Biology subjects

Denman, S.

Publications and source records attributed to Denman, S..

3 recordsLinked to original sources

bioRxiv2023

Chemical cues from beetle larvae trigger proliferation and virulence of a plant pathogen

Agricultural crop productivity and global forest biomes are coming under increasing threat from insect pests and microbial pathogens. This impact is worsened by inter- kingdom insect-microbe interactions that can increase transmission and disease severity in affected plants. Whilst bacterial chemical cues have been shown to directly influence insect behaviour, the impact of insect-derived compounds on phytopathogens is poorly understood. Here, we investigated the chemical basis for interactions between beetle larvae and bacteria in acute oak decline (AOD), a disease characterised by inner bark necrosis and involving a polymicrobial consortium including Brenneria goodwinii and larval galleries of Agrilus biguttatus. We found that A. biguttatus larval extracts contain chemical elicitors that increase bacterial growth rate and final cell density during in vitro culture, and stimulate the differential expression of [~]600 genes, including the Type III Secretion System and its effectors, which are major virulence factors in plant pathogens. Chemical compounds from closely related insect species did not have this effect. These findings highlight the importance of inter-kingdom interactions in plant disease and suggests a novel mode-of-action for insect-derived chemical elicitors in facilitating the virulence of phytopathogens.

ecology↗

bioRxiv2023

Leaf susceptibility of Macaronesian laurel forest species to Phytophthora ramorum

Phytophthora ramorum (Pr) is an invasive oomycete in Europe and North America and the causal agent of sudden oak death (SOD), which occurs along the coastal fog belt of California and southwestern Oregon, and it also causes sudden larch death in the UK. The Macaronesian laurel forest (MLF), a relict subtropical evergreen forest of the North Atlantic islands, shares climatic and some taxonomic affinities with those areas affected by SOD. To assess the disease risk, we tested the foliage susceptibility of MLF species and their capacity to sustain Pr sporulation and compared the climatic suitability with other areas where the pathogen is established. Detached leaves of 15 species were inoculated with zoospores and mycelium (through wounding) with five Pr isolates belonging to the EU1 and NA1 clonal lineages. MLF species showed diverse responses to Pr, ranging from extensive necroses on Viburnum tinus to asymptomatic sporulation on Picconia excelsa. Eleven species developed necrotic lesions to different degrees through zoospore inoculation while this increased to 13 species through wound treatment. Overall, small necrotic lesions (i.e. tolerance) were predominant, but Pr was rather aggressive to V. tinus, Arbutus canariensis and Ilex canariensis. Although the mean sporangial production was generally low (25-201 sporangia) in all species, the number of sporangia per leaf in five MLF species was similar to those reported for Umbellularia californica, a key host driving the SOD epidemics in California. Climatic suitability indexes in MLF areas were similar to those where SOD is found in California. Our results indicate a moderate to high risk of Pr establishment if the pathogen is introduced in the MLF.

plant biology↗

bioRxiv2021

Genomic structure and diversity of oak populations in British Parklands

The two predominant oak species in Britain are Quercus robur (English or pedunculate oak) and Q. petraea (sessile oak). We sequenced the whole genomes of 386 oak trees from four British parkland sites and found over 50 million nuclear single nucleotide polymorphisms (SNPs), allowing us to identify 360 Q. robur, ten Q. petraea and 16 hybrid individuals using clustering methods. Comparing Q. robur and Q. petraea trees from Attingham Park, we found that the nuclear genomes of the two species are largely undifferentiated but identified 81 coding regions exhibiting strong interspecific differentiation. The nuclear genomes of our 360 Q. robur individuals showed no clear differentiation among the four parkland sites. Scans for selective sweeps in Q. robur highlighted regions containing genes with putative involvement in stress tolerance, one of which was moderately differentiated from Q. petraea. Reconstructions of past effective population sizes suggested a long population size decline in both Q. robur and Q. petraea over the Pleistocene, but population growth after the last glacial maximum. We assembled the whole chloroplast genomes of 287 Q. robur, 8 Q. petraea and 14 hybrid trees. In a phylogenetic network, these fell into five major haplotypes, which were shared among species but differed in frequency among parkland sites. We matched our chloroplast genome haplotypes to restriction enzyme fragment haplotypes identified in older studies that had surveyed ancient woodlands in Britain and much of Europe. This suggested that the parkland populations in our study derive from local seed sources.

genomics↗