Interfering small ubiquitin modifiers (SUMO) exhibits apple's enhanced tolerance to nitrogen deficiency

Abstract

Nitrogen is one of the most critical macroelements required for apple biomass accumulation and quality formation. Thus, identification and characterization of candidate genes involved in nitrogen deficiency stress is of great importance to the sustainable development of the apple industry. SUMOylation is a kind of post-translational modification, which is widely involved in plant life processes, including responses to nitrogen (N) deficiency. Here, we identified apple small ubiquitin modifiers (SUMO) that participated in responding to nitrogen deficiency. Firstly, all isoforms of apple SUMOs were induced by N deficiency stress. Under N deficiency stress conditions, the MdSUMO2 RNAi transgenic apple plants showed better growth potential than the wild type GL-3, including more new leaves, increased height, thicker stems, and heavier fresh weight. In addition, the MdSUMO2 RNAi transgenic apple plants exhibited darker green leaves and greater root volume than GL-3 in response to N deficient conditions. Finally, the activated glutamine synthetase (GS) activity, nitrate reductase (NR) activity, as well as the induced expression of genes involved in nitrogen assimilation in the root might contribute to the tolerance of MdSUMO2 RNAi transgenic apple plants in response to nitrogen deficiency. Taken together, our finding provides insight to further study the mechanisms underlying the essential roles of apple MdSUMOs in responding to N deficient conditions.