Investigation of the Chemical Interface in the Soybean–Aphid and Rice–Bacteria Interactions Using MALDI-Mass Spectrometry Imaging

Abstract

Mass spectrometry imaging (MSI) is an emerging technology for high-resolution plant biology. It has been utilized to study plant-pest interactions, but limited to the surface interfaces. Here we expand the technology to explore the chemical interactions occurring inside the plant tissues. Two sample preparation methods, imprinting and fracturing, were developed and applied, for the first time, to visualize internal metabolites of leaves in matrix-assisted laser desorption ionization (MALDI)-MSI. This is also the first time nanoparticle-based ionization was implemented to ionize diterpenoid phytochemicals that were difficult to analyze with traditional organic matrices. The interactions between rice-bacterium and soybean-aphid were investigated as two model systems to demonstrate the capability of high-resolution MSI based on MALDI. Localized molecular information on various plant- or pest-derived chemicals provided valuable insight for the molecular processes occurring during the plant-pest interactions. Specifically, salicylic acid and isoflavone based resistance was visualized in the soybean-aphid system and antibiotic diterpenoids in rice-bacterium interactions.

Large Scale Nanoparticle Screening for Small Molecule Analysis in Laser Desorption Ionization Mass Spectrometry

“…Recently, we were able to analyze phytocassanes and momilactones (both terpenes) with TiO 2 and Fe 3 O 4 NPs but not with any organic matrixes. 44 Fe 3 O 4 NPs showed higher sensitivity for this class of terpenes than TiO 2 NPs, which contrasts with parthenolide in the current study where Fe 3 O 4 NPs are mostly inefficient. Further study is necessary to achieve a more detailed understanding, but we tentatively conclude that (1) high temperature is essential for terpenes considering their high boiling point compared to other analytes and high LDI efficiency with some metal oxide NPs and diamond NPs, and (2) chemical interactions also play an important role for these hydrophobic compounds that are difficult to ionize (e.g., momilactones and phytocassanes have hydroxyl groups but not parthenolide).…”

Matrix assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI) for direct visualization of plant metabolites in situ

“…Recently, nanoparticle based matrices have shown promise for positive mode application. In bacterial resistant rice leaves, metal-oxide nanoparticles TiO2 and Fe3O4 were used to monitor metabolite accumulation of phytoalexins in response to infection by Xanthomonas oryzae bacterium, which was not possible with any other matrices [15].…”

“…A number of years ago, the Caprioli group pioneered the development of mass spectrometry imaging for localizing molecules of interest directly on the sections of mammalian tissues [2,3]. This methodology, termed matrix assisted laser desorption/ionization-mass spectrometry imaging (MALDI-MSI, also referred to as imaging mass spectrometry (IMS)), has since been expanded to visualize molecules directly in plant tissues and surfaces for the localization of lipids [4,5,6,7], proteins [8], secondary metabolites [9,10,11,12,13], and various small molecules [14,15,16,17] at unprecedented spatial and chemical resolution.…”

Jasmonate-dependent plant defenses mediate soybean thrips and soybean aphid performance on soybean

“…2b). Insect herbivores with piercing-sucking mouthparts, such as whiteflies and aphids, have previously been shown to induce SA-mediated responses (Broekgaarden et al 2011;Foyer et al 2015;Heidel-Fischer et al 2014;Klein et al 2015).…”