Genetics of Flowering
Genes play a significant role in controlling flowering. Our understanding of floral genetics has advanced significantly in recent years. Much research effort has been focussed on the flowering of Arabidopsis thaliana and certain agricultural crops such as peas (Pisum sativum). Discoveries made in researching these species help scientists understand floral genetics more broadly.
Research has shown that in many species, small genetic mutations can alter the patterning of flowering. Mutations are used in research to categorically prove that a particular gene has a certain function. By adding a mutation (or removing one), a change takes place in the plant and this provides the final evidence of gene function.
A mutation is a "mistake" in the DNA itself which causes a change in the appearance or function of a part of that organism. A mutation could be as little as one base pair of DNA. A mutation can be either good, bad, or neutral depending on what it is. A mutation which makes a pink petunia white could be considered 'neutral' from a biological perspective (neither good nor bad) if this colour change had no effect on the plant's ability to grow and reproduce.
From a horticultural perspective, the mutation in the plant may be 'good' because many people might find the result more attractive (eg: flower colour).
Some long-day plants (plants which flower in response to short nights) can be mutated to develop into day-neutral plants; that is, plants which flower regardless of the dark period by altering a few key genes. (For more on day length and flowering, see Circadian Rhythms). The plant's sensitivity to day length can be removed through genetic engineering. Other mutations can cause changes in autonomous flowering, or a plant's response to other stimuli so that flowering is either promoted or delayed. Put simply, genes determine which stimulus or combination of stimuli will influence the timing of flowering in a species.
Only a small fraction of the world's plants have been studied in sufficient detail to determine the genetic and/or other mechanisms which control their flowering. Since the mechanisms that control flowering such as phase change, circadian rhythms, photoperiod and temperature are discussed elsewhere on this website, I'll continue by outlining some key genetic discoveries which have made a significant contribution to the understanding of flowering. Genes which are directly involved with these other flower control mechanisms are discussed on the relevant pages.
LEAFY (LFY) Gene
You'll observe that genes are often given 'odd' names as you progress through this website.
One of the most significant genetic discoveries has been of the role of the LEAFY or LFY gene in Arabidopsis. This gene has been found to have a pivotal role in the transition from the vegetative ("leafy") phase to reproductive phase. When flower induction stimuli are detected by an Arabidopsis plant, the LFY gene is expressed in addition to APETALA1 (AP1) and CAULIFLOWER (CAL).
These three genes cause the meristems to become determined (for a definition of this, see Phase Changes) meaning that they are committed to developing into flowers. A number of researchers have found that mutations to LFY genes causes shoot or shoot-like structures to develop where flowers would normally form, yet plants still produce a spike with a series of branches where the flowers were supposed to be.
LFY genes have also been found to have an effect on leaf shape. Not all plants have the LFY gene, but seem to have an equivalent; UNIFOLIATA (UFI) in peas and FLORICAULA in snapdragons are two examples.
GIGANTEA and ELF3
Two more genetic discoveries relating to Arabidopsis flowering are of the GIGANTEA (gi) andELF3 genes. The gi gene has been found to promote flowering. A study by R. Amasino found that a mutant of gi in Arabidopsis delayed flowering significantly, meaning that the normal role of that gene is to promote flowering. In reverse, the ELF3 gene has been found to repress flowering!
This shows that flowering is controlled by a number of genes which have a complex relationship to each other.
Floral Identity Genes
Not only are there genes which control floral initiation, but there are genes which control floral development and identity. These are called homeotic genes and control the development of floral organs.
Next: Internal Clocks