title: SOBIR1 requires the GxxxG dimerization motif in its transmembrane domain to form constitutive complexes with receptor-like proteins.
abstract: Receptor-like proteins (RLPs), forming an important group of transmembrane receptors in plants, play roles in development and immunity. RLPs contain extracellular leucine-rich repeats (LRRs) and, in contrast with receptor-like kinases (RLKs), lack a cytoplasmic kinase required for the initiation of downstream signalling. Recent studies have revealed that the RLK SOBIR1/EVR (SUPPRESSOR OF BIR1-1/EVERSHED) specifically interacts with RLPs. SOBIR1 stabilizes RLPs and is required for their function. However, the mechanism by which SOBIR1 associates with RLPs and regulates RLP function remains unknown. The Cf immune receptors of tomato (Solanum lycopersicum), mediating resistance to the fungus Cladosporium fulvum, are RLPs that also interact with SOBIR1. Here, we show that both the LRR and kinase domain of SOBIR1 are dispensable for association with the RLP Cf-4, whereas the highly conserved GxxxGxxxG motif present in the transmembrane domain of SOBIR1 is essential for its interaction with Cf-4 and additional RLPs. Complementation assays in Nicotiana benthamiana, in which endogenous SOBIR1 levels were knocked down by virus-induced gene silencing, showed that the LRR domain as well as the kinase activity of SOBIR1 are required for the Cf-4/Avr4-triggered hypersensitive response (HR). In contrast, the LRRs and kinase activity of SOBIR1 are not required for facilitation of Cf-4 accumulation. Together, these results suggest that, in addition to being a stabilizing scaffold for RLPs, SOBIR1 is also required for the initiation of downstream signalling through its kinase domain.
authors.affiliation: College of Horticulture, Northeast Agricultural University, Harbin, 150030, China.|Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands.
authors.forename: Guozhi
authors.initials: G
authors.lastname: Bi
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands.
authors.forename: Thomas W H
authors.initials: TW
authors.lastname: Liebrand
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands.
authors.forename: Ruby R
authors.initials: RR
authors.lastname: Bye
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, NR4 7UH, UK.
authors.forename: Jelle
authors.initials: J
authors.lastname: Postma
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands.
authors.forename: Aranka M
authors.initials: AM
authors.lastname: van der Burgh
authors.affiliation: The Sainsbury Laboratory, Norwich Research Park, Norwich, NR4 7UH, UK.
authors.forename: Silke
authors.initials: S
authors.lastname: Robatzek
authors.affiliation: College of Horticulture, Northeast Agricultural University, Harbin, 150030, China.
authors.forename: Xiangyang
authors.initials: X
authors.lastname: Xu
authors.affiliation: Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands.
authors.forename: Matthieu H A J
authors.initials: MH
authors.lastname: Joosten
mesh_terms: D020816:Amino Acid Motifs; D000595:Amino Acid Sequence; D008969:Molecular Sequence Data; D046912:Multiprotein Complexes / Q000378:metabolism*; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry* / Q000378:metabolism*; D030821:Plants, Genetically Modified; D011485:Protein Binding; D055503:Protein Multimerization; D017434:Protein Structure, Tertiary; D017386:Sequence Homology, Amino Acid; D013329:Structure-Activity Relationship; D014026:Nicotiana / Q000821:virology
chemical_list: D046912:Multiprotein Complexes; D010940:Plant Proteins
keywords: SOBIR1; defence signalling; development; plant immunity; receptor complex; receptor-like kinase (RLK); receptor-like protein (RLP)