Analysis of spruce genomes reveals important evolutionary mechanisms related to adaptation

The genomes of new spruce species have just been deciphered. Notwithstanding their size seven times that of the human genome (thus among the largest genomes in the living world), the study confirmed that the largest part of their genomes is made up of repeated and non-coding DNA. As for the genes, most of them were grouped into large families, some of them being in expansion. Also, some genes were found to evolve faster than others at the level of the proteins they encode. They were found to be mainly involved in species differential adaptation to biotic and abiotic stresses, just like for expanding gene families. Therefore, this study sheds light on two important mechanisms of evolution of conifer genomes in response to the multiple environmental stresses that they face since their inception, millions of years ago. Link to the complete publication here.

Limits of climate change adaptation in forest trees

In the context of climate change, an article has just been published by the researchers of the Chair on the maladaptation of trees in the face of severe climatic stress caused by the growing climate instability. Spring 2021 was exceptionally warm and early under our northern latitudes, leading to an early shoot bud burst up to two weeks earlier than usual. However, at the end of May 2021, the Quebec province was hit by a major cold snap caused by the instability of the polar vortex, which resulted in severe frost damages to the annual growing shoots in young white spruce plantations, and the cancellation of the growth of 2021. The study of young comparative plantations of various seed sources indicated that there was no significant genetic variation in resistance to such severe late frosts. The researchers will follow growth recovery in 2022 to check if significant genetic variation exists and if it is related to previous tree vigor. Link to the complete publication here.

Trembling aspen, a widespread species genetically diverse and heterogeneous throughout its range

A vast collaborative study has just been published by researchers from the Chair on the distribution of genetic diversity throughout the entire range of this pioneer species, which covers most of the North American continent from Canada to Mexico. The distribution of genomic diversity, estimated using a large number of populations, appeared highly geographically structured. Signatures of genetic adaptation to regional climate were detected, especially for water stress. Other factors were also investigated, such as polyploidy and seed germination, for which significant regional differences were also observed. Link to the complete publication here.

Improving drought response through genomic selection

The Chair’s researchers have just published an article on the potential for improving the response to drought in white spruce, thanks to genomic selection. Based on the dendrochronological profiles of trees established on two experimental sites over the past twenty years, they were able to assess the genetic variability in the responses to two distinct droughts suffered by the trees obtained from controlled crosses. In particular, they discovered that the trees that responded best to water stress were those that displayed the best vigor throughout their life. The genomic selection models were as accurate as those developed using conventional approaches, making it possible to accelerate the selection of more resilient trees in the context of climate change, and in particular in relation to the intensification of stress due to droughts. Link to the complete publication here.

A new article on the genetic basis of drought adaptation in white spruce elected for the cover of the journal Molecular Ecology

In a recent work elected for the cover page of the August 2021 issue of the journal Molecular Ecology, Depardieu et al. combined the results of dendrochronology analyses of mature trees replicated in a common garden, genotype-phenotype associations and genotype-environment associations for thousands of candidate genes, as well as transcriptomics to study the genomic basis of drought resistance in white spruce. In total, they identify 285 genes likely involved in drought resistance including differentially expressed genes in seedlings submitted to water stress. This publication was also the subject of an editorial comment on pages 3893-95 of the same issue. Link to the complete publication.

Two new articles on the genomics of phenolic defence compounds in white spruce, as well as the detection by genomic means of pollen contamination and the impact of selection in a white spruce seed orchard from Alberta

In a recent publication, Laoué and collaborators combined QTL and transcriptomic approaches to identify a set of genes involved in the synthesis of phenolic defence compounds in white spruce. A major QTL responsible for the constitutive production of neolignane-2 was discovered, as well as 50 genes involved in the phenylpropanoid pathway, which were differentially expressed among trees showing high and low concentrations in flavonoids, stilbenoids and neolignans. This work sheds new light regarding the genes involved in response to biotic and abiotic stress in white spruce. Link to the publication.

An article by Galeano and collaborators based on SNP genotyping showed that on average, 30% of seedlots were contaminated by exogenous pollen in a white spruce open-pollinated seed orchard of Alberta. The source of pollen contamination was located one kilometer away from the seed orchard upstream of dominant winds. In addition, this study showed that the achievement of 5% genetic gain in height through eliminating two-thirds of the orchard generated an eight-fold loss in effective population size, while observed heterozygosity and inbreeding remained largely unaffected by tree selection. Link to the publication.

New publications on resistance to spruce budworm and adaptation to drought in white spruce

A study by Beaulieu and collaborators has shown that needle concentration in acetophenone aglycons (secondary metabolites involved in resistance to spruce budworm) could be genetically improved in white spruce using genomic selection, and that this trait could be integrated to multi-trait selection also implicating growth and wood quality (full article here).

A study by Depardieu and collaborators relying on the retrospective analysis of tree-ring and genetic data in 43 natural populations of white spruce has shown that growth resilience after extreme drought events was under genetic control, and that this trait represents a promising avenue for breeders to improve spruce resistance to drought in the context of climate change (full article here).