title: A family of small cyclic amphipathic peptides (SCAmpPs) genes in citrus.
abstract: BACKGROUND
  Citrus represents a crop of global importance both in economic impact and significance to nutrition. Citrus production worldwide is threatened by the disease Huanglongbing (HLB), caused by the phloem-limited pathogen Candidatus Liberibacter spp.. As a source of stable HLB-resistance has yet to be identified, there is considerable interest in characterization of novel disease-associated citrus genes.
  
  
  RESULTS
  A gene family of Small Cyclic Amphipathic Peptides (SCAmpPs) in citrus is described. The citrus genomes contain 100-150 SCAmpPs genes, approximately 50 of which are represented in the citrus EST database. These genes encode small ~50 residue precursor proteins that are post-translationally processed, releasing 5-10 residue cyclic peptides. The structures of the SCAmpPs genes are highly conserved, with the small coding domains interrupted by a single intron and relatively extended untranslated regions. Some family members are very highly transcribed in specific citrus tissues, as determined by representation in tissue-specific cDNA libraries. Comparison of the ESTs of related SCAmpPs revealed an unexpected evolutionary profile, consistent with targeted mutagenesis of the predicted cyclic peptide domain. The SCAmpPs genes are displayed in clusters on the citrus chromosomes, with apparent association with receptor leucine-rich repeat protein arrays. This study focused on three SCAmpPs family members with high constitutive expression in citrus phloem. Unexpectedly high sequence conservation was observed in the promoter region of two phloem-expressed SCAmpPs that encode very distinct predicted cyclic products. The processed cyclic product of one of these phloem SCAmpPs was characterized by LC-MS-MS analysis of phloem tissue, revealing properties consistent with a K(+) ionophore.
  
  
  CONCLUSIONS
  The SCAmpPs amino acid composition, protein structure, expression patterns, evolutionary profile and chromosomal distribution are consistent with designation as ribosomally synthesized defense-related peptides.
authors.affiliation: USDA-ARS, Western Regional Research Center, Albany, CA, USA. william.belknap@ars.usda.gov.
authors.forename: William R
authors.initials: WR
authors.lastname: Belknap
authors.affiliation: USDA-ARS, Western Regional Research Center, Albany, CA, USA. kent.mccue@ars.usda.gov.
authors.forename: Kent F
authors.initials: KF
authors.lastname: McCue
authors.affiliation: USDA-ARS, Western Regional Research Center, Albany, CA, USA. leslie.harden@ars.usda.gov.
authors.forename: Leslie A
authors.initials: LA
authors.lastname: Harden
authors.affiliation: USDA-ARS, Western Regional Research Center, Albany, CA, USA. william.vensel@ars.usda.gov.
authors.forename: William H
authors.initials: WH
authors.lastname: Vensel
authors.affiliation: USDA-ARS, U. S. Horticultural Research Laboratory, Fort Pierce, FL, USA. michael.bausher@ars.usda.gov.
authors.forename: Michael G
authors.initials: MG
authors.lastname: Bausher
authors.affiliation: USDA-ARS, U. S. Horticultural Research Laboratory, Fort Pierce, FL, USA. ed.stover@ars.usda.gov.
authors.forename: Ed
authors.initials: E
authors.lastname: Stover
mesh_terms: D000595:Amino Acid Sequence; D002851:Chromatography, High Pressure Liquid; D002957:Citrus / Q000235:genetics*; D030541:Databases, Genetic; D020224:Expressed Sequence Tags; D017343:Genes, Plant; D000090263:Leucine-Rich Repeat Proteins; D013058:Mass Spectrometry; D008969:Molecular Sequence Data; D010456:Peptides, Cyclic / Q000032:analysis / Q000235:genetics* / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment
chemical_list: D000090263:Leucine-Rich Repeat Proteins; D010456:Peptides, Cyclic; D011506:Proteins