The apparent non‐host resistance of Ethiopian mustard to a radish‐infecting strain of Turnip mosaic virus is largely determined by the C‐terminal region of the P3 viral protein

Abstract

Two different isolates of Turnip mosaic virus (TuMV: UK 1 and JPN 1) belonging to different virus strains were tested on three different Brassica species, namely turnip (Brassica rapa L.), Indian mustard (Brassica juncea L.) and Ethiopian mustard (Brassica carinata A. Braun). Although all three hosts were readily infected by isolate UK 1, isolate JPN 1 was able to establish a visible systemic infection only in the first two. Ethiopian mustard plants showed no local or systemic symptoms, and no virus antigens could be detected by enzyme-linked immunosorbent assay (ELISA). Thus, this species looks like a non-host for JPN 1, an apparent situation of non-host resistance (NHR). Through an experimental approach involving chimeric viruses made by gene interchange between two infectious clones of both virus isolates, the genomic region encoding the C-terminal domain of viral protein P3 was found to bear the resistance determinant, excluding any involvement of the viral fusion proteins P3N-PIPO and P3N-ALT in the resistance. A further determinant refinement identified two adjacent positions (1099 and 1100 of the viral polyprotein) as the main determinants of resistance. Green fluorescent protein (GFP)-tagged viruses showed that the resistance of Ethiopian mustard to isolate JPN 1 is only apparent, as virus-induced fluorescence could be found in discrete areas of both inoculated and non-inoculated leaves. In comparison with other plant-virus combinations of extreme resistance, we propose that Ethiopian mustard shows an apparent NHