SummaryRoot nodule symbioses (RNS) allow plants to acquire atmospheric nitrogen by establishing an intimate relationship with either rhizobia, the symbionts of legumes or Frankia in the case of actinorhizal plants. In legumes, NIN (Nodule INception) genes encode key transcription factors involved in nodulation.Here we report the characterization of CgNIN, a NIN gene from the actinorhizal tree Casuarina glauca using both phylogenetic analysis and transgenic plants expressing either ProCgNIN::reporter gene fusions or CgNIN RNAi constructs.We have found that CgNIN belongs to the same phylogenetic group as other symbiotic NIN genes and CgNIN is able to complement a legume nin mutant for the early steps of nodule development. CgNIN expression is correlated with infection by Frankia, including preinfection stages in developing root hairs, and is induced by culture supernatants. Knockdown mutants were impaired for nodulation and early root hair deformation responses were severely affected. However, no mycorrhizal phenotype was observed and no induction of CgNIN expression was detected in mycorrhizas.Our results indicate that elements specifically required for nodulation include NIN and possibly related gene networks derived from the nitrate signalling pathways.

Lateral root organogenesis plays an essential role in elaborating plant root system architecture. InArabidopsis, the AP2 family transcription factor PUCHI controls cell proliferation in lateral root primordia. To identify potential targets of PUCHI, we analyzed a time course transcriptomic dataset of lateral root formation. We report that multiple genes coding for very long chain fatty acid (VLCFA) biosynthesis enzymes are induced during lateral root development in a PUCHI-dependent manner. Significantly, several mutants perturbed in VLCFA biosynthesis show similar lateral root developmental defects aspuchi-1. Moreover,puchi-1roots display the same disorganized callus formation phenotype as VLCFA biosynthesis-deficient mutants when grown on auxin-rich callus-inducing medium. Lipidomic profiling ofpuchi-1roots revealed reduced VLCFA content compared with WT. We conclude that PUCHI-regulated VLCFA biosynthesis is part of a pathway controlling cell proliferation during lateral root and callus formation.