Increasing the resilience of plant immunity to a warming climate

Extreme weather conditions associated with climate change affect many aspects of plant and animal life, including the response to infectious diseases. Production of salicylic acid (SA), a central plant defence hormone, is particularly vulnerable to suppression by short periods of hot weather above the normal plant growth temperature range via an unknown mechanism. Here we show that suppression of SA production in Arabidopsis thaliana at 28 °C is independent of PHYTOCHROME B (phyB) and EARLY FLOWERING 3 (ELF3), which regulate thermo-responsive plant growth and development. Instead, we found that formation of GUANYLATE BINDING PROTEIN-LIKE 3 (GBPL3) defence-activated biomolecular condensates (GDACs) was reduced at the higher growth temperature. The altered GDAC formation in vivo is linked to impaired recruitment of GBPL3 and SA-associated Mediator subunits to the promoters of CBP60g and SARD1, which encode master immune transcription factors. Unlike many other SA signalling components, including the SA receptor and biosynthetic genes, optimized CBP60g expression was sufficient to broadly restore SA production, basal immunity and effector-triggered immunity at the elevated growth temperature without significant growth trade-offs. CBP60g family transcription factors are widely conserved in plants. These results have implications for safeguarding the plant immune system as well as understanding the concept of the plant–pathogen–environment disease triangle and the emergence of new disease epidemics in a warming climate

Bacteria establish an aqueous living space in plants crucial for virulence

High humidity has a strong influence on the development of numerous diseases affecting the above-ground parts of plants (the phyllosphere) in crop fields and natural ecosystems, but the molecular basis of this humidity effect is not understood. Previous studies have emphasized immune suppression as a key step in bacterial pathogenesis. Here we show that humidity-dependent, pathogen-driven establishment of an aqueous intercellular space (apoplast) is another important step in bacterial infection of the phyllosphere. Bacterial effectors, such as Pseudomonas syringae HopM1, induce establishment of the aqueous apoplast and are sufficient to transform non-pathogenic P. syringae strains into virulent pathogens in immunodeficient Arabidopsis thaliana under high humidity. Arabidopsis quadruple mutants simultaneously defective in a host target (AtMIN7) of HopM1 and in pattern-triggered immunity could not only be used to reconstitute the basic features of bacterial infection, but also exhibited humidity-dependent dyshomeostasis of the endophytic commensal bacterial community in the phyllosphere. These results highlight a new conceptual framework for understanding diverse phyllosphere–bacterial interactions

Pseudomonas syringae pv. tomato DC3000 HopPtoM (CEL ORF3) is important for lesion formation but not growth in tomato and is secreted and translocated by the Hrp type III secretion system in a chaperone-dependent manner. Mol Microbiol 49

Summary Pseudomonas syringae pv. tomato DC3000 is a pathogen of tomato and Arabidopsis that injects virulence effector proteins into host cells via a type III secretion system (TTSS). TTSS-deficient mutants have a Hrp D hopPtoM :: nptII mutant was constructed and found to grow like the wild type in tomato but to be strongly reduced in its production of necrotic lesion symptoms. HopPtoM expression in DC3000 was activated by the HrpL alternative sigma factor, and the protein was secreted by the Hrp TTSS in culture and translocated into Arabidopsis cells by the Hrp TTSS during infection. Secretion and translocation were dependent on ShcM, which was neither secreted nor translocated but, like typical TTSS chaperones, could be shown to interact with HopPtoM, its cognate effector, in yeast twohybrid experiments. Thus, HopPtoM is a type III effector that, among known plant pathogen effectors, is unusual in making a major contribution to the elicitation of lesion symptoms but not growth in host tomato leaves

MOESM1 of Leucine-rich-repeat-containing variable lymphocyte receptors as modules to target plant-expressed proteins

Additional file 1: Figure S1. Production of VLRB antibodies after HopM11–300 immunization in lampreys. ELISA results for VLRB production from dilutions of plasma from three lampreys immunized with HopM11–300 conjugated to Jurkat T cells and a control non-immunized lamprey (naïve). Binding of VLRBs to HopM11–300-coated plates was detected with a mouse monoclonal antibody and an alkaline peroxidase-conjugated goat α-mouse IgG polyclonal antibody. Absorbance at 405 nm (A405) was measured 30 min after addition of an alkaline peroxidase substrate. Lamprey-1 showed the highest response to HopM11–300. Figure S2. VLRBs can be targeted to intracellular compartments. Visualization of intracellular accumulation of YFP, syntaxin SYP61 (At1g28490), and VLRM1 fused to SYP61 in N. benthamiana. Images were taken with the Olympus IX71 inverted microscope using the YFP filter (excitation 500/24, emission 542/27). White bar length represents 50 µm. Image brightness increased 15% for YFP, and 20% for the other 2 images. Notice how the YFP fluorescence pattern is similar for SYP61 (which localizes to the early endosome/trans-Golgi network) [34, 37] and for VLRM1-SYP61. Figure S3. In planta interaction of HopM1 with VLRM1. Co-immunoprecipitation (co-IP) of HopM1 and its corresponding VLR in Nicotiana benthamiana. Interactions between HopM1 and VLRM1 were tested with both proteins fused to 2 different epitope tags (HA and c-Myc). Highlighted in orange are those proteins detected in the Western blot, while in black are those proteins also expressed but not detected. As negative controls for the co-immunoprecipitations, different proteins that had low or no expression were co-expressed with HopM1 or VLRM1 (data not shown). No reducing agents were used in the buffers. Abbreviations used: VLRM1 = SP-VLRM1, and M1–300 = SP-HopM11–300. a Total protein input of HA and c-Myc tagged proteins. Proteins were detected with α-HA and α-c-Myc antibodies, respectively. Ponceau S staining of the PVDF membrane is shown below the Western blot image. b Immunoprecipitation (IP) using α-HA agarose beads. The IP (α-HA antibodies) and co-IP (α-c-Myc antibodies) Western blots are shown. c Reciprocal immunoprecipitation using α-c-Myc agarose beads. The IP (α-c-Myc antibodies) and co-IP (α-HA antibodies) Western blots are shown. Figure S4. Hypothetical modifications to VLRs to diversify their in planta use. Abbreviations used: NBS = nucleotide-binding site, RLK = receptor-like kinase, RLP = receptor-like protein, and VLR = variable lymphocyte receptor

MOESM2 of Leucine-rich-repeat-containing variable lymphocyte receptors as modules to target plant-expressed proteins

Additional file 2: Table S1. Strains used in this study. Table S2. Primers used in this study