Survival of perennial plants, including long-lived trees, depends on their ability to adapt to seasonal changes in environmental conditions. These plants have developed sophisticated mechanisms to sense changes in environmental conditions and modulate their growth and development accordingly. The first project in my lab focuses on understanding how perennial plants sense the changing environmen-
tal conditions, by analysing the molecular basis of short-dayinduced growth cessation and dormancy in hybrid aspen. The second project is focused on understanding how cell elongation is regulated
in plants. Cell elongation in plant cells presents a unique problem, as plant cells are enclosed in a rigid cell wall that needs to be remodelled in order for cell elongation to occur. The research in my group aims to identify the key components that are involved in regulation of cell elongation and cell wall remodelling in the model plant Arabidopsis.

Molecular basis of growth cessation and dormancy in perennial plants
Perennial plants need to undergo growth cessation and establish dormancy prior to the onset of winter, in order to survive low temperatures.These plants anticipate the approach of winter by sensing the reduction in day length. Reduction in day length (short day signal) induces growth cessation that is apparent in the form of bud formation at the apex and eventually the establishment of dormancy. Once dormancy is established, prolonged exposure to chilling temperatures is essential for release from dormancy. Once release from dormancy has occurred, warm temperatures can re-initiate new growth. In my group, we are investigating the molecular basis of short-day-induced growth cessation and dormancy. In particular we are addressing the following questions::
1. What are the signal transduction components mediating short day regulated growth cessation?
2. How is dormancy established and what is the molecular mechanism regulating the release from dormancy?

Elucidating the control of cell elongation in Arabidopsis thaliana
The final size of plants and their constituent organs is deter- mined by cell division and cell expansion.While cell division serves to increase the number of cells, cell expansion serves to increase the cell size. Mechanistically, cell expansion in plants poses a unique problem compared with animal animal cells. Unilike animal cells, plant cells are surrounded by a rigid cell wall that encompasses the plasma membrane. For cell expan- sion to occur, the cell wall structure must be remodelled.The process of cell wall remodelling involves loosening of the cell wall by alteration of the interactions between the three major components of the primary plant cell wall, namely cellulose, hemicellulose (of which xyloglucans are the major components) and pectins.This process involves the breakdown of linkages between the various cell wall components, accompanied by the addition of newly synthesized components to growing cell walls as cell size increases. Importantly, at the cellular level cell expansion can be polar.This is the case in root hair formation where cell wall loosening and eventual elongation is localised to the basal end of trichoblast cells. Here the cell wall components and the proteins needed for cell wall remodeling need to be delivered to the specific locations where cell wall expansion will take place.Thus, to understand how cell expansion is regulated, an important question that needs to be answered is:
How do cells regulate the delivery of various cell wall components and the proteins involved in cell wall remodelling to their site of action during cell expansion?
How do cells regulate the delivery of various cell wall components and the proteins involved in cell wall remodelling to their site of action during cell expansion?
We are currently addressing this question in the model plant Arabidopsis.We have identified several Arabidopsis mutants altered in cell elongation and these are being characterized using genetic and cell biology techniques. Our results so far indicate a key role for the components of trafficking machinery in the regulation of cell elongation and cell wall remodelling..

Key Publications
- Petterle A., Karlberg A and Bhalerao RP (2013). Daylength mediated control of seasonal growth patterns in perennial trees. CurrentOpinion in Plant Biology, in press
- Boutté Y., Jönsson K., McFarlane HE:, Johnson E., Gendre D., Swarup R., Friml J., Samuels L.,Rbert S and Bhalerao RP (2013). ECHIDNA-mediated post-golgi Trafficking of Auxin Carriers for Differential Cell Elongation in Arabidopsis. PNAS, in press
- Gendre D., Macfarlane H., Johnson E., Mouille G., Sjödin A., Oh J., Levesque-Tremblay G., Watanabe Y., Samuels L and Bhalerao RP
- (2013). Trans-Golgi Network localised ECH/YIP4 complex is required for the secretion of cell wall polysaccharides in Arabidopsis thalia- na. Plant Cell, in press
- Karlberg A., Bako L and Bhalerao RP (2011). Short day mediated cessation of growth requires the downregulation of AINTEGUMEN- TALIKE1 transcription factor in hybrid aspen. PLOS GENETICS e1002361
- Baba K., Karlberg A., Schmidt J., Schrader J., Hvidsten T., Bako L and Bhalerao RP (2011). Activity-dormancy transition in the cambial meristem involves stage specific modulation of auxin response in Hybrid Aspen. Proc Natl Acad Sci U S A. 108: 3418-3423
- Gendre D., Oh J., Boutté Y., Best JG., Samuels L., Nilsson R., Uemura T., Marchant A., Bennett MJ., Grebe M., and Bhalerao RP(2011). Conserved Arabidopsis ECHIDNA protein mediates trans-Golgi-network trafficking and cell elongation. Proc Natl Acad Sci U S A. 108: 8048-8053