The DNA β satellite component associated with ageratum yellow vein disease encodes an essential pathogenicity protein (βC1)

Abstract

Ageratum yellow vein disease (AYVD) is caused by the geminivirus ageratum yellow vein virus (AYVV) and an associated DNA beta satellite. We have mapped a DNA beta transcript to a highly conserved open reading frame (betaC1 ORF). The most abundant transcript 5'-terminus is located 8 bases upstream of the betaC1 ORF putative initiation codon while the transcript terminates at multiple sites downstream from the putative termination codon. Disruption of betaC1 protein expression by the introduction of an internal nonsense codon prevented infection of the AYVV-satellite complex in ageratum and altered the phenotype in Nicotiana benthamiana to that produced by AYVV alone although the mutant was maintained in systemically infected tissues. Modification of the putative initiation codon to a nonsense codon produced an intermediate phenotype in N. benthamiana and a mild yellow vein phenotype in ageratum, suggesting that betaC1 protein expression could be initiated from an alternative site. N. benthamiana plants containing a dimeric DNA beta transgene produced severe developmental abnormalities, vein-greening, and cell proliferation in the vascular bundles. Expression of betaC1 protein from a potato virus X (PVX) vector also induced abnormal plant growth. Our results demonstrate that the satellite encodes at least one protein that plays a major role in symptom development and is essential for disease progression in ageratum, the natural host of the AYVD complex.

Replication promiscuity of DNA-β satellites associated with monopartite begomoviruses; deletion mutagenesis of the Ageratum yellow vein virus DNA-β satellite localizes sequences involved in replication

“…2a) contained large deletions outside of this region. All N. benthamiana plants co-agroinoculated with AYVV, and mutants D1 and D2 (five plants in each case) produced upward leaf roll symptoms indistinguishable from those associated with AYVV alone, consistent with disruption of the bC1 gene (Saunders et al, 2004). Mutant D3 retained an intact bC1 gene and produced symptoms identical to those produced by wild-type DNA-b in all five co-agroinoculated plants.…”

“…Because begomo-viruses can systemically infect N. benthamiana in the absence of DNA-b (Fig. 1a-d) and non-functional satellites can be maintained in plants (Cui et al, 2004;Saunders et al, 2004;Saeed et al, 2005), the inability to detect a satellite in systemically infected tissues suggests trans-replication incompatibility rather than a defect in satellite systemic movement mediated by the helper virus. With the exception of CLCuMV, which could maintain a low level of EpYVV DNA-b replication that was not detected in systemically infected tissues (Fig.…”

“…This region includes the bC1 open reading frame (ORF), which encodes a gene essential for pathogenicity (Saunders et al, 2004), and an A-rich region that may serve to maintain the size integrity of the satellite (Saunders et al, 2000). We have previously shown that an intact bC1 ORF is not required for systemic infection of N. benthamiana (Saunders et al, 2004) and our current finding that the entire ORF is dispensable (mutants D1 and D2) is consistent with the findings of Qian & Zhou (2005) for the satellite associated with tomato yellow leaf curl China virus (TYLCCNV). In addition, removal of the Arich region from TYLCCNV DNA-b was tolerated, although the deletion mutant was associated with milder symptoms than those produced by the wild-type satellite .…”

“…Binary vector clones were introduced into Agrobacterium tumefaciens strain GV3850 (Zambryski et al, 1983) and used to agroinoculate Nicotiana benthamiana and A. conyzoides plants as described by Saunders et al (2004). N. benthamiana leaf disks were prepared and maintained as described by Klinkenberg et al (1989) and DNA was extracted from plant tissues and analysed by Southern blot hybridization as described by Saunders et al (2004).…”

Tomato SlSnRK1 Protein Interacts with and Phosphorylates βC1, a Pathogenesis Protein Encoded by a Geminivirus β-Satellite

“…Full-length b-satellite molecules encode an approximately 13.5-kD protein known as bC1 on the complementary sense strand. bC1 is a pathogenicity determinant and a suppressor of RNA silencing (Jose and Usha, 2003;Cui et al, 2004Cui et al, , 2005Saunders et al, 2004;Qian and Zhou, 2005;Saeed et al, 2005;Gopal et al, 2007;Kon et al, 2007). Previous studies showed that bC1 interacts with ASYMMETRIC LEAVES1 to alter leaf development and suppress selected jasmonic acid responses (Yang et al, 2008).…”