Up-regulation of CmNRTs and CmANR1 genes expression contribute to root configuration changes for efficient capturing NO3− in the roots of chrysanthemum

- Nitrate nitrogen nutrition improved the growth and development of chrysanthemum.
- Improvement in growth and development of chrysanthemum treated with 5 mM KNO3 depended on the overexpression of CmNRTs and CmANR1 genes, and the growth of lateral roots.
- Enhancement in endogenous hormones (IAA and CTK) contents, NO3− nitrogen contents and vascular bundle structure changes can influence chrysanthemum roots morphological structure.

Nitrogen is very important to the yield and quality of chrysanthemum. However, excessive application not only negatively affects the yield and quality of chrysanthemum, but also can not be timely absorbed and utilized for chrysanthemum, so causes a lot of waste of fertilizer resources and serious pollution of groundwater environment. Nitrate nitrogen is the main form of nitrogen uptake by the roots of chrysanthemum. The uptake of NO3− by plants is mostly achieved by NO3− transporters (NRTs) and lateral root formation. However, the morphological structure and molecular mechanism of the response to nitrate signaling in the roots of chrysanthemum are poorly understood. In this study, we investigated that the response to NO3− signaling from the viewpoint of roots morphology and anatomical structure, roots NO3− contents, endogenous hormones contents and expression of related genes in the roots of chrysanthemum. A hydroponic experiment was performed using the rooted cuttings of chrysanthemum, with KNO3 treatments (control for Hogland nutrient solution without N element) for seven times at 0, 1, 2, 3, 4, 5, 6 days, respectively. The results showed that the roots morphological indexes increased significantly in the KNO3 treatments compared to those of the controls at 6 days after treatments, which were associated with the high expression of CmNRT1.1, CmNRT2.1, CmNAR2.1 and CmANR1, which related to NO3− transport genes and lateral root development gene, the contents of NO3−, indole-3-acetic acid (IAA) and cytokinin (CTK) in the roots and the improved root microscopic structure in KNO3 treatment. The promoting effect of KNO3 shows an obvious time-effect. The results from correlation analysis indicated that the responses of chrysanthemum root to NO3− signaling could be related with the induction of NO3− signaling, the gene expression of NO3− transporter genes and lateral root development gene due to regulating the IAA, CTK levels and adjusting the root architecture of the root system.