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

Abstract

Crops experience herbivory by arthropods and microbial infections. In the interaction between plants and chewing herbivores, lepidopteran larval oral secretions (OS) and plant-derived damage-associated molecular patterns (DAMPs) trigger plant defense responses. However, the mechanisms underlying anti-herbivore defense, especially in monocots, have not been elucidated. The receptor-like cytoplasmic kinase Broad-Spectrum Resistance 1 (BSR1) of Oryza sativa L. (rice) mediates cytoplasmic defense signaling in response to microbial pathogens and enhances disease resistance when overexpressed. Here, we investigated whether BSR1 contributes to anti-herbivore defense responses. BSR1 knockout suppressed rice responses triggered by OS from the chewing herbivore Mythimna loreyi Duponchel (Lepidoptera: Noctuidae) and peptidic DAMPs OsPeps, including the activation of genes required for biosynthesis of diterpenoid phytoalexins (DPs). BSR1-overexpressing rice plants exhibited hyperactivation of DP accumulation and ethylene signaling after treatment with simulated herbivory and acquired enhanced resistance to larval feeding. As the biological significance of herbivory-induced accumulation of rice DPs remains unexplained, their physiological activities in M. loreyi were analyzed. The addition of momilactone B, a rice DP, to the artificial diet suppressed the growth of M. loreyi larvae. Altogether, this study revealed that BSR1 and herbivory-induced rice DPs are involved in the defense against chewing insects, in addition to pathogens.

Improvement of Broad-Spectrum Disease-Resistant Rice by the Overexpression of BSR1 via a Moderate-Strength Constitutive Promoter and a Pathogen-Inducible Promoter

“…We have previously reported that BSR1 is involved in chitin-, peptidoglycan-, and lipopolysaccharide-triggered ROS production and defense responses and ROS production is enhanced in BSR1 -OX rice [ 14 , 16 ]. Furthermore, it has been reported that BSR1 is involved in plant responses to OsPeps and damage-associated molecular patterns (DAMPs), and these responses are enhanced in BSR1 -OX rice [ 17 ]. Thus, the browning observed at the pathogen infection may be caused by cell death due to excessive ROS production by the recognition of microbe-associated molecular patterns (MAMPs) or DAMPs.…”

“…Recently, P OsUbi7 - BSR1 rice was also reported to confer resistance to the chewing herbivore Mythimna loreyi Duponchel (Lepodoptera: Noctuidae), a rice pest [ 17 ]. As described above, by optimizing the expression level of BSR1 using a suitable promoter such as OsUbi7 , we were able to generate rice plants with BSR to four major diseases and one pest while minimizing the adverse effects of overexpression.…”

“…Construction of the P OsUbi7 -BSR1 plasmid and generation of P OsUbi7 -BSR1 rice lines have been previously reported briefly [17]. In detail, the BSR1 cDNA was amplified by PCR using the following primers: 5 ′ -GCAAAAGAAGAAGCTGTGCGTGCGTGCGTGCTTGC-3 ′ and 5 ′ -TGATTTCAGCGGATCTGCTCTCTGTGTCTCTCTTT-3 ′ .…”

“…BSR1 is an SNS BSR gene, and the BSR1 protein (OsRLCK278) is classified in the RLCK-VII protein family as BIK1 [ 11 ], PBL19, and PBL20 [ 12 ], which are well known to encode receptor-like cytoplasmic kinases (RLCKs) involved in providing disease resistance in Arabidopsis [ 13 ]. We have previously reported the disease resistance mechanism of BSR1 [ 14 , 15 , 16 , 17 ].…”

Signaling of Plant Defense Mediated by Receptor-like Kinases, Receptor-like Cytoplasmic Protein Kinases and MAPKs Triggered by Fungal Chitin in Horticultural Crops

“…Despite lacking an extracellular or transmembrane domain, RLCKs possess a serine and threonine protein kinase intracellular domain. This domain consists of 11 kinase subdomains (I to XI), which are highly preserved, in addition to a small C-end region and a brief N-end region [59,60]. The serine and threonine (Ser/Thr) motifs of the intracellular domain of RLCK proteins have been shown to be essential in interacting with these receptors [40].…”