Abstract
Thrips palmi is a widely distributed major agricultural pest in the tropics and subtropics, causing significant losses in cucurbit and solanaceous crops through feeding damage and transmission of tospoviruses. Thrips palmi is a vector of capsicum chlorosis virus (CaCV) in Australia. The present understanding of transmission biology and potential effects of CaCV on T. palmi is limited. To gain insights into molecular responses to CaCV infection, we performed RNA-Seq to identify thrips transcripts that are differentially-abundant during virus infection of adults. De-novo assembly of the transcriptome generated from whole bodies of T. palmi adults generated 166,445 contigs, of which ~24% contained a predicted open reading frame. We identified 1,389 differentially-expressed (DE) transcripts, with comparable numbers up- (708) and down-regulated (681) in virus-exposed thrips compared to non-exposed thrips. Approximately 59% of these DE transcripts had significant matches to NCBI non-redundant proteins (Blastx) and Blast2GO identified provisional functional categories among the up-regulated transcripts in virus-exposed thrips including innate immune response-related genes, salivary gland and/or gut-associated genes and vitellogenin genes. The majority of the immune-related proteins are known to serve functions in lysosome activity and melanisation in insects. Most of the up-regulated oral and extra-oral digestion-associated genes appear to be involved in digestion of proteins, lipids and plant cell wall components which may indirectly enhance the likelihood or frequency of virus transmission or may be involved in the regulation of host defence responses. Most of the down-regulated transcripts fell into the gene ontology functional category of ‘structural constituent of cuticle’. Comparison to DE genes responsive to tomato spotted wilt virus in Frankliniella occidentalis indicates conservation of some thrips molecular responses to infection by different tospoviruses. This study assembled the first transcriptome in the genus Thrips and provides important data to broaden our understanding of networks of molecular interactions between thrips and tospoviruses.
Highlights
Thrips belong to the family Thripidae in the order Thysanoptera which contains nearly 7700 described thrips species [1]
We identified transcriptome-wide responses of T. palmi to capsicum chlorosis virus (CaCV) infection, some of which were conserved in other thrips species in response to infection with different tospoviruses
The raw sequence read data generated from the six samples have been deposited in the NCBI Sequence Read Archive as BioProject PRJNA498538 with accession numbers SAMN10316162—SAMN10316167
Summary
Thrips belong to the family Thripidae in the order Thysanoptera which contains nearly 7700 described thrips species [1]. Frankliniella occidentalis is world-wide the most devastating invasive species, with a broad host range, transmitting multiple tospoviruses (genus Orthotospovirus, family Tospoviridae, Order Bunyavirales) including the economically important tomato spotted wilt virus (TSWV) [4]. Melon thrips (Thrips palmi) originated in Southeast Asia [5] and have become a serious invasive pest in tropical and subtropical countries [6]. Several tospoviruses are known to be transmitted by T. palmi including calla lily chlorotic spot virus [7], groundnut bud necrosis virus [8], melon yellow spot virus [9], tomato necrotic ringspot virus [10], watermelon bud necrosis virus [11] and watermelon silver mottle virus [12]. In Australia, capsicum chlorosis virus (CaCV) is transmitted by T. palmi [13]
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