title: Comparative transcriptome analysis of stylar canal cells identifies novel candidate genes implicated in the self-incompatibility response of Citrus clementina.
abstract: BACKGROUND
  Reproductive biology in citrus is still poorly understood. Although in recent years several efforts have been made to study pollen-pistil interaction and self-incompatibility, little information is available about the molecular mechanisms regulating these processes. Here we report the identification of candidate genes involved in pollen-pistil interaction and self-incompatibility in clementine (Citrus clementina Hort. ex Tan.). These genes have been identified comparing the transcriptomes of laser-microdissected stylar canal cells (SCC) isolated from two genotypes differing for self-incompatibility response ('Comune', a self-incompatible cultivar and 'Monreal', a self- compatible mutation of 'Comune').
  
  
  RESULTS
  The transcriptome profiling of SCC indicated that the differential regulation of few specific, mostly uncharacterized transcripts is associated with the breakdown of self-incompatibility in 'Monreal'. Among them, a novel F-box gene showed a drastic up-regulation both in laser microdissected stylar canal cells and in self-pollinated whole styles with stigmas of 'Comune' in concomitance with the arrest of pollen tube growth. Moreover, we identify a non-characterized gene family as closely associated to the self-incompatibility genetic program activated in 'Comune'. Three different aspartic-acid rich (Asp-rich) protein genes, located in tandem in the clementine genome, were over-represented in the transcriptome of 'Comune'. These genes are tightly linked to a DELLA gene, previously found to be up-regulated in the self-incompatible genotype during pollen-pistil interaction.
  
  
  CONCLUSIONS
  The highly specific transcriptome survey of the stylar canal cells identified novel genes which have not been previously associated with self-pollen rejection in citrus and in other plant species. Bioinformatic and transcriptional analyses suggested that the mutation leading to self-compatibility in 'Monreal' affected the expression of non-homologous genes located in a restricted genome region. Also, we hypothesize that the Asp-rich protein genes may act as Ca2+ "entrapping" proteins, potentially regulating Ca2+ homeostasis during self-pollen recognition.
authors.affiliation: Dipartimento di Scienze delle Produzioni Agrarie e Alimentari, Università degli Studi di Catania, Via Valdisavoia 5, 95123 Catania, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Caruso
authors.forename: Paz
authors.initials: P
authors.lastname: Merelo
authors.forename: Gaetano
authors.initials: G
authors.lastname: Distefano
authors.forename: Stefano
authors.initials: S
authors.lastname: La Malfa
authors.forename: Angela Roberta
authors.initials: AR
authors.lastname: Lo Piero
authors.forename: Francisco R
authors.initials: FR
authors.lastname: Tadeo
authors.forename: Manuel
authors.initials: M
authors.lastname: Talon
authors.forename: Alessandra
authors.initials: A
authors.lastname: Gentile
mesh_terms: D000595:Amino Acid Sequence; D002957:Citrus / Q000235:genetics* / Q000502:physiology; D018744:DNA, Plant / Q000235:genetics; D020224:Expressed Sequence Tags; D035264:Flowers / Q000166:cytology / Q000235:genetics / Q000502:physiology; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D005838:Genotype; D061346:Laser Capture Microdissection; D008969:Molecular Sequence Data; D020411:Oligonucleotide Array Sequence Analysis; D010802:Phylogeny; D011058:Pollen / Q000235:genetics / Q000502:physiology; D053205:Pollen Tube / Q000254:growth & development; D060436:Self-Incompatibility in Flowering Plants; D059467:Transcriptome
chemical_list: D018744:DNA, Plant