Adventitious rooting is an essential step in the vegetative propagation of economically important horticultural and woody species. Adventitious roots may develop from different aerial organs (hypocotyl, stem, leaves) and from different tissues (pericycle, mesophyl, parenchyma, cambium, inter-fascicular cambium, non-differentiated secondary phloem, protoxylem, epidermis). It is a complex process, which is affected by multiple factors including phytohormones, phenolic compounds, nutritional status, associated stress responses such as wounding, and genetic characteristics. Adventitious root formation on vegetative explants allows clonal propagation and rapid fixation of superior genotypes prior to their introduction into production or breeding programs. This strategy is often used for long-lived woody species. Nevertheless the inability to initiate adventitious roots remains an obstacle for elite genotypes of many crop and woody species.

The mechanisms by which adventitious roots are formed are still not well understood. Data from a limited number of genetic studies suggest that competence to form adventitious roots is a heritable quantitative trait. Quantitative genetic analyses have shown that major genes in poplar as well as in eucalyptus control in vitro adventitious root regeneration. Nevertheless, despite potential benefits of improved rooting capacity in woody species, their long life cycle limits the possibilities to study the basic molecular mechanisms as well as the identification of genes controlling this process. Although important structural and developmental differences exist between herbaceous and woody species, the recent results in plant genomics and developmental biology indicate that basic information is likely to be transferred between different plant species.

We have previously identified and characterised Arabidopsis thaliana mutants that are altered in their aptitude to form adventitious roots. The superroot (sur1 and 2) mutants, two auxin over-producers, and argonaute (ago1) mutants appear to be valuable tools for the elucidation of the adventitious rooting process and its regulation. sur1 mutant behaves like a "hairy root" induced by Agrobacterium rhizogenes, as it spontaneously produces adventitious roots from different organs. Conversely ago1 mutant is unable to develop adventitious roots from the hypocotyl or other aerial organs in response to auxin whereas roots respond normally. We will take advantage of these mutants to identify putative candidate genes involved in the control of adventitious rooting in response to auxin. We will look for suppressors of the superroot mutations and characterise mutants and double mutants using more global approaches including transcript profiling and proteomics analyses.

 

Bellec, Y., Harrar, Y., Bréard, C., Darnet, S., Bellini, C. and Faure, J.D. () PASTICCINO2 is a protein tyrosine phosphatase-like involved in cell proliferation and différentiation in Arabidopsis. The Plant 32, 713-22.

 

Schrick, K., Mayer, U., Martin,G., Bellini, C., Kuhnt, C., Schmidt, J. and Jürgens, G. () Interactions between sterol biosynthesis genes reveal non-linearity of this pathway in Arabidopsis. Plant J. 31, 1, 61-73.

 

Barlier, I., Kovalczyk, M., Marchant, A., Ljung, K., Bhalearo, R.P., Bennett, M., Sandberg, G. and Bellini, C. () The SUPERROOT2 gene of Arabidopsis thaliana, encodes the Cytochrome P450 CYP83B1 - a modulator of auxin homeostasis. Proc. Natl. Acad. Sci. USA, 97, .

 

Fagard, M., Boutet, S., Morel, J.M., Bellini, C. and Vaucheret, H. () AGO1, QDE-2 and RDE-1 are related proteins required for PTGS in plants, quelling in fungi and RNA interference in animals. Proc. Natl. Acad. Sci. USA, 97, .

 

Schrick, K., Ulrike Mayer, U., Horrichs, A., Kuhnt, C., Bellini, C., Dangl, J., Schmidt, J. and Jürgens, G. () FACKEL is a sterol C-14 reductase required for organized cell division and expansion in Arabidopsis. Genes and Development 14, .

 

Delarue, M., Prinsen, E., Van Onckelen, H., Caboche, M. and Bellini, C. () Sur2 mutations of Arabidopsis thaliana define a new locus involved in the control of auxin homeostasis. Plant J. 14, 5, 603-611.

 

Vittorioso, P., Cowling, R., Faure, J.D., Caboche, M. and Bellini, C. () Mutation in the Arabidopsis PASTICCINO 1 gene, which encodes a new FK506-BindingProtein-like protein has a dramatic effect on plant development. Mol. Cell Biol. 18, 5, .

 

Faure, J.D., Vittorioso, P., Santoni, V., Fraisier, V., Prinsen, E., Barlier, I., Van Onckelen, H., Caboche, M. and Bellini, C. () The PASTICCINO genes of Arabidopsis thaliana are involved in the control of cell division and proliferation. Development 125, 909-918.

 

Bohmert, K., Camus, I., Bellini, C., Bouchez, D., Caboche, M. and Benning, C. () AGO1 defines a novel locus of Arabidopsis controlling leaf development. EMBO J. 17, 1, 170-180.

 

Boerjan, W., Cervera, MT., Delarue, M., Beekman, T., Dewitte, W., Bellini, C., Caboche, M., Van Onckelen, H., Van Montagu, M., Inzé, D. () SUPER ROOT, a recessive mutation in Arabidopsis, confers auxin overproduction. Plant Cell Plant Cell 7, .