Forest ecosystem genomics and adaptation: EVOLTREE conference report

This article is a summary report of the international conference "Forest ecosystem genomics and adaptation" organized by the EVOLTREE Network of Excellence in San Lorenzo de El Escorial (Madrid), Spain, from 9 to 11 June 2010. Main achievements and results of the network are presented for the eight thematic sessions and a stakeholder session. The conference has shown that adaptive responses of trees to biotic or abiotic selection pressures can now be investigated at the gene level for traits of adaptive significance. Candidate genes have been catalogued for phenological and drought-related traits in important tree families (Salicaceae, Fagaceaea and Pinaceae), and their variation in natural populations is being explored. Genomics can now be integrated in ecological research to investigate evolutionary response to climate changes in a wide range of species. New avenues of research were also highlighted as the exploration of gene networks involved in adaptive responses and the combination of experimental and modelling approaches to disentangle components of evolutionary changes triggered by climate change. The main focus of the conference was the adaptation of trees to environmental changes. The conference was organized in eight thematic sessions ranging from genomic approaches aiming at identifying genes of adaptive significance to practical issues regarding mitigation options for combating climate change. A dialogue between scientists and end users took place in the form of an ad hoc stakeholder session. A panel of end users from various forest and policy-making institutions expressed their expectations, and the discussions with the scientists addressed the potential applications of research findings to the management of genetic resources in the context of climate changes. The conference was introduced by two keynote speakers Dr. Pierre Mathy from the European Commission, Directorate General of Research, and Dr. Allen Solomon, former National Program Leader for Global Change, US Forest Service. All the thematic sessions were introduced by high-level invited speakers from the respective fields.     

Characterization of PR-10 genes from eight Betula species and detection of Bet v 1 isoforms in birch pollen

Background  

Bet v 1 is an important cause of hay fever in northern Europe. Bet v 1 isoforms from the European white birch (Betula pendula) have been investigated extensively, but the allergenic potency of other birch species is unknown. The presence of Bet v 1 and closely related PR-10 genes in the genome was established by amplification and sequencing of alleles from eight birch species that represent the four subgenera within the genus Betula. Q-TOF LC-MS^E was applied to identify which PR-10/Bet v 1 genes are actually expressed in pollen and to determine the relative abundances of individual isoforms in the pollen proteome.     

Dinucleotide repeat microsatellite markers for buck’s‐horn plantain (Plantago coronopus)

Eleven polymorphic microsatellite loci were obtained from a GA enriched genomic library, constructed from DNA of buck’s‐horn plantain (Plantago coronopus). The microsatellite loci were tested on 24 genotypes. These plants were collected from meadows along the coast, located on 11 sites ranging from the southwest to the northeast of the Netherlands. In this set of plants the isolated microsatellites were highly polymorphic with 3–24 alleles per locus and a maximum observed heterozygosity of 0.91. Some of the microsatellite loci also showed amplification in two other plantain species (P. lanceolata and P. maritima).     

Genetic impoverishment of the last black grouse (Tetrao tetrix) population in the Netherlands: detectable only with a reference from the past

We have studied a small isolated population of black grouse (Tetrao tetrix) in the Netherlands to examine the impact of isolation and reduction in numbers on genetic diversity. We compared the genetic diversity in the last extant Dutch population with Dutch museum samples and three other black grouse populations (from England, Austria and Norway, respectively) representing isolated and continuous populations. We found significantly lower allelic richness, observed and expected heterozygosities in the present Dutch population compared to the continuous populations (Austria and Norway) and also to the historical Dutch population. However, using a bottleneck test on each population, signs of heterozygosity excess were only found in the likewise isolated English population despite that strong genetic drift was evident in the present Dutch population in comparison to the reference populations, as assessed both in pairwise F(ST)and STRUCTURE analyses. Simulating the effect of a population reduction on the Dutch population from 1948 onwards, using census data and with the Dutch museum samples as a model for the genetic diversity in the initial population, revealed that the loss in number of alleles and observed heterozygosity was according to genetic drift expectations and within the standard error range of the present Dutch population. Thus, the effect of the strong decline in the number of grouse on genetic diversity was only detectable when using a reference from the past. The lack of evidence for a population reduction in the present Dutch population by using the program bottleneck was attributed to a rapidly found new equilibrium as a consequence of a very small effective population size.     

