Biology subjects

van Loo, M.

Publications and source records attributed to van Loo, M..

4 recordsLinked to original sources

bioRxiv2026

Bark beetle protein elicitors trigger biphasic immune responses in Norway spruce seedlings

Norway spruce (Picea abies) responds to attacks by the spruce bark beetle (Ips typographus) through the rapid activation of local defense mechanisms, but field studies can be difficult to standardize due to variable attack pressure and environmental heterogeneity. Here, we developed a phytotron-based assay that mimics early beetle-associated stress using insect-derived protein extracts, enabling reproducible molecular analyses under controlled conditions. Ten-week-old spruce seedlings were stem-treated with mock buffer or beetle protein extracts, followed by transcriptomic analyses of stem tissues and targeted metabolomic profiling of needles at 2 and 48 h post-inoculation. RT-qPCR analysis revealed rapid transcriptional activation of signaling and defense genes in Norway spruce, with NP-40-based protein extracts producing the most consistent early response. RNA-seq analysis revealed transcriptional dynamics, with 488 differentially expressed genes detected at 2 h and 84 at 48 h post-inoculation relative to mock-treated controls. Early responses at 2 h were characterized by activation of genes associated with immune perception and signal transduction. By 48 h, the response shifted toward accumulation of transcripts encoding defense proteins such as chitinases, defensins, proteinase inhibitors, and pathogenesis-related (PR) proteins. Importantly, a substantial proportion of differentially expressed genes overlapped with those previously identified in mature Norway spruce trees during pioneer bark beetle attack under field conditions, supporting the biological relevance of the assay. In contrast, targeted analyses of secondary metabolites performed in needle tissue revealed limited systemic changes across time points, suggesting that early induced defenses may remain largely localized to the stem. Together, these results demonstrate that beetle-derived proteins trigger a rapid and temporally structured defense response in Norway spruce seedlings and establish a reproducible elicitor-based platform that may provide a broadly applicable framework for investigating bark beetle-induced defenses across conifers. HighlightBark beetle protein elicitors trigger temporally structured immune responses in Norway spruce seedlings that overlap with responses observed in mature trees, with rapid immune signaling at 2 h followed by defense protein accumulation at 48 h.

plant biology↗

bioRxiv2025

Unravelling the intraspecific variation in drought responses in seedlings of European black pine (Pinus nigra J.F. Arnold)

O_LIUnderstanding intraspecific variation in drought tolerance is essential for predicting the adaptive capacity of forest species under climate change. Yet, the molecular basis of this variation remains poorly understood in ecologically and economically important conifers. C_LIO_LIWe integrated high-throughput phenotyping with metabolomics and transcriptomics under standardized soil drying to investigate drought responses across nine climatically distinct provenances of the conifer Pinus nigra. We tested whether drought tolerance--measured as decline in maximum quantum yield of the photosystem II (Fv/Fm)--varies among provenances, follows a climatic cline, and involves trade-off with growth. To identify the underlying molecular basis, we performed metabolomics and transcriptomics in four provenances representing contrasting drought tolerance. C_LIO_LIDrought tolerance varied significantly among provenances and was decoupled from growth, yet showed no differentiation along the climatic cline. Drought tolerant provenances differed from sensitive ones in both constitutive and drought-induced levels of flavonoid and diterpene metabolites. Transcriptomic profiles further highlighted provenance-specific differences in gene expression related to flavonoids. C_LIO_LIOur results demonstrate the utility of integrating automated phenotyping with molecular profiling to uncover the metabolic basis of drought adaptation, laying the groundwork for targeted studies on metabolite function and tolerance strategies in non-model conifers. C_LI

plant biology↗

bioRxiv2025

Pioneer bark beetle attacks induce multifaceted localized defense responses in Norway spruce

Conifer forests worldwide are increasingly threatened by environmental stressors, especially bark beetle infestations. In a novel experimental field setup with controlled attacks on clonal trees, we investigated the molecular defense responses of 35-year-old Norway spruce trees to colonization attempts by the spruce bark beetle, Ips typographus. A multi-omics approach was used to study tree responses to bark beetle pioneers under natural conditions. At the site of the attacks, increased levels in jasmonic acid, together with changes in other phytohormones, induced differential gene expression of up to 1,900 genes from multiple defense-related pathways. These transcriptomic alternations were corroborated by proteomic and metabolomic shifts, which ultimately showed increased levels of compounds involved in deterring bark beetle attacks, such as phenolic aglycones, diterpene resin acids, mono- and sesquiterpenes, and lignin. Our study highlights the intricate yet rapid and effective local defense response of Norway spruce against pioneer bark beetle attacks and lays a foundation for in-depth studies of this and other conifers resistance to phloem-feeding insects.

plant biology↗

bioRxiv2020

Looking for the needle in a downsized haystack: Whole-exome sequencing unravels how selection and gene flow have shaped climatic adaptation in Douglas-fir (Pseudotsuga menziesii)

The widespread Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) occurs along a steep gradient of diverse climates throughout its natural range, which is expected to result in spatially varying selection to local climate conditions. However, phenotypic signals of climatic adaptation can often be confounded, because unraveled clines covary with signals caused by neutral evolutionary processes such as gene flow and genetic drift. Here, we present phenotypic and genotypic data from a common garden experiment showing a putative signal of adaptation to climate after trees have been growing for 40 years in a common environment. Sixteen Douglas-fir provenances originating from a North-to-South gradient of approx. 1,000 km were analyzed and genomic information was obtained from exome capture, which resulted in an initial genomic dataset of >90,000 single nucleotide polymorphisms. We used a restrictive and conservative filtering approach which permitted us to include only SNPs and individuals in environmental association analysis (EAA) that were free of potentially confounding effects (LD, relatedness among trees, heterozygosity deficiency and deviations from Hardy-Weinberg proportions). We used four conceptually different genome scan methods based on FST outlier detection and gene-environment association in order to disentangle truly adaptive SNPs from neutral SNPs and found that a relatively small proportion of the exome showed a truely adaptive signal (0.01-0.17%) when population substructuring and multiple testing was accounted for. Nevertheless, the unraveled SNP candidates showed significant relationship with climate at provenance origins which strongly suggests that they have most likely featured adaption in Douglas-fir across a steep climatic gradient. Two SNPs were independently found by three of the employed algorithms and one could be assigned with high probability to a Picea abies homolog gene involved in circadian clock control as was also found in Populus balsamifera.

evolutionary biology↗