Abstract
The hemibiotrophic fungus Magnaporthe oryzae (Mo) is the causative agent of rice blast and can infect aerial and root tissues of a variety of Poaceae, including the model Brachypodium distachyon (Bd). To gain insight in gene regulation processes occurring at early disease stages, we comparatively analyzed fungal and plant mRNA and sRNA expression in leaves and roots. A total of 310 Mo genes were detected consistently and differentially expressed in both leaves and roots. Contrary to Mo, only minor overlaps were observed in plant differentially expressed genes (DEGs), with 233 Bd-DEGs in infected leaves at 2 days post inoculation (DPI), compared to 4978 at 4 DPI, and 138 in infected roots. sRNA sequencing revealed a broad spectrum of Mo-sRNAs that accumulated in infected tissues, including candidates predicted to target Bd mRNAs. Conversely, we identified a subset of potential Bd-sRNAs directed against fungal cell wall components, virulence genes and transcription factors. We also show a requirement of operable RNAi genes from the DICER-like (DCL) and ARGONAUTE (AGO) families for fungal virulence. Overall, our work elucidates the extensive reprogramming of transcriptomes and sRNAs in both plant host (Bd) and fungal pathogen (Mo), further corroborating the critical role played by sRNA species in the establishment of the interaction and its outcome.
Highlights
Accepted: 1 January 2021The ascomycete fungus Magnaporthe oryzae (Mo) is the causal agent of rice blast, one of the most devastating and widespread diseases of cultivated rice, reducing yields up to 30% annually [1,2,3]
The corresponding protein sequences were obtained from NCBI: XP_003714515.1 (MGG_01541T0, MoDCL1), XP_003715365.1 (MGG_12357T0, MoDCL2), XP_003716704.1 (MGG_14873T0, MoAGO1), XP_003717504.1 (MGG_13617T0, MoAGO2) and XP_003714217.1 (MGG_01294T0, MoAGO3); they were included in new phylogenetic trees to corroborate previous findings (Figure S1A,B)
Multiple sequence alignment (MSA) confirmed the conservation of the DEDD catalytic tetrad (Asp/Glu/Asp/Asp) and the QF-V motif (Glu/Phe/Val) in the MoAGO PIWI domains (Figure S2). Both MoDCLs have the four conserved domains required for the cleavage of double-stranded RNA (dsRNA): DEXDc, HELICc, dicer-dimer and RIBOc (Figure S1D; Table S1)
Summary
Accepted: 1 January 2021The ascomycete fungus Magnaporthe oryzae (Mo) (anamorph: Pyricularia grisea) is the causal agent of rice blast, one of the most devastating and widespread diseases of cultivated rice, reducing yields up to 30% annually [1,2,3]. Members of the Magnaporthe genus can infect a variety of other cereals, including barley, rye and wheat, making Mo a major threat to global food security [4,5]. The fungus forms secondary hyphae and spreads to neighboring cells, undertaking a lifestyle change switching to a necrotrophic growth, with the appearance of the characteristic blast lesions on leaves [5]. Mo is able to infect all aerial parts of rice including nodes, panicles and necks, and has been shown to produce necrotic lesions on both rice and barley roots, its lifestyle in roots seems to depend on the inoculation method [4,10].
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