Strong decline of gene diversity in local populations of the highly endangered Common hamster (Cricetus cricetus) in the western part of its European range

The Common hamster (Cricetus cricetus) has declined by more than 99% in the westernmost part of its range in Belgium, the Netherlands and the adjacent German federal state of North Rhine-Westphalia (BNN region) during recent decades. Various conservation schemes are ongoing to support the remaining populations, including restoration of the habitat, captive breeding and reintroductions. One of the factors determining the success of conservation actions is the genetic constitution of the remaining populations. We therefore measured the genetic variation in current BNN hamster populations and compared the outcome with the genetic variation in museum samples from the historical, non-fragmented, population. Most of the current populations have lost the majority of their rare alleles and individual animals have become nearly homozygous. Since different alleles became fixed in different populations, this has resulted in strong genetic differentiation between current populations and reflects the strength of drift and inbreeding processes in small and isolated populations. Despite this differentiation, the total gene diversity of these small populations combined is not much less than that of the historical population. Hence, the main genetic difference between historical and present is not in terms of total genetic variation or number of alleles in the BNN region, but in the distribution of this variation over the populations.     

Variation in restorer genes and primary sexual investment in gynodioecious Plantago coronopus: the trade-off between male and female function

In many gynodioecious species the nuclear inheritance of male fertility is complex and involves multiple (restorer) genes. In addition to restoring plants from the female (male sterile) to the hermaphrodite (male fertile) state, these genes are also thought to play a role in the determination of the quantity of pollen produced by hermaphrodites. The more restorer alleles a hermaphroditic plant possesses, the higher the pollen production. To test this hypothesis I combined the results of crossing studies of the genetics of male sterility with phenotypic data on investment in stamens and ovules among the progeny of plants involved in these studies. The sex ratio (i.e. the frequency of hermaphrodites among the progeny), being a measure of the number of restorer alleles of the maternal plant, was positively related to the investment in pollen (male function), but negatively related to the investment in ovules (female function), in both field and greenhouse experiments. Consequently, a negative correlation between male and female function was observed (trade-off) and it is suggested that antagonistic pleiotropic effects of restorer genes might be the cause. Phenotypic gender, a measure combining investment in both pollen and ovules, was highly repeatable between field and greenhouse, indicating genetic determination of a more male- or female-biased allocation pattern among the studied plants.     

Genetics of Male Sterility in Gynodioecious Plantago Coronopus. II. Nuclear Genetic Variation

Inheritance of male sterility was studied in the gynodioecious species Plantago coronopus using five plants and their descendants from an area of ~50 m(2) from each of four locations. In each location, crosses between these five plants yielded the entire array of possible sex phenotypes. Both nuclear and cytoplasmic genes were involved. Emphasis is placed on the nuclear (restorer) genetics of two cytoplasmic types. For both types, multiple interacting nuclear genes were demonstrated. These genes carried either dominant or recessive restorer alleles. The exact number of genes involved could not be determined, because different genetic models could be proposed for each location and no common genetic solution could be given. At least five genes, three with dominant and two with recessive restorer allele action, were involved with both cytoplasmic types. Segregation patterns of partially male sterile plants suggested that they are due to incomplete dominance at restorer loci. Restorer genes interact in different ways. In most instances models with independent restorer gene action were sufficient to explain the crossing results. However, for one case we propose a model with epistatic restorer gene action. There was a consistent difference in the segregation of male sterility between plants from the two cytoplasmic types. Hermaphrodites of cytoplasmic type 2 hardly segregated male steriles, in contrast to plants with cytoplasmic type 1.