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Fig. 2. Schematic representations of Arabidopsis plants summarizing the
genetic control of vernalization requirement and response. The flowering
phenotype of Arabidopsis is represented as either a rapid cycler
(e.g. top right), which produces a flowering inflorescence, or as a winter
annual accession (e.g. top left), which continues to produce rosette leaves.
Rapid-cycling accessions do not require a vernalization treatment to flower
early and are commonly used as laboratory backgrounds. By contrast, the
majority of Arabidopsis accessions are winter annuals, which flower
late unless they have been exposed to a prior vernalization treatment.
Typically, 6 weeks of growth at 4°C produces a saturated vernalization
response in Arabidopsis. Growth habit is indicated either with (+VRN)
or without (–VRN) a vernalization treatment. When both FRI and
FLC are active, the plant is vernalization responsive, as is found in
many winter annual accessions. Mutations in either fri or
flc can lead to rapid cycling. A vernalization-responsive FRI
FLC accession is rendered insensitive to vernalization by a vrn
mutation. Finally, a rapid-cycling fri FLC genotype becomes a winter
annual background in the presence of an autonomous pathway mutation such as
fca.
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