New Insights into the Methylation Status of Virulent Diuraphis noxia (Hemiptera: Aphididae) Biotypes

Abstract

Epigenetic modifications provide a means for aphid biotype development that a lack of genetic variation, owing to an anholocyclic reproduction lifecycle, fails to do. Here we present data on the DNA methylation status in four South African Russian wheat aphids (RWA), Diuraphis noxia (Kurdjomov) (Hemiptera: Aphididae) biotypes expressing different levels of virulence against its host, Triticum aestivum L. (Poales: Poaceae, Triticeae). The DNA methylation status of these biotypes was determined through the use of methylation-sensitive amplification polymorphism analysis, restriction site-specific fluorescence labeling-a novel technique, and measuring relative global DNA methylation and hydroxymethylation. The least virulent RWA biotype, SA1, was methylated, while biotypes displaying intermediate virulence, SA2 and SA3, exhibited intermediate levels of hemimethylation. The genome of the most virulent RWA biotype, SAM, seems to be hypomethylated, which is likely attained through the process of demethylation.

DNA Methylation and Demethylation Are Regulated by Functional DNA Methyltransferases and DnTET Enzymes in Diuraphis noxia

“…Hemimethylated DNA arises during DNA replication, as the newly synthesized daughter strand contains unmodified cytosines (Jeltsch, 2002;Goll and Bestor, 2005). When the levels of 5-hmC were measured using the antibody based method, earlier observations (Breeds et al, 2018) were confirmed, as the levels of 5hmC differed significantly between the aphid biotypes, with SAM much higher than that measured in the less virulent SA1 (p < 0.05; Figure 9).…”

“…However, interestingly the difference between the methylation of the top and bottom strands were significantly more in the more virulent SAM (0.09%), than SA1 (0.02%). This was not an unexpected finding, as biotype SAM was previously found to exhibit the highest level of hemimethylation (at the external cytosine) when its methylation was investigated using the Methylation-Sensitive Amplification Polymorphism (MSAP) technique (Breeds et al, 2018). Hemimethylated DNA arises during DNA replication, as the newly synthesized daughter strand contains unmodified cytosines (Jeltsch, 2002;Goll and Bestor, 2005).…”

“…For whole genome bisulfite sequencing and measurement of global methylation (5mC) and hydroxymethylation (5hmC) levels, colonies of apterous parthenogenetic female aphids of South African RWA biotypes SA1 and SAM were separately established in BugDorm cages (MegaView Science Education Services Co. Ltd., Taiwan) in an insectary with the following conditions: 22.5 ± 2.5 • C, 40% relative humidity, and continuous artificial lighting from high pressure sodium lamps as previously described (Breeds et al, 2018). In all instances triplicate colonies of each biotype were established.…”

“…In 2012, Gong et al investigated the methylation of four genes encoding salivary gland proteins (putative effector genes) in RWA biotypes US1 and US2, and found these genes to be differentially methylated in the different biotypes. In the initial investigation of South African RWA methylation (Breeds et al, 2018), the different biotypes exhibited different banding patterns (after restriction of their DNA with methylationsensitive enzymes), methylation levels and methylation trends, all of which support a role for methylation in biotypification.…”

“…The known genealogy of SA1 and SAM (Swanevelder et al, 2010), their genetic similarity and their position on either end of the virulence spectrum, renders them particularly useful in the present study, to improve the understanding of the process of biotypification. The possibility of a link between RWA methylation and biotype virulence has previously been suggested (Gong et al, 2012;Breeds et al, 2018). In 2012, Gong et al investigated the methylation of four genes encoding salivary gland proteins (putative effector genes) in RWA biotypes US1 and US2, and found these genes to be differentially methylated in the different biotypes.…”