Increased resistance to biotrophic pathogens in the Arabidopsis constitutive induced resistance 1 mutant is EDS1 and PAD4-dependent and modulated by environmental temperature

The Arabidopsis constitutive induced resistance 1 ( cir1 ) mutant displays salicylic acid (SA)-dependent constitutive expression of defence genes and enhanced resistance to biotrophic pathogens. To further characterise the role of CIR1 in plant immunity we conducted epistasis analyses with two key components of the SA-signalling branch of the defence network, ENHANCED DISEASE SUSCEPTIBILITY1 (EDS1) and PHYTOALEXIN DEFICIENT4 (PAD4). We demonstrate that the constitutive defence phenotypes of cir1 require both EDS1 and PAD4, indicating that CIR1 lies upstream of the EDS1-PAD4 regulatory node in the immune signalling network. In light of this finding we examined EDS1 expression in cir1 and observed increased protein, but not mRNA levels in this mutant, suggesting that CIR1 might act as a negative regulator of EDS1 via a post-transcriptional mechanism. Finally, as environmental temperature is known to influence the outcome of plant-pathogen interactions, we analysed cir1 plants grown at 18, 22 or 25°C. We found that susceptibility to Pseudomonas syringae pv. tomato ( Pst ) DC3000 is modulated by temperature in cir1 . Greatest resistance to this pathogen (relative to PR-1:LUC control plants) was observed at 18°C, while at 25°C no difference in susceptibility between cir1 and control plants was apparent. The increase in resistance to Pst DC3000 at 18°C correlated with a stunted growth phenotype, suggesting that activation of defence responses may be enhanced at lower temperatures in the cir1 mutant

Effects of conversion of native cerrado vegetation to pasture on soil hydro-physical properties, evapotranspiration and streamflow on the Amazonian agricultural frontier

Understanding the impacts of land-use change on landscape-hydrological dynamics is one of the main challenges in the Northern Brazilian Cerrado biome, where the Amazon agricultural frontier is located. Motivated by the gap in literature assessing these impacts, we characterized the soil hydro-physical properties and quantified surface water fluxes from catchments under contrasting land-use in this region. We used data from field measurements in two headwater micro-catchments with similar physical characteristics and different land use, i.e. cerrado sensu stricto vegetation and pasture for extensive cattle ranching. We determined hydraulic and physical properties of the soils, applied ground-based remote sensing techniques to estimate evapotranspiration, and monitored streamflow from October 2012 to September 2014. Our results show significant differences in soil hydro-physical properties between the catchments, with greater bulk density and smaller total porosity in the pasture catchment. We found that evapotranspiration is smaller in the pasture (639 ± 31% mm yr-1) than in the cerrado catchment (1,004 ± 24% mm yr-1), and that streamflow from the pasture catchment is greater with runoff coefficients of 0.40 for the pasture and 0.27 for the cerrado catchment. Overall, our results confirm that conversion of cerrado vegetation to pasture causes soil hydro-physical properties deterioration, reduction in evapotranspiration reduction, and increased streamflow

Susceptibility to <i>Pst</i> DC3000 is modulated by temperature in <i>cir1</i>.

<p>Four-week-old <i>cir1</i> and <i>PR-1:LUC</i> plants grown at 18, 22 or 25°C were pressure inoculated with <i>Pst</i> DC3000 (10⁶ cfu mL-1) and bacterial titres determined at 48 hpi. Data shown are mean values ± SEM (n = 8–10). ANOVA revealed a significant effect of host genotype (<i>p</i><0.001) and temperature (<i>p</i><0.001) on bacterial titres at 48 hpi, A significant interaction between these two variables (<i>p</i> = 0.015) indicates that they combine non-additively to influence bacterial growth. Mean bacterial titres (cfu cm⁻²) with different letters are significantly different (<i>p</i><0.05).</p

EDS1 protein but not mRNA levels are constitutively higher in the <i>cir1</i> mutant.

<p>(A) Total protein from 4-week-old plants grown at 22°C was separated by SDS–PAGE, transferred to nitrocellulose membrane and probed with an EDS1 antibody. Equal loading of the gel was verified by Ponceau staining of the membrane after protein transfer. This experiment was repeated twice with the same results. (B) Relative <i>EDS1</i> expression in 4-week-old <i>cir1</i> and <i>PR-1:LUC</i> plants was determined using qPCR, with normalization to <i>Actin2</i> expression levels. Each value is the mean of three independent biological repeats ± SEM. This experiment was repeated three times with the same results.</p

EDS1 and PAD4 are required for <i>cir1</i>-mediated resistance to <i>Pst</i> DC3000.

<p>Four-week old plants grown at 22°C were pressure inoculated with <i>Pst</i> DC3000 (10⁶ cfu mL⁻¹) and bacterial titres determined at 48 hpi. Data shown are mean values ± SEM (n = 3) from one experiment representative of three independent experiments. Mean bacterial titres (cfu cm⁻²) with different letters are significantly different (<i>p</i><0.05).</p

<i>SNC1</i> transcript levels are not elevated in <i>cir1</i>.

<p>Relative <i>SNC1</i> expression in 4-week-old <i>cir1</i> and <i>PR-1:LUC</i> plants grown at 18 or 22°C was determined using qPCR, with normalization to <i>Actin2</i> expression levels. Each value is the mean of three independent biological repeats ± SEM.</p