The transcriptional co-regulators NBCL1 and NBCL2 redundantly coordinate aerial organ development and root nodule identity in legumes.

Medicago truncatula NODULE ROOT1 (MtNOOT1) and Pisum sativum COCHLEATA1 (PsCOCH1) are orthologous genes belonging to the NOOT-BOP-COCH-LIKE (NBCL) gene family which encodes key transcriptional co-regulators of plant development. In Mtnoot1 and Pscoch1 mutants, the development of stipule, flower and symbiotic nodules is altered. MtNOOT2 and PsCOCH2 represent the single paralogs of MtNOOT1 and PsCOCH1, respectively. In M. truncatula, MtNOOT1 and MtNOOT2 are both required for the establishment and maintenance of the symbiotic nodule identity. In contrast to the NBCL1 genes, the role of NBCL2 genes in legume above-ground development is not known. To better understand the roles of NBCL genes in legumes, we used M. truncatula and P. sativum nbcl mutants from the literature, isolated a knockout mutant for the PsCOCH2 locus and generated Pscoch1coch2 double mutants in P. sativum. These new mutant lines enabled to compare the roles of MtNOOT2 and PsCOCH2 in both M. truncatula and P. sativum legume development. Our work shows that the single Mtnoot2 and Pscoch2 mutants develop wild-type stipules, flowers and symbiotic nodules. However, the number of flowers was increased and the pods and seeds were smaller in comparison to wild type. Furthermore, in comparison to the corresponding nbcl1 single mutants, both the M. truncatula and P. sativum nbcl double mutants show a drastic alteration in stipule, inflorescence, flower and nodule development. Remarkably, in both M. truncatula and P. sativum nbcl double mutants, stipules are transformed into a range of aberrant leaf-like structures.