Arch Virol (2001) 146: 1139–1153
Plant virus transmission by plasmodiophorid fungi is associated
with distinctive transmembrane regions of virus-encoded proteins
M. J. Adams
, J. F. Antoniw
, and J. G. L. Mullins
Plant Pathology Department, IACR-Rothamsted, Harpenden, U.K.
Bioinformatics Department, IACR-Rothamsted, Harpenden, U.K.
Department of Biology and Health Science, University of Luton, Luton, U.K.
Accepted November 9, 2000
Summary. Computer analysis of published sequence data has consistently identi-
ﬁed two complementary transmembrane domains in the coat protein readthrough
domains of benyviruses, furoviruses and pomoviruses and in the P2 proteins
of bymoviruses. These viruses differ in genome organisation but are all trans-
mitted by plasmodiophorid fungi. The second domain is absent or disrupted in
naturally-occurring deletion mutants that cannot be fungally-transmitted. In a
non-transmissible substitution mutant of Beet necrotic yellow vein virus [Tamada
et al. (1996) J Gen Virol 77: 1359–1367], the alignment of the helices is dis-
rupted. From conserved patterns detected in transmembrane helix sequences and
calculated relative helix tilts, structural arrangements consistent with tight pack-
ing of transmembrane helices were identiﬁed. These included ridge/groove ar-
rangements between the two helices and strong electrostatic associations at the
interfacial regions of the membrane. The data strongly suggest that these trans-
membrane helices facilitate the movement of virus particles across the fungal
Fungi in the genera Polymyxa and Spongospora (order Plasmodiophorales) trans-
mit about 20 plant viruses. The fungi are obligate parasites conﬁned to various
types of root cell, and the viruses are carried within the fungus zoospores and rest-
ing spores, probably as intact virions. They are transmitted to the plant host, or
acquired from it, while the undifferentiated fungal plasmodium is growing within
the plant cell. There is no evidence that the viruses can multiply within the vectors
[2, 4]. All these viruses have multipartite RNA genomes and are prone to loss of
parts of their genome when they are propagated by repeated mechanical trans-
mission. Some of these deletions have been shown to affect fungus transmission.
The viruses and relevant sequence accession numbers are listed in Table 1.