A New Type of Satellite Associated with Cassava Mosaic Begomoviruses

Abstract

Cassava mosaic disease (CMD), which is caused by single-stranded DNA begomoviruses, severely limits cassava production across Africa. A previous study showed that CMD symptom severity and viral DNA accumulation increase in cassava in the presence of a DNA sequence designated as SEGS-2 ( s equence e nhancing g eminivirus s ymptoms). We report here that when SEGS-2 is co-inoculated with African cassava mosaic virus (ACMV) onto Arabidopsis thaliana , viral symptoms increase. Transgenic Arabidopsis with an integrated copy of SEGS-2 inoculated with ACMV also display increased symptom severity and viral DNA levels. Moreover, SEGS-2 enables Cabbage leaf curl virus (CaLCuV) to infect a geminivirus resistant Arabidopsis thaliana accession. Although SEGS-2 is related to cassava genomic sequences, an earlier study showed that it occurs as episomes and is packaged into virions in CMD-infected cassava and viruliferous whiteflies. We identified SEGS-2 episomes in SEGS-2 transgenic Arabidopsis. The episomes occur as both double-stranded and single-stranded DNA, with the single-stranded form packaged into virions. In addition, SEGS-2 episomes replicate in tobacco protoplasts in the presence, but not the absence, of ACMV DNA-A. SEGS-2 episomes contain a SEGS-2 derived promoter and an open reading frame with the potential to encode a 75-amino acid protein. An ATG mutation at the beginning of the SEGS-2 coding region does not enhance ACMV infection in A. thaliana . Together, the results established that SEGS-2 is a new type of begomovirus satellite that enhances viral disease through the action of a SEGS-2 encoded protein that may also be encoded in the cassava genome. IMPORTANCE Cassava is an important root crop in the developing world and a food and income crop for more than 300 million African farmers. Cassava is rising in global importance and trade as the demands for biofuels and commercial starch increase. More than half of the world’s cassava is produced in Africa, where it is primarily grown by smallholder farmers, many of whom are from the poorest villages. Although cassava can grow under high temperature, drought and poor soil conditions, its production is severely limited by viral diseases. Cassava mosaic disease (CMD) is one of the most important viral diseases of cassava and can cause up to 100% yield losses. We provide evidence that SEGS-2, which was originally isolated from cassava crops displaying severe and atypical CMD symptoms in Tanzanian fields, is a novel begomovirus satellite that can compromise the development of durable CMD resistance.

Cassava begomovirus species diversity changes during plant vegetative cycles

“…Whiteflies are separated into genetic biotypes based on mtCOI sequences (Mugerwa et al, 2012 , 2018 ; Manani et al, 2017 ). The SSA1-SG1 and SSA1-SG2 biotypes have been associated with severe CMD (Ndunguru et al, 2016 ; Aimone et al, 2021a ). A recent study found SSA1-SG1, SSA1-SG2, and SSA2 biotypes in western Kenya and SSA2 and SSA1-SG3 biotypes in coastal Kenya (Munguti et al, 2021 ).…”

Rapid multilocus adaptation of clonal cabbage leaf curl virus populations toArabidopsis thaliana

“…The geminivirus beet curly top virus also causes strong symptoms on Sei-0, likely because it accumulates to high levels (Park et al 2004; Lee et al 1994), but differences in DNA-A and DNA-B levels in Col-0 vs. Sei-0 were variable in our experiment (Supplemental Table S1). Sei-0 can be infected with African cassava mosaic virus, whereas Col-0 cannot (Aimone et al 2021a). The genetic basis for the hypersusceptibility of Sei-0 is currently unknown but could be genetically mapped.…”

Applications of Virus-Induced Gene Silencing in Cotton

“…Single-stranded DNA (ssDNA) viruses belong to the largest known family of plant DNA viruses [ 16 ]. Other types of DNA-based viruses, such as African cassava mosaic virus (ACMV) and Cotton leaf crumple virus (CLCrV), have been efficiently converted into VIGS vectors and successfully applied to cassava and cotton plants [ 17 , 18 ]. RNA viruses are the earliest and most widely used viral vector to establish the VIGS system, due to their small molecular weight and high infection efficiency.…”