Quorum Sensing in Gram-Negative Plant Pathogenic Bacteria

Abstract

Plant pathogenic bacteria regulate expression of specific genes through quorum sensing (QS). Some bacteria encode a single or more than one QS system while others encode a single LuxI and two or more LuxR homologs. Not all plant pathogenic bacteria encode the LuxI and in these situations the LuxR modulates cell behavior in a cell density man ner by utilizing signal molecules that are produced by their plant hosts. The advantage of having more than one system is still not well understood. However, it has been specu lated that it is essential for regulation of QS traits in different environmental conditions. Quorum sensing systems in plant pathogenic bacteria include those that use acyl homo serine lactones, 3-hydroxy palmitic acid methyl ester or methyl 3-hydroxypalmitate, vir - ulence factor modulation genes and diffusible signal factors. This chapter discusses the various QS systems in Gram-negative plant pathogenic bacteria, notably those listed as the top 10 plant pathogenic bacteria that cause significant reduction in yields and inflict economic losses in agriculture. In addition, it explores the various biological processes influenced by QS and the extent of QS regulons in these bacteria. receptor molecule. The AHL binds to the protein receptor molecule, the complex then binds to specific promoters and trigger multiple gene expression. The traits that are regulated by this system include pathogenicity, production of secondary metabolites, motility, secretion systems, stress response, conjugation, growth inhibition, biofilm formation and clustered regularly interspaced short Palindromic repeats (CRISPR-Cas). binds to promoters of the vfmAZCBD and vfmE kinase. This results in activation of production of a transcriptional activator, AraC (encoded by vfmE ) and regulation of specific phenotypes. Phenotypes regulated by the VFM QS include production of plant cell wall degrading enzymes and pathogenicity. system include motility, biofilm formation, production of plant cell wall degrading enzymes, iron acquisition, lipopolysaccharide/ exopolysaccharides (EPS) synthesis and secretion, expression of type IV pili and fitness. Other traits regulated include chemotaxis, multidrug resistance and detoxification, pathogenicity, metabolism, transport, interspecies competition and pigmentation.