Identification of nodule-inception-like protein (NLP) transcription factor family and analysis of their expression under abiotic stresses in Rhododendron henanense subsp. lingbaoense

Nodule-inception-like protein (NLP) is a plant-specific transcription factor, which plays a key role in the response to nitrogen deficiency and nitrogen signaling regulation. In this study, the members of RhlNLP transcription factor family were identified in Lingbao rhododendron, and their expression in response to abiotic stresses was explored. A total of 11 NLP members containing RWP-RK and PB1 conserved domains were identified in Lingbao rhododendron. The genes were distributed on five chromosomes. Phylogenetic analysis indicated that the 11 RhlNLPs were divided into three subfamilies. Interspecific collinearity analysis suggested that the collinearity of NLP gene between Lingbao rhododendron and other three dicots was higher than that between Lingbao rhododendron and monocots. Each subfamily of RhlNLPs had unique motifs. Overall, 31 main cis-elements were observed in RhlNLP promoter sequences, e.g., light-responsive element, hormone-responsive element, defense- and stress-responsive element, and development-responsive element. RhlNLPs were highly expressed in certain tissues. The GO analysis of RhlNLP proteins revealed that they were involved in biological process and molecular functions. miRNA169 and miRNA171 families participated in NLP-mediated nitrogen response. From the network of NLP protein interactions, RhlNLP11 may be related to nitrogen absorption, transport, and assimilation. RhlNLPs were upregulated under PEG and low-temperature stresses, and their expression was remarkably inhibited by nitrogen starvation. This study enhanced the understanding of the biological functions of NLP gene family and its regulatory functions under various abiotic stresses.