Overexpressed BSR1-Mediated Enhancement of Disease Resistance Depends on the MAMP-Recognition System

Abstract

Plant plasma membrane-localized receptors recognize microbe-associated molecular patterns (MAMPs) and activate immune responses via various signaling pathways. Receptor-like cytoplasmic kinases (RLCKs) are considered key signaling factors in plant immunity. BROAD-SPECTRUM RESISTANCE 1 (BSR1), a rice RLCK, plays a significant role in disease resistance. Overexpression of BSR1 confers strong resistance against fungal and bacterial pathogens. Our recent study revealed that MAMP-triggered immune responses are mediated by BSR1 in wild-type rice and are hyperactivated in BSR1-overexpressing rice. It was suggested that hyperactivated immune responses were responsible for the enhancement of broad-spectrum disease resistance; however, this remained to be experimentally validated. In this study, we verified the above hypothesis by disrupting the MAMP-recognition system in BSR1-overexpressing rice. To this end, we knocked out OsCERK1, which encodes a well-characterized MAMP-receptor-like protein kinase. In the background of BSR1 overaccumulation, the knockout of OsCERK1 nearly abolished the enhancement of blast resistance. This finding indicates that overexpressed BSR1-mediated enhancement of disease resistance depends on the MAMP-triggered immune system, corroborating our previously suggested model.

Enhanced Resistance to Fungal and Bacterial Diseases Due to Overexpression of BSR1, a Rice RLCK, in Sugarcane, Tomato, and Torenia

“…We reported that BSR1 plays a role in chitin-, peptidoglycan-, and lipopolysaccharide-triggered defense responses and promotes reactive oxygen species (ROS) production [ 15 , 16 ]. In addition, OsCERK1, a hub-RLK, is necessary for enhanced PTI response and blast resistance by BSR1 overexpression [ 17 ]. Hence, BSR1 plays a major regulatory role in various MAMP-induced PTI responses under OsCERK1 in rice.…”

BSR1, a Rice Receptor-like Cytoplasmic Kinase, Positively Regulates Defense Responses to Herbivory

“…OsPep3 and OsPep4 were purchased from Pepmic (Suzhou, China) following custom synthesis. H 2 O 2 concentration was measured at the indicated times using a previously described luminol-dependent chemiluminescence assay using luminol (Nacalai Tesque, Kyoto, Japan) and a TD-20/20 luminometer (Turner Designs, San Jose, CA, USA) [ 35 , 69 , 71 ]. A standard curve was constructed to calculate the concentration of H 2 O 2 .…”

Recent Progress in Rice Broad-Spectrum Disease Resistance

“…Defense regulator genes are different from pathogen-specific R genes, which can confer resistance to multiple pathogens. For instance, Lysin motif-containing protein genes LYP4 and LYP6 , transcriptional regulator genes OsWRKY67 and IPA1 , the host basal transcription factor IIA subunit genes OsTFIIA α and OsTFIIA β, germin-like protein gene OsGLP2 -1, sucrose nonfermenting 1-related protein kinase 1 genes OsSnRK1a and OsSnRK1b / OSK35 , calcium-dependent protein kinase gene OsCPK4 , and receptor-like cytoplasmic kinase gene broad-spectrum resistance 1 (BSR1) play a positive role in basal resistance against M. oryzae and Xoo [ 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 ]. In contrast, mutations in E3 ubiquitin ligase gene EBR1 (enhanced blight and blast resistance 1), RhoGAP SPIN6 , rice wall-associated kinase gene OsWAK25 , Cullin 3-based RING E3 ligase gene OsCUL3a , dynamin-related protein gene OsDRP1E , eEF1A-like protein gene SPL33 , eukaryotic translation elongation factor 1A-like genes LMM5 .1 and LMM5 .4, eukaryotic release factor 1 gene LMM1 , abscisic acid 2 (OsABA2) , and CUE domain-containing protein gene SPL35 result in lesion mimic leaves and enhanced broad-spectrum resistance to M. oryzae and Xoo [ 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 ].…”