ICTV Virus Taxonomy Profile: Geminiviridae 2021

1Geminiviruses have a unique particle morphology of twinned (geminate) icosahedra. For maize streak virus (genus Mastrevirus), virions are 22×38 nm, consisting of two incomplete icosahedra (T=1) containing 110 capsid protein (CP) subunits organized as 22 pentameric capsomers (Table 1, Fig. 1a). The structure of Ageratum yellow vein virus (genus Begomovirus) at 3.3 Å resolution shows that the N-terminus of CP adopts three different conformations essential for building the interface between geminate halves (Fig. 1b).

2Viruses in most genera of the family have monopartite genomes, whereas those in the genus Begomovirus have mono- or bipartite genomes. The genomes of bipartite begomoviruses (Fig. 2) consist of two circular single-stranded components, DNA-A and DNA-B, each of 2.5–2.6 kb. The two components share approximately 200 bases of sequence (common region) that includes the replication origin. DNA-A encodes a capsid protein (ORF AV1, CP), a putative movement protein (ORF AV2, MP, absent in New World begomoviruses), a replication-associated protein (ORF AC1, Rep), a transcriptional activator (ORF AC2, TrAP), a replication enhancer (ORF AC3, REn) and the C4 protein (ORF AC4, C4). DNA-B encodes a nuclear shuttling protein (ORF BV1, NSP) and a movement protein (ORF BC1, MP). The genomes of monopartite begomoviruses (Fig. 2) resemble the DNA-A component of bipartite begomoviruses. The genome organization of members of each of the genera in the family Geminiviridae is shown in the ICTV Report (ictv.global/report/geminiviridae). DNA satellites are associated with many begomoviruses and some mastreviruses.

3Complementary-sense DNA synthesis to produce dsDNA depends solely on host factors. Virus ssDNA synthesis is initiated by cleavage of the virion-sense strand by Rep in the 5′-TAATATTAC-3′ sequence conserved in most geminiviruses within the intergenic region (IR)/ long intergenic region (LIR). Geminiviruses do not encode a DNA polymerase, relying on host factors recruited during the early stages of replication. Coding regions in both strands diverge from the IR/LIR, and transcription is bi-directional. Geminiviruses use multiple overlapping transcripts for gene expression. The begomovirus tomato yellow leaf curl virus replicates in the salivary glands of whiteflies.

4Current taxonomy: ictv.global/taxonomy. The family includes multiple genera collectively including >500 species, the most diverse genera being Begomovirus (>440 species) and Mastrevirus (>40 species). Host are dicots except for maldoviruses and mastreviruses (dicots and monocots) and eragroviruses (monocots). Vectors are whiteflies (begomoviruses), aphids (capulaviruses), treehoppers (grabloviruses, topocuviruses), leafhoppers (becurtoviruses, curtoviruses, mastreviruses, mulcrileviruses, turncurtoviruses), or unknown (citlodaviruses, eragroviruses, maldoviruses, opunviruses, topileviruses).

5Full ICTV Report on the family Geminiviridae: ictv.global/report/geminiviridae.