Regulation of flowering time in Arabidopsis

 

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flowering pathway

Gibberellin pathway

References

 

Introduction

 

 

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 complex network.

The many genes regulating the floral transition in Arabidopsis have been identified by two different strategies:

Firstly, using natural populations (ecotypes) from different climates, differing in their flowering time, then identifying the mutant genes, and secondly, by induced mutagenesis.

Several reviews detail different aspects of flowering time regulation in Arabidopsis.

The complex network of gene interaction regulating flowering time in Arabidopsis can be divided into 4 main pathways:

  • 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.
  •  The 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 genes