Focus on DnaJ protein research from Arabidopsis to crop improvement.
DnaJ proteins (Hsp40s) are essential components of the cellular proteostasis network, functioning as molecular co-chaperones that regulate protein folding, stability, and stress-responsive homeostasis in plants. Beyond their classical role as Hsp70 partners, accumulating evidence demonstrates that DnaJ proteins participate in diverse biological processes by integrating proteostasis with hormonal, developmental, and defense signaling pathways. This review synthesizes recent advances in the structural diversity, evolutionary distribution, and functional specialization of DnaJ proteins across model plants and crops, including Arabidopsis, rice, maize, tomato, soybean, grapevine, citrus, cucumber, and other economically important species. We summarize mechanistic evidence demonstrating their involvement in abiotic stress tolerance, including heat, drought, salinity, osmotic, oxidative, and cold stress, through regulation of protein quality control, reactive oxygen species detoxification, ion homeostasis, abscisic acid and melatonin signaling, and transcriptional stress networks. Emerging studies further reveal their roles in biotic stress responses by modulating immune signaling, pathogen resistance, and host-microbe interactions, while additional evidence links DnaJ proteins to reproductive development, root architecture, chloroplast stability, fruit ripening, and postharvest quality maintenance. Advances in genome-wide identification, transcriptomic profiling, gene editing, transgenic validation, and functional genomics have substantially expanded understanding of DnaJ-mediated molecular networks and their contributions to climate resilience. By integrating mechanistic biology with translational breeding strategies, this review highlights DnaJ proteins as promising molecular targets for crop improvement and climate-smart agriculture aimed at increasing productivity, stress tolerance, and postharvest performance under changing environmental conditions.