Functional expression of the leftward open reading frames of the A component of tomato golden mosaic virus in transgenic tobacco plants.

Abstract

The genome of the geminivirus tomato golden mosaic virus (TGMV) consists of two circular DNA molecules designated as components A and 6. We have constructed Nicotiana benthamiana plants that are transgenic for the three overlapping open reading frames, AL1, AL2, and AL3, from the left side of TGMV A. In the transgenic plants, the AL open reading frames are under the control of the cauliflower mosaic virus (CaMV) 35s promoter. In TGMV infectivity assays, seven of 10 transgenic lines complemented TGMV A variants with mutations in AL1, AL2, or AL3 when co-inoculated with the 6 component. The 35s-AL construct was transcribed as a single RNA species in the transgenic plants, indicating that AL1, AL2, and AL3 were expressed from a polycistronic mRNA. This differs from the complex transcription pattern in TGMV-infected plants, which contains five AL transcripts. There was no quantitative correlation between the efficiency of complementation in the infectivity assay and the leve1 of expression of transgenic AL RNA in the leaves of a transgenic line. One line that failed to complement defects in AL1, AL2, and

Promoters, Transcripts, and Regulatory Proteins of Mungbean Yellow Mosaic Geminivirus

“…However for TGMV, in addition to that transcript, a complex pattern of longer leftward transcripts was detected (18,50). This, together with a transgenic plant study (19), suggested alternative mechanisms for AC2 and AC3 expression, including translation of AC1, AC2, and AC3 from a single polycistronic RNA (19). Our results for MYMV argue against this latter hypothesis, because of the presence of a precisely mapped and highly abundant separate AC2/3 transcript driven by the strong promoter located just upstream of the AC2 ORF.…”

“…Transcription start and poly(A) sites on both DNA-A and -B have been partially or completely mapped for African cassava mosaic virus (ACMV) (54), Tomato golden mosaic virus (TGMV) (19,36,45,50), Abutilon mosaic virus (AbMV) (14), and the monopartite Tomato leaf curl virus (TLCV) (34). However, major gaps in our understanding of the structural organization of begomovirus promoters and transcription units, and of the regulation of transcription by viral proteins, remain.…”

“…Members of the largest genus, Begomovirus (10), infect primarily dicotyledonous plants and are transmitted by the whitefly Bemisia tabaci. Many begomoviruses have a bipartite genome, with a DNA-A component encoding all the protein functions necessary for virus replication in a single cell while the DNA-B component provides movement functions required for systemic spread.Transcription regulation in begomoviruses has been extensively studied in both transgenic plants (13,19,23,40,48,60) and protoplast systems (8,9,13,16,17,24,46,47,49,51,52,53,60). Transcription start and poly(A) sites on both DNA-A and -B have been partially or completely mapped for African cassava mosaic virus (ACMV) (54), Tomato golden mosaic virus (TGMV) (19,36,45,50), Abutilon mosaic virus (AbMV) (14), and the monopartite Tomato leaf curl virus (TLCV) (34).…”

Synthesis of the tomato golden mosaic virus AL1, AL2, AL3 and AL4 proteins in vitro

“…Analysis of TGMVspecific RNAs in infected plants has identified putative mRNAs for the ALl and AR1 genes starting at nucleotides 61 or 62 and 319 or 320 respectively Sunter et al, 1989;Sunter & Bisaro, 1989;Hanley-Bowdoin et al, 1989 (Fig. 1) and may act as a polycistronic mRNA for all these ORFs.…”

Mutagenesis of the AC3 open reading frame of African cassava mosaic virus DNA A reduces DNA B replication and ameliorates disease symptoms

“…Recently, transgenic plants expressing the complementary-sense ORFs from TGMV DNA A have been used to investigate the requirements for replication of TGMV DNA (Hayes & Buck, 1989;Hanley-Bowdoin et al, 1989. Hanley-Bowdoin et al (1990) reported that expression of ALl can direct synthesis of both single-and double-stranded forms of DNA B in leaf discs.…”