Nitrogen nutrition modifies the susceptibility of Arabidopsis thaliana to the necrotrophic fungus, Alternaria brassicicola

Abstract

The impact of the form of nitrogen (N) source (nitrate versus ammonium) on the susceptibility to Alternaria brassicicola, a necrotrophic fungus, has been examined in Arabidopsis thaliana at the rosette stage. Nitrate nutrition was found to increase fungal lesions considerably. There was a similar induction of defence gene expression following infection under both N nutritions, except for the phytoalexin deficient 3 gene, which was overexpressed with nitrate. Nitrate also led to a greater nitric oxide production occurring in planta during the saprophytic growth and lower nitrate reductase (NIA1) expression 7 days after inoculation. This suggests that nitrate reductase-dependent nitric oxide production had a dual role, whereby, despite its known role in the generic response to pathogens, it affected plant metabolism, and this facilitated fungal infection. In ammonium-grown plants, infection with A. brassicicola induced a stronger gene expression of ammonium transporters and significantly reduced the initially high ammonium content in the leaves. There was a significant interaction between N source and inoculation (presence versus absence of the fungus) on the total amino acid content, while N nutrition reconfigured the spectrum of major amino acids. Typically, a higher content of total amino acid, mainly due to a stronger increase in asparagine and glutamine, is observed under ammonium nutrition while, in nitrate-fed plants, glutamate was the only amino acid which content increased significantly after fungal inoculation. N nutrition thus appears to control fungal infection via a complex set of signalling and nutritional events, shedding light on how nitrate availability can modulate disease susceptibility.

Nitrogen metabolic rate and differential ammonia volatilization regulate resistance against opportunistic fungus Alternaria alternata in tobacco

“…The lower N level in the disease-resistant cultivar may have resulted in nutrient demands of Alternaria alternata not being met limiting infection and spread. This variation in N content between disease-resistant and susceptible cultivars may be an important factor responsible for the differences between the cultivars in their resistance to Alternaria alternata infection (Barrit et al, 2022).…”

Does Potassium (K⁺) Contributes to High-Nitrate (NO3^-) Weakening of Plant’s Defense System against Necrotrophic Fungi?

“…Similarly, susceptibility of Arabidopsis thaliana to Alternaria brassisicola at the rosette stage was largely higher under nitrate (5 mM) compared to ammonium (5 mM) condition [20]. The lesion area was tiny on leaves of ammonium-fed plants while it was almost 10 times bigger (ca 0.7 mm 2 at 7 days' post-infection) in nitratefed plants [20].…”

“…Several studies report that high concentrations of NO3 -in growing media increase susceptibility of plants towards necrotrophic fungi e.g tomato / Oidium lycopersicum [19], Arabidopsis thaliana / Botrytis cinerea [15,16] and Arabidopsis thaliana / Alternaria brassisicola [20]. Tests of pathogenicity of Botrytis cinerea on Arabidopsis thaliana were carried out on plants grown on 0.5, 2 and 10 mM NO3 -.…”

“…Furthermore, the lesion propagation rate (cm 2 /24h) was positively correlated to NO3 concentration in the medium; for example, the propagation rate of the wild type strain Bd90 was nil on leaves of plants grown on 0.5 mM NO3 -, increased to 0.1 at 2 mM NO3 -and doubled to reach 0.2 at 10 mM NO3 [16]. Similarly, susceptibility of Arabidopsis thaliana to Alternaria brassisicola at the rosette stage was largely higher under nitrate (5 mM) compared to ammonium (5 mM) condition [20]. The lesion area was tiny on leaves of ammonium-fed plants while it was almost 10 times bigger (ca 0.7 mm 2 at 7 days' post-infection) in nitratefed plants [20].…”

Seed Protection of Solanum lycopersicum with Pythium oligandrum against Alternaria brassicicola and Verticillium albo-atrum

“…In particular, Verticillium albo-atrum infects the vascular system of many dicotyledonous plant species, and its fungal isolates secrete an arsenal of enzymes that degrade plant cell wall components, such as cellulose, pectin, hemicelluloses, and proteins, and secrete necrosis- and ethylene-inducing proteins, which play a key role in pathogenesis [ 2 ]. In turn, A. brassicicola , a necrotrophic fungal pathogen, stands out for producing AB mycotoxin (protein approximately 35 kDa), hydrolytic enzymes, and necrosis-related proteins on crops grown worldwide [ 3 , 4 ]. Accordingly, to avoid using fungicides, fungal pathogens, such as A. brassicicola and V. albo-atrum , must be prevented from destroying crops through biological control agents (BCAs).…”