Adaptive regulation of virulence genes by microRNA‐like RNAs in Valsa mali

Abstract

Summary MicroRNAs play important roles in the regulation of gene expression in plants and animals. However, little information is known about the action mechanism and function of fungal microRNA‐like RNAs (milRNAs). In this study, combining deep sequencing, molecular and histological assays, milRNAs and their targets in the phytopathogenic fungus Valsa mali were isolated and identified. A critical milRNA, Vm‐milR16, was identified to adaptively regulate the expression of virulence genes. Fourteen isolated milRNAs showed high expression abundance. Based on the assessment of a pathogenicity function of these milRNAs, Vm‐milR16 was found to be a critical milRNA in V. mali by regulating sucrose non‐fermenting 1 (VmSNF1), 4,5‐DOPA dioxygenase extradiol (VmDODA), and a hypothetical protein (VmHy1). During V. mali infection, Vm‐milR16 is downregulated, while its targets are upregulated. Overexpression of Vm‐milR16, but not mutated Vm‐milR16, significantly reduces the expression of targets and virulence of V. mali. Furthermore, deletion of VmSNF1, VmDODA and VmHy1 significantly reduce virulence of V. mali. All three targets seem to be essential for oxidative stress response and VmSNF1 is required for expression of pectinase genes during V. mali–host interaction. Our results demonstrate Vm‐milRNAs contributing to the infection of V. mali on apple trees by adaptively regulating virulence genes.

Vm‐milR37 contributes to pathogenicity by regulating glutathione peroxidase gene VmGP in Valsa mali

“…In pathogenic fungi, many virulence genes have been predicted and confirmed to be regulated by sRNAs (Gowda et al, 2010;Guo et al, 2019;Jin et al, 2019;Raman et al, 2017;Xu et al, 2020). We also found that many virulence genes of V. mali could be regulated by milRNAs (Xu et al, 2020). In this study, VmGP, as an important virulence gene, was further demonstrated to be regulated F I G U R E 7 Deletion of VmGP reduces the pathogenicity of Valsa mali.…”

“…Thus, we speculated that Vm-milR37 may play an important role in vegetative growth and pathogenicity. To analyse the function of miRNAs or mil-RNAs, overexpression is an important and widely used method (Jin et al, 2019;Li et al, 2013;Xu et al, 2020). Based on overexpression of Vm-milR37 and pathogenicity assays, Vm-milR37 was confirmed to be involved in the pathogenicity of V. mali.…”

“…In a previous study, VM1G_06866, which encodes a glutathione peroxidase, a protein of 229 amino acids with typical glutathione peroxidase conserved domains ( Figure S3), was identified as a target gene of Vm-milR37 (Xu et al, 2020). VM1G_06866 was designated as VmGP.…”

“…The RNAi pathway components of V. mali , such as Dicer‐like and AGO, were identified as associated with pathogenicity, which indicated posttranscriptional regulation may also be an important pathway (Feng et al, 2017a,b). Multiple omics analyses revealed that Vm ‐milRNAs can regulate pathogenicity factors to promote V. mali infection (Xu et al, 2020). However, the detailed regulatory mechanism of Vm ‐milRNAs is still largely not understood.…”

Fungal species associated with apple Valsa canker in East Asia

“…Thus, monitoring pathogenic modes becomes a necessary preventative step in management of canker disease. Decoding genome sequences (Yin et al 2015) and identifying genes associated with virulence and pathogenicity of the pathogens (Li et al 2015;Song et al 2017;Feng et al 2017aFeng et al , 2017bWu et al 2018;Nie et al 2019;Zhang et al 2019;Xu et al 2020), as well as molecules involved in immunological response of hosts (Feng et al 2017c) will contribute to innovative strategies for management of apple Valsa canker in the future.…”