Comparative Physiological and Transcriptomic Analyses of Oat () Seedlings under Salt Stress Reveal Salt Tolerance Mechanisms.

Soil salinity is a major abiotic stress limiting crop production globally. Oat () is an annual cereal with a strong salt tolerance, a high yield, and nutritional quality, although the mechanisms underlying its salt stress response remain largely unknown. We examined the physiological and transcriptomic responses of seedlings to salt stress in tolerant cultivar Qingyongjiu 195 and sensitive cultivar 709. Under salt stress, Qingyongjiu 195 maintained a higher photosynthetic efficiency, antioxidant enzymes activity, and leaf K accumulation but a lower Na uptake than 709. RNA-seq revealed 6616 differentially expressed genes (DEGs), including 4265 up- and 2351 downregulated. These were enriched in pathways like plant-pathogen interaction, phenylpropanoid biosynthesis, and MAPK signaling. We specifically highlight DEGs involved in photosynthesis (, , , ) and antioxidants (, ). Qingyongjiu 195 also appeared to enhance K uptake via and and sequester Na in vacuoles via . Additionally, restricted Na while promoting K transport to shoots, maintaining K/Na. The expression levels of , , , , and in Qingyongjiu 195 were higher than those in 709. Oats regulated Ca concentration through CAX and ACA after salt stress, decoded Ca signals through CML, and then transferred Ca signals to downstream receptors through the Ca sensors CaM and CDPK, thereby activating K/Na transporters, such as SOS1 and NHX, etc. Our results shed light on plant salt stress response mechanisms and provide transcriptomic resources for molecular breeding in improving salt tolerance in oats.