ABSTRACT
The receptor-like protein kinases (RLKs) constitute a large and diverse group of proteins controlling numerous plant physiological processes, including development, hormone perception and stress responses. The cysteine-rich RLKs (CRKs) represent a prominent subfamily of transmembrane-anchored RLKs. We have identified a putative barley (Hordeum vulgare) CRK gene family member, designated HvCRK1. The mature putative protein comprises 645 amino acids, and includes a putative receptor domain containing two characteristic 'domain 26 of unknown function' (duf26) domains in the N-terminal region, followed by a rather short 17-amino-acid transmembrane domain, which includes an AAA motif, two features characteristic of endoplasmic reticulum (ER)-targeted proteins and, finally, a characteristic putative protein kinase domain in the C-terminus. The HvCRK1 transcript was isolated from leaves inoculated with the biotrophic fungal pathogen Blumeria graminis f.sp. hordei (Bgh). HvCRK1 transcripts were observed to accumulate transiently following Bgh inoculation of susceptible barley. Transient silencing of HvCRK1 expression in bombarded epidermal cells led to enhanced resistance to Bgh, but did not affect R-gene-mediated resistance. Silencing of HvCRK1 phenocopied the effective penetration resistance found in mlo-resistant barley plants, and the possible link between HvCRK1 and MLO was substantiated by the fact that HvCRK1 induction on Bgh inoculation was dependent on Mlo. Finally, using both experimental and in silico approaches, we demonstrated that HvCRK1 localizes to the ER of barley cells. The negative effect on basal resistance against Bgh and the functional aspects of MLO- and ER-localized HvCRK1 signalling on Bgh inoculation are discussed.
Subject(s)
Ascomycota/physiology , Disease Resistance/immunology , Hordeum/microbiology , Plant Diseases/microbiology , Plant Proteins/metabolism , Protein Kinases/metabolism , Receptors, Cell Surface/metabolism , Amino Acid Sequence , Cysteine/metabolism , DNA, Complementary/genetics , DNA, Complementary/isolation & purification , Disease Resistance/drug effects , Gene Expression Regulation, Plant/drug effects , Gene Silencing/drug effects , Hordeum/drug effects , Hordeum/genetics , Hydrogen Peroxide/pharmacology , Hydrophobic and Hydrophilic Interactions/drug effects , Molecular Sequence Data , Phylogeny , Plant Diseases/genetics , Plant Diseases/immunology , Plant Leaves/drug effects , Plant Leaves/genetics , Plant Leaves/microbiology , Plant Proteins/chemistry , Plant Proteins/genetics , Protein Kinases/chemistry , Protein Kinases/genetics , Protein Structure, Tertiary , Protein Transport/drug effects , RNA, Messenger/genetics , RNA, Messenger/metabolism , Receptors, Cell Surface/chemistry , Receptors, Cell Surface/genetics , Salicylic Acid/pharmacology , Subcellular Fractions/drug effects , Subcellular Fractions/enzymologyABSTRACT
Sheath blight caused by Rhizoctonia solani (teleomorph: Thanatephorus cucumeris) is a major cause of crop loss in intensive rice production systems. No economically viable control methods have been developed. We screened aqueous extracts of common herbal plants that could reduce sheath blight lesions and found that foliar spraying and seed soaking application of extracts of either fresh or dried leaves of Chromolaena odorata gave up to 68% reduction in sheath blight lesion lengths under controlled and semi-field conditions. The observed reductions were not dependent on growth conditions of C. odorata and rice cultivar. The effect was observed until 21 days after inoculation and was not dependent on microbial activity. Under semi-field conditions, extracts also reduced severity of other important rice diseases, i.e., blast (Pyricularia oryzae) using foliar spray (up to 45%), brown spot (Bipolaris oryzae) using seed treatment (up to 57%), and bacterial blight (Xanthomonas oryzae pv. oryzae) using both application methods (up to 50%).