My group is conducting research in two different areas using the plant model system Arabidopsis thaliana. The first project is tackling the regulation of adventitious root initiation, which is a key limiting step during vegetative propagation of economically important tree species. Nothing is known about the molecular mechanisms involved and a better understanding will allow the optimisation of conditions for vegetative propagation.
The second project is aimed at understanding the function of genes expressed in the phloem, the vascular compartment involved in the distribution of photosynthetic products produced in the leaves. Since malfunction of the phloem has a considerable impact on crop yield, production of biomass, fruits, seeds, and on wood development, it is important to get better insights into the regulatory mechanisms involved in phloem function.

Catherine Bellini 1150
bellini_1Poplar in vitro propagation. Top left: microcutting in vitro. Bottom left: microcutting unable to develop adventitious roots and make a callus instead. Top right: the microcutting developed proper adventitious roots that will allow future transfer to soil (bottom right).

Control of
adventitious root initiation (this project is developed at the UPSC, Umeå, Sweden)

The root system of a plant is composed of the primary, lateral and adventitious roots. Lateral roots always develop from roots, whereas adventitious roots form from the stem or leaf-derived cells. Many species, including strawberries and blackberries, mainly propagate vegetatively from stolons or stems from which adventitious roots regenerate to anchor the new plants to the ground. The adventitious rooting process is also crucial for the propagation of valuable plants or plants for which final yield, whether fruit or dry matter, is influenced by the proper development of adventitious roots, such as maize, wheat or rice. Over the years, cloning has become an intrinsic step in breeding programmes for the production and propagation of elite genotypes of horticultural and woody species. It is used extensively by horticultural and forest industries, which can lose millions of dollars every year because of difficult-to-root genotypes.

In the last few years, we have identified, through the characterization of Arabidopsis mutants altered in their aptitude to produce adventitious roots, several genes that control adventitious root initiation. Some of these genes are supposed to act in the crosstalk of the phytohormone auxin and light signalling pathways. Ongoing experiments aim to better understand the respective contribution of these genes in the control of adventitious rooting. We also expect to understand how auxin and light interact in this developmental process. In addition, poplar orthologues have been identified and transgenic poplar plants altered in their expression could be produced to check their role in adventitious rooting in a tree species. In the future, we expect our results to help in the development of new methods for rooting of difficult-to-root genotypes.

Functional characterisation of phloem expressed genes (this project is developed at the IJPB, INRA, Versailles, France) 
bellini_3Transverse section of a flower stem from Arabidopsis thaliana. The specific phloem expression of a transcription factor was analysed using a promotor:GUS marker gene.The complexity of phloem functions at different structural and physiological levels has begun to be recognized. Nevertheless, despite playing key roles in plant life and adaptation, genes controlling phloem differentiation and its functions are poorly known. Recently, analysis of phloem-enriched fractions of plant tissues have enabled the establishment of libraries of genes preferentially expressed in the phloem and potentially involved in specific functions.

We address the mechanisms controlling phloem functions through a functional genomic approach. From several available transcriptome databases, we selected genes showing high expression in the phloem compartment, encoding transcription factors or membrane proteins. Through an integrative approach combining modern genetics, molecular biology and cell biology, we are now gaining further insights into their role in regulating phloem functioning.

sweden_greySvensk sammanfattning