Quorum Sensing in Gram-Negative Plant Pathogenic Bacteria

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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 manner 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 speculated 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 homoserine lactones, 3-hydroxy palmitic acid methyl ester or methyl 3-hydroxypalmitate, virulence 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.Keywords: plant pathogenic bacteria, quorum sensing, signal molecules, QS regulon, inter kingdom signaling