Biological, Serological, and Molecular Differences Among Isolates of Potato A Potyvirus

Abstract

Sequences of the coat protein (CP) and 3'-end nontranslated region (3'NTR) of 13 isolates and the helper component proteinase (HC) of nine isolates of potato A potyvirus (PVA) were determined and compared with the eight previously determined PVA CP and 3'NTR sequences and one HC sequence. CP amino acid (aa), 3'NTR nucleotide, and HC aa sequence identities were 92.9, 93.4, and 94.8%, respectively. Sequence data, serological tests, and the necrotic local lesions induced in the leaves of the potato hybrid 'A6' confirmed that tamarillo mosaic virus is a strain of PVA. The aa substitutions A6T and G7S in the CP N-terminus were correlated with loss of aphid transmissibility. Development of necrotic lesions or nonnecrotic symptoms in the systemically infected leaves or lack of systemic spread in potato cv. King Edward were used to place the PVA isolates into four strain groups, but this grouping was not correlated with any differences in CP, HC, or 3'NTR. Recognition of CP by three monoclonal antibodies was used to place the PVA isolates into three groups different from the four groups above. The epitopes of two mono-clonal antibodies were mapped by site-directed mutagenesis to the same lysine residue at the CP aa 34.

Potyvirus helper component-proteinase and coat protein (CP) have coordinated functions in virus-host interactions and the same CP motif affects virus transmission and accumulation.

“…The PVA-B11 CP contains a DAS motif (aa 5-7) at the CP N terminus and is not aphid-transmissible ; this is in contrast to PVA-U, which contains a DAG motif at this position and is transmitted by aphids (Rajama$ ki et al, 1998). The S7G amino acid substitution was introduced into the B11 CP (Table 1) and this point-mutated PVA-B11 CP gene and the wild-type CP gene of PVA-U were transferred to PVA-B11 icDNAs and designated B11-DAG and B11-U CP , respectively (Fig.…”

“…A full-length cDNA clone (icDNA) of PVA-B11 is available, from which infectious in vitro transcripts can be produced (Puurand et al, 1996). A comparison of the deduced HC-Pro (458 aa) and CP (269 aa) amino acid sequences of PVA-U and PVA-B11 has been published (Rajama$ ki et al, 1998) and numbering of amino acids in these proteins follows that study. HC-Pro of PVA-B11 and PVA-U differ in six amino acids, of which E88K and H89Y are located within the N-terminal part, and G153S and A330T are in the central area (Fig.…”

“…One half of the leaf was tested for PVA by DAS-ELISA and the other half used for mechanical inoculation of tobacco and potato plants as previously described (Rajama$ ki et al, 1998). Three plants of tobacco and potato cv.…”

“…Aquila) (two full-grown leaves of each) were mechanically inoculated in two experiments in the greenhouse in Helsinki (temperature 24\19 mC) and in an additional experiment in a growth chamber in Uppsala (Weiss Tekhnik ; photoperiod 18 h, light intensity 250 µE\m#, temperature 19\17 mC). Detection of PVA by DAS-ELISA was carried out as previously described using MAb 58\0 (Adgen, UK), which detects a linear epitope defined by amino acid 34 (Lys) in the PVA CP (Rajama$ ki et al, 1998). The second leaf above the inoculated leaf was sampled by taking 0n3-0n5 g of the basal part of the leaf.…”

“…A previous study has reported that the CP amino acid sequences of 21 potato A potyvirus (PVA) isolates show 92n9 % identity, whereas the HC-Pro amino acid sequences of 10 PVA isolates show 94n8 % identity (Rajama$ ki et al, 1998). Significant biological differences have also been observed.…”