Comparative Genomics of Cassava Bacterial Blight Strains

Cassava Bacterial Blight (CBB), incited by Xanthomonas axonopodis pv. manihotis (Xam), negatively affects beleaguered farmers in tropical regions of the world who rely on cassava as a major food source. We report Illumina based-high quality draft genomes for 65 Xam strains and deduce the phylogenetic relatedness of Xam across all areas where cassava is grown. Using an extensive database of type three effector proteins from animal and plant pathogens, we identify the effector repertoire for each sequenced strain. While effector repertoire size only loosely correlated with pathogen virulence levels, our data identified the core components of the Xam virulence arsenal which have been maintained over 12 countries, 3 continents and 70 years of evolution. We predict that resistance strategies targeting these highly conserved effectors will result in the most durable resistance phenotypes in the field. Further, we extend our analysis to a specific class of bacterial virulence components, the transcription activator-like (TAL) effectors. TAL effectors bind specific promoter sequences within the host cell nucleus and activate transcription of downstream genes. We report our progress elucidating the diversity, function and regulation of TAL effectors as well as identification of their corresponding plant gene targets.