Two novel DNAs that enhance symptoms and overcome CMD2 resistance to cassava mosaic disease
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Date
Authors
Ndunguru, Joseph
De León, L.
Doyle, C.D.
Sseruwagi, P.
Plata, G.
Legg, J.P.
Thompson, G.
Tohme, J.
Aveling, T.A.S. (Terry)
Ascencio-Ibáñez, J.T.
Journal Title
Journal ISSN
Volume Title
Publisher
American Society for Microbiology
Abstract
Cassava mosaic begomoviruses (CMBs) cause cassava mosaic disease (CMD) across Africa and the Indian subcontinent. Like all
members of the geminivirus family, CMBs have small, circular single-stranded DNA genomes. We report here the discovery of
two novel DNA sequences, designated SEGS-1 and SEGS-2 (for sequences enhancing geminivirus symptoms), that enhance
symptoms and break resistance to CMD. The SEGS are characterized by GC-rich regions and the absence of long open reading
frames. Both SEGS enhanced CMD symptoms in cassava (Manihot esculenta Crantz) when coinoculated with African cassava
mosaic virus (ACMV), East African cassava mosaic Cameroon virus (EACMCV), or East African cassava mosaic virus-Uganda
(EACMV-UG). SEGS-1 also overcame resistance of a cassava landrace carrying the CMD2 resistance locus when coinoculated
with EACMV-UG. Episomal forms of both SEGS were detected in CMB-infected cassava but not in healthy cassava. SEGS-2 episomes
were also found in virions and whiteflies. SEGS-1 has no homology to geminiviruses or their associated satellites, but the
cassava genome contains a sequence that is 99% identical to full-length SEGS-1. The cassava genome also includes three sequences
with 84 to 89% identity to SEGS-2 that together encompass all of SEGS-2 except for a 52-bp region, which includes the
episomal junction and a 26-bp sequence related to alphasatellite replication origins. These results suggest that SEGS-1 is derived
from the cassava genome and facilitates CMB infection as an integrated copy and/or an episome, while SEGS-2 was originally
from the cassava genome but now is encapsidated into virions and transmitted as an episome by whiteflies.
Description
Keywords
Resistance, Cassava mosaic begomoviruses (CMBs), Cassava mosaic disease (CMD), DNA sequence
Sustainable Development Goals
Citation
Ndunguru, J, De León, L, Doyle, CD, Sseruwagi, P, Plata, G, Legg, JP, Thompson, G, Tohme, J, Aveling, T, Ascencio-Ibáñez, JT & Hanley-Bowdoin, L 2016, 'Two novel DNAs that enhance symptoms and overcome CMD2 resistance to cassava mosaic disease', Journal of Virology, vol. 90, n. 8, pp. 4160-4173.