Transcriptome analysis of apple leaves infected by the rust fungus Gymnosporangium yamadae at two sporulation stages (spermogonia and aecia) reveals specific host responses, rust pathogenesis-related genes and a shift in the phyllosphere fungal community composition

Abstract

1 Gymnosporangium yamadae at two sporulation stages (spermogonia and 2 aecia) reveals specific host responses, rust pathogenesis-related genes and 3 a shift in the phyllosphere fungal community composition 4 5 Abstract 17Apple rust disease caused by Gymnosporangium yamadae is one of the major threats to 18 apple orchards. In this study, dual RNA-seq analysis was conducted to simultaneously 19 monitor gene expression profiles of G. yamadae and infected apple leaves during the 20 formation of rust spermogonia and aecia. The molecular mechanisms underlying this 21 compatible interaction at 10 and 30 days post inoculation (dpi) indicate a significant 22 reaction from the host plant and comprise detoxication pathways at the earliest stage and 23 the induction of secondary metabolism related pathways at 30dpi. Such host reactions 24 have been previously reported in other rust pathosystems and may represent a general 25 reaction to rust infection. G. yamadae transcript profiling indicates a conserved genetic 26 program in spermogonia and aecia that is shared with other rust fungi, whereas secretome 27 prediction reveals the presence of specific secreted candidate effector proteins expressed 28 during apple infection. Unexpectedly, the survey of fungal unigenes in the transcriptome 29 assemblies of inoculated and mock-inoculated apple leaves reveals that G. yamadae 30 infection modifies the fungal community composition in the apple phyllosphere at 30 dpi. 31 Collectively, our results provide novel insights into the compatible apple-apple rust 32 interaction and advance the knowledge of this heteroecious demicyclic rust fungus. 33 34