Stefan Jansson in front of his favourite aspen treePhoto: Fredrik Larsson

Trees have evolved to survive the harsh winters of the boreal forests, but deciduous trees and conifers have chosen different strategies; either to shed their leaves or to stay green over the winter. We are trying to understand the molecular details behind these strategies.

How do aspens know it is autumn?

We are learning how to identify the genetic differences that make trees different from each other. Forest trees are, in general, more genetically diverse than most other organisms and aspens are, in this respect, extreme. We have built many genomic resources for Populus in general and aspen (P. tremula) in particular, for example clone collections (the SwAsp and UmAsp collections), ESTs, genome sequences as well as bioinformatic tools and databases.

Stefan Jansson's “favourite" aspen tree in front of Umeå University.Our “favourite" aspen tree, growing on the University campus in Umeå.

Using these tools, we study how aspens acclimate and adapt to the environment. Particular attention is paid to the process of phenology, in particular autumn senescence, trying to answer the question: How do trees know it is autumn? We are studying gene expression, photosynthesis and metabolism of the leaves during autumn senescence. In these studies, we use transgenic plants but, more importantly, natural variation. There is a steep cline in autumn senescence; trees from northern latitudes enter senescence much earlier than those from southern latitudes, and by using the aspen genome sequence, the collection of aspen clones and genetic tools like association mapping, we hope to understand the genetic basis of this important trait.

Yellow and red coloured aspen leafHow does the tree know that it is autumn?

How can conifers stay green in the winter?

In the photosynthetic apparatus of green plants, the light- harvesting chlorophyll a/b-binding (LHC) proteins serve as antennae for photosystems I and II. Members of the LHC protein family have three membrane-spanning regions and bind the majority of the photosynthetic pigments (chlorophyll and carotenoids), make the photosynthetic light reaction efficient and regulate the photosynthetic light reaction, for example by dissipating excess light and adjusting the excitation balance between the photosystems. There are a group of proteins that are more distant members of this protein family. This group includes PsbS and ELIPs. PsbS is necessary for a light dissipation process – the qE type of non-photochemical quenching (NPQ) - that operates when the plants are exposed to "excess light".

We are now focusing on how the photosynthetic apparatus of conifers have been adapted to make it possible for conifers to keep their leaves (needles) green over the winter. We are using molecular biology, biochemistry, biophysics etc. to study conifers grown in the field, over the season. Have the conifers evolved specific molecular mechanisms that allow them to stay green in the winter, or do they employ the same mechanisms as other plants, but to a higher extent?

Key Publications

  • Nystedt B, Street NR et al. (2013). The Norway spruce genome sequence gives insights into conifer genome evolution.Nature 497:579-584
  • Tuskan GA, DiFazio S, Jansson S, et al. (2006). The genome of black cottonwood, Populus trichocarpa (Torr. & Gray) Science 313:1596-1604
  • Sterky F, Bhalerao RR, Unneberg P, Segerman B, Nilsson P, Brunner AM, Campaa L, Jonsson Lindvall J, Tandre K, Strauss SH, Sundberg B, Gustafsson P, Uhlén M, Bhalerao RP, Nilsson O, Sandberg G, Karlsson J, Lundeberg J, Jansson S (2004). A Populus EST resource for plant functional genomics. PNAS 101 13951–13956
  • Külheim C, Ågren J, Jansson S (2002). Rapid regulation of light harvesting is crucial for plant fitness in the field. Science 297:91-93
  • Li, X-P, Björkman, O, Shih C, Grossman, AR, Rosenquist, M, Jansson, S, Niyogi, KK (2000). A pigment binding protein essential for regulation of photosynthetic light harvesting. Nature 40: 391-395