Abstract
Geminiviruses are major plant pathogens that threaten food security globally. They have a unique architecture built from two incomplete icosahedral particles, fused to form a geminate capsid. However, despite their importance to agricultural economies and fundamental biological interest, the details of how this is realized in 3D remain unknown. Here we report the structure of Ageratum yellow vein virus at 3.3 Å resolution, using single-particle cryo-electron microscopy, together with an atomic model that shows that the N-terminus of the single capsid protein (CP) adopts three different conformations essential for building the interface between geminate halves. Our map also contains density for ~7 bases of single-stranded DNA bound to each CP, and we show that the interactions between the genome and CPs are different at the interface than in the rest of the capsid. With additional mutagenesis data, this suggests a central role for DNA binding-induced conformational change in directing the assembly of geminate capsids.
Highlights
Geminiviruses are major plant pathogens that threaten food security globally
Other Begomoviruses, such as Ageratum yellow vein virus (AYVV) studied here, have a single genomic DNA (DNA-A, ~2.7 kb), along with an array of satellite DNAs (α & β, each of ~1.3–1.4 kb). β satellite (DNA-β), whose replication is totally dependent upon gene functions encoded within DNA-A, encodes a gene which is essential for AYVV infectivity in its natural host plant[3]
Based on an ~25 Å resolution cryo-EM structure of maize streak virus (MSV), a model for the geminate interface was proposed with an α-helix from each subunit extending across the geminate interface[7]
Summary
Geminiviruses are major plant pathogens that threaten food security globally They have a unique architecture built from two incomplete icosahedral particles, fused to form a geminate capsid. The closest plant virus relatives of the geminiviruses are the nanoviruses, which have multipartite, single-stranded DNA genomes that are separately encapsidated and are ~1 kb in size[5,6]. Each such DNA molecule typically encodes a single gene product. STNV has a much smaller genome than a geminivirus (~1250 vs ~2700 nucleotides), so geminate capsids again can package more genetic material than a simple T = 1 particle, despite encoding a single CP sequence. We show details of single-stranded DNA binding and propose a model for geminivirus capsid assembly
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