Genome-wide identification and expression analysis of RsNRT gene family reveals their potential roles in response to low-nitrogen condition in radish (Raphanus sativus L.)

Abstract

Radish is an important economical vegetable crop that requires adequate nitrogen supply for taproot formation and enlargement. Nitrate transporter (NRT) family represents a key gatekeeper in modulating nitrogen uptake and utilization in plants. However, the comprehensive characterization of the NRT gene family remains largely unexplored in radish. Herein, a total of 39 RsNRT genes were identified from the radish genome, which were unevenly distributed onto eight chromosomes except Chr3. Phylogenetic analysis indicated that the NRT1 and NRT2 subfamily members from radish, Arabidopsis and Brassica rapa were classified into Cluster I and Cluster II, indicating that the NRT proteins were relatively conserved in the Brassicaceae family. A range of cis-regulatory elements (e.g. AuxRE, ABRE and LTR) in the promoter of RsNRTs were involved in phytohormone and abiotic stress response. Transcriptome-based expression analysis indicated that several RsNRTs showed differential expression under heat, salt or heavy metal stresses. RT-qPCR analysis revealed that six RsNRT genes, including RsNRT1.1a, RsNRT1.2a, RsNRT1.5a, RsNRT2.1b, RsNRT2.2a and RsNRT2.3b, exhibited significantly up-regulated expression under NO3− deficiency condition. Notably, the expression of RsNRT1.1a was significantly increased in both the ‘NAU-WXQ’ (low-N-sensitive) and ‘NAU-ZYQ’ (low-N-tolerant) genotypes under 5 mM NO3− treatment, indicating that it might act as a critical participator in root NO3− uptake under low-N supply condition. These results would provide fundamental basis to decipher the molecular mechanisms underlying RsNRT-mediated N absorption and translocation in radish.