Substitution of a single amino acid in the 2b protein of Pea early-browning virus affects nematode transmission

Abstract

The 2b protein of Pea early-browning virus (PEBV) is required for transmission of the virus by nematodes. Comparison of the 2b proteins of highly transmissible (TpA56) and poorly transmissible (SP5) isolates of PEBV identified two amino acid substitutions (G90S and G177R) that might be responsible for the poor transmission of isolate SP5. Hybrid viruses were created in which the TpA56 2b protein carried SP5-specific substitutions at residue 90 or 177, and in which the SP5 2b protein carried TpA56-specific substitutions at these positions. Transmission tests showed that the G177R substitution is sufficient to prevent nematode transmission of the virus. Examination of the 2b proteins from PEBV and other tobraviruses predicted the presence of a coiled-coil domain in the central region of the protein. This structural element is important for the association of interacting proteins and, thus, might mediate interaction of the 2b protein with the virus coat protein or with the vector nematode.Tobraviruses, which include Pea early-browning virus (PEBV), Tobacco rattle virus (TRV) and Pepper ringspot virus (PepRSV) are transmitted between plants by soil-inhabiting nematodes (Taylor & Brown, 1997). Glasshouse tests have demonstrated that particular tobravirus isolates can be transmitted only by certain nematode species. For example, TRV isolate PpK20 can be transmitted by Paratrichodorus pachydermus but not by P. anemones or Trichodorus primitivus (Herna! ndez et al., 1997). In contrast, TRV isolate PaY4 can be transmitted by both P. pachydermus and P. anemones (Vassilakos, 2000 ; Vassilakos et al., 2001), whereas PEBV isolate TpA56 is transmitted by T. primitivus but not by P. pachydermus (MacFarlane & Brown, 1995).Tobraviruses have two positive-stranded genomic RNAs, each of which is encapsidated separately in a rod-shaped particle. The larger RNA (RNA1) encodes proteins involved in Author for correspondence : Stuart MacFarlane.Fax j44 1382 562426. e-mail s.macfarlane!scri.sari.ac.uk the replication and spread of the virus in plants, and can infect plants systemically in the complete absence of the second, smaller genomic RNA (RNA2) (Harrison & Robinson, 1986). RNA2 was shown to carry the determinants for nematode transmission by the analysis of pseudorecombinant isolates of TRV in which the genomic RNAs from the nematodetransmissible PpK20 isolate and the non-transmissible PLB isolate were re-assorted (Ploeg et al., 1993). These experiments showed that inclusion of RNA2 from TRV PpK20 led to the transmission of TRV PLB RNA1, and the replacement of PpK20 RNA2 with PLB RNA2 resulted in failure to transmit PpK20 RNA1. Thus, RNA2 of TRV PpK20 encoded a transmission determinant(s) that was lacking in RNA2 of TRV PLB.RNA2 has been sequenced from many tobravirus isolates, revealing a great variation in the size and gene content (MacFarlane, 1999). All isolates encode a coat protein (CP), although deleted forms of RNA2 lacking the CP gene can be generated in infected plants (Herna! ndez et al., 1996). Many isolates include at ...

Plant to Plant Movement

“…Tobravirus RNA2 is variable in size and, as well Harrison et al (1974) and panel (B) from Wang and Gergerich (1998) (Vellios et al, 2002a;MacFarlane, 2003;Holeva and MacFarlane, 2006). Changing amino acid 177, which lies in a predicted coiledcoil domain in PEBV 2b protein, controls nematode transmissibility (Vellios et al, 2002b). It is suggested that this coiled-coil might mediate the interaction between 2b and CPs.…”

A Stretch of 11 Amino Acids in the βB-βC Loop of the Coat Protein of Grapevine Fanleaf Virus Is Essential for Transmission by the Nematode Xiphinema index

“…For Cauliflower mosaic virus (CaMV; genus Caulimovirus, family Caulimoviridae), a single amino acid change in protein P2, which acts as HC, is sufficient to abolish aphid transmission (24). In the case of nematode-transmitted viruses, a single mutation in the HC protein 2b of Pea early-browning virus (PEBV; genus Tobravirus, unassigned family) is sufficient to prevent transmission (38). Similarly, a 15-amino-acid deletion at the C terminus of the CP abolishes transmission of PEBV (22).…”

Subcellular localization of p29, a putative movement protein of pepper ringspot virus

“…The PepRSV RNA 2 segment is 1799 bases long and encodes only the coat protein (CP) gene (NC_003670). However, the RNA 2 of TRV and PEBV additionally encodes one or two nonstructural proteins (2b and 2c) [11][12][13][14], which are involved in nematode transmission [12, [15][16][17][18].…”