Characterization of LRP, a leucine‐rich repeat (LRR) protein from tomato plants that is processed during pathogenesis

Abstract

This paper describes the isolation and characterization of LRP, a new gene from tomato plants. The deduced amino acid sequence showed that the encoded protein is enriched in leucine, and contains interesting structural motifs. LRP contains four tandem repeats of a canonical 24 amino acid leucine-rich repeat (LRR) sequence present in different proteins that mediates molecular recognition and/or interaction processes. Genomic organization and intron-exon arrangement of LRP favor the hypothesis that the LRR domains present in LRP evolved by exon duplication and shuffling. LRP expression analysis and immunohistochemical localization studies of the encoded protein indicate that the gene is under developmental regulation exhibiting tissue-specificity, particularly in certain cell types of the stele, like phloem fibers, parenchyma cells of the protoxylem, and in the cell files that constitute the rays of the secondary xylem. It is shown that this gene is upregulated in diseased tomato plants infected with citrus exocortis viroid. However, in this pathogenic context, LRP is processed proteolytically to a lower molecular weight form by a host-induced extracellular protease. The structural characteristics of LRP, its spatio-temporal pattern of expression, and its post-translational processing during pathogenesis, suggest this protein as a candidate molecule that may mediate recognition and interaction events taking place in the plant extracellular matrix under normal and/or pathogenesis-related conditions.

The I2C family from the wilt disease resistance locus I2 belongs to the nucleotide binding, leucine-rich repeat superfamily of plant resistance genes.

“…This may indicate evolutionary processes and hint at mechanisms that generate new R gene specificities, such as duplications, unequal crossing over, or slippage during DNA replication. Analysis of the genomic organization of the disease-related LRR protein from tomatoes suggests that a duplication mechanism was involved in the evolution of LRRs (Tornero et al, 1996). LRRs have been described as being involved in many protein-protein interactions (Kobe and Deisenhofer, 1995a).…”

Functional roles of the pepper leucine-rich repeat protein and its interactions with pathogenesis-related and hypersensitive-induced proteins in plant cell death and immunity

“…R proteins recognize specific pathogen effectors and then modify their host plant targets (or decoys) to initiate strong defense responses such as ETI (Dangl et al 2013). NLR-type proteins have intracellular LRR domains that determine their cytoplasmic localization (Gururani et al 2012 Tornero et al 1996), potato StRSI7 (accession no. JQ315227; Jung et al 2004), and pepper CaLRR1 (accession no.…”

“…A number of pepper cDNAs have been isolated that appear to correspond to mRNAs that increased in abundance during avirulent Xcv strain Bv5-4a infection (Jung and Hwang 2000). The DNA sequence of CaLRR1 [accession numbers AF082727 (EST clone) and AY237117 (full-length cDNA)], which is strongly induced by pathogen infection in pepper leaves, displays high homology with the small LRR proteins SbLRR and LeLRP (Hipskind et al 1996;Tornero et al 1996). These LRRs comprise approximately 65% of the entire mature protein.…”

“…SbLRR2, OsLRR1, NtLRR2, and LeLRP are differentially induced by Colletotrichum sublineolum, X. oryzae pv. oryzae, tobacco mosaic virus, and citrus exocortis viroid, respectively (Tornero et al 1996;Xu et al 2009;Zhou et al 2009;Zhu et al 2015). However, it is not fully understood whether MAMP/PAMP molecules are required for the induction of small LRR genes in host plant cells.…”

“…Different subcellular locations of CaLRR1 play important roles in host cell death and immunity. Small LRR proteins are generally located in the plant plasma membrane, and LRR domains may be exposed to the extracellular space, which contains active components capable of regulating cell-cell interactions during development and in response to biotic or abiotic stresses (Steinmayer et al 1994;Hipskind et al 1996;Tornero et al 1996).…”