Molecular Soil Biology 2024, Vol.15, No.1, 8-16 http://bioscipublisher.com/index.php/msb 11 PGPR like Pseudomonas and Bacillus species produce antibiotics, siderophores, and lytic enzymes that inhibit the growth of pathogenic microbes (Bhattacharyya and Jha, 2011; Hayat et al., 2012; Mohanty et al., 2021). PGPR produce a variety of antimicrobial compounds such as hydrogen cyanide, phenazines, and pyrrolnitrin, which directly inhibit the growth of phytopathogens (Bhattacharyya and Jha, 2011; Hayat et al., 2012; Mohanty et al., 2021). These compounds disrupt the cell membranes of pathogens, interfere with their metabolic processes, and ultimately lead to their death. PGPR can induce systemic resistance in plants, making them more resilient to pathogen attacks. This is achieved through the activation of plant defense mechanisms, including the production of pathogenesis-related proteins and secondary metabolites (Bhattacharyya and Jha, 2011; Hayat et al., 2012). For example, the production of volatile organic compounds (VOCs) by PGPR can trigger systemic resistance in plants, enhancing their overall immunity against a wide range of pathogens (Bhattacharyya and Jha, 2011; Hayat et al., 2012). In summary, PGPR offer multifaceted benefits in crop growth by enhancing nutrient acquisition, improving stress tolerance, and suppressing diseases through various biochemical and molecular mechanisms. These attributes make PGPR a valuable tool in sustainable agriculture, reducing the reliance on chemical fertilizers and pesticides while promoting healthier and more resilient crops. 3 Genomic and Proteomic Insights 3.1 Genomic studies Recent advancements in sequencing technologies have significantly enhanced our understanding of the genomic landscape of Plant Growth-Promoting Rhizobacteria (PGPR). High-throughput sequencing methods, such as next-generation sequencing (NGS), have enabled comprehensive genomic analyses, facilitating the identification of key genes and regulatory networks involved in PGPR-plant interactions. These technologies have allowed researchers to sequence entire genomes of various PGPR strains, providing insights into their genetic makeup and potential functional capabilities (Verma et al., 2018). Genomic studies have identified several key genes that play crucial roles in the interaction between PGPR and plants. These genes are involved in various processes such as nitrogen fixation, production of phytohormones, and synthesis of antimicrobial compounds. For instance, genes responsible for the production of indole-3-acetic acid (IAA), a plant hormone that promotes root elongation, have been identified in multiple PGPR strains (Ambrosini and Passaglia, 2017). Additionally, genes encoding for enzymes involved in phosphate solubilization and siderophore production, which enhance nutrient availability to plants, have also been characterized (Verma et al., 2018). The expression of these genes is often regulated in response to plant signals, highlighting the dynamic nature of PGPR-plant interactions. 3.2 Proteomic studies Proteomic analyses have revealed a diverse array of proteins and enzymes secreted by PGPR that contribute to plant growth promotion and stress resistance. For example, the proteomic study of Paenibacillus polymyxa E681 interacting with Arabidopsis thaliana identified 41 differentially expressed proteins, including those involved in amino acid metabolism, antioxidant activity, and defense responses (Kwon et al., 2016). These proteins play vital roles in enhancing plant growth and providing resistance against environmental stresses. The functional roles of PGPR proteins in promoting plant growth are multifaceted. Proteins involved in nitrogen fixation, such as nitrogenase, facilitate the conversion of atmospheric nitrogen into a form that plants can readily assimilate (Ambrosini and Passaglia, 2017). Enzymes like ACC deaminase lower plant ethylene levels, which can otherwise inhibit root growth under stress conditions (Ambrosini and Passaglia, 2017). Additionally, proteins involved in the synthesis of antimicrobial compounds help in suppressing plant pathogens, thereby protecting the plants and promoting healthier growth (Verma et al., 2018). The upregulation of defense-related proteins in plants treated with PGPR, as observed in proteomic studies, further underscores the role of these proteins in enhancing plant resilience against biotic and abiotic stresses (Kwon et al., 2016; Dhawi, 2020).
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