Abstract
In Arabidopsis, several L-type lectin receptor kinases (LecRKs) have been identified as putative immune receptors. However, to date, there have been few analyses of LecRKs in crop plants. Virus-induced gene silencing of CaLecRK-S.5 verified the role of CaLecRK-S.5 in broad-spectrum resistance. Compared with control plants, CaLecRK-S.5-silenced plants showed reduced hypersensitive response, reactive oxygen species burst, secondary metabolite production, mitogen-activated protein kinase activation, and defense-related gene expression in response to Tobacco mosaic virus pathotype P0 (TMV-P0) infection. Suppression of CaLecRK-S.5 expression significantly enhanced the susceptibility to Pepper mild mottle virus pathotype P1,2,3, Xanthomonas campestris pv. vesicatoria, Phytophthora capsici, as well as TMV-P0 Additionally, β-aminobutyric acid treatment and a systemic acquired resistance assay revealed that CaLecRK-S.5 is involved in priming of plant immunity. Pre-treatment with β-aminobutyric acid before viral infection restored the reduced disease resistance phenotypes shown in CaLecRK-S.5-silenced plants. Systemic acquired resistance was also abolished in CaLecRK-S.5-silenced plants. Finally, RNA sequencing analysis indicated that CaLecRK-S.5 positively regulates plant immunity at the transcriptional level. Altogether, these results suggest that CaLecRK-S.5-mediated broad-spectrum resistance is associated with the regulation of priming.
Highlights
Plants are constantly threatened by a broad spectrum of pathogens in nature
CaLecRK-S.5 shared 90%, 91%, 89%, and 60% amino acid identity at the protein level with SlLecRK-S.5, StLecRK-S.5, NbLecRK-S.5, and AtLecRK-S.5, respectively (Supplementary Fig. S2A). These results suggested that the PEPPERS0010681 gene encodes an L-type lectin receptor kinase protein, CaLecRK-S.5, that harbors a transmembrane domain (TM) domain like other pattern recognition receptor (PRR) and that its transcription is induced by Tobacco mosaic virus pathotype P0 (TMV-P0) infection
One of the emerging examples of inducible lectin receptor kinases with a role as PRR in the immune response is a lectin S-domain receptor kinase, which mediates lipopolysaccharide sensing in Arabidopsis (Ranf et al, 2015)
Summary
Plants are constantly threatened by a broad spectrum of pathogens in nature. To survive in the presence of these pathogens, they have evolved multilayered immune systems that recognize pathogens at various infection stages. The first layer of plant immunity, referred to as pattern-triggered immunity (PTI), relies on the detection of pathogen-associated molecular patterns (PAMPs) by cell surface-localized pattern recognition receptors (PRRs). Successful pathogens have evolved the ability to avoid or subvert PTI by secretion of effector proteins to the apoplast or into the plant cells. The two layers of immunity share common defense mechanisms such as reactive oxygen species (ROS) burst, activation of mitogen-activated protein kinase (MAPK) cascades, biosynthesis of antimicrobial metabolites, trigger of transcriptional reprogramming, and in some cases, hypersensitive response (HR) in infected cells (Lorrain et al, 2003; Boller and Felix, 2009; Tsuda and Katagiri, 2010; Segonzac et al, 2011)
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