Secretory molecules from secretion systems fine-tune the host-beneficial bacteria (PGPRs) interaction

Abstract

Numerous bacterial species associate with plants through commensal, mutualistic, or parasitic association, affecting host physiology and health. The mechanism for such association is intricate and involves the secretion of multiple biochemical substances through dedicated protein systems called secretion systems SS. Eleven SS pathways deliver protein factors and enzymes in their immediate environment or host cells, as well as in competing microbial cells in a contact-dependent or independent fashion. These SS are instrumental in competition, initiation of infection, colonization, and establishment of association (positive or negative) with host organisms. The role of SS in infection and pathogenesis has been demonstrated for several phytopathogens, including Agrobacterium, Xanthomonas, Ralstonia, and Pseudomonas. Since there is overlap in mechanisms of establishing association with host plants, several studies have investigated the role of SSs in the interaction of plant and beneficial bacteria, including symbiotic rhizobia and plant growth bacteria (PGPB). Therefore, the present review updates the role of different SSs required for the colonization of beneficial bacteria such as rhizobia, Burkholderia, Pseudomonas, Herbaspirillum, etc., on or inside plants, which can lead to a long-term association. Most SS like T3SS, T4SS, T5SS, and T6SS are required for the antagonistic activity needed to prevent competing microbes, including phytopathogens, ameliorate biotic stress in plants, and produce substances for successful colonization. Others are required for chemotaxis, adherence, niche formation, and suppression of immune response to establish mutualistic association with host plants.

Omics approaches in understanding the benefits of plant-microbe interactions

“…These elements facilitate genetic exchange through tra genes, such as traD, traR, and traG, which are analogous to virD4 and are essential for conjugative transfer within rhizobial populations. Additionally, Mesorhizobium loti strain R7A utilizes its T4SS to transfer specific proteins, such as Msi059 (a protease) and Msi061 (involved in ubiquitinylation), contributing to various cellular processes and interactions with host plants (Gupta et al, 2024 ). Furthermore, T6SS genes are prevalent in plant-associated bacteria, including rhizobial species, and play a crucial role in interbacterial competition, providing advantages in multimicrobial plant environments (De Sousa et al, 2023 ).…”

Effects of T3SS-positive Pseudomonas isolates on sugar beet growth stimulation and pathogen resistance

“…Recent advances in molecular biology and high-throughput sequencing methods have provided unprecedented insights into the diversity of microbial communities. Microorganisms modulate host physiology through the secretion of bioactive substances whose precise delivery mechanisms exert a signi cant in uence on host cellular processes (Gupta et al 2024). In particular, syringe-shaped secretion systems such as the type 3 secretion system (T3SS), which is widespread in Gram-negative bacteria, serve as conduits that enable the direct injection of protein effectors into the cytoplasm of host cells.…”