Synchrotron X-ray fluorescence microscopy-enabled elemental mapping illuminates the 'battle for nutrients' between plant and pathogen.

Fatima Naim,Lilian M V P Sanglard,Mark J Hackett,Mark R Gibberd,Georgina Sauzier,David J Paterson,Ayalsew Zerihun,Juliane Reinhardt,Karina Khambatta

doi:10.1093/jxb/erab005

Abstract

Metal homeostasis is integral to normal plant growth and development. During plant–pathogen interactions, the host and pathogen compete for the same nutrients, potentially impacting nutritional homeostasis. Our knowledge of outcome of the interaction in terms of metal homeostasis is still limited. Here, we employed the X-ray fluorescence microscopy (XFM) beamline at the Australian Synchrotron to visualize and analyse the fate of nutrients in wheat leaves infected with Pyrenophora tritici-repentis, a necrotrophic fungal pathogen. We sought to (i) evaluate the utility of XFM for sub-micron mapping of essential mineral nutrients and (ii) examine the spatiotemporal impact of a pathogen on nutrient distribution in leaves. XFM maps of K, Ca, Fe, Cu, Mn, and Zn revealed substantial hyperaccumulation within, and depletion around, the infected region relative to uninfected control samples. Fungal mycelia were visualized as thread-like structures in the Cu and Zn maps. The hyperaccumulation of Mn in the lesion and localized depletion in asymptomatic tissue surrounding the lesion was unexpected. Similarly, Ca accumulated at the periphery of the symptomatic region and as microaccumulations aligning with fungal mycelia. Collectively, our results highlight that XFM imaging provides the capability for high-resolution mapping of elements to probe nutrient distribution in hydrated diseased leaves in situ.

Highlights

Plants rely on finely balanced transport and distribution of mineral nutrients to support normal growth and development
We employed the X-ray fluorescence microscopy (XFM) beamline at the Australian Synchrotron to visualize and analyse the fate of nutrients in wheat leaves infected with Pyrenophora tritici-repentis, a necrotrophic fungal pathogen
Representative optical images in addition to XFM false-colour Compton scattering and elemental maps (K, Ca, Mn, Fe, Cu, and Zn) from a control wheat leaf sample (Fig. 1A–H) and an age-matched infected sample (8 dpi with Pyrenophora tritici-repentis (Ptr)) (Fig. 1I–P) were compared.The optical image of a Ptr-infected sample (Fig. 1I) shows the damage caused by the necrotrophic fungus, as a characteristically distinct central necrotic lesion surrounded by a chlorotic zone.The chlorotic zone extends beyond the necrotized tissue and fades away into asymptomatic tissue, apical and basal to the lesion

Summary

Introduction

Plants rely on finely balanced transport and distribution of mineral nutrients to support normal growth and development. Deprivation of macronutrients such as potassium (K) and calcium (Ca) results in major developmental defects and yield losses (Loneragan and Snowball, 1969; Pettigrew, 2008). Specific examples are necrotrophic fungi, which elicit toxins to initiate plant cell death, enabling the fungi to extract nutrients from the dead tissue.These toxins may be cell wall-degrading enzymes, proteins, or secondary metabolites that promote necrotization of plant tissue and proliferation of the fungal pathogen (Faris and Friesen, 2020)

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Discussion

Conclusion