Identification of Low-Nitrogen-Related miRNAs and Their Target Genes in Sugarcane and the Role of in Nitrogen Assimilation.

Chemical nitrogen (N) fertilizer is widely used in sugarcane production, especially in China and India. Understanding the molecular mechanisms and mining miRNAs and their target genes associated with nitrogen use efficiency (NUE) in sugarcane can aid in developing the N-efficient varieties, and thus is beneficial to reduce N fertilizer application. In this study, the root miRNA database of N-efficient sugarcane variety ROC22 under low N stress (0.3 mM NHNO) for 3 h was constructed, along with their transcriptome-rearranged data. KEGG analysis indicated that those candidate target genes, corresponding to differentially expressed miRNAs, were mainly enriched in N metabolism, amino acid metabolism, carbohydrate metabolism, photosynthesis, and hormone signal transduction pathways. It was found that under low N stress for 0-24 h, there was a negative correlation between and , along with and . Furthermore, the expression of in the roots of ROC22 was significantly up-regulated under low N treatment. Compared with the wild-type, the plants overexpressing sugarcane exhibited significantly improved length and surface area of roots, while the expression of one NO transporter gene , three N assimilation key genes (, , and ), and the activity of two N assimilation key enzymes (NR and GS) were up-regulated under low N treatment. It can be reasonably deduced that sugarcane can enhance the nitrogen assimilation ability of the overexpressed plants under low N application, and thus has a potential ability for improving sugarcane NUE. The present study should be helpful for understanding the molecular regulatory network in the N-efficient sugarcane genotype responding to low N stress and could provide the candidate miRNAs with a potential function in improving sugarcane NUE.