A recombinant begomovirus resulting from exchange of the C4 gene.

A begomovirus isolated from Malvastrum coromandelianum and tomato originating from Yunnan province (China) was shown to be representative of a new begomovirus species, for which the name tomato leaf curl Yunnan virus (TLCYnV) is proposed. TLCYnV has high levels of sequence identity to tomato yellow leaf curl China virus (TYLCCNV) across the whole genome, except for sequences encompassing the C4 gene. Agrobacterium-mediated inoculation showed TLCYnV to be highly infectious to a range of plant species but poorly infectious to M. coromandelianum. In contrast to TYLCCNV, TLCYnV was shown to infect tomato in the absence of a betasatellite. In field-collected samples, TLCYnV was identified most frequently in tomato in which it was not associated with a betasatellite. Transgenic expression in Nicotiana benthamiana showed that the C4 protein of TYLCCNV did not induce developmental abnormalities, whereas the C4 of TLCYnV induced severe developmental abnormalities, reminiscent of virus symptoms. The genome of TLCYnV was shown to be significantly less methylated in plants than that of TYLCCNV and the C4 protein of TLCYnV was shown to suppress post-transcriptional gene silencing and transcriptional gene silencing more effectively than the C4 of TYLCCNV. The results indicate that TLCYnV evolved from TYLCCNV by recombination, acquiring a more virulent C4, allowing it to dispense with the requirement for a betasatellite. The implications of these findings in relation to the evolution of monopartite begomoviruses are discussed.

Etiology of Ageratum Yellow Vein Diseases in South China.

Ageratum conyzoides is a common weed in agricultural regions in Asia. A. conyzoides plants exhibiting yellow vein symptoms were collected from Yunnan and Guangxi provinces of China. Polymerase chain reaction detection and sequence analysis showed that samples collected from Yunnan were mainly infected by Tobacco curly shoot virus (TbCSV) associated with Ageratum yellow vein China betasatellite (AYVCNB), while samples from Guangxi were mostly infected by Papaya leaf curl China virus (PaLCuCNV) and AYVCNB, or by Ageratum yellow vein China virus (AYVCNV) and AYVCNB, with a few exhibiting dual infections by PaLCuCNV, AYVCNV, and AYVCNB. Agrobacterium-mediated inoculation of infectious clones showed that both TbCSV and AYVCNB or PaLCuCNV and AYVCNB produced typical yellow vein symptoms in A. conyzoides. Consequently, Ageratum yellow vein diseases in Yunnan and Guangxi provinces were caused by TbCSV/AYVCNB, PaLCuCNV/AYVCNB, or AYVCNV/ AYVCNB. The implications of these results in relation to the prevalence of begomoviruses in cultivated plants are discussed.

Characterization of alphasatellites associated with monopartite begomovirus/betasatellite complexes in Yunnan, China.

BACKGROUND: Alphasatellites are single-stranded molecules that are associated with monopartite begomovirus/betasatellite complexes. RESULTS: Alphasatellites were identified in begomovirus-infected plant samples in Yunnan, China. All samples that contained alphasatellites also contained betasatellites, but only some samples that contained betasatellites contained alphasatellites. Thirty-three alphasatellites were sequenced, and they ranged from 1360 to 1376 nucleotides. All alphasatellites contain 3 conserved features: a single open reading frame (Rep), a conserved hairpin structure, and an adenine-rich (A-rich) region. On the basis of the phylogenetic tree of the complete nucleotide sequences, the alphasatellites were divided into 3 types with one exception. Type 1 was associated with Tomato yellow leaf curl China virus (TYLCCNV)/Tomato yellow leaf curl China betasatellite (TYLCCNB) complex. Type 2 was associated with Tobacco curly shoot virus (TbCSV)/Tobacco curly shoot betasatellite (TbCSB) complex. Type 3 was associated with TbCSV/Ageratum yellow vein betasatellite (AYVB) complex. Within each type, nucleotide sequence identity ranged from 83.4 to 99.7%, while 63.4-81.3% identity was found between types. Mixed infections of alphasatellites associated with begomovirus/betasatellite complexes were documented. CONCLUSIONS: Our results validate that alphasatellites are only associated with begomovirus/betasatellite complexes. Thirty-three sequenced alphasatellites isolated from Yunnan Province, China were divided into 3 types--each associated with a specific begomovirus/betasatellite complex. Mix-infections of alphasatellite molecules may not be unusual.

Molecular characterization and pathogenicity of tomato yellow leaf curl virus in China.

Several tomato production regions in China were surveyed for tomato yellow leaf curl disease (TYLCD), and 31 tomato leaf samples showing TYLCD-like symptoms were collected. The partial or full-length genomes of these isolates were sequenced and tomato yellow leaf curl virus (TYLCV) was detected in Shanghai, Zhejiang, Jiangsu Shandong and Hebei provinces of China. The TYLCV isolates found in China share high sequence identity ([98%) and have more than 97% sequence identity with TYLCVIL[ IL:Reo] (X15656). Phylogenetic relationship analysis reveals that although with little genetic variability, they can form two groups and all the TYLCV isolates in China belong to the group I. An infectious clone of TYLCV-[CN:SH2] (AM282874) was constructed and agro-inoculated into Nicotiana benthamiana, N. tabacum Samsun, N. glutinosa, Solanum lycopersicum, Petunia hybrida, Cucumis sativus, Gossypium hirsutum, S. melongena, and Capsicum annuum. TYLCV-[CN:SH2] can induce severe leaf curling and stunting symptoms in these plants except C. sativus, G. hirsutum, S. melongena and C. annuum.We verified that TYLCV can trans-replicate tomato yellow leaf curl China virus DNA-b in N. benthamiana and S. lycopersicum and induced more severe symptoms with distortion and yellow vein.