RESUMO
Legume plants have developed the capacity to establish symbiotic interactions with soil bacteria (known as rhizobia) that can convert N2 to molecular forms that are incorporated into the plant metabolism. The first step of this relationship is the recognition of bacteria by the plant, which allows to distinguish potentially harmful species from symbiotic partners. The main molecular determinant of this symbiotic interaction is the Nod Factor, a diffusible lipochitooligosaccharide molecule produced by rhizobia and perceived by LysM receptor kinases; however, other important molecules involved in the specific recognition have emerged over the years. Secreted exopolysaccharides and the lipopolysaccharides present in the bacterial cell wall have been proposed to act as signaling molecules, triggering the expression of specific genes related to the symbiotic process. In this review we will briefly discuss how transcriptomic analysis are helping to understand how multiple signaling pathways, triggered by the perception of different molecules produced by rhizobia, control the genetic programs of root nodule organogenesis and bacterial infection. This knowledge can help to understand how legumes have evolved to recognize and establish complex ecological relationships with particular species and strains of rhizobia, adjusting gene expression in response to identity determinants of bacteria.
Assuntos
Fabaceae/microbiologia , Modelos Biológicos , Rhizobiaceae/metabolismo , Transdução de Sinais , Simbiose/fisiologia , Fabaceae/genética , Fabaceae/metabolismo , Proteínas Fúngicas/química , Proteínas Fúngicas/metabolismo , Proteínas Adaptadoras de Sinalização NOD/química , Proteínas Adaptadoras de Sinalização NOD/metabolismo , Proteínas Adaptadoras de Sinalização NOD/fisiologia , Proteínas de Plantas/química , Proteínas de Plantas/genética , Proteínas de Plantas/metabolismo , Nódulos Radiculares de Plantas/genética , Nódulos Radiculares de Plantas/metabolismo , Nódulos Radiculares de Plantas/microbiologia , Especificidade da Espécie , Simbiose/genética , TranscriptomaRESUMO
Early sensing of pathogenic bacteria by the host immune system is important to develop effective mechanisms to kill the invader. Microbial recognition, activation of signaling pathways, and effector mechanisms are sequential events that must be highly controlled to successfully eliminate the pathogen. Host recognizes pathogens through pattern-recognition receptors (PRRs) that sense pathogen-associated molecular patterns (PAMPs). Some of these PRRs include Toll-like receptors (TLRs), nucleotide-binding oligomerization domain-like receptors (NLRs), retinoic acid-inducible gene-I- (RIG-I-) like receptors (RLRs), and C-type lectin receptors (CLRs). TLRs and NLRs are PRRs that play a key role in recognition of extracellular and intracellular bacteria and control the inflammatory response. The activation of TLRs and NLRs by their respective ligands activates downstream signaling pathways that converge on activation of transcription factors, such as nuclear factor-kappaB (NF-κB), activator protein-1 (AP-1) or interferon regulatory factors (IRFs), leading to expression of inflammatory cytokines and antimicrobial molecules. The goal of this review is to discuss how the TLRs and NRLs signaling pathways collaborate in a cooperative or synergistic manner to counteract the infectious agents. A deep knowledge of the biochemical events initiated by each of these receptors will undoubtedly have a high impact in the design of more effective strategies to control inflammation.