Day length perception and the flowering response in
Arabidopsis
1. Why do you think many plants have evolved to flower under particular day lengths and why is Arabidopsis a good model for this process?
Organisms need to be able to predict the conditions that will occur months in advance in order to have time to initiate a response to the environmental stresses they will experience such as winter (especially at high altitudes as shown by fig 1).
Figure 1: The affect of altitude on day length throughout the year. The photoperiodic responses of plants to flower under a particular day length and therefore in a particular season can be beneficial to plants in many aspects. It can reduce competition (by flowering when other species do not in order to create its own niche) and increase probability of successful reproduction. This is achieved by pollinators as well as coordinating arrival at reproductive maturity (in this case flowering in plants), and the most favorable conditions for reproduction. Arabidopsis is a good model for day length perception for many reasons. When studying any aspect of plant biology it is important to understand the model.
This is why roughly 115 Mb out of the 125 Mb genome of Arabidopsis has being sequenced as well as annotated is very useful. There are also extensive genetic and physical maps of all 5 chromosomes.
Other reasons for choosing Arabidopsis Include: A short life cycle of about 6 weeks (to seed maturation from germination), Self-‐Fertile, plentiful seed production and easy cultivation (even in restricted spaces), contains many mutant lines and is easily transformed with the use of Agrobacterium tumefaciens.
2. How is the expression of CO modified by light and dark cycles a) at the mRNA and b) at the protein level to ensure that FT is only expressed in long days?
According to the widely accepted External coincidence model which states that photoperiodism is coordinated by circadian clock-‐regulated expression of a crucial element and the influence of light on the activity of this component, flowering happens in Long day Arabidopsis when the circadian rhythm of the gene CONSTANS (CO) peaks in the afternoon, when it is light during long days but dark when the days are short. The floral promoter CONSTANS (CO) plays a critical role in day-‐length perception and exhibits complex regulation; the circadian clock regulates CO mRNA and CO protein is stabilized by light and
