Abstract
Pattern recognition receptors (PRRs) belonging to the multigene family of receptor-like kinases (RLKs) are the sensing devices of plants for microbe- or pathogen-associated molecular patterns released from microbial organisms. Here we describe Rnr8 (for Required for non-host resistance 8) encoding HvLEMK1, a LRR-malectin domain-containing transmembrane RLK that mediates non-host resistance of barley to the non-adapted wheat powdery mildew fungus Blumeria graminis f.sp. tritici. Transgenic barley lines with silenced HvLEMK1 allow entry and colony growth of the non-adapted pathogen, although sporulation was reduced and final colony size did not reach that of the adapted barley powdery mildew fungus B. graminis f.sp. hordei. Transient expression of the barley or wheat LEMK1 genes enhanced resistance in wheat to the adapted wheat powdery mildew fungus while expression of the same genes did not protect barley from attack by the barley powdery mildew fungus. The results suggest that HvLEMK1 is a factor mediating non-host resistance in barley and quantitative host resistance in wheat to the wheat powdery mildew fungus.
Highlights
Plants recognize interacting beneficial or parasitic organisms via pathogen recognition receptors (PRRs) belonging to the highly complex and functionally diversified superfamily of receptorlike kinases (RLKs) that are involved in plant development and abiotic-stress signaling (Macho and Zipfel, 2014)
Transient silencing of HvLEMK1 was reported to weaken non-host resistance of barley to the wheat powdery mildew fungus B. graminis f.sp. tritici (Bgt), and we searched for the presence of an orthologous protein in wheat, which is the natural host for Bgt (Douchkov et al, 2014)
Because some of the nonTriticum plant species are not infected by any known powdery mildew fungus, HvLEMK1 might function in sensing stressrelated endogenous signals or highly conserved pathogenassociated molecular patterns (PAMPs) present in different pathogens, or act as co-receptor in RLK complexes
Summary
Plants recognize interacting beneficial or parasitic organisms via pathogen recognition receptors (PRRs) belonging to the highly complex and functionally diversified superfamily of receptorlike kinases (RLKs) that are involved in plant development and abiotic-stress signaling (Macho and Zipfel, 2014). RLKs typically contain extracellular ligand-binding, transmembrane and cytoplasmic kinase domains. They are grouped into several sub-families depending on the presence of specific sequence motifs in their extracellular ligand binding domain, including leucine-rich repeats (LRRs), LysM, lectin-like, cysteine-rich or malectin domains, most of which bind to a corresponding class of ligands. Upon ligand binding and activation, RLKs phosphorylate themselves or substrate proteins, which triggers signaling cascades such as the interacting mitogen-associated protein kinase kinase kinases cascade and leads to the execution of developmental or defense-related programs including the PAMP-triggered immunity (PTI) pathway (Jones and Dangl, 2006). One of the preferred models for the efficiency and durability of non-host resistance states that, after host speciation, lack of co-evolution leads to gradual erosion of effector functionality in terms of their capacity to manipulate factors for defense or pathogen accommodation of previous host(s)
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