Genome-Wide Analysis of NLP Genes in Peanut Reveals Significant Roles of AhNINa and AhNINb in Root Nodule Development

Nitrogen is an indispensable nutrient for plant growth and crop production, but it is not directly accessible to plants without the help of nitrogen-fixing bacteria. Legume plants can form root nodules in symbiosis with rhizobia. NODULE INCEPTION (NIN), a founding member of the NIN-like protein (NLP) family, is essential for nodulation in legume species. However, the knowledge of functional characteristics of the NLP family members in peanuts is limited. In this study, a genome-wide analysis of the NLP genes was carried out. A total of 16 NLP genes were identified in the peanut genome, including 2 AhNIN and 14 AhNLP, which were unevenly distributed on nine chromosomes of the peanut genome. Furthermore, transcriptomic profiles and expression pattern analysis showed that both AhNINa and AhNINb genes were specifically expressed in root nodules. Subcellar localization and transcriptional activity analysis revealed that both AhNINa and AhNINb encode transcriptional activators. In addition, the roots that down-regulated the expression of AhNINa and AhNINb genes failed to form nodules. These findings provide significant insights into the molecular functions of AhNINa and AhNINb genes in regulating peanut nodule development.