Advanced spectroscopy-based phenotyping offers a potential solution to the ash dieback epidemic.

Natural and urban forests worldwide are increasingly threatened by global change resulting from human-mediated factors, including invasions by lethal exotic pathogens. Ash dieback (ADB), incited by the alien invasive fungus Hymenoscyphus fraxineus, has caused large-scale population decline of European ash (Fraxinus excelsior) across Europe, and is threatening to functionally extirpate this tree species. Genetically controlled host resistance is a key element to ensure European ash survival and to restore this keystone species where it has been decimated. We know that a low proportion of the natural population of European ash expresses heritable, quantitative resistance that is stable across environments. To exploit this resource for breeding and restoration efforts, tools that allow for effective and efficient, rapid identification and deployment of superior genotypes are now sorely needed. Here we show that Fourier-transform infrared (FT-IR) spectroscopy of phenolic extracts from uninfected bark tissue, coupled with a model based on soft independent modelling of class analogy (SIMCA), can robustly discriminate between ADB-resistant and susceptible European ash. The model was validated with populations of European ash grown across six European countries. Our work demonstrates that this approach can efficiently advance the effort to save such fundamental forest resource in Europe and elsewhere.

Ash leaf metabolomes reveal differences between trees tolerant and susceptible to ash dieback disease.

European common ash, Fraxinus excelsior, is currently threatened by Ash dieback (ADB) caused by the fungus, Hymenoscyphus fraxineus. To detect and identify metabolites that may be products of pathways important in contributing to resistance against H. fraxineus, we performed untargeted metabolomic profiling on leaves from five high-susceptibility and five low-susceptibility F. excelsior individuals identified during Danish field trials. We describe in this study, two datasets. The first is untargeted LC-MS metabolomics raw data from ash leaves with high-susceptibility and low-susceptibility to ADB in positive and negative mode. These data allow the application of peak picking, alignment, gap-filling and retention-time correlation analyses to be performed in alternative ways. The second, a processed dataset containing abundances of aligned features across all samples enables further mining of the data. Here we illustrate the utility of this dataset which has previously been used to identify putative iridoid glycosides, well known anti-herbivory terpenoid derivatives, and show differential abundance in tolerant and susceptible ash samples.

Identification of proteins interacting with Arabidopsis ACD11.

The Arabidopsis ACD11 gene encodes a sphingosine transfer protein and was identified by the accelerated cell death phenotype of the loss of function acd11 mutant, which exhibits heightened expression of genes involved in the disease resistance hypersensitive response (HR). We used ACD11 as bait in a yeast two-hybrid screen of an Arabidopsis cDNA library to identify ACD11 interacting proteins. One interactor identified is a protein of unknown function with an RNA recognition motif (RRM) designated BPA1 (binding partner of ACD11). Co-immunoprecipitation experiments confirmed the ACD11-BPA1 interactions in vivo and in vitro. Two other ACD11 interactors (PRA7 and PRA8) are homologous to each other and to mammalian PRA1, and both were subsequently shown to interact with BPA1 in yeast. A fourth interactor (VAP27-1) is homologous to mammalian VAP-A, and was found to interact more strongly with a homolog of ACD11 than ACD11 itself. All interactors were shown to be associated with membrane fractions, suggesting that ACD11 function could be related to the regulation of membrane compartments.

Human GLTP and mutant forms of ACD11 suppress cell death in the Arabidopsis acd11 mutant.

The Arabidopsis acd11 mutant exhibits runaway, programmed cell death due to the loss of a putative sphingosine transfer protein (ACD11) with homology to mammalian GLTP. We demonstrate that transgenic expression in Arabidopsis thaliana of human GLTP partially suppressed the phenotype of the acd11 null mutant, resulting in delayed programmed cell death development and plant survival. Surprisingly, a GLTP mutant form impaired in glycolipid transfer activity also complemented the acd11 mutants. To understand the relationship between functional complementarity and transfer activity, we generated site-specific mutants in ACD11 based on homologous GLTP residues required for glycolipid transfer. We show that these ACD11 mutant forms are impaired in their in vitro transfer activity of sphingolipids. However, transgenic expression of these mutant forms fully complemented acd11 mutant cell death, and transgenic plants showed normal induction of hypersensitive cell death upon infection with avirulent strains of Pseudomonas syringae. The significance of these findings with respect to the function(s) of ACD11 in sphingolipid transport and cell death regulation is discussed.