An R2R3-MYB Transcription Factor CmMYB42 Improves Low-Nitrogen Stress Tolerance in Chrysanthemum

Plant roots can sense the nitrogen level in the environment and change the expression of related genes to maintain normal life activities. However, their regulatory mechanism in Chrysanthemum has not been fully clarified. In this study, an R2R3-MYB transcription factor CmMYB42 was isolated from Chrysanthemum ‘Jinba.’ Tissue expression analysis showed that the gene was mainly expressed in the root and could rapidly up-regulate the expression of CmMYB42 under low-nitrogen conditions. Subcellular localization analysis showed that CmMYB42 was located in the nucleus. Under low-nitrogen stress, overexpressing CmMYB42 Chrysanthemum’s total root length, lateral root number, plant height, and biomass accumulation were significantly higher than wild type and slowed down the damage to photosynthetic system and improved NO3− content and nitrogen metabolism assimilation enzyme activity. In addition, we also found that CmMYB42 increased the expression of nitrogen stress-related genes. These results indicated that CmMYB42 acts as a positive regulator to improve the tolerance of Chrysanthemum to low-nitrogen stress, providing a theoretical basis for further exploring the molecular mechanism of low-nitrogen tolerance in Chrysanthemum.