Abstract
Bri1-associated kinase 1 (BAK1)-interacting receptor-like kinase (BIR) proteins have been shown to play important roles in regulating growth and development, pathogen associated molecular pattern (PAMP)-triggered immunity (PTI) responses, and cell death in the model plant, Arabidopsis thaliana. We identified four BIR family members in tomato (Solanum lycopersicum), including SlBIR3, an ortholog of AtBIR3 from A. thaliana. SlBIR3 is predicted to encode a membrane localized non-arginine-aspartate (non-RD) kinase that, based on protein sequence, does not have autophosphorylation activity but that can be phosphorylated in vivo. We established that SlBIR3 interacts with SlBAK1 and AtBAK1 using yeast two-hybrid assays and co-immunoprecipitation and maltose-binding protein pull down assays. We observed that SlBIR3 overexpression in tomato (cv. micro-tom) and A. thaliana has weak effect on growth and development through brassinosteroid (BR) signaling. SlBIR3 overexpression in A. thaliana suppressed flg22-induced defense responses, but did not affect infection with the bacterial pathogen Pseudomonas syringae (PstDC3000). This result was confirmed using virus-induced gene silencing (VIGS) in tomato in conjunction with PstDC3000 infection. Overexpression of SlBIR3 in tomato (cv. micro-tom) and A. thaliana resulted in enhanced susceptibility to the necrotrophic fungus Botrytis cinerea. In addition, co-silencing SlBIR3 with SlSERK3A or SlSERK3B using VIGS and the tobacco rattle virus (TRV)-RNA2 vector containing fragments of both the SlSERK3 and SlBIR3 genes induced spontaneous cell death, indicating a cooperation between the two proteins in this process. In conclusion, our study revealed that SlBIR3 is the ortholog of AtBIR3 and that it participates in BR, PTI, and cell death signaling pathways.
Highlights
Plants are often subjected to various adverse environmental conditions during their entire life cycle, which are detrimental to growth and development [1,2,3,4]
To clone the ortholog of A. thaliana AtBIR3 from tomato, a basic local alignment search tool (BLAST) search was conducted amongst the protein sequences released with the tomato genome (ITAG release 3.10) database, using the AtBIR3 amino acid sequence as a query
Phylogenetic analysis showed Solyc02g067560.1.1 and Solyc02g087460.1.1 clustered together with AtBIR2, and Solyc05g006570.1.1 aligned within the same clade as AtBIR3 and AtBIR4 (Figure S2), suggesting that the closest ortholog of AtBIR3 in tomato is Solyc05g006570.1.1, which we renamed SlBIR3
Summary
Plants are often subjected to various adverse environmental conditions during their entire life cycle, which are detrimental to growth and development [1,2,3,4]. Response mechanisms include leucine-rich repeats receptor-like protein kinases (LRR-RLKs), the largest subgroup of the receptor-like protein kinase (RLKs) family in plants, which play vital roles in transmitting extracellular environmental stimuli to intracellular chemical signals [5,6,7]. Typical LRR-RLKs are composed of an extracellular leucine-rich repeat domain that senses a specific external environmental stimulus, a single-pass transmembrane domain that localizes the protein to the plasma membrane and an intracellular domain that relays the downstream intracellular signal via a sequential phosphorylation mechanism [8,9,10]. The non-RD kinases are usually associated with plant innate immunity signaling [15]
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