Abstract
Variation in life history contributes to reproductive success in different environments. Divergence of annual and perennial angiosperm species is an extreme example that has occurred frequently. Perennials survive for several years and restrict the duration of reproduction by cycling between vegetative growth and flowering, whereas annuals live for 1 year and flower once. We used the tribe Arabideae (Brassicaceae) to study the divergence of seasonal flowering behaviour among annual and perennial species. In perennial Brassicaceae, orthologues of FLOWERING LOCUS C (FLC), a floral inhibitor in Arabidopsis thaliana, are repressed by winter cold and reactivated in spring conferring seasonal flowering patterns, whereas in annuals, they are stably repressed by cold. We isolated FLC orthologues from three annual and two perennial Arabis species and found that the duplicated structure of the A. alpina locus is not required for perenniality. The expression patterns of the genes differed between annuals and perennials, as observed among Arabidopsis species, suggesting a broad relevance of these patterns within the Brassicaceae. Also analysis of plants derived from an interspecies cross of A. alpina and annual A. montbretiana demonstrated that cis‐regulatory changes in FLC orthologues contribute to their different transcriptional patterns. Sequence comparisons of FLC orthologues from annuals and perennials in the tribes Arabideae and Camelineae identified two regulatory regions in the first intron whose sequence variation correlates with divergence of the annual and perennial expression patterns. Thus, we propose that related cis‐acting changes in FLC orthologues occur independently in different tribes of the Brassicaceae during life history evolution.
Highlights
Life history varies greatly among higher organisms and can diverge rapidly during evolution (Partridge & Harvey 1988)
Analysis of plants derived from an interspecies cross of A. alpina and annual A. montbretiana demonstrated that cis-regulatory changes in FLOWERING LOCUS C (FLC) orthologues contribute to their different transcriptional patterns
Remarkable sequence variation at FLC genes occurs within and between Brassicaceae species, and increasing complexity of these loci has been suggested to be linked to perenniality in A. alpina and in Arabidopsis species (Alonso-Blanco & Mendez-Vigo 2014)
Summary
Life history varies greatly among higher organisms and can diverge rapidly during evolution (Partridge & Harvey 1988). Two major life history strategies have been described, which are represented by semelparous organisms that reproduce only once in their lifetime and iteroparous organisms that undergo several. Variation in life history is associated with adaptation to different environments. Annuals are usually found in open, dry habitats prone to seasonal drought but where seedlings have high survival rates if germination is appropriately timed. Perennials are more commonly found in mesic habitats where seedling mortality is high (Stebbins 1950; Silvertown & Charlesworth 2001). Perennial populations of Mimulus guttatus (Scrophulariaceae) have access to moisture throughout the year, while annual populations grow in areas that are arid during the summer months, and reciprocal transplant experiments indicate that each type is adapted to its respective environment (Hall & Willis 2006)
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