Comparative analysis of virus-derived small RNAs within cassava (Manihot esculenta Crantz) infected with cassava brown streak viruses
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Date
2016
Journal Title
Journal ISSN
Volume Title
Publisher
Virus research
Abstract
Infection of plant cells by viral pathogens triggers RNA silencing, an innate antiviral defense
mechanism. In response to infection, small RNAs (sRNAs) are produced that associate with
Argonaute (AGO)-containing silencing complexes which act to inactivate viral genomes by
posttranscriptional gene silencing (PTGS). Deep sequencing was used to compare virus-derived
small RNAs (vsRNAs) in cassava genotypes NASE 3, TME 204 and 60444 infected with the
positive sense single-stranded RNA (+ssRNA) viruses Cassava brown streak virus (CBSV) and
Ugandan cassava brown streak virus (UCBSV), the causal agents of cassava brown streak
disease (CBSD). An abundance of 21-24 nt vsRNAs was detected and mapped, covering the
entire CBSV and UCBSV genomes. The 21 nt vsRNAs were most predominant, followed by the
22 nt class with a slight bias toward sense compared to antisense polarity, and a bias for adenine
and uracil bases present at the 5’-terminus. Distribution and frequency of vsRNAs differed
between cassava genotypes and viral genomes. In susceptible genotypes TME 204 and 60444,
CBSV-derived sRNAs were seen in greater abundance than UCBSV-derived sRNAs. NASE 3, known to be resistant to UCBSV, accumulated negligible UCBSV-derived sRNAs but high
populations of CBSV-derived sRNAs. Transcript levels of cassava homologues of AGO2, DCL2
and DCL4, which are central to the gene-silencing complex, were found to be differentially
regulated in CBSV- and UCBSV-infected plants across genotypes, suggesting these proteins play
a role in antiviral defense. Irrespective of genotype or viral pathogen, maximum populations of
vsRNAs mapped to the cytoplasmic inclusion, P1 and P3 protein-encoding regions. Our results
indicate disparity between CBSV and UCBSV host-virus interaction mechanisms, and provide
insight into the role of virus-induced gene silencing as a mechanism of resistance to CBSD.
Description
Keywords
Deep sequencing, Cassava brown streak disease, Cassava, Virus-derived small RNA
Citation
Ogwok, E., Ilyas, M., Alicai, T., Rey, M. E., & Taylor, N. J. (2016). Comparative analysis of virus-derived small RNAs within cassava (Manihot esculenta Crantz) infected with cassava brown streak viruses. Virus research, 215, 1-11. http://dx.doi.org/doi:10.1016/j.virusres.2016.01.015