Abstract
Many plants flower in response to seasonal changes in daylength. This response often varies between accessions of a single species. We studied the variation in photoperiod response found in the model species Arabidopsis (Arabidopsis thaliana). Seventy-two accessions were grown under six daylengths varying in 2-h intervals from 6 to 16 h. The typical response was sigmoidal, so that plants flowered early under days longer than 14 h, late under days shorter than 10 h, and at intermediate times under 12-h days. However, many accessions diverged from this pattern and were clustered into groups showing related phenotypes. Thirty-one mutants and transgenic lines were also scored under the same conditions. Statistical comparisons demonstrated that some accessions show stronger responses to different daylengths than are found among the mutants. Genetic analysis of two such accessions demonstrated that different quantitative trait loci conferred an enhanced response to shortening the daylength from 16 to 14 h. Our data illustrate the spectrum of daylength response phenotypes present in accessions of Arabidopsis and demonstrate that similar phenotypic variation in photoperiodic response can be conferred by different combinations of loci.
Highlights
Many plants flower in response to seasonal changes in daylength
Detailed genetic analysis based on crossing both types identified the semidominant locus FLOWERING LOCUS C (FLC) and the dominant locus FRIGIDA (FRI), which are present in winter annuals and are required for the vernalization response (Burn et al, 1993; Clarke and Dean, 1994; Koornneef et al, 1994; Lee et al, 1994)
The response curves of most accessions were sigmoidal, as described previously for Ws and Landsberg erecta (Ler) (Pouteau et al, 2008; Wilczek et al, 2009). These curves are in agreement with the classical description of Arabidopsis as a facultative long-day species (Laibach, 1951), flowering earlier under long days (LDs) than short days (SD)
Summary
Many plants flower in response to seasonal changes in daylength. This response often varies between accessions of a single species. Transcription of each of these genes is regulated by the circadian clock (Fowler et al, 1999; Park et al, 1999; Suarez-Lopez et al, 2001), while CO activity is promoted by exposure to light both at the transcriptional and posttranscriptional levels (Valverde et al, 2004; Imaizumi et al, 2005) This complex regulation ensures that CO activates FT transcription only under LDs. In addition to the mutational analysis performed in Arabidopsis accessions commonly used in the laboratory, natural genetic variation has been studied by analyzing genetic differences between a wider range of accessions. Mutations at FRI and FLC appear to have occurred independently many times, conferring the summer annual habit (Johanson et al, 2000; Le Corre et al, 2002; Gazzani et al, 2003; Michaels et al, 2003; Lempe et al, 2005; Shindo et al, 2005)
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