In-Silico Characterization and Expression Analysis of NB-ARC Genes in Response to Erwinia mallotivora in Carica papaya

Disease resistance in plants is commonly associated with resistance (R) genes that encode nucleotide binding site-leucine rich repeat (NBS-LRR) domains that are essential for pathogen recognition and defence signalling. In this study, we identified and analyzed the sequence of putative pathogen-responsive NB-ARC transcripts from Carica papaya transcriptome database, carried out the structural and phylogenetic analysis, and determined the expression profile of the transcripts in C. papaya challenged with Erwinia mallotivora. The findings indicate CpNBS1, the only pathogen-responsive NB-ARC protein identified in this study belongs to the CC-NBS-LRR group. Semi-quantitative PCR showed CpNBS1 was differentially expressed in response to E. mallotivora. Structural analysis of the 4993-Eksotika and 4993-Viorica translated proteins showed striking differences in terms of the number of β-sheets and α-helixes as well their ligand-binding surface, suggesting the role of the LRR domain in determining the specificity of recognition of E. mallotivora effector. Collectively, this study provides new insights into the role of NBS-LRR genes in C. papaya and its implications for enhancing of plant disease resistance through genetic engineering.

Piriformospora indica Primes Onion Response against Stemphylium Leaf Blight Disease

The root-endophytic fungus Piriformospora indica (=Serendipita indica) has been revealed for its growth-promoting effects and its capacity to induce resistance in a broad spectrum of host plants. However, the bioefficacy of this fungus had not yet been tested against any pathogen affecting onion (Allium cepa). In this study, the biocontrol potency of P. indica against onion leaf blight, an impacting disease caused by the necrotrophic fungal pathogen Stemphylium vesicarium, was evaluated. First, it was proved that colonisation of onion roots by P. indica was beneficial for plant growth, as it increased leaf development and root biomass. Most relevantly, P. indica was also effective in reducing Stemphylium leaf blight (SLB) severity, as assessed under greenhouse conditions and confirmed in field trials in two consecutive years. These investigations could also provide some insight into the biochemical and molecular changes that treatment with P. indica induces in the main pathways associated with host defence response. It was possible to highlight the protective effect of P. indica colonisation against peroxidative damage, and its role in signalling oxidative stress, by assessing changes in malondialdehyde and H2O2 content. It was also showed that treatment with P. indica contributes to modulate the enzymatic activity of superoxide dismutase, catalase, phenylalanine ammonia-lyase and peroxidase, in the course of infection. qPCR-based expression analysis of defence-related genes AcLOX1, AcLOX2, AcPAL1, AcGST, AcCHI, AcWRKY1, and AcWRKY70 provided further indications on P. indica ability to induce onion systemic response. Based on the evidence gathered, this study aims to propose P. indica application as a sustainable tool for improving SLB control, which might not only enhance onion growth performance but also activate defence signalling mechanisms more effectively, involving different pathways.

Understanding and Exploiting Post-Translational Modifications for Plant Disease Resistance

Plants are constantly threatened by pathogens, so have evolved complex defence signalling networks to overcome pathogen attacks. Post-translational modifications (PTMs) are fundamental to plant immunity, allowing rapid and dynamic responses at the appropriate time. PTM regulation is essential; pathogen effectors often disrupt PTMs in an attempt to evade immune responses. Here, we cover the mechanisms of disease resistance to pathogens, and how growth is balanced with defence, with a focus on the essential roles of PTMs. Alteration of defence-related PTMs has the potential to fine-tune molecular interactions to produce disease-resistant crops, without trade-offs in growth and fitness.

Pathogen effector recognition-dependent association of NRG1 with EDS1 and SAG101 in TNL receptor immunity

Plants utilise intracellular nucleotide-binding, leucine-rich repeat (NLR) immune receptors to detect pathogen effectors and activate local and systemic defence. NRG1 and ADR1 “helper” NLRs (RNLs) cooperate with enhanced disease susceptibility 1 (EDS1), senescence-associated gene 101 (SAG101) and phytoalexin-deficient 4 (PAD4) lipase-like proteins to mediate signalling from TIR domain NLR receptors (TNLs). The mechanism of RNL/EDS1 family protein cooperation is not understood. Here, we present genetic and molecular evidence for exclusive EDS1/SAG101/NRG1 and EDS1/PAD4/ADR1 co-functions in TNL immunity. Using immunoprecipitation and mass spectrometry, we show effector recognition-dependent interaction of NRG1 with EDS1 and SAG101, but not PAD4. An EDS1-SAG101 complex interacts with NRG1, and EDS1-PAD4 with ADR1, in an immune-activated state. NRG1 requires an intact nucleotide-binding P-loop motif, and EDS1 a functional EP domain and its partner SAG101, for induced association and immunity. Thus, two distinct modules (NRG1/EDS1/SAG101 and ADR1/EDS1/PAD4) mediate TNL receptor defence signalling.

Pathogen effector recognition-dependent association of NRG1 with EDS1 and SAG101 in TNL receptor immunity

Plants utilise intracellular nucleotide-binding, leucine-rich repeat (NLR) immune receptors to detect pathogen effectors and activate local and systemic defence. NRG1 and ADR1 "helper" NLRs (RNLs), cooperate with enhanced disease susceptibility 1 (EDS1), senescence-associated gene 101 (SAG101) and phytoalexin-deficient 4 (PAD4) lipase-like proteins to mediate signalling from TIR domain NLR receptors (TNLs). However, the mechanism of RNL/ EDS1 family protein cooperation is poorly understood. Here, we provide genetic and molecular evidence for exclusive EDS1/SAG101/NRG1 and EDS1/PAD4/ADR1 co-functions in TNL immunity. Using immunoprecipitation and mass spectrometry, we show effector recognition dependent association of NRG1 with EDS1 and SAG101, but not PAD4. An EDS1-SAG101 complex associates with NRG1, and EDS1-PAD4 associates with ADR1, only in an immune-activated state. NRG1 requires an intact nucleotide-binding P-loop motif, and EDS1 a functional EP domain and its partner SAG101, for induced association and immunity. Thus, two distinct modules (NRG1/EDS1/SAG101 and ADR1/EDS1/PAD4) are required to execute TNL receptor defence signalling.

Author Correction: Increased insect herbivore performance under elevated CO2 is associated with lower plant defence signalling and minimal declines in nutritional quality

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Increased insect herbivore performance under elevated CO2 is associated with lower plant defence signalling and minimal declines in nutritional quality

Changes in insect herbivore performance under elevated atmosphere carbon dioxide concentrations e[CO2] are often driven by changes in the nutritional and defensive chemistry of their host plants. Studies addressing how the prolific pest cotton bollworm (Helicoverpa armigera) responds to e[CO2] show that performance usually declines, often associated with lower nutritional (e.g. nitrogen (N) concentrations) quality of host plants under e[CO2]. We investigated the impacts of e[CO2] on nutritional quality and anti-herbivore (jasmonate) defensive signalling in lucerne (Medicago sativa) when challenged by H. armigera. While foliar N decreased under e[CO2], other aspects of nutritional quality (soluble protein, amino acids, foliar C:N) were largely unaffected, potentially due to increased root nodulation under e[CO2]. In contrast, e[CO2] greatly reduced jasmonate signalling in M. sativa following H. armigera attack; jasmonic acid concentrations were ca. 56% lower in attacked plants grown under e[CO2]. Concurrent with this, relative growth rates of H. armigera were ca. 66% higher when feeding on e[CO2]-grown plants. In contrast with previous reports, which we meta-analytically summarise, we provide the first evidence that H. armigera performance can increase under e[CO2]. This may occur in plants, such as M. sativa, where e[CO2] has limited impacts on nutritional quality yet reduces jasmonate defence signalling.