Unravelling the distinctive growth mechanism of proso millet (Panicum miliaceum L.) under salt stress: From root‐to‐leaf adaptations to molecular response

Proso millet (Panicum miliaceum L.) has potential applications as a new source of bioenergy owing to its high‐yielding C4 attribute. Besides, it has a short life cycle, high harvest index, low planting costs, and strong adaptability and resistance. This study comprehensively reveals the sodium ion (Na+) toxicity resistance strategies from germination to the seedling stage, root to leaf, outside to inside, macro to micro, and the phenotype to the mechanism. Comparative phenotypic and physiological analysis suggested that salt‐tolerant proso millet (ST 47) had better salt tolerance, biomass accumulation, and osmo‐protection than salt‐sensitive proso millet (SS 212). Microstructural analysis indicated that ST 47 could maintain better internal surfaces and intact structures to resist Na+ toxicity and maintain optimal growth. Further, digital RNA sequence analysis indicated that ST 47 could maintain better Na+ and K+ homeostasis by coordinated regulation of transporter genes; the abundance of transcripts involved in chlorophyll metabolism and photosynthesis pathways was higher in ST 47 than SS 212, which contributed to the biomass accumulation. These results suggest that ST 47 resists Na+ toxicity via coordinated physiological, morphological, and molecular mechanisms. Therefore, this crop can serve as an emerging salt‐tolerant bioenergy crop for sustainable saline agriculture and simultaneous phytoremediation.