The structural diversity of xanthomonadin aryl polyenes and functional analysis of the genes required for their synthesis by Xanthomonas phytopathogens

Abstract Xanthomonas is a genus of plant-associated Gram-negative bacteria which infect more than 400 plant species. A characteristic feature of Xanthomonas bacteria is the production of yellow membrane-bound pigments called xanthomonadins. Xanthomonadins are phospholipid-like bio-macromolecules located at the outer membrane. The chemical structure and biosynthetic mechanism of xanthomonadin production remain to be fully elucidated. In this study, a total of 24 Xanthomonas strains from five different species were collected for methylated ester of aryl polyene (MEAP) preparation. High-Performance Liquid Chromatography (HPLC) and Quadrupole Time-of-Flight Mass Spectrometry (Q-TOF–MS) analysis identified three dominant MEAPs, methylated di-brominated MEAP-1, di-brominated MEAP-2, and mono-brominated MEAP-3. MEAP-1 corresponded to the previously reported aryl polyene in Xanthomonas juglandis XJ103. The 24 Xanthomonas strains could be grouped into three categories based on their MEAP profiles. Further, bacterial ooze was collected from X . oryzae pv. oryzae ( Xoo )-infected rice leaves and MEAP was prepared. The dominant MEAP in the Xoo ooze was MEAP-2. This is the first demonstration of in-planta MEAP production during plant infection of any Xanthomonas pathogen. In addition, a xan biosynthetic cluster, which is responsible for xanthomonadin biosynthesis, and the roles of the individual xan genes in MEAP biosynthesis were studied via deletion and subsequent complementation analysis. HPLC and Q-TOF–MS analysis identified the essential genes for MEAP biosynthesis, as well as the genes associated with methylation and bromination. These results provide new insights into the structural diversity of Xanthomona s MEAPs and xanthomonadin biosynthetic mechanisms.