The actinorhizal symbiosis of Datisca
glomerata: Search for nodule-specific
marker genes
Irina V. Demina
Academic dissertation for the Degree of Doctor of Philosophy in Plant
Physiology at Stockholm University to be publicly defended on Wednesday
25 September 2013 at 13:00 in föreläsningssalen, Institutionen för ekologi,
miljö och botanik, Lilla Frescativägen 5.
Abstract
The actinorhizal symbiosis is entered by nitrogen-fixing actinobacteria of the genus Frankia
and a large group of woody plant species distributed among eight dicot families. The
actinorhizal symbiosis, as well as the legume-rhizobia symbiosis, involves the stable intracellular
accommodation of the microsymbionts in special organs called root nodules. Within the nodules,
the nitrogen-fixing bacteria are provided with carbon sources by the host plant while supplying the
plant with fixed nitrogen, which is often a limiting factor in plant growth and development.
Datisca glomerata (C. Presl.) Baill. (Datiscaceae, Cucurbitales) is a suffruticose plant with a
relatively short generation time of six months, and therefore represents the actinorhizal species
most suited as a genetic model system. In order to obtain an overview of nodule development and
metabolism, the nodule transcriptome was analyzed. Comparison of nodule vs. root transcriptomes
allowed identification of potential marker genes for nodule development. The activity of the
promoters of two of these genes was studied in planta. Furthermore, auxins and cytokinins were
quantified in roots and nodules, and the auxin responses in roots were compared in D. glomerata
and the model legume Medicago truncatula.
Our results indicate that in actinorhizal plants signaling in the root epidermis leading to
nodule organogenesis follows the common symbiosis pathway described for the legume-rhizobia
symbiosis and arbuscular mycorrhiza. Moreover, we discovered a group of nodule-specific genes
encoding defensin-like peptides with an unusual C-terminal domain that had not been found in other
plant species. A possible role in the symbiosis-specific differentiation of the microsymbiont and
in nodule development was suggested for these cysteine-rich peptides. Finally, we showed that D.
glomerata and M. truncatula differ in their auxin and cytokinin requirements for the development
of both nodules and lateral roots.
Keywords: actinorhizal symbiosis, Datisca glomerata, nodule transcriptome, nodule-specific
marker genes, cysteine-rich peptides, auxins and cytokinins.
Stockholm 2013
http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-92857
ISBN 978-91-7447-691-0
Department of Ecology, Environment and Plant
Sciences
Stockholm University, 106 91 Stockholm