Cauliflower mosaic virus gene VI product N-terminus contains regions involved in resistance-breakage, self-association and interactions with movement protein

Abstract

Cauliflower mosaic virus (CaMV) gene VI encodes a multifunctional protein (P6) involved in the translation of viral RNA, the formation of inclusion bodies, and the determination of host range. Arabidopsis thaliana ecotype Tsu-0 prevents the systemic spread of most CaMV isolates, including CM1841. However, CaMV isolate W260 overcomes this resistance. In this paper, the N-terminal 110 amino acids of P6 (termed D1) were identified as the resistance-breaking region. D1 also bound full-length P6. Furthermore, binding of W260 D1 to P6 induced higher β-galactosidase activity and better leucine-independent growth in the yeast two-hybrid system than its CM1841 counterpart. Thus, W260 may evade Tsu-0 resistance by mediating P6 self-association in a manner different from that of CM1841. Because Tsu-0 resistance prevents virus movement, interaction of P6 with P1 (CaMV movement protein) was investigated. Both yeast two-hybrid analyses and maltose-binding protein pull-down experiments show that P6 interacts with P1. Although neither half of P1 interacts with P6, the N-terminus of P6 binds P1. Interestingly, D1 by itself does not interact with P1, indicating that different portions of the P6 N-terminus are involved in different activities. The P1-P6 interactions suggest a role for P6 in virus transport, possibly by regulating P1 tubule formation or the assembly of movement complexes.

The Cauliflower Mosaic Virus Protein P6 Forms Motile Inclusions That Traffic along Actin Microfilaments and Stabilize Microtubules

“…The 126-kD protein colocalized with MP-GFP in virus replication complexes during virus infections in both N. benthamiana leaves and BY-2 tobacco protoplasts (Liu et al, 2005). The P6 protein has been shown to physically interact with its MP (P1) in a yeast two-hybrid screen (Hapiak et al, 2008). The fact that both of these proteins have been shown to traffic along actin microfilaments demonstrates that association with the host cytoskeleton is a strategy employed by diverse viruses and further reveals that viruses often rely upon more than just the classically defined MPs to facilitate movement (for review, see Lucas, 2006;Harries and Nelson, 2008).…”

Cauliflower mosaic virus Tav protein induces leaf chlorosis in transgenic tobacco through a host response to virulence function of Tav

“…CaMV Tav has been well studied not only as a translational transactivator and the major component of CaMV (Hohn and Rothnie 2013), but also as a pathogenesis factor that determines the viral host range (Hapiak et al 2008;Schoelz et al 1986;Wintermantel et al 1993) and symptom expression (Kobayashi and Hohn 2004), most likely through the regulation of host innate immunity (Love et al 2012) and RNA silencing (Haas et al 2008;Laird et al 2013;Love et al 2007a). In transgenic Arabidopsis thaliana, Tav enhances the expression of jasmonic acid (JA) responsive genes and resistance to necrotrophic fungi and suppresses the salicylic acid (SA) response, basal resistance and gene-for-gene resistance to hemibiotrophic bacteria and SA-dependent, Tomato bushy stunt virus (TBSV) P19-mediated cell death, probably by affecting NPR1 function (Love et al 2012).…”

Association of the P6 Protein of Cauliflower mosaic virus with Plasmodesmata and Plasmodesmal Proteins

“…6-9). The pull-down assays between P6 and CaMV MP (Hapiak et al, 2008) further suggest that P6 I-LBs associate with plasmodesmata. This additionally was supported through the consistent association of P6 I-LBs with cell wall regions stained with aniline blue, a marker for plasmodesmata (Thomas et al, 2008).…”

“…Third, P6 is an important pathogenicity determinant. P6 functions as an avirulence determinant in some solanaceous and cruciferous species (Daubert et al, 1984;Schoelz et al, 1986;Hapiak et al, 2008) and is a chlorosis symptom determinant in susceptible hosts (Daubert et al, 1984;Baughman et al, 1988;Goldberg et al, 1991;Cecchini et al, 1997). Finally, P6 has the capacity to compromise host defenses, as it is a suppressor of RNA silencing and cell death (Love et al, 2007;Haas et al, 2008), and it modulates signaling by salicylic acid, jasmonic acid, ethylene, and auxin (Geri et al, 2004;Love et al, 2012;Laird et al, 2013).…”

“…The vast majority of CaMV virions accumulate in association with P6-containing IBs. Furthermore, P6 physically interacts with the CaMV capsid and MP, as well as the two proteins necessary for aphid transmission, P2 and P3 (Himmelbach et al, 1996;Ryabova et al, 2002;Hapiak et al, 2008;Lutz et al, 2012). Recent studies have indicated that P6 IBs serve as a reservoir for virions, in which the virions may be rapidly transferred to P2 electron-lucent IBs for acquisition by aphids (Bak et al, 2013).…”