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Potato mop-top virus TGB1 co-opts HIPP26 to activate abiotic stress signalling for long distance virus movement

Lesley Torrance: James Hutton Inst

<div><em>Potato mop-top virus</em> (PMTV) is soil-borne and typically occurs in potato producing regions that have cooler climates. The PMTV genome contains three overlapping open reading frames (known as a triple gene block; TGB) encoding three movement proteins that facilitate cell-to cell and long distance (systemic) movement. In PMTV the largest movement protein, TGB1, is involved in the long distance movement of both viral ribonucleoprotein complexes and virions. Previously we showed that nuclear passage of TGB1 was required for long distance movement. To gain a mechanistic understanding of the role of TGB1 we conducted a yeast two-hybrid screen to identify interacting host proteins. The screen returned 50 clones 29 of which were ranked with the highest confidence level and were all identified as <em>N. benthamiana</em> homologs of Arabidopsis HIPP26. HIPP26 is a member of the heavy metal associated isoprenylated plant protein family, a large family that contain heavy metal-binding and C-terminal isoprenylation motifs unique to vascular plants. HIPP26 is thought to act as a plasma membrane to nucleus abiotic stress signalling relay. We found that NbHIPP26 was lipid modified and localisation at the plasma membrane and plasmodesmata was mediated by lipidation. NbHIPP26 promoter-reporter fusions revealed vascular tissue specific expression with NbHIPP26 gene expression being upregulated by drought and PMTV infection. In addition, PMTV infection protected plants from drought. The data support a mechanism where interaction with TGB1 alters NbHIPP26 lipidation, releasing and redirecting membrane-associated NbHIPP26 to the nucleus thereby activating the drought stress response and facilitating virus long distance movement.</div>