Abstract
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 Arabidopsis thaliana 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 FLOWERING LOCUS T (FT) region, and the FT 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 CONSTANTS (CO), 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 FT.
Highlights
Plants have evolved the ability to alter morphology and the timing of flowering as an adaptation to changes in the local environment
As expected many accessions did not respond with greatly accelerated flowering after vernalization, but only a small subset of the accessions did not respond to FR-enrichment with accelerated flowering (Fig 1; Experiment 1)
To explore whether or not the FLOWERING LOCUS T (FT) alleles would be expressed at different levels, we evaluated F3 plants that are heterozygous at FT from 3 populations for allele-specific expression (Fig 6B)
Summary
Plants have evolved the ability to alter morphology and the timing of flowering as an adaptation to changes in the local environment. One such mechanism is the shade-avoidance response, which allows plants to compete with neighboring vegetation for sunlight. PHYB is the primary phytochrome that elicits a response to decreasing R:FR ratio, with PHYD and PHYE having mostly redundant roles with PHYB in light perception [4]. Natural variation in PHYB can result in different responses to changes in the ratio of R:FR light, providing an avenue for local adaptation [5]. The active form of PHYB elicits a response to changes in light quality by entering the nucleus and affecting transcription of a number of genes [6]
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