Abstract
To reveal whether the response of mulberry to phytoplasma infection is associated with genome-wide DNA methylation changes, the methylome and transcriptome patterns of mulberry in response to phytoplasma infection were explored. Though the average methylation level of the infected leaves showed no significant difference from that of healthy leaves, there were 1,253 differentially methylated genes (DMGs) and 1,168 differentially expressed genes (DEGs) in the infected leaves, and 51 genes were found simultaneously to be differently methylated and expressed. It was found that the expression of G-type lectin S-receptor-like serine/threonine protein kinase gene (Mu-GsSRK) was increased, but its methylation level was decreased in the pathogen-infected or salicylic acid (SA)-treated leaves. Overexpression of Mu-GsSRK in Arabidopsis and in the hairy roots of mulberry enhanced transgenic plant resistance to the phytoplasma. Moreover, overexpression of Mu-GsSRK enhanced the expressions of pathogenesis-related protein 1, plant defensin, and cytochrome P450 protein CYP82C2 genes in transgenic plants inoculated with pathogens, which may contribute to the enhanced disease resistance against various pathogens. Finally, the DNA methylation dynamic patterns and functions of the differentially expressed and methylated genes were discussed. The results suggested that DNA methylation has important roles in mulberry responses to phytoplasma infection.
Highlights
Phytoplasmas are cell wall-less plant pathogens of the class, Mollicutes (Sugio et al, 2011), and they are associated with hundreds of diseases in more than 1,000 plants in the world and cause serious losses in vegetables, fruit crops, and ornamental plants (Bertaccini and Duduk, 2009; Cao et al, 2019)
It was reported that DNA methylation plays important roles in regulating responses to biotic stresses in plants, and evidence showed that DNA methylation levels were altered in potato (Solanum tuberosum), Arabidopsis thaliana, and tomato (S. lycopersicum) plants infected by pathogenic fungi, bacteria, or virus (Pavet et al, 2006; Torchetti et al, 2016; Zhu et al, 2016; De Palma et al, 2019)
The first category of gene was involved in stress and environment response, and the genes associated with catabolic process belonged to the second category, and the third category included the genes involved in transcription and post-transcription regulation
Summary
Phytoplasmas are cell wall-less plant pathogens of the class, Mollicutes (Sugio et al, 2011), and they are associated with hundreds of diseases in more than 1,000 plants in the world and cause serious losses in vegetables, fruit crops, and ornamental plants (Bertaccini and Duduk, 2009; Cao et al, 2019). Some studies showed that phytoplasmas were involved in the methylation changes of host genes. In Candidatus Phytoplasma aurantifolia-infected periwinkle (Catharanthus roseus) and tomato plants, sterol-Cmethyltransferase and some methylase and demethylase genes were downregulated (Jagoueix-Eveillard et al, 2001), and it was found that DNA methylation was involved in the epigenetic regulation of SlDEFICIENS (Ahmad et al, 2012). It has been shown that the global DNA methylation level was reduced in the phytoplasma-infected Paulownia seedlings (Cao et al, 2014). Taken together, these studies suggested that DNA methylation may play an important role in regulating gene expression in phytoplasma-infected plants
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