Genetics of xanthomonas oryzae pv. oryzae: studies on pigment biosynthesis

Abstract

Xanthomonas oryzae pv. oryzae is the causal agent of a serious newlinedisease of rice called bacterial leaf blight. The vast majority of newlinemembers of the genus Xanthomonas are phytopathogenic, with some newlineof them causing considerable economic loss. Almost all newlinexanthomonads produce yellow, membrane bound, brominated aryl newlinepolyene pigments called xanthomonadinsJ_ which are the newlinecharacteristic pigments of this genus. The role of the pigment in the newlinelife cycle of the pathogen is unclear. The long polyene moiety that newlineoccurs in xanthomonadin is similar to what is seen in carotenoids. newlineCarotenoid pigments that are found in photosynthetic and nonphotosynthetic newlinebacteria have been observed to provide protection newlineagainst damaging photolytic and photodynamic reactions. Evidence newlinefrom studies on a non-pigmented mutant of Xanthomonas juglandis, newlinesuggests that the pigment might be involved in protecting the newlinebacteria against photobiological damage. However, very little newlineinformation is available about the genes that are involved in pigment newlinebiosynthesis and their regulation. Recently, the xanthomonadin newlinebiosynthetic gene cluster, spanning a region of 23 Kb has been newlineisolated from Xanthomonas campestris pv. campestris. Transposon newlinemutagenesis and complementation analysis suggest that they include newlines.even complementation groups and that genes required for pigment newlinebiosynthesis are interspersed with those that are not required. newlineTo date, not many laboratories in the world work with X. oryzae newlinepv. oryzae and when molecular genetic studies on an Indian isolate of newlinethis pathogen were initiated in our laboratory, it was thought to be newlineX newlineworthwhile to focus on visual phenotypes like pigment production newlineover complicated traits like virulence functions. The objectives of newlinethis study was to ascribe a function to the pigment, xanthomonadin newlineusing X. oryzae pv. oryzae as the model; to identify the genes that newlineare involved in xanthomonadin biosynthesis and understand their newlinepattern of regulation.