Abstract
Plant disease resistance gene (R gene)-like sequences were screened from the Physcomitrella patens genome. We found 603 kinase-like, 475 Nucleotide Binding Site (NBS)-like and 8594 Leucine Rich Repeat (LRR)-like sequences by homology searching using the respective domains of PpC24 (Accession No. BAD38895), which is a candidate kinase-NBS-LRR (kinase-NL) type R-like gene, as a reference. The positions of these domains in the genome were compared and 17 kinase-NLs were predicted. We also found four TIR-NBS-LRR (TIR-NL) sequences with homology to Arabidopsis TIR-NL (NM_001125847), but three out of the four TIR-NLs had tetratricopeptide repeats or a zinc finger domain in their predicted C-terminus. We also searched for kinase-LRR (KLR) type sequences by homology with rice OsXa21 and Arabidopsis thaliana FLS2. As a result, 16 KLRs with similarity to OsXa21 were found. In phylogenetic analysis of these 16 KLRs, PpKLR36, PpKLR39, PpKLR40, and PpKLR43 formed a cluster with OsXa21. These four PpKLRs had deduced transmembrane domain sequences and expression of all four was confirmed. We also found 14 homologs of rice OsXB3, which is known to interact with OsXa21 and is involved in signal transduction. Protein–protein interaction was observed between the four PpKLRs and at least two of the XB3 homologs in Y2H analysis.
Highlights
Plants are frequently exposed to pathogens, against which they can protect themselves in several ways, e.g., specific recognition and subsequent expression of disease response genes, accumulation of antibiotics, and elimination of the pathogen and infected tissue by programmed cell death
The most abundant group comprises the Nucleotide Binding Site (NBS) and Leucine Rich Repeat (LRR) (NL) types, which are divided into groups by their N-terminal domains: Toll/interleukin-1 like receptor (TIR) or coiled coil (CC)
It was reported that Oryza sativa Xanthomonas resistance 21 (OsXa21) and OsAx21 are in the relation between so-called pattern recognition receptors (PRRs) and pathogen associated molecular patterns (PAMPs) [5]
Summary
Plants are frequently exposed to pathogens, against which they can protect themselves in several ways, e.g., specific recognition and subsequent expression of disease response genes, accumulation of antibiotics, and elimination of the pathogen and infected tissue by programmed cell death These responses are triggered by so-called disease resistance genes (R gene products). The second group is called the KLR type and has intracellular kinase, transmembrane (TM) and extracellular LRR domains. The third and fourth groups are composed only of intracellular kinases or membrane-anchored LRRs. KLR type R gene products are predicted to be receptors and the rice protein Oryza sativa Xanthomonas resistance 21 (OsXa21) is one of the best studied examples. When OsXa21 recognizes pathogens, the kinase domain may interact with OsXB3 and induce signal transduction [14]. The functions of KLRs in disease resistance are largely unclear
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