Protecting potatoes from blight

Using X-ray fluorescence imaging at Diamond’s Microfocus Spectroscopy beamline (I18), as well as optical emission spectroscopy, a team of researchers analysed the elemental composition, or the ionome, of different potato plants. They discovered that the elements in the potatoes were dynamic and were subject to strong rearrangements when the plant was infected by P. infestans. One of the strongest findings was that when a potato plant became infected, the researchers saw a decrease in the amount of potassium at the infection sites with an increase in the amount of iron and manganese. These findings were corroborated by a thorough literature search. The publication in The Plant Journal noted that adding potassium to fertiliser decreased the chance of an infection occurring.

The research team went on to test potato plants that were known to be resistant to infection by P. infestans. They discovered a remarkable difference in the elemental composition at the inoculation site with respect to the non-resistant plants. The distribution of calcium, magnesium and silicon were all unique and are a signature that the plants are resistant. The changes in the levels of these important elements could be a signal of an immune response in the potato plants.

Overview of techniques and plant lines used in this study. (a) Summary of the different methods used to analyse elemental concentrations and distributions in potato leaves used in this paper: benchtop‐ and synchrotron‐based micro‐X‐ray fluorescence (µXRF) and inductively coupled plasma optical emission spectroscopy (ICP‐OES). (b) Representative photographs of leaflets from the three plant lines 120 hpi with Phytophthora infestans. For the susceptible cv. Désirée, the three different infection zones within the disease lesion (adapted from van West et al., 1998) are indicated with a dotted line on the photograph and in the schematic drawing next to it. Zone 1 corresponds to the necrotic tissue with the inoculation spot in the middle, zone 2 corresponds to chlorotic potato tissue and the area where P. infestans is sporulating, whereas zone 3 contains green tissue.

Image reused from DOI: 10.1111/tpj.15469 under the CC BY 2.0 license.

Another study investigating the same pathogen looked at how P. infestans is able to digest the surface tissue and penetrate the plant during the infection process. Research published in the journal Science uncovered a new family of enzymes that the plant pathogen is able to use to break down plant tissue.

Researchers discovered copper-dependent lytic polysaccharide monooxygenases (LPMOs) which are a family of enzymes that are produced at high levels by P. infestans when it is invading plant tissue. Data collected using a variety of methods including X-ray crystallography at Diamond’s I04 Macromolecular Crystallography (MX) beamline showed that the LPMOs are able to efficiently degrade pectin, a charged polysaccharide that gives strength to the plant cell wall. The LPMOs were able to cleave the backbone of the pectin molecule which weakened the plant tissue enough to allow the pathogen to enter.

To confirm this finding, the researchers used double-stranded RNA as a genetic tool to prevent P. infestans from being able to produce the LPMOs. In this case, the pathogen could not invade the plant tissue, indicating that the LPMOs are an essential component in the destruction of crops.

Structural and spectroscopic characterization of PiAA17C.(A) Continuous-wave X-band EPR spectrum of PiAA17C (~0.5 mM) in sodium phosphate buffer (pH 7.0, 20 mM) collected at 150 K (black) and spectral simulation (red). (B) Overall structure of PiAA17C, showing the antiparallel β sheet (in green) and histidine brace (sticks), featured in all LPMOs, and the long α helix (in purple), which is not present in other LPMO families (see fig. S4). (C) Electrostatic surface potential of PiAA17C, showing the cleft surrounding the active site and the negatively charged groove (red) leading toward it. (D) Sequence conservation analysis (ConSurf, based on 401 AA17 sequences) of PiAA17C looking down on the active site. The surface is colored by ConSurf score according to the indicated scoring scheme. (E) Highly conserved residues around the active site of PiAA17C, based on ConSurf analysis of 401 AA17 sequences (LPMO domain only). Color shades indicate the level of conservation, calculated using ConSurf.

Image reused from DOI: 10.1126/science.abj1342 under the CC BY 2.0 license.

Understanding the ways that food can spoil is essential for food security as well as reducing the environmental impact caused by food spoilage and waste. The research carried out at Diamond produced new insights that can directly impact on the way we cultivate crops and can be applied to the study of other pests.

To find out more about the I18 beamline or discuss potential applications, please contact Principal Beamline Scientist Konstantin Ignatyev: konstantin.ignatyev@diamond.ac.uk. For further information on I04, contact Principal Beamline Scientist Ralf Flaig: ralf.flaig@diamond.ac.uk.