Integrative transcriptomic and physiological analyses uncover mechanisms by which arbuscular mycorrhizal fungi mitigate salt stress in sugar beet

Abstract

Sugar beet (Beta vulgaris L.) is cultivated extensively worldwide as an important cash crop, and soil salinity is a critical factor influencing both its yield and sugar content. Consequently, enhancing the salt tolerance of sugar beet is of paramount importance. Arbuscular mycorrhizal (AM) fungi form symbiotic associations with approximately 80% of vascular plants, thereby improving the adaptability of host plants to adverse conditions. However, the mechanisms by which the AM symbiosis assists sugar beet in coping with salt stress remain poorly understood. To investigate the adaptation strategies employed by AM symbiotic sugar beet under salt stress, we examined physiological and transcriptomic changes in sugar beet seedlings subjected to various treatments, using the KWS1176 variety as the experimental material. The results indicated that AM symbiotic sugar beet demonstrated superior performance under salt stress, characterized by improved seedling growth, alterations in antioxidant enzyme activities, modifications in osmoregulatory substance levels, reduced Na⁺ uptake, and enhanced K⁺ influx within the root system. Notably, most of the differentially expressed genes were implicated in pathways related to reactive oxygen species scavenging, phenylpropanoid biosynthesis, and phytohormone signal transduction. Furthermore, pivotal genes identified through weighted gene co-expression network analysis were validated via reverse transcription-quantitative PCR, revealing that the salt tolerance of AM symbiotic sugar beet may be associated with its ionic homeostasis, antioxidant enzyme activities, and regulation of photosynthesis at both transcriptional and physiological levels.

Keywords: Arbuscular mycorrhizal fungi; Gene expression; Physiology and biochemistry; Salt stress; Sugar beet; Weighted correlation network analysis.