Discerning role of a functional arsenic resistance cassette in evolution and adaptation of a rice pathogen

Arsenic (As) is highly toxic element to all forms of life and is a major environmental contaminant. Understanding acquisition, detoxification, and adaptation mechanisms in bacteria that are associated with host in arsenic-rich conditions can provide novel insights into dynamics of host-microbe-microenvironment interactions. In the present study, we have investigated an arsenic resistance mechanism acquired during the evolution of a particular lineage in the population of Xanthomonas oryzae pv. oryzae (Xoo), which is a serious plant pathogen infecting rice. Our study revealed the horizontal acquisition of a novel chromosomal 12kb ars cassette in Xoo IXO1088 that confers high resistance to arsenate/arsenite. The ars cassette comprises several genes that constitute an operon induced in the presence of arsenate/arsenite. This cassette has spread in lineage with highly virulent strains owing to a particular lineage’s evolutionary success. Further, we performed the transcriptomic analysis of Xoo strain IXO1088 under arsenate/arsenite exposure using RNA sequencing. The transcriptomic analysis revealed that arsenic detoxification and efflux, oxidative stress response, iron acquisition/storage, and damage repair are the main cellular responses to arsenic exposure. The study provides useful insights into the acquisition, detoxification, and adaptation mechanisms among Xoo populations to adapt under arsenic-rich environmental conditions.