VIRAL SEQUENCES INTEGRATED INTO PLANT GENOMES

Abstract

Sequences of various DNA plant viruses have been found integrated into the host genome. There are two forms of integrant, those that can form episomal viral infections and those that cannot. Integrants of three pararetroviruses, Banana streak virus (BSV), Tobacco vein clearing virus (TVCV), and Petunia vein clearing virus (PVCV), can generate episomal infections in certain hybrid plant hosts in response to stress. In the case of BSV and TVCV, one of the parents contains the integrant but is has not been seen to be activated in that parent; the other parent does not contain the integrant. The number of integrant loci is low for BSV and PVCV and high in TVCV. The structure of the integrants is complex, and it is thought that episomal virus is released by recombination and/or reverse transcription. Geminiviral and pararetroviral sequences are found in plant genomes although not so far associated with a virus disease. It appears that integration of viral sequences is widespread in the plant kingdom and has been occurring for a long period of time.

Assessment of Banana Streak MY virus-based infectious clone vectors in Musa ssp.

“…Both negative and positive DNA strands are synthesised by the viral reverse transcriptase (RT) using the host tRNA met and the viral encoded ribonuclease H (RNaseH) (Harper and Hull, 1998;Harper, Hull, et al, 2002). Members are distinguished by the number of open reading frames (ORFs), host range and the transmitting vectors (Geering and Hull, 2011;Purkayastha et al, 9 2010; Rothnie et al, 1994 …”

“…However, fragmented sequences have been identified in different plants such as tobacco (Tobacco vein clearing virus (TVCV; Jakowitsch et al, 1999), petunia (Petunia vein clearing virus (PVCV;Richert-Poggeler et al, 1997) and banana (BSV; Harper et al, 2002). These endogenous sequences, in some cases, can become activated and result in infectious virus, particularly in the case of BSV in bananas Ndowara et al, 1999;Fort et al, 2017).…”

“…BSVs are transmitted in a semi-persistent manner by mealybugs, which colonise the pseudostem or the rhizome of the banana plant (Harper et al, 2002;Jones, 1999). The spread of the disease is believed to be either by ants which move the mealybugs from one plant to the other or through infected suckers (Jones, 1999).…”

“…Most experiments were conducted in the field and there is no clear information on specific BSV species infecting and displaying specific patterns of symptoms (Dahal et al, 2000;Daniells et al, 2001;Harper et al, 2002;James et al, 2011;Jones, 1999). Jones (1999) assigned specific symptom description to the specific genotype 'Mysore' (AAB) in Honduras as having chlorotic stripes, spindle and eye-shaped streaks on the leaf with the pseudostem having black streaks.…”

“…However, the BSV isolate causing the disease was not mentioned. Harper et al, (2002) also gave a range of symptom descriptions (chlorotic and necrotic, fine, long and narrow to short and broad, diamond-or lozenge-shaped, speckling rather than streaking, interveinal mottle and mosaic)…”