In Arabidopsis, the transition to flowering is
controlled both by external
(temperature, photoperiod, hormones), and endogenous
cues (developmental stage). Many genes are involved in the regulation
of this transition, and interact with each other in a
The many genes regulating the floral transition in
Arabidopsis have been identified by two different
Firstly, using natural populations (ecotypes) from
different climates, differing in their
flowering time, then identifying the mutant genes, and
secondly, by induced mutagenesis.
detail different aspects of flowering time regulation in
The complex network of gene interaction regulating
flowering time in Arabidopsis can be divided into 4 main
- The photoperiod pathway: In Arabidopsis, long
daylengths induce flowering. Particular light
wavelengths can also either induce or repress flowering.
The photoperiod pathway comprises several light
receptors (such as phytochromes and cryptochromes),
and clock genes. The photoperiod mutants flower late
in inductive photoperiods.
- The autonomous pathway: This pathway is
independent of the plant environment, and its
regulation depends mostly on the age (and
developmental stage) of the plant. The mutants of
the autonomous pathway are photoperiod-independent.
- The vernalization pathway: This pathway is induced
by prolonged periods of cold. In the relevant
climates, this is an adaptation to winter, which
makes the plant is unable to flower until the winter
is over. The vernalization mutants are able to
flower in absence of vernalization.
gibberellin pathway: Gibberellins are plant
hormones that affect many aspects of plant
development and metabolism, and have an inductive
effect on Arabidopsis flowering. The mutants of the gibberellin response pathway are late-flowering in
SD, but are not delayed in LD. This indicates the
importance of this pathway when the photoperiod
pathway is not active.
All the signals perceived by these different
pathways are integrated thanks to several genes called
the floral integrators (CO, FT, SOC1), which in turn
regulate the expression of the floral meristem identity