Host-mediated phosphorylation of type III effector AvrPto promotes Pseudomonas virulence and avirulence in tomato

The AvrPto protein from Pseudomonas syringae pv tomato is delivered into plant cells by the bacterial type III secretion system, where it either promotes host susceptibility or, in tomato plants expressing the Pto kinase, elicits disease resistance. Using two-dimensional gel electrophoresis, we obtained evidence that AvrPto is phosphorylated when expressed in plant leaves. In vitro phosphorylation of AvrPto by plant extracts occurs independently of Pto and is due to a kinase activity that is conserved in tomato (Solanum lycopersicum), tobacco (Nicotiana tabacum), and Arabidopsis thaliana. Three Ser residues clustered in the C-terminal 18 amino acids of AvrPto were identified in vitro as putative phosphorylation sites, and one site at S149 was directly confirmed as an in vivo phosphorylation site by mass spectrometry. Substitution of Ala for S149 significantly decreased the ability of AvrPto to enhance disease symptoms and promote growth of P. s. tomato in susceptible tomato leaves. In addition, S149A significantly decreased the avirulence activity of AvrPto in resistant tomato plants. Our observations support a model in which AvrPto has evolved to mimic a substrate of a highly conserved plant kinase to enhance its virulence activity. Furthermore, residues of AvrPto that promote virulence are also monitored by plant defenses.     

A tribute to Dr. Serge N. Timasheff,our mentor

Dr. Serge N. Timasheff, our mentor and friend, passed away in 2019. This article is a collection of tributes from his postdoctoral fellows, friends, and daughter, who all have been associated with or influenced by him or his research. Dr. Timasheff is a pioneer of research on thermodynamic linkage between ligand interaction and macromolecular reaction. We all learned a great deal from Dr. Timasheff, not only about science but also about life.     

An internal carbon source for improving biological nutrient removal

This study investigates the potential of mechanically disintegrated surplus activated sludge (SAS) to be used as an internal carbon source for biological nutrient removal (BNR) using two laboratory tests. In the phosphorus release test, the addition of disintegrated sludge as a carbon source was able to enhance phosphate (PO(4)-P) release by 14.9 mg l(-1) PO(4)-P when compared with acetate (7.9 mg l(-1) PO(4)-P), considering the 4.3 mg l(-1) PO(4)-P released in the control vessel, without carbon addition. Similarly, in the denitrification test, the nitrate (NO(3)-N) consumption rate was improved after the addition of disintegrated sludge (14.9 mg NO(3)-Ng(-1)VSS h(-1)) compared with acetate (7.0 mg NO(3)-Ng(-1)VSS h(-1)), taking in consideration the rate obtained in the control vessel (6.9 mg NO(3)-Ng(-1)VSS h(-1)). Two to five minutes of SAS disintegration time in the deflaker (2300-6200 kJ kg(-1) total solids) is recommended for this application.     

Abiotic drivers and plant traits explain landscape‐scale patterns in soil microbial communities

The controls on aboveground community composition and diversity have been extensively studied, but our understanding of the drivers of belowground microbial communities is relatively lacking, despite their importance for ecosystem functioning. In this study, we fitted statistical models to explain landscape‐scale variation in soil microbial community composition using data from 180 sites covering a broad range of grassland types, soil and climatic conditions in England. We found that variation in soil microbial communities was explained by abiotic factors like climate, pH and soil properties. Biotic factors, namely community‐weighted means (CWM) of plant functional traits, also explained variation in soil microbial communities. In particular, more bacterial‐dominated microbial communities were associated with exploitative plant traits versus fungal‐dominated communities with resource‐conservative traits, showing that plant functional traits and soil microbial communities are closely related at the landscape scale.     

Global change pressures on soils from land use and management

Soils are subject to varying degrees of direct or indirect human disturbance, constituting a major global change driver. Factoring out natural from direct and indirect human influence is not always straightforward, but some human activities have clear impacts. These include land‐use change, land management and land degradation (erosion, compaction, sealing and salinization). The intensity of land use also exerts a great impact on soils, and soils are also subject to indirect impacts arising from human activity, such as acid deposition (sulphur and nitrogen) and heavy metal pollution. In this critical review, we report the state‐of‐the‐art understanding of these global change pressures on soils, identify knowledge gaps and research challenges and highlight actions and policies to minimize adverse environmental impacts arising from these global change drivers. Soils are central to considerations of what constitutes sustainable intensification. Therefore, ensuring that vulnerable and high environmental value soils are considered when protecting important habitats and ecosystems, will help to reduce the pressure on land from global change drivers. To ensure that soils are protected as part of wider environmental efforts, a global soil resilience programme should be considered, to monitor, recover or sustain soil fertility and function, and to enhance the ecosystem services provided by soils. Soils cannot, and should not, be considered in isolation of the ecosystems that they underpin and vice versa. The role of soils in supporting ecosystems and natural capital needs greater recognition. The lasting legacy of the International Year of Soils in 2015 should be to put soils at the centre of policy supporting environmental protection and sustainable development.     

Integrating plant–soil interactions into global carbon cycle models

1.  Plant–soil interactions play a central role in the biogeochemical carbon (C), nitrogen (N) and hydrological cycles. In the context of global environmental change, they are important both in modulating the impact of climate change and in regulating the feedback of greenhouse gas emissions (CO₂, CH₄ and N₂O) to the climate system.
2.  Dynamic global vegetation models (DGVMs) represent the most advanced tools available to predict the impacts of global change on terrestrial ecosystem functions and to examine their feedbacks to climate change. The accurate representation of plant–soil interactions in these models is crucial to improving predictions of the effects of climate change on a global scale.
3.  In this paper, we describe the general structure of DGVMs that use plant functional types (PFTs) classifications as a means to integrate plant–soil interactions and illustrate how models have been developed to improve the simulation of: (a) soil carbon dynamics, (b) nitrogen cycling, (c) drought impacts and (d) vegetation dynamics. For each of these, we discuss some recent advances and identify knowledge gaps.
4.  We identify three ongoing challenges, requiring collaboration between the global modelling community and process ecologists. First, the need for a critical evaluation of the representation of plant–soil processes in global models; second, the need to supply and integrate knowledge into global models; third, the testing of global model simulations against large-scale multifactor experiments and data from observatory gradients.
5.   Synthesis . This paper reviews how plant–soil interactions are represented in DGVMs that use PFTs and illustrates some model developments. We also identify areas of ecological understanding and experimentation needed to reduce uncertainty in future carbon coupled climate change predictions.     

Simulation of greenhouse gases following land‐use change to bioenergy crops using the ECOSSE model: a comparison between site measurements and model predictions

This article evaluates the suitability of the ECOSSE model to estimate soil greenhouse gas (GHG) fluxes from short rotation coppice willow (SRC‐Willow), short rotation forestry (SRF‐Scots Pine) and Miscanthus after land‐use change from conventional systems (grassland and arable). We simulate heterotrophic respiration (R_h), nitrous oxide (N₂O) and methane (CH₄) fluxes at four paired sites in the UK and compare them to estimates of R_h derived from the ecosystem respiration estimated from eddy covariance (EC) and R_h estimated from chamber (IRGA) measurements, as well as direct measurements of N₂O and CH₄ fluxes. Significant association between modelled and EC‐derived R_h was found under Miscanthus, with correlation coefficient (r) ranging between 0.54 and 0.70. Association between IRGA‐derived R_h and modelled outputs was statistically significant at the Aberystwyth site (r = 0.64), but not significant at the Lincolnshire site (r = 0.29). At all SRC‐Willow sites, significant association was found between modelled and measurement‐derived R_h (0.44 ≤ r ≤ 0.77); significant error was found only for the EC‐derived R_h at the Lincolnshire site. Significant association and no significant error were also found for SRF‐Scots Pine and perennial grass. For the arable fields, the modelled CO₂ correlated well just with the IRGA‐derived R_h at one site (r = 0.75). No bias in the model was found at any site, regardless of the measurement type used for the model evaluation. Across all land uses, fluxes of CH₄ and N₂O were shown to represent a small proportion of the total GHG balance; these fluxes have been modelled adequately on a monthly time‐step. This study provides confidence in using ECOSSE for predicting the impacts of future land use on GHG balance, at site level as well as at national level.