Using RNA-Seq to identify oospore wall-specific Carbohydrate-Active Enzyme (CAZyme) coding genes of Pythium ultimum var. ultimum, an oomycete plant pathogen

Oospores are propagules resulting from oomycete sexual recombination and act as long-term survival structures. In Pythium ultimum, and many other oomycete species, the glucan-rich walls of dormant oospores can account for 50% of the total volume of the oospore. Oospore walls can be digested quickly and used as a food source to propel oospores towards a germinable state. Whether digestion occurs by enzymes resulting from genes transcribed at this stage, or prepackaged transcripts/proenzymes released upon wall rehydration is currently unknown. Since oospore walls are composed predominantly of β-glucans, enzymatic digestion by glucanases may represent the earliest stage-specific molecular development ocurring at this point in its life cycle. We used RNA-Seq to investigate the oospore conversion process and to identify genes encoding oospore wall-specific enzyme products. Some enzymes were expressed solely during oospore conversion, and among those, some are only present in Pythium species when compared to other oomycetes.