Short and long term low temperature responses in Arabidopsis thaliana

A unique aspect of plant biology is their ability to respond very rapidly to shifts in their ever-changing environment. To do this, plants need to have evolved mechanisms that enable them to sense their environment and to rapidly respond to different stresses and different combinations of stress. The main focus of my thesis has been on plant responses to low temperature. One way in which the plant cell is thought to sense low temperature is via the rigidification of the plasma membrane that occurs when the temperature falls rapidly. I showed that CRMK1, a leucine-rich-repeat-receptor-like kinase, located in the plasma membrane is a key component of the cold sensing machinery. I show that a T-DNA insertion mutant of CRMK1 attenuated the expression of marker cold genes in response to cold stress and decreased the plants ability to acquire freezing tolerance after 3 days of exposure to low temperature. I described a protective mechanism in the thylakoid membranes by which excess electrons, which can accumulate at low temperature and under high light in cold acclimated plants, can be dissipated. In order to properly respond to a changing surroundings cells not only have to sense the fluctuations but they need to communicate this changes to the nucleus and I showed that organelles such as the chloroplasts can act as a sensor of changing temperature and communicate this information to the nucleus to change the expression of cold regulated genes. I presented and identified factors in addition to low temperature that regulate the expression of genes for cold tolerance. I showed that a circadian signal, together with plastid and light signals, influence the expression of nuclear encoded cold tolerance genes (CBF3 and COR15). The response of plants to low temperature also depends on the duration of the cold stress. There are plants, such as over-wintering herbaceous and perennial woody plants, that have to survive and grow for prolonged periods at low temperature and there are those from extreme polar or alpine environments that spend entire life in cold. I provided a comprehensive overview of the biological processes and genes that enable plants to survive and develop the full cold acclimated state during long-term over wintering and growth in the low temperature