title: LRR-RLK family from two Citrus species: genome-wide identification and evolutionary aspects.
abstract: Leucine-rich repeat receptor-like kinases (LRR-RLKs) represent the largest subfamily of plant RLKs. The functions of most LRR-RLKs have remained undiscovered, and a few that have been experimentally characterized have been shown to have important roles in growth and development as well as in defense responses. Although RLK subfamilies have been previously studied in many plants, no comprehensive study has been performed on this gene family in Citrus species, which have high economic importance and are frequent targets for emerging pathogens. In this study, we performed in silico analysis to identify and classify LRR-RLK homologues in the predicted proteomes of Citrus clementina (clementine) and Citrus sinensis (sweet orange). In addition, we used large-scale phylogenetic approaches to elucidate the evolutionary relationships of the LRR-RLKs and further narrowed the analysis to the LRR-XII group, which contains several previously described cell surface immune receptors.
  
  
  
  We built integrative protein signature databases for Citrus clementina and Citrus sinensis using all predicted protein sequences obtained from whole genomes. A total of 300 and 297 proteins were identified as LRR-RLKs in C. clementina and C. sinensis, respectively. Maximum-likelihood phylogenetic trees were estimated using Arabidopsis LRR-RLK as a template and they allowed us to classify Citrus LRR-RLKs into 16 groups. The LRR-XII group showed a remarkable expansion, containing approximately 150 paralogs encoded in each Citrus genome. Phylogenetic analysis also demonstrated the existence of two distinct LRR-XII clades, each one constituted mainly by RD and non-RD kinases. We identified 68 orthologous pairs from the C. clementina and C. sinensis LRR-XII genes. In addition, among the paralogs, we identified a subset of 78 and 62 clustered genes probably derived from tandem duplication events in the genomes of C. clementina and C. sinensis, respectively.
  
  
  
  This work provided the first comprehensive evolutionary analysis of the LRR-RLKs in Citrus. A large expansion of LRR-XII in Citrus genomes suggests that it might play a key role in adaptive responses in host-pathogen co-evolution, related to the perennial life cycle and domestication of the citrus crop species.
authors: Instituto Agronômico, Centro de Citricultura Sylvio Moreira, Cordeirópolis, São Paulo, Brazil.|Departamento de Genética e Biologia Molecular, Universidade Estadual de Campinas, Campinas, São Paulo, Brazil.
authors: Diogo M
authors: DM
authors: Magalhães
authors: Instituto Nacional de Ciência e Tecnologia em Doenças Tropicais, Grupo de Genômica e Biologia Computacional, Centro de Pesquisas René Rachou, Fundação Oswaldo Cruz, Belo Horizonte, Minas Gerais, Brazil.
authors: Larissa L S
authors: LL
authors: Scholte
authors: Instituto Agronômico, Centro de Citricultura Sylvio Moreira, Cordeirópolis, São Paulo, Brazil.
authors: Nicholas V
authors: NV
authors: Silva
authors: Instituto Nacional de Ciência e Tecnologia em Doenças Tropicais, Grupo de Genômica e Biologia Computacional, Centro de Pesquisas René Rachou, Fundação Oswaldo Cruz, Belo Horizonte, Minas Gerais, Brazil.|Instituto Tecnológico Vale - ITV, Belém, Pará, Brazil.
authors: Guilherme C
authors: GC
authors: Oliveira
authors: The Sainsbury Laboratory, Norwich Research Park, Norwich, NR4 7UH, UK.
authors: Cyril
authors: C
authors: Zipfel
authors: Instituto Agronômico, Centro de Citricultura Sylvio Moreira, Cordeirópolis, São Paulo, Brazil.
authors: Marco A
authors: MA
authors: Takita
authors: Instituto Agronômico, Centro de Citricultura Sylvio Moreira, Cordeirópolis, São Paulo, Brazil. alessandra@centrodecitricultura.br.
authors: Alessandra A
authors: AA
authors: De Souza
mesh_terms: D017360:Arabidopsis / Q000235:genetics; D029681:Arabidopsis Proteins / Q000235:genetics; D002874:Chromosome Mapping; D032461:Chromosomes, Plant / Q000235:genetics / Q000378:metabolism; D002957:Citrus / Q000235:genetics* / Q000378:metabolism; D019143:Evolution, Molecular; D018745:Genome, Plant; D005810:Multigene Family; D010802:Phylogeny; D010940:Plant Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D008565:Membrane Proteins
chemical_list: D029681:Arabidopsis Proteins; D010940:Plant Proteins; D017346:Protein Serine-Threonine Kinases; C588365:AT3g23750 protein, Arabidopsis; D008565:Membrane Proteins
keywords: Citrus clementina; Citrus sinensis; Leucine-rich repeat receptor-like kinase; Phylogeny