PI: Alan Marchant

Staff: Emma Hörnblad, PhD student; Ai-Min Wu, postdoc; Ellinor Edvardsson, PhD student (Research School in Forest Genetics and Breeding)

Background

The process of secondary growth is of fundamental importance in plant development yet little is currently understood about the genetic control governing its formation. Glycosyltransferases represent a major and diverse group of enzymes which are thought to play a major role in cell wall synthesis. However, the large number of glycosyltransferases in plants coupled with the diverse range of possible products they synthesise makes it difficult to identify genes which may be involved in particular developmental processes. The wood forming tissues of poplar represent a valuable system to identify potential genetic regulators of secondary thickening in plants due to the spatial separation of the different developmental stages. By dissecting tissues from these distinct developmental stages it has been possible to construct a "roadmap" of genes involved in specific phases of wood formation (Hertzberg et al. 2001, Schrader et al. 2004). These poplar genes represent potential candidates to be involved in secondary cell wall biosynthesis or in the regulation of this process. The poplar genes can then used to identify putative orthologs from Arabidopsis and the gene function during secondary growth determined using insertional knockout mutants. By adopting this approach a number of potentially interesting genes have already been identified including a GT2 (AtCSLA2), GT47 (AtGUT2) and a gene with unknown function. Characterisation of the Arabidopsis knockout mutants suggests that orthologs of these genes may function during wood formation in poplar.

Aims

The aim of this project will be to determine the function of poplar genes which have been identified as being upregulated during the secondary cell wall formation phase of wood development. Initial work will focus on up to six GT47 PttGUT genes in poplar which all show elevated expression in the zone of secondary cell wall formation. RNAi technology will be used to generate transgenic poplar lines having a range of levels of reduced gene expression. PttGUT genes will be downregulated either individually or multiply to assess overlapping functions. Trees with downregulated PttGUT gene expression will be analysed for their wood properties using a range of techniques including FT-IR, NMR, fiber analysis and microscopy within the FuncFiber platform. Further genes which may function during secondary growth will be selected based on the poplar transcript profiling data and knockout mutants will be analysed initially in Arabidopsis. For any that show relevant and interesting phenotypes in Arabidopsis, further work on homologous genes will also be carried out in poplar. Using both Arabidopsis and poplar systems it is also hoped to identify further proteins which form functional complexes with the GUT family of sequences using immunoprecipitation and TAP-TAG technologies. In this way greater insight will be gained into the overall machinery which functions during secondary growth in plants.

References

• Hertzberg M, Aspeborg H, Schrader J, Andersson A, Erlandsson R, Blomqvist K, Bhalerao R, Uhlén M, Teeri TT, Lundeberg J, Sundberg B, Nilsson P, Sandberg G (2001) A transcriptional roadmap to wood formation. Proc Natl Acad Sci USA 98: 14732-14737
• Schrader J, Nilsson J, Mellerowicz E, Berglund A, Nilsson P, Hertzberg M, Sandberg G (2004) A high-resolution transcript profile across the wood-forming meristem of poplar identifies potential regulators of cambial stem cell identity. Plant Cell 16: 2278-2292