Defining the role of PIF3-like bHLH transcription factors in the integration of light and cold signalling in Arabidopsis

Project: Research project (funded)Research

Project Details

Key findings

Plants have evolved an amazing ability to alter how they grow and develop in response to signals from their environment. This is critical for their survival as it allows them to synchronise growth and development with seasonal changes. A good example of this is the process of seed germination, which marks the start of growth following a period of quiescence or dormancy. The dormancy state enables seeds to survive in the soil for months to years until the conditions are favourable for growth. The ability to sense environmental conditions is critical for a seed, because once it starts to grow the fragile seedling is extremely vulnerable to all sorts of environmental challenges. Temperature and light are two key environmental signals that influence seed dormancy breakage.

In the model plant, Arabidopsis thaliana, dormancy is removed by a combination of cold temperatures and light. This requirement for cold temperatures as experienced in winter ensures that seeds only germinate in spring when conditions are good for growth. The light requirement means that seeds will only germinate when they are at or near the soil surface.

Very little is known about how plants integrate cold and light signals. We previously discovered that a protein called SPT represses germination until seeds are exposed to light. Both SPT and PIL5 belong to a class of proteins called transcription factors, because they regulate expression of specific genes. SPT and PIL5 lead to the repression of key genes involved in the synthesis of a plant hormone called gibberelic acid (GA). This hormone promotes seed germination.

GA also promotes a host of other responses where it acts mainly by decreasing the activity of DELLA proteins. These DELLA proteins are well know to inhibit plant growth and we previously showed that their removal leads to increased seed germination.

Our recent BBSRC funded work has led to a number of breakthroughs in our understanding of how germination and plant growth in general is controlled in response to signals from the environment. We now have a new appreciation of the role of the SPT transcription factor. Before the work started we had thought that the SPT protein acts as a messenger of signals from the environment that influence the all-important DELLA proteins. We now know that SPT acts in parallel with the DELLA proteins to restrain growth. SPT acts as a transcription factor that regulates the expression of other genes by binding to their promoter regions. We have found that SPT does not directly bind to genes involved in GA biosynthesis but instead binds to the regulatory regions of at least two other related transcription factors, one of which has been shown to regulate seed germination and the other to regulate growth in response to shade avoidance.

Perhaps the most exciting aspect of our work is the demonstration that the SPT protein accumulates and inhibits plant growth under cool (4-20 degrees C) daytime temperature conditions. This discovery raises the possibility of using the SPT gene to develop crops that can grow better at lower temperatures.
Effective start/end date21/12/0620/06/10