Journal Article

PIRLs: A Novel Class of Plant Intracellular Leucine-rich Repeat Proteins

Nancy R. Forsthoefel, Kerry Cutler, Martha D. Port, Tori Yamamoto and Daniel M. Vernon

in Plant and Cell Physiology

Published on behalf of Japanese Society of Plant Physiologists

Volume 46, issue 6, pages 913-922
Published in print June 2005 | ISSN: 0032-0781
Published online June 2005 | e-ISSN: 1471-9053 | DOI:
PIRLs: A Novel Class of Plant Intracellular Leucine-rich Repeat Proteins

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  • Biochemistry
  • Molecular and Cell Biology
  • Plant Sciences and Forestry


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Leucine-rich repeat (LRR) proteins feature tandem leucine-rich motifs that form a protein–protein interaction domain. Plants contain diverse classes of LRR proteins, many of which take part in signal transduction. We have identified a novel family of nine Arabidopsis LRR proteins that, based on predicted intracellular location and LRR motif consensus sequence, are related to Ras-binding LRR proteins found in signaling complexes in animals and yeast. This new class has been named plant intracellular Ras group-related LRR proteins (PIRLs). We have characterized PIRL cDNAs, rigorously defined gene and protein annotations, investigated gene family evolution and surveyed mRNA expression. While LRR regions suggested a relationship to Ras group LRR proteins, outside of their LRR domains PIRLs differed from Ras group proteins, exhibiting N- and C-terminal regions containing low complexity stretches and clusters of charged amino acids. PIRL genes grouped into three subfamilies based on sequence relationships and gene structures. Related gene pairs and dispersed chromosomal locations suggested family expansion by ancestral genomic or segmental duplications. Expression surveys revealed that all PIRL mRNAs are actively transcribed, with three expressed differentially in leaves, roots or flowers. These results define PIRLs as a distinct, plant-specific class of intracellular LRR proteins that probably mediate protein interactions, possibly in the context of signal transduction. T-DNA knock-out mutants have been isolated as a starting point for systematic functional analysis of this intriguing family.

Keywords: Arabidopsis thaliana; G-proteins; Gene knockouts; Leucine-rich repeats; Linker protein; Signal transduction; EST, expressed sequence tag; LRR, leucine-rich repeat; NBS-LRR, nucleotide-binding site-LRR; PGIP, polygalacturonase inhibitor protein; PIRL, plant intracellular Ras group-related LRR; RACE, rapid amplification of cDNA ends; RT–PCR, reverse transcription–polymerase chain reacion

Journal Article.  7301 words.  Illustrated.

Subjects: Biochemistry ; Molecular and Cell Biology ; Plant Sciences and Forestry

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