Regulation of nodule identity

SYMUNITY team / Pascal Ratet

Characterization of symbiotic mutants affected in nodule identity: (Couzigou et al., 2012; Magne et al., 2018a; 2018b)

We have investigated the role of NOOT-LIKE genes, belonging to the NOOT-BOP-COCH-like (NBCL) gene family, in the regulation of nodule identity. These genes encode orthologs to Arabidopsis BOP1 and BOP2 proteins and contain a BTP/POZ domain and ankyrin regions. We have shown that the Medicago NOOT1 and NOOT2 genes are required for nodule identity (Figure 2). Genetic studies have been performed in different legumes such as Medicago truncatula, Lotus japonicus and Pisum sativum. This Evo-Devo approach allows us to have a better vision of the role of NBCL genes in these different legumes.

Figure 2. Magne et al. (2018a), cover of the 'Plant Physiology' journal: The Medicago truncatula homeotic noot1noot2 double mutant exhibits a complete loss of nodule identity, characterized by a complete reversion of nodule identity to root. This homeotic conversion confirms that the nodule vascular system is ontologically related to the root and highlights the evolutionary pathway by which the symbiotic organ originated.

Role of NOOT-like / NBCL genes in the cereal plant Brachypodium distachyon (Magne et al., 2020; Liu et al., 2022)

We have also investigated the role of NOOT/BOP homologs in monocotyledonous plants (cereals) to determine if their role in organ identity is conserved between these plants. These genes, named BdUNICULME4-LIKE (BdCUL4-LIKE) and BdLAXATUM-A-LIKE (BdLAXA-LIKE) in Brachypodium distachyon are orthologous to the HvCul4 and HvLax-a genes in barley. In order to investigate the roles of the BdCUL4-LIKE and BdLAXA-LIKE genes in the development of the undomesticated cereal B. distachyon, we studied allelic mutants obtained by TILLING or CRISPR-Cas9 technologies. Analysis of these mutants (single or double) showed their important role in development in monocots.