The methylation analysis and comparison between Banana bunchy top virus and Banana streak Mysore virus
Date Issued
2011
Date
2011
Author(s)
Chang, Hsin-Yuan
Abstract
Banana bunchy top virus (BBTV) and Banana streak Mysore virus (BSMysV) are DNA viruses that causing Banana bunchy top disease and Banana streak virus disease in bananas (Musa spp.), respectively. Generally, BSMysV presents as a free virus, an episome, in hosts. However, BSMysV has integrated into the genome of M. balbisiana, thus, many banana cultivars contain non-infectious BSMysV (eBSMysV). Endogenous pararetrovirus sequences may be activated to become infectious due to stress. BSMysV have an impact on the banana production because of not only its episomal form infecting bananas directly but also eBSMysV which is likely to become infectious. In plants, cytosine methylation is one of the ways to regulate the level of activation of DNA. Some DNA viruses were shown to be methylated by host plants, and among these viruses, the levels of methylation in several viruses are related to the symptom severity. In this study, to determine whether DNA viruses in the banana were transcriptionally silenced, we analyzed the methylation patterns of BBTV and BSMysV by bisulfite sequencing. The methylation levels of DNA-R and DNA-M of BBTV were quite low, and it indicated that BBTV did not induce strong transcriptional gene silencing. By comparing the average percentages of methylation between severe strain and mild strain of BBTV, it showed that the methylation levels of BBTV did not reflect the symptom severity. The difference in the level of methylation between the heart leaf and the old leaf was not statistically significant, so it suggested that the methylation levels of BBTV did not change drastically in different pathogenesis stages. For BSMysV, episomal BSMysV is hypomethylated and doesn’t induce strong transcriptional gene silencing. On the contrary, eBSMysV is hypermethylated, and the methylation rate is significantly higher in symmetric (CG and CHG) than in asymmetric (CHH) cytosines. It indicated that eBSMysV may be transcriptionally silenced. However, there was almost no methylation observed in a partial region of ORF III in eBSMysV, so we speculated that eBSMysV is probable to be activated.
Subjects
Banana bunchy top virus
Banana streak Mysore virus
eBSMysV
methylation
bisulfite sequencing
Type
thesis
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