintenance of a haploid—diploid life cycle in the species Gracilaria verrucosa were studied. This species is a red alga, where haploid plants have separate sexes. In the two natural populations studied, male and female haploid individuals were in equal proportions, and the frequency of diploid individuals reached 0.5.



A two-fold advantage in viability for diploid relative to haploid juveniles was observed in the field. This advantage can account for a frequency of 0.5 of diploid individuals in natural populations. Different types of anomalies in the reproduction of diploid individuals were observed, all of which lead to a reduction of the haploid stage.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1420-9101.1989.2050317.x

What controls haploid—diploid ratio in the red alga, Gracilaria verrucosa?

The wild beet ( Beta vulgaris ssp. maritima , a perennial species from the Mediterranean and the European Atlantic coasts) shows marked variation in flowering time in terms of both the year of first flowering and flowering date in a given year. Much of this variability is related to latitude. Beta vulgaris plants flower either in the same year as they germinate or in their second year. This is mainly due to differences in their requirement for vernalization, which is determined by a single gene B/b and by quantitative trait loci. The more southern the origin of the plants, the less vernalization is required. Also the B allele, which cancels vernalization requirement completely, has a high frequency in the Mediterranean region, but is completely absent in the northern part of the distribution of this species. We found that flowering date variation in relation to the latitude of origin is maintained under greenhouse conditions but does not follow a simple clinal relationship. From the Mediterranean northwards to the west coast of Brittany, flowering occurs progressively earlier, but from Brittany northwards to south-east England and The Netherlands it is progressively later. A possible explanation for this difference is that in the southern part of the range sensitivity to daylength and warmth control flowering time, whereas further north vernalization requirement is also a key factor. A substantial part of all differences in flowering time was heritable: heritability within populations was measured as 0.33 under greenhouse conditions. The high heritability implies evolutionary change may occur in this character.

Flowering time in wild beet (Beta vulgaris ssp. maritima) along a latitudinal cline

Gynodioecious populations of Beta vulgaris ssp maritima were found all along the French coasts; 42% of the populations were gynodioecious. Locally, there were large sex-ratio differences between populations, ranging from 0 to 76% of females. This large variation was even found between populations less than 1 km apart. Molecular analysis of mitochondrial polymorphism revealed a high variability; 11 different mitochondrial types were found. The Nvulg type, which is the most frequent type among the maintainers of male sterility used in sugar beet breeding programs, was also the most frequent type in natural populations. Conversely, the characteristic pattern of the Owen CMS (cytoplasmic male sterility), ie the Svulg type, was not found. The mitochondrial variability detected within the populations was large; there were 2.10 different mitotypes on average among the 5 individuals sampled per population. There was a highly significant overall difference in mitotype frequencies between populations (Fst = 0.466; P < 0.001), distributed both between (Fst = 0.138; P < 0.001) and within regions (Fst = 0.381; P < 0.001). Female plants were found with almost all of the different mitotypes. Nevertheless, 2 groups of mitotypes were clearly distinguished: the mitotypes Nvulg, A and B were rarely associated with the female phenotype, whereas female plants were often found among the plants having the mitotypes E and G.

/pdf/gynodioecy-and-mitochondrial-dna-polymorphism-in-natural-2v4mvezmlu.pdf

Philippe Vernet

Papers

Cytoplasmic male sterility in plants: molecular evidence and the nucleocytoplasmic conflict.

Variation in sexual and asexual reproduction among young and old populations of the perennial macrophyte Sparganium erectum

What controls haploid—diploid ratio in the red alga, Gracilaria verrucosa?

Flowering time in wild beet (Beta vulgaris ssp. maritima) along a latitudinal cline

Gynodioecy and mitochondrial DNA polymorphism in natural populations of Beta vulgaris ssp maritima