Abstract
Mineral nutrients are essential for plant growth and reproduction, yet only a few studies connect the nutritional status to plant innate immunity. The backbone of plant defense response is mainly controlled by two major hormones: salicylic acid (SA) and jasmonic acid (JA). This study investigated changes in the macronutrient concentration (deficiency/excess of nitrogen, phosphorus, potassium, magnesium, and sulfur) on the expression of PR1, a well-characterized marker in the SA-pathway, and PDF1.2 and LOX2 for the JA-pathway, analyzing plants carrying the promoter of each gene fused to GUS as a reporter. After histochemical GUS assays, we determined that PR1 gene was strongly activated in response to sulfur (S) deficiency. Using RT-PCR, we observed that the induction of PR1 depended on the function of Non-expressor of Pathogenesis-Related gene 1 (NPR1) and SA accumulation, as PR1 was not expressed in npr1-1 mutant and NahG plants under S-deprived conditions. Plants treated with different S-concentrations showed that total S-deprivation was required to induce SA-mediated defense responses. Additionally, bioassays revealed that S-deprived plants, induced resistance to the hemibiotrophic pathogen Pseudomonas syringae pv. DC3000 and increase susceptibility to the necrotrophic Botrytis cinerea. In conclusion, we observed a relationship between S and SA/JA-dependent defense mechanisms in Arabidopsis.
Highlights
Soil fertility practices have revolved around general indicators characterising water availability, effective disease control, and soil mineral content to improve crop productivity
To assess the effect of macro-nutrient concentrations on the growth and stress responses in Arabidopsis, four different lines carrying the promoter of the marker gene fused to GUS (PR1::GUS for salicylic acid (SA)-mediated responses; PDF1.2::GUS for jasmonic acid (JA)- and ET-mediated responses; LOX2::GUS for JA-mediated responses; and PG15:: GUS as a constitutive expressed control) were grown in vitro and subjected to MS treatments, either without (0%) or with excessive amounts (200% more for N and 400% for the rest of nutrients) of the macronutrient of interest (N, K, S, Mg, and P)
It has been demonstrated that S-deprivation induces SA-mediated PR1 gene expression, and excess of S suppresses SA-responses
Summary
Soil fertility practices have revolved around general indicators characterising water availability, effective disease control, and soil mineral content to improve crop productivity. The nutritional balance, which indicates whether a soil maintains a proper balance based on the ratios between specific nutrients, is a significant factor of importance to manage soil fertility, as this balance is associated with the production and productivity of many crops [1]. Evolution forced plants to develop an extensive network of defense mechanisms to protect themselves [6]. Their innate immune system recognizes invading microorganisms through pattern recognition receptors (PPRs), which trigger many downstream defenses cascades, which in turn proved to be most effective for a plant’s survival [7,8]
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