Nodule ontogenesis - Molecular Biology

Thesis subjects Nodule ontogenesis

On this page descriptions of thesis projects of the nodule ontogenesis group are given:


  1. Nodule meristem formation
  2. The role of peptide growth regulator enod40 in plant and nodule development


1. Nodule meristem formation


In plants two meristems are laid down during embryogenesis at the apices, the shoot and the root meristem, respectively. Organ formation during post-embryonal development originates from either of these two meristems. In Arabidopsis thaliana, meristem formation and organization has well been documented. From these studies it has become clear that both root and shoot meristems contain a number of undifferentiated stem cells. Organizing cells are keeping the stem cells in an undifferentiated state and together with the stem cells form the stem cell niche. Medicago  orthologs of  stem cell expressed genes have been isolated. These genes have been used to study the nodule meristem organization and revealed that this meristem consists of two different stem cell niches (fig.1). Functional analyses of stem cell maintenance PLETHORA (PLT) genes showed that root developmental programs also direct nodule development. Currently, we are studying the role of these PLT genes in forming the central nodule tissue, containing the cells that harbour the rhizobium symbiont. 


Figure 1. promoter::GUS patterns of stem cell markers MtPLT1-3 and organizing centre marker WOX5.
Figure 1. promoter::GUS patterns of stem cell markers MtPLT1-3 and organizing centre marker WOX5.


2. Peptide growth regulator enod40


One of the earliest legume genes induced during root nodule development is ENOD40. This gene is essential for nodule organogenesis. Furthermore, it is one of the first genes identified in plants that encode a peptide; in animals, peptides often have a role as signal molecules. Strikingly, the major part of the ENOD40 mRNA is a 3’UTR, which contains a domain involved in translational regulation of ENOD40 mRNA (fig.2).

ENOD40 is present in nonlegumes, like Arabidopsis. Here, this gene is involved in hormone-controlled root growth. Currently, we are dissecting the working mechanism of the peptide in this process in Arabidopsis. It is anticipated that this can be instructive on how legumes have co-opted  ENOD40 in nodule development as this is also a hormone-controlled process.


Figure 2. The 3’UTR of Arabidopsis ENOD40 (A,B) and Medicago (C_F) contains a domain that upon deletion (B, D) leads to a higher level of ENOD40-GFP/RFP production. E and F are bright field micrographs of roots C and D. In both plants ENOD40 is expressed in the pericycle.
Figure 2. The 3’UTR of Arabidopsis ENOD40 (A,B) and Medicago (C_F) contains a domain that upon deletion (B, D) leads to a higher level of ENOD40-GFP/RFP production. E and F are bright field micrographs of roots C and D. In both plants ENOD40 is expressed in the pericycle.



Practical work


  • Molecular biology techniques for construction of genes of interest.
  • Functional analyses using RNA interference, over-expression constructs.
  • Expression analyses (promoter-GUS reporter constructs, Real-time RT-PCR (qPCR), in situ hybridization).
  • Light, Confocal Laser Scanning Microscopy.
  • Agrobacterium rhizogenes/tumefaciens-mediated plant root transformation.
  • Genetics and pheno/geno-typing.