title: Differential expression of genes important for adaptation in Capsella bursa-pastoris (Brassicaceae).
abstract: Understanding the genetic basis of natural variation is of primary interest for evolutionary studies of adaptation. In Capsella bursa-pastoris, a close relative of Arabidopsis (Arabidopsis thaliana), variation in flowering time is correlated with latitude, suggestive of an adaptation to photoperiod. To identify pathways regulating natural flowering time variation in C. bursa-pastoris, we have studied gene expression differences between two pairs of early- and late-flowering C. bursa-pastoris accessions and compared their response to vernalization. Using Arabidopsis microarrays, we found a large number of significant differences in gene expression between flowering ecotypes. The key flowering time gene FLOWERING LOCUS C (FLC) was not differentially expressed prior to vernalization. This result is in contrast to those in Arabidopsis, where most natural flowering time variation acts through FLC. However, the gibberellin and photoperiodic flowering pathways were significantly enriched for gene expression differences between early- and late-flowering C. bursa-pastoris. Gibberellin biosynthesis genes were down-regulated in late-flowering accessions, whereas circadian core genes in the photoperiodic pathway were differentially expressed between early- and late-flowering accessions. Detailed time-series experiments clearly demonstrated that the diurnal rhythm of CIRCADIAN CLOCK-ASSOCIATED1 (CCA1) and TIMING OF CAB EXPRESSION1 (TOC1) expression differed between flowering ecotypes, both under constant light and long-day conditions. Differential expression of flowering time genes was biologically validated in an independent pair of flowering ecotypes, suggesting a shared genetic basis or parallel evolution of similar regulatory differences. We conclude that genes involved in regulation of the circadian clock, such as CCA1 and TOC1, are strong candidates for the evolution of adaptive flowering time variation in C. bursa-pastoris.
authors.affiliation: Department of Evolution, Genomics and Systematics, Uppsala University, SE-752 36 Uppsala, Sweden. tanja.slotte@ebe.uu.se
authors.forename: Tanja
authors.initials: T
authors.lastname: Slotte
authors.forename: Karl
authors.initials: K
authors.lastname: Holm
authors.forename: Lauren M
authors.initials: LM
authors.lastname: McIntyre
authors.forename: Ulf
authors.initials: U
authors.lastname: Lagercrantz
authors.forename: Martin
authors.initials: M
authors.lastname: Lascoux
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics*; D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism; D029687:Capsella / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D032461:Chromosomes, Plant; D035264:Flowers / Q000502:physiology*; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D014644:Genetic Variation; D020411:Oligonucleotide Array Sequence Analysis; D012621:Seasons; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; C114425:CCA1 protein, Arabidopsis; C411822:TOC1 protein, Arabidopsis; D014157:Transcription Factors