Petiole phenotypes, a classic FR enrichment response, are independent of flowering phenotypes.

<p>While having variable FR induced flowering phenotypes, all accessions tested display petiole elongation.</p

Flowering phenotypes of Arabidopsis accessions under various conditions.

<p>The x-axis shows Arabidopsis accessions (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0187768#pone.0187768.s004" target="_blank">S1 Table</a>) sorted according to flowering time in LD. Experiment 1. Initial screen for flowering behavior using one or two plants per accession. FR was on for 24hrs, white light was on for 16hrs. Outdoors experiments were conducted in a partially (70%) shaded plot. All the y-axes are from 0-80RLN, except for FR, which is from 0-20RLN. Experiment 2. Secondary screen for flowering behavior. FR enrichment was only during the light period (16hrs). All axes are 0-80RLN, except for FR, which is from 0-20RLN. 3 plants were evaluated for each accession. Error bars represent standard deviation. Legend; LD (long days), FR (far-red enriched conditions), Out (outside experiment), Ve40 (40 day vernalization), Ve70 (70 vernalization, GA (gibberellic acid treatment), and VeFR (70 day vernalization + far-red enriched conditions).</p

Two loci, <i>FRI</i> and <i>FT</i>, are sufficient to confer FR insensitivity.

<p>An <i>FT</i> mutant in Col was integrated into the ColFRI background, to demonstrate the role of <i>FT</i> in a late-flowering strain. In the ColFRI background, <i>FT</i> is necessary for FR sensitivity.</p

F2, and F3 FR induced flowering phenotypes of the Hau-0xColFRI population, and linkage to the <i>FT</i> region (24Mb).

<p>Hau-0/ColFRI F1 plants are responsive to FR enrichment similar to ColFRI; thus the causative allele(s) are dominant. The Hau/ColFRI F2 population segregates in a 3:1 manner, suggesting a single large effect locus. Genotyping and phenotyping of a Hau/ColFRI F3 population maps the phenotype to the <i>FT</i> region (24Mb).</p

Flowering phenotypes of Arabidopsis accessions in SD and with temperature cycling.

<p>The x-axis shows Arabidopsis accessions sorted according to SD or Cyc flowering time. The FR effect on flowering is negligible under SD growth conditions. Temperature cycling does not substitute for, nor curtail FR induced flowering. Y-axes are 0-80RLN.</p

Variation in shade-induced flowering in <i>Arabidopsis thaliana</i> results from <i>FLOWERING LOCUS T</i> allelic variation

<div><p>Plants have evolved developmental mechanisms to ensure reproduction when in sub-optimal local environments. The shade-avoidance syndrome is one such mechanism that causes plants to elongate and accelerate flowering. Plants sense shade via the decreased red:far-red (R:FR) ratio that occurs in shade. We explored natural variation in flowering behavior caused by a decrease in the R:FR ratio of <i>Arabidopsis thaliana</i> accessions. A survey of accessions revealed that most exhibit a vigorous rapid-flowering response in a FR-enriched environment. However, a subset of accessions appeared to be compromised in the accelerated-flowering component of the shade-avoidance response. The genetic basis of the muted response to FR enrichment was studied in three accessions (Fl-1, Hau-0, and Mir-0). For all three accessions, the reduced FR flowering-time effect mapped to the <i>FLOWERING LOCUS T</i> (<i>FT</i>) region, and the <i>FT</i> alleles from these accessions are expressed at a lower level in FR-enriched light compared to alleles from accessions that respond robustly to FR enrichment. In the Mir-0 accession, a second genomic region, which includes <i>CONSTANTS</i> (<i>CO</i>), also influenced flowering in FR-enriched conditions. We have demonstrated that variation in the degree of precocious flowering in shaded conditions (low R:FR ratio) results from allelic variation at <i>FT</i>.</p></div

The twelve representative accessions/strains exhibit distinct flowering-time behaviors separable into 5 classes.

<p>The twelve representative accessions/strains exhibit distinct flowering-time behaviors separable into 5 classes.</p

In multiple isogenic lines, <i>FT</i> expression is linked to FR sensitivity in an allele specific manner.

<p>A) Three accessions (Hau-0, Mir-0 and Fl-1) and the laboratory strain ColFRI were evaluated for <i>FT</i> expression. Plants were grown in LD conditions for 4 weeks and then moved to LD or LD + FR. Samples were collected 1 week and 5 weeks after being moved. B) Allele specific <i>FT</i> expression in F3 plants heterozygous for <i>FT</i>. BsmBI cuts the ColFRI and Hau-0 allele, whereas Cac8I cuts the Fl-1 allele. In the figure for allele specific <i>FT</i> expression, (C) = allele is cut with the enzyme, whereas (U) = allele is not cut by that specific enzyme.</p