Effects of Date Palm Waste Compost Application on Root Proteome Changes of Barley (Hordeum vulgare L.)

is one of the world's major cereal crops with high protein content and ranked fifth, after wheat, corn, and rice. In temperate regions, such as Tunisia, barley is commonly used for human food, animal feed, and malt production. It is better suited to dry conditions and is usually grown in semi-arid and arid regions. Barley is the most salt-tolerant cereal plant and is considered to be a moderately salt-tolerant crop. Low soil fertility and poor agronomic practices are among the major constraints for low productivity of barley in southern areas of Tunisia. The average barley grain yield was 0.85 t ha−1 lower than that of worldwide yields (3.25 t ha−1). Yields are characterized by instability and vary significantly from year to year. The use of organic amendments such as compost has been shown to improve soil quality and fertility, promoting plant growth, and increasing crop productivity. Compost increased soil microorganisms, total soil carbon, and nitrogen, resulting in improved radish growth and increased biomass. Similar results were reported in tomato and roselle plants. Compost positively affects root growth and biomass increase in grapevine and has a beneficial effect on soil fertility, yield, and grape quality. A significant increase in the germination rate of green bean seeds was observed upon the addition of different composts derived from municipal solid waste. Compost consistently promotes biological activity, which can increase germination. The application of date palm waste compost at 30 t ha−1 induces the expression of nutrient transporter genes in roots of barley, leading to improved macronutrient uptake by the plant and promoting plant growth, yield, and yield of barley grains. Compost applications may be an effective strategy for plant growth and development through physiological events and improving agricultural productivity. However, the modes of action describing the molecular mechanisms underlying compost effects on plants are largely unknown. Proteomics approaches, such as proteomic, proteomic, and proteomic, have contributed to the characterization of the molecular mechanism of action of some biostimulants and identifying their regulatory role in molecular and biochemical pathways. Several studies have successfully used proteomics as a discovery tool to uncover the mode of action of biostimulants and biofertilizers on plants at the cellular level. Understanding the subcellular localization and post-translational modifications of proteins is crucial for a comprehensive understanding of plant responses to organic amendments, biostimulants, and biofertilizer application. Proteomics, as a multidisciplinary omics, provides key fundamental knowledge on the mode of action of compost on crop plants, including barley. Unfortunately, no emerging studies in the literature reveal the potential and effectiveness of proteomics approaches in understanding the molecular mechanisms of compost action. Proteome analysis of the barley malt rootlet proteome revealed the upregulation of secondary metabolism, reactive oxygen species (ROS) detoxification, and protein biosynthesis pathways coordinated by phytohormones, such as jasmonic acid and auxin. Furthermore, proteomic analysis revealed that the upregulation of proteins is mainly related to genetic information and carbohydrate metabolism pathways during barley seed germination. The objective of the present study was to understand the physiological mechanisms underlying the effects of compost application on proteome, transcriptome, and metabolome changes in barley. The study aimed to investigate the differentially abundant proteins (DAPs) in barley roots during the tillering stage. Bioinformatic tools were used to interpret the biological function, biological function analysis, and visualization of the network amongst the identified proteins. A total of 72 DAPs (33 upregulated and 39 downregulated) were identified in response to compost treatment, suggesting multiple pathways of primary and secondary metabolism, such as carbohydrates and energy metabolism, phenylpropanoid pathway, glycolysis pathway, protein synthesis, redox homeostasis, RNA processing, stress response, cytoskeleton organization, and phytohormone metabolic pathways. The expression of DAPs was further validated by qRT-PCR. The effects of compost application on barley plant development, such as the promotion of root growth and biomass increase, were associated with a change in energy and protein synthesis. The activation of enzymes involved in redox homeostasis and stress response suggests a protective effect of compost, consequently improving barley growth and stress acclimation. Overall, these results facilitate a better understanding of the molecular mechanism of compost-promoted plant growth and provide information for the identification of genes/proteins in barley as potential targets of compost.