Magnesium response in tobacco seedlings: Insights from proteome and phosphoproteome analyses

Tobacco (Nicotiana tabacum L.) requires magnesium for its leaf yield and quality, though its application is often neglected in the production of this industrial crop. This study used the four-dimensional data-independent acquisition-based quantitative proteomic and phosphoproteomic technology to elucidate the mechanisms of the responses of tobacco root and shoot to low (L), medium (M), and high (H), consisting mainly of 2.5, 250, and 2.5 × 10³ μM of Mg, respectively. The most significantly enriched pathways in the proteome were starch and sucrose metabolism in the root under high Mg supply and photosynthesis in the shoot under low Mg supply. The differential phosphoproteins were significantly enriched in the ribosome in roots and spliceosome in shoots. Magnesium transporters (MRS2–1, MRS2–3, MRS2–5, MRS2-I and NIPA3), ABC transporters, nitrogen, phosphorus, potassium, and calcium-associated transporters, and transcription factors (TFs), such as VIP1, WRKY46, WRKY32, WRKY6, HY5, CAMTA4, HSFA1, MYC2, ERF25 and TCP11, were considered differentially expressed proteins or phosphoproteins under deficiency or excess in Mg. However, CDPKs, RLKs, and MAPK3s were the differential phosphoproteins in both roots and shoots under Mg deficiency. An increase or decrease in the abundance of these transporters, TFs, and kinases modulates the activity of the proteins or phosphoproteins under different Mg supplies. It may also play essential roles in the ion homeostasis of tobacco cells, transduction of Mg signal, and transcriptional regulation of genes that respond to low or high Mg stress. Therefore, these findings provide new insights into the molecular mechanisms of the responses of tobacco to low or high Mg stress and a theoretical basis for the production of high-quality tobacco.