Summary: We identified a wheat stripe rust (Puccinia striiformis) effector candidate (PEC6) with pattern‐triggered immunity (PTI) suppression function and its corresponding host target. PEC6 compromised PTI host species‐independently. In Nicotiana benthamiana, it hampers reactive oxygen species (ROS) accumulation and callose deposition induced by Pseudomonas fluorescens. In Arabidopsis, plants expressing PEC6 were more susceptible to Pseudomonas syringae pv. tomato (Pto) DC3000 ΔAvrPto/ΔAvrPtoB. In wheat, PEC6‐suppression of P. fluorescens‐elicited PTI was revealed by the fact that it allowed activation of effector‐triggered immunity by Pto DC3000. Knocking down of PEC6 expression by virus‐mediated host‐induced gene silencing decreased the number of rust pustules, uncovering PEC6 as an important pathogenicity factor. PEC6, overexpressed in plant cells without its signal peptide, was localized to the nucleus and cytoplasm. A yeast two‐hybrid assay showed that PEC6 interacts with both wheat and Arabidopsis adenosine kinases (ADKs). Knocking down wheat ADK expression by virus‐induced gene silencing reduced leaf growth and enhanced the number of rust pustules, indicating that ADK is important in plant development and defence. ADK plays essential roles in regulating metabolism, cytokinin interconversion and methyl transfer reactions, and our data propose a model where PEC6 may affect one of these processes by targeting ADK to favour fungal growth.

Plasma membrane (PM) H⁺-ATPases are the electrogenic proton pumps that export H⁺ from plant and fungal cells to acidify the surroundings and generate a membrane potential. Plant PM H⁺-ATPases are equipped with a C‑terminal autoinhibitory regulatory (R) domain of about 100 amino acid residues, which could not be identified in the PM H⁺-ATPases of green algae but appeared fully developed in immediate streptophyte algal predecessors of land plants. To explore the physiological significance of this domain, we created in vivo C-terminal truncations of autoinhibited PM H⁺‑ATPase2 (AHA2), one of the two major isoforms in the land plant Arabidopsis thaliana. As more residues were deleted, the mutant plants became progressively more efficient in proton extrusion, concomitant with increased expansion growth and nutrient uptake. However, as the hyperactivated AHA2 also contributed to stomatal pore opening, which provides an exit pathway for water and an entrance pathway for pests, the mutant plants were more susceptible to biotic and abiotic stresses, pathogen invasion and water loss, respectively. Taken together, our results demonstrate that pump regulation through the R domain is crucial for land plant fitness and by controlling growth and nutrient uptake might have been necessary already for the successful water-to-land transition of plants.

Antibiosis is a key feature widely exploited to develop biofungicides based on the ability of biological control agents (BCAs) to produce fungitoxic compounds. A less recognised attribute of plant-associated beneficial microorganisms is their ability to stimulate the plant immune system, which may provide long-term, systemic self-protection against different types of pathogens. By using conventional antifungal in vitro screening coupled with in planta assays, we found antifungal and non-antifungal Bacillus strains that protected the ornamental plant Kalanchoe against the soil-borne pathogen Fusarium oxysporum in experimental and commercial production settings. Further examination of one antifungal and one non-antifungal strain indicated that high protection efficacy in planta did not correlate with antifungal activity in vitro. Whole-genome sequencing showed that the non-antifungal strain EC9 lacked the biosynthetic gene clusters associated with typical antimicrobial compounds. Instead, this bacterium triggers the expression of marker genes for the jasmonic and salicylic acid defence pathways, but only after pathogen challenge, indicating that this strain may protect Kalanchoe plants by priming immunity. We suggest that the stimulation of the plant immune system is a promising mode of action of BCAs for the development of novel biological crop protection products.

Maize rayado fino marafivirus (MRFV) was mechanically transmitted to kernels of three Costa Rican maize cultivars by the vascular puncture technique. A transmission rate of up to 43.2% was obtained for cultivar HC‐57. The rate of MRFV transmission to maize was possibly affected by the morphology of the kernel, which may influence physical access to the vascular tissue after water imbibition. Transmission to maize was confirmed by western blot and immunosorbent electron microscopy. By slight modifications of the procedure, MRFV was also transmitted to barley. This is the first report of MRFV infecting a species outside the supertribe Andropogonodae. Virus infection and replication in barley were confirmed by RT‐PCR detection of MRFV RNA and by detection of the virus by ELISA.