Arabidopsis ABCG34 contributes to defense against necrotrophic pathogens by mediating the secretion of camalexin

Abstract

Plant pathogens cause huge yield losses. Plant defense often depends on toxic secondary metabolites that inhibit pathogen growth. Because most secondary metabolites are also toxic to the plant, specific transporters are needed to deliver them to the pathogens. To identify the transporters that function in plant defense, we screened Arabidopsis thaliana mutants of full-size ABCG transporters for hypersensitivity to sclareol, an antifungal compound. We found that atabcg34 mutants were hypersensitive to sclareol and to the necrotrophic fungi Alternaria brassicicola and Botrytis cinerea. AtABCG34 expression was induced by A. brassicicola inoculation as well as by methyl-jasmonate, a defense-related phytohormone, and AtABCG34 was polarly localized at the external face of the plasma membrane of epidermal cells of leaves and roots. atabcg34 mutants secreted less camalexin, a major phytoalexin in A. thaliana, whereas plants overexpressing AtABCG34 secreted more camalexin to the leaf surface and were more resistant to the pathogen. When treated with exogenous camalexin, atabcg34 mutants exhibited hypersensitivity, whereas BY2 cells expressing AtABCG34 exhibited improved resistance. Analyses of natural Arabidopsis accessions revealed that AtABCG34 contributes to the disease resistance in naturally occurring genetic variants, albeit to a small extent. Together, our data suggest that AtABCG34 mediates camalexin secretion to the leaf surface and thereby prevents A. brassicicola infection.AtABCG34 | ABC transporters | camalexin | A. brassicicola | B. cinerea P lants are exposed to a multitude of pathogens, but they usually resist infection by using their unique defense systems and compounds, including secondary metabolites produced either constitutively (phytoanticipins) or in response to pathogen attack (phytoalexins). Plants produce tens of thousands of secondary metabolites, which are classified as phenolics, terpenoids, alkaloids, glucosinolates, cyanogenic glucosides, and betanins. Secondary metabolites are secreted from the infected cells and their surrounding cells after pathogen attack or are released, hydrolyzed, and become toxic when the cells are destroyed by pathogens (1), thus inhibiting pathogen growth on the plant. Many secondary metabolites are dangerous to the plants because of their toxicity to cellular metabolism. To avoid self-toxicity, plants either secrete these compounds to the leaf surface or sequester them in the vacuole, a compartment with low metabolic activity. In both cases, specific transporters are required either to deliver the secondary metabolites to the site where the pathogens are located or to store them as weapons against pathogen attack.Several full-size ABCG transporters are involved in the transport of secondary metabolites. Nicotiana plumbaginifolia PDR1/ABC1 and Nicotiana tabacum PDR1 are induced by jasmonate, a defense-related hormone highly expressed in the leaf epidermal cells and trichomes, and transport sclareol, a diterpene alcohol secreted by Nicotiana species in response to p...

A Comparison of the Antibacterial and Antifungal Activities of Thiosulfinate Analogues of Allicin

“…Evans Blue was used to stain dead BY-2 cells 54 and the trend observed with A549 adenocarcinoma cells, that DMTS was least toxic and DATS most toxic, was clearly reiterated (Fig. 13 ).…”

“…Dye bound to dead cells was solubilized in 50% methanol with 1% SDS for 30 min at 50 °C and quantified by absorbance at 600 nm in a plate reader. Negative controls were not treated with thiosulfinates and positive controls were heated to 99 °C for 30 minutes 54 . Negative and positive controls were set as 0% and 100%, respectively.…”

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“…The production of chemical substances and their transportation through protein channels to the site of infection and to other parts of the plant (Khare et al 2017 ) undergoing a stressful condition is a direct approach to the sustenance of plant’s health and vitality. The plant Arabidopsis thaliana possess high numbers of transport proteins (ABCG34) and has the ability to resist invasion of the fungus ( Alternaria brassicicola ) by producing and transporting the fungicidal substance camelexin to the surface of the plant leaves.…”

“…Every creature possesses one or more defense tools and plants are no exception. To sustain its health, vitality, and existence, plants must ward off and counteract the actions of their enemies (pathogens) through many different modes including the production of secondary metabolites known as phytoalexins or phytoanticipins (Khare et al 2017 ).…”

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