Phosphoproteomics revealed salt stress tolerance mechanisms in the roots of sugar beet monomeric addition line M14.

Soil salinity is a major abiotic stress that limits global crop production and food security. It is necessary to explore the mechanisms of salt stress tolerance in order to cultivate high-quality salt-tolerant varieties. Sugar beet M14 line exhibits capability of salt stress tolerance. Here we conducted a phosphoproteomic study of the sugar beet M14 roots treated with 200 mM and 400 mM NaCl. Using phosphopeptide enrichment and LC-MS/MS based phosphoproteomics techniques, 1427 differential abundant phosphoproteins (DAPPs) and 983 unique phosphoproteins were identified under 200 mM NaCl. 1234 DAPPs and 769 unique phosphopeptides were identified under 400 mM NaCl. The two datasets were significantly enriched for terms associated with protein kinases and transcription factors. Meanwhile, the biological pathways enriched between 200 mM and 400 mM NaCl containing signaling pathways, metabolism and transport were prominently represented, suggesting that distinct signaling cascades may converge in key biological processes (e.g., glycolysis, transport and reactive oxygen metabolism) to mediate the salt stress response and tolerance. Furthermore, unlike the DAPPs enriched in sugar beet M14 leaves, the DAPPs enriched in roots specifically participated in the plant-pathogen interaction and prenyltransferase pathways. Significance: Sugar beet is an important sugar-producing crop, and its roots are the primary organ usually affected by salt stress. However, the phosphoproteomics of sugar beet M14 roots under salt stress remains unclear. This study emphasizes the changes in the phosphorylation level of sugar beet M14 roots proteins under different salt concentrations. We analyzed the similarities and differences in function and participating pathways of the DAPPs and unique phosphoproteins obtained at different salt stresses. These findings not only provide important insights into the mechanisms mediated by phosphorylation modification in sugar beet M14 response to salt stress, but also will inform efforts toward improving crop yield and quality.