• Energy Research

The cambial meristem is responsible for bark and wood formation in woody plants. The activity of the cambial meristem is controlled by various factors; one of them is the plant hormone cytokinin. Here, we have explored different approaches to genetically engineering cambial activity in poplar plants by the ectopic expression of a cytokinin biosynthesis gene with enhanced activity (named ROCK4) or of a gene encoding a constitutively active cytokinin receptor variant (ROCK3). Both genes are derived from Arabidopsis thaliana and were expressed in poplar trees under the control of their own promoter or the cambium-specific pHB8 promoter. pIPT3:ROCK4- and pHB8:ROCK4-expressing plants were smaller than wild-type plants and formed more lateral branches; pHB8:ROCK4 transgenic plants additionally showed an increased stem diameter. In contrast, pAHK3:ROCK3- and pHB8:ROCK3-expressing plants grew taller than wild type without an altered branching pattern and formed more cambial cells, leading to increased radial stem growth. The effectivity of ROCK3 when expressed in either secondary phloem cells or in cambial cells is consistent with a dual, tissue-autonomous and non-autonomous activity of cytokinin in regulating cambial activity. We propose ROCK3 as a novel gene to enhance biomass formation in woody plants.

Biotechnology can greatly improve the efficiency of forest tree breeding for the production of biomass, energy, and materials. However, EU regulations impede the market introduction of genetically modified (GM) trees so their socioeconomic and environmental benefits are not realized. European policy makers should concentrate on a science-based regulatory process.

AbstractLocal adaptation is key for ecotypic differentiation and species evolution. Understanding underlying genomic patterns can allow the prediction of future maladaptation and ecosystem stability. Here, we report the whole-genome resequencing of 874 individuals from 100 range-wide populations of European beech (Fagus sylvatica L.), an important forest tree species in Europe. We show that genetic variation closely mirrors geography with a clear pattern of isolation-by-distance. Genome-wide analyses for genotype-environment associations (GEAs) identify relatively few potentially adaptive variants after correcting for an overwhelming signal of statistically significant but non-causal GEAs. We characterize the single high confidence genomic region and pinpoint a candidate gene possibly involved in winter temperature adaptation via modulation of spring phenology. Surprisingly, allelic variation at this locus does not result in any apparent fitness differences in a common garden. More generally, reciprocal transplant experiments across large climate distances suggest extensive phenotypic plasticity. Nevertheless, we find indications of polygenic adaptation which may be essential in natural ecosystems. This polygenic signal exhibits broad- and fine-scale variation across the landscape, highlighting the relevance of spatial resolution. In summary, our results emphasize the importance, but also exemplify the complexity, of employing natural genetic variation for forest conservation under climate change.