The research in my group is focused on understanding the regulation of flowering time and tree phenology, with a special interest in comparative biology studies of the genetic pathways that are conserved in controlling the two processes. With this approach we aim to contribute to our understanding of the evolution of annual vs. perennial life strategies.

Ove Nilsson at the UPSC tree phenotyping platform (photo: Fredrik Larsson)Ove Nilsson at the UPSC tree phenotyping platform (photo: Fredrik Larsson)

My group has a special interest in the regulation and function of FT-like genes. We contributed to the first studies of the molecular mechanisms controlling flowering time in trees, showing that FT-like genes, that are central in the regulation of flowering time in annual plants, are functionally conserved in being very potent activators of flowering in trees.

Surprisingly, we could also show that FT-like genes in poplar trees control another important aspect of perennial growth behaviour: the short day-induced growth cessation and bud set that occurs in the fall. We have shown that the activity of the CO/FT regulon is partly 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-like genes.

Figure1: Four Poplars in four seasons

Subsequent studies in many different annual plants have now shown that these genes have a much more general role in controlling photoperiodic regulation of plant growth and development than was previously anticipated, based on work in Arabidopsis. We could also show that in sugar beet, only a two amino acid difference is critical in determining the sub-functionalization of two FT paralogs into either activators or repressors of flowering, and that the flowering repressor BvFT1 has a central role in the regulation of the biennial growth strategy in sugar beet.

Folding prediction of BvFT1 and BvFT2. The structures are shown as solid three-dimensional traces with an alignment diversity color setting. Down-regulation of BvFT2 by RNAi of BvFT1 result in bolting repression in sugar beet. 400-day old BvFT2 RNAi annual plant grown in LDs.

We are now extending our comparative biology approach to study the similarities and differences in the regulation of flowering in Arabidopsis and the regulation of flowering and phenology in aspen (poplar) trees. Aspen trees have also two sub-functionalized FT-like genes, and we want to understand how these genes contribute to the regulation of growth cessation and bud set in the fall, as well as to the regulation of bud flush and growth in the spring.

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 been involved in work showing that polymorphisms within one of the FT-like genes is the most important association that can be found to natural variation in adaptation to growth at different latitudes in Swedish aspen trees. We are investigating the mechanism for this adaptation in detail by studying the role of upstream regulators in the regulation of FT transcription in trees. We have also a long standing interest in extending this work to gymnosperm trees, like Norway spruce. Here, I have been involved in leading several large projects determining the genome sequences and developing genomic resources of conifers, including the first sequence of a gymnosperm, Norway spruce.

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.