The research in my group is focused on various aspects of the regulation of meristem identity and flowering time in the two model systems, Arabidopsis and poplar. We want to understand the level of functional conservation of genes regulating flowering time between the two systems and to identify new regulators of this transition. With this approach, we aim to gain more insight into the regulation of flowering in both annuals and perennials. In other projects, we are studying the regulation of plant development in response to light and the regulation of vascular cambium identity.

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The transition to flowering is one of the most important events during the life of a plant.Although we know a lot about how this process is regulated in annual plants like Arabidopsis and rice, we still know very little about what controls flowering in perennial trees.

We have shown that the role of the Arabidopsis gene FT in regulating flowering time is functionally conserved in a plant with a completely different life strategy: the poplar tree. Surprisingly, we could also show that the FT gene in poplar trees controls another important aspect of perennial growth behaviour: the shortday induced growth cessation and bud set that occurs in the fall. We have shown that the activity of the CO/FT regulon is conserved in the aspen tree and that short days induce a down-regulation of the activity of this regulon, leading to growth cessation and bud set.These findings have led to a completely new way of looking at the function of FT. It seems that this gene has a much more general role in controlling photoperiodic regulation of plant growth and development than was previously anticipated, based on work in Arabidopsis.We have also shown that in sugarbeet only two amino acids are critical in determining if the two FT paralogs are acting as activators or repressors of flowering, and that the flowering repressor BvFT1 has a central role in the regulation of flowering in biennial sugar beet.We are now extending our comparative biology approach to study the similarities and differences in the regulation of flow- ering in Arabidopsis and the regulation of flowering and growth cessation in aspen (poplar) trees,This work will provide us with a better understanding of the genetic pathways responsible for photoperiodic regulation of plant growth and development. It will also allow us to design new ways to enhance the speed of tree breeding through accelerated flowering and to adapt the growing period of trees to new climate zones and to a changing climate.
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Transgenic hybrid aspen tree forming inflorescences and flowers after 6 months instead of after 10-15 years The Nilsson group is also studying the genes controlling growth cessation, bud set and bud burst in trees

We have also cloned and characterized the BLADE-ON-PET- IOLE (BOP) genes, which have important roles in controlling the growth and development of lateral organs and appear to be important regulators of plant development in response to light. There is also an interes- ting interaction with the flower meristem identity-gene LEAFY (LFY) during flower initiation,in which BOP and LFY act together to initiate flower primordia and to suppress the outgrowth of flower-subtending leaves (bracts).

Recently,we identified a poplar ortholog of the shoot apical meristem identity gene WUSCHEL (WUS) ex- pressed in the vascular cambium and we have shown that this gene is important for vascular cambium activity and stem secondary growth.This is actually one of the genes that allow a tree to grow as a tree, i.e. to be the tallest plant in the forest.We are now characterizing several genes with a vascular cambium-specific expression pattern that could interact with this WUS-like gene in controlling the activity and identity of the vascular cambium. This knowledge will help to design methods to enhance wood production.

We are also extending our work on the regulation of flow- ering time and secondary growth into the conifer Norway spruce (Picea abies), where we recently led the effort to generate the first complete genome sequence.
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