Abstract
Members of the virus order Bunyavirales cause serious diseases in animals, humans and plants. Family Tospoviridae in this order contains only one genus Orthotospovirus, and members in this genus exclusively infect plants. Tomato spotted wilt tospovirus (TSWV) is considered one of the most economically important plants viruses. Little is known about the regulatory elements in the TSWV genome. Here we show that, when in the cDNA form, the 5′-upstream region of the TSWV-coded GN/GC gene (pGN/GC) possesses putative cis-regulatory elements, including an auxin responsive element (AuxRE) for binding of auxin response factors (ARFs), as well as a circadian clock-associated 1 (CCA1) protein binding site (CBS). Due to the lack of a reverse genetics system, we verified the functionality of these elements in Arabidopsis. pGN/GC showed light-suppressive promoter activity in transgenic Arabidopsis, and mutation in the CBS was sufficient to switch the activity to light inducible. Additionally, exogenous auxin treatments repressed the promoter activity of both wild type and CBS-mutated pGN/GC. Mutation in AuxRE in both promoters abolished their sensitivity to auxin. As transcriptional repressors, both CCA1 and ARF2 were able to bind to pGN/GC directly. To our knowledge, this is the first report that a 5′-terminal sequence of an RNA virus has light-and hormone-responsive promoter activities when expressed as cDNA in host plant’s nuclear background. Our findings suggest new clues on the possible origin, evolution and function of the TSWV genomic sequence and its non-coding regions.
Highlights
Viruses in the order Bunyavirales are characterized by segmented RNA genome with three RNAs packaged in enveloped virus particles (Briese et al, 2013)
All three genomic cDNAs of TSWV isolate T were scanned for potential transcription initiation and transcription factor (TF) binding elements
Our results suggest that the TSWV has regulatory elements that are found to be responsive to light and auxin when expressed as cDNA in the plant’s nuclear background
Summary
Viruses in the order Bunyavirales are characterized by segmented RNA genome with three RNAs packaged in enveloped virus particles (Briese et al, 2013). Tospoviridae contains only one genus Orthotospovirus (Siddell et al, 2019). Viruses in this genus exclusively infect plants, and tospoviruses are unique in that the large RNA is in negative sense while the medium and small RNAs possess an ambisense genome organization (Prins and Goldbach, 1998; Adkins, 2000). Tomato spotted wilt tospovirus (TSWV), a member of the genus Orthotospovirus, is considered one of the. Light- and Auxin-Responsiveness of TSWV cDNA world’s most important plant viruses (Scholthof et al, 2011). Considerable progress has been made on elucidating the tospovirus genome organization, replication, transcription, and molecular interactions with its host plants (Turina et al, 2016)
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