Abstract
Cnaphalocrocis medinalis is a major pest of rice in South and South-East Asia. Insecticides are the major means farmers use for management. A naturally occurring baculovirus, C. medinalis granulovirus (CnmeGV), has been isolated from the larvae and this has the potential for use as microbial agent. Here, we described the complete genome sequence of CnmeGV and compared it to other baculovirus genomes. The genome of CnmeGV is 112,060 base pairs in length, has a G+C content of 35.2%. It contains 133 putative open reading frames (ORFs) of at least 150 nucleotides. A hundred and one (101) of these ORFs are homologous to other baculovirus genes including 37 baculovirus core genes. Thirty-two (32) ORFs are unique to CnmeGV with no homologues detected in the GeneBank and 53 tandem repeats (TRs) with sequence length from 25 to 551 nt intersperse throughout the genome of CnmeGV. Six (6) homologous regions (hrs) were identified interspersed throughout the genome. Hr2 contains 11 imperfect palindromes and a high content of AT sequence (about 73%). The unique ORF28 contains a coiled-coil region and a zinc finger-like domain of 4–50 residues specialized by two C2C2 zinc finger motifs that putatively bound two atoms of zinc. ORF21 encoding a chit-1 protein suggesting a horizontal gene transfer from alphabaculovirus. The putative protein presents two carbohydrate-binding module family 14 (CBM_14) domains rather than other homologues detected from betabaculovirus that only contains one chit-binding region. Gene synteny maps showed the colinearity of sequenced betabaculovirus. Phylogenetic analysis indicated that CnmeGV grouped in the betabaculovirus, with a close relation to AdorGV. The cladogram obtained in this work grouped the 17 complete GV genomes in one monophyletic clade. CnmeGV represents a new crambidae host-isolated virus species from the genus Betabaculovirus and is most closely relative of AdorGV. The analyses and information derived from this study will provide a better understanding of the pathological symptoms caused by this virus and its potential use as a microbial pesticide.
Highlights
The rice leaffolder, Cnaphalocrocis medinalisGüenée (Lepidoptera: Crambidae), is a migratory and important insect pest of rice in Asia [1, 2]
The genome consisted of 112,060 bp, which was within the sizes of the 17 sequenced betabaculovirus genomes ranging from 99,657 bp in AdorGV [12] to 178,733 bp inXcGV [13] (Table 1)
Seventy (70) open reading frames (ORFs) were in the same orientation as the granulin ORF and 63 were opposite, indicating that CnmeGV ORFs have no obvious preferred orientation
Summary
The rice leaffolder, Cnaphalocrocis medinalisGüenée (Lepidoptera: Crambidae), is a migratory and important insect pest of rice in Asia [1, 2]. The larvae fold the leaves, feed on the photosynthetic leaf tissues in the folded leaves and such damages can result in reduction of rice yields [3]. In China frequent outbreaks have occurred in rice production regions and have caused rice yield reduction and farmers’ overuse of insecticides. Insecticide control is the main measure farmers in China use and the pests have developed resistance to some insecticides [4]. Bioassay showed that CnmeGV is a highly virulent baculovirus and suggested the potential of its use as an environmentally friendlier microbial agent for future rice leaffolder management [5]
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