Natural Variation of Adventitious Root Formation in Etiolated Arabidopsis thaliana Hypocotyls

Adventitious root formation on the hypocotyl (HAR) of etiolated Arabidopsis thaliana seedlings is a commonly used system to study non-wound-induced root formation. However, the major signaling pathways and regulating mechanisms are still to be discovered. Our results show a significant difference in the capacity to form HAR between the Arabidopsis thaliana accessions Col-0 and Ler-0. Both in their natural HAR induction and in their response to a HAR inducing compound named ‘Hysparin¹’ (Fig. 1). Whole chromosome substitution lines (CSLs)² were used to identify relationships between the genetic background of these accessions and the capacity to form HAR. In the untreated situation (free of compounds), a Ler-0 allele on chromosome 2 and a Col-0 allele on chromosome 3 is associated with an increased number of HAR. In the Hysparin treated situation, Col-0 alleles on chromosome 1 and 3 are associated with a stronger response. Through crossing of specific CSLs, mapping populations are constructed where the chromosomes of interest (1, 2 and 3) are segregating whereas the other chromosomes are either Col-0 or Ler-0. The CSL population allows accurate mapping of chromosome regions that are associated with a high or low HAR phenotype. Variant analysis of Col-0 and Ler-0 based on available whole genome sequence data is used to identify candidate variants that are responsible for the natural variation between Col-0 and Ler-0. Currently we are identifying genes that underlie the phenotypic variation and we will test their contribution to the HAR formation process.

¹Verstraeten et al., unpublished

²CSL lines were obtained from Joost Keurentjes, WUR, NL

Figure 1: A) Average number of HAR on the hypocotyl of Col-0 and Ler-0 etiolated seedlings after 7 days of light growth in vitro. Untreated or with 10µM Hysparin. Error bars show SE. Letters indicate groups of significance. B) Phenotype of etiolated Col-0 seedlings after 7 days of light growth in vitro. Untreated or with 10µM Hysparin.