Fusarium graminearum is one of the most destructive plant pathogens worldwide, causing fusarium head blight (FHB) on cereals. F. graminearum colonizes wheat plant surfaces with specialized unbranched hyphae called runner hyphae (RH), which develop multicelled complex appressoria called
infection cushions (IC). IC generate multiple penetration sites, allowing the fungus to enter the plant cuticle. Complex
infection structures are typical for several economically important plant pathogens, yet with unknown molecular basis. In this study, RH and IC formed on the surface of wheat paleae were isolated by
laser capture microdissection.
RNA-Seq-based transcriptomic analyses were performed on RH and IC and compared to mycelium grown in complete medium (MY). Both RH and IC displayed a high number of
infection up-regulated genes (982), encoding, among others,
carbohydrate-active
enzymes (CAZymes: 140), putative effectors (PE: 88), or secondary metabolism gene clusters (SMC: 12 of 67 clusters). RH specifically up-regulated one SMC corresponding to
aurofusarin biosynthesis, a broad activity
antibiotic. IC specifically up-regulated 248 genes encoding mostly putative
virulence factors such as 7 SMC, including the
mycotoxin deoxynivalenol and the newly identified fusaoctaxin A, 33 PE, and 42 CAZymes. Furthermore, we studied selected candidate
virulence factors using cellular biology and reverse genetics. Hence, our results demonstrate that IC accumulate an arsenal of proven and putative
virulence factors to facilitate the invasion of epidermal cells.