Cleaner production of proso millet (Panicum miliaceum L.) in salt-stressed environment using re-watering: From leaf structural alleviations to multi-omics responses

Severe environmental conditions inhibit plant growth, which is rapidly restored when conditions improve. However, the mechanisms underlying re-watering to relieve Na+ toxicity and promote growth in proso millet are unclear. Herein, comparative phenotypic, physiological, phytohormone and multi-omics analyses between salt-sensitive (SSR) and salt-tolerant (STIM) proso millet cultivars were performed under salt stress and subsequent re-watering. Phenotypic and physiological analyses suggested that the accumulation of biomass and growth rate of STIM were not only higher after stress recovery than SSR but also higher than its control condition (STIM_CK), showing a compensation effect. A microstructural analysis indicated that STIM maintained a better surface structure, internal structure, and chloroplasts after stress recovery compared with its reactions under salt stress. A phytohormone analysis showed that the jasmonic acid (JA) and jasmyl-L-isoleucine (JA-Ile) contents specifically and significantly increased in STIM under salt stress and recovered with re-watering. Transcriptome analysis suggested that 3160 differentially expressed genes (DEGs) (1671 DEGs were downregulated, and 1589 DEGs were upregulated) and 1319 DEGs (565 DEGs were downregulated, and 751 DEGs were upregulated) were specifically identified in STIM under salt stress and re-watering, respectively, whereas 6184 DEGs (2666 DEGs were downregulated, and 3518 DEGs were upregulated) and 2721 DEGs (1175 DEGs were downregulated, and 1546 DEGs were upregulated) were detected in SSR. Proteomes analyses showed that up to 38.28% and 44.68% of proteins were individually expressed specifically at the protein level in SSR under salt stress and subsequent re-watering, respectively, and 43.56% and 39.31% in STIM, respectively, indicating the involvement of posttranscriptional regulation under salt stress and subsequent re-watering. Subsequently, the functions of commonly regulated DEGs and differentially expressed proteins (DEPs) were analyzed, which were significantly enriched in photosynthesis and porphyrin and chlorophyll metabolism pathways. Therefore, this study provides guidelines for phytoremediation and utilization of saline soils, and cleaner crop production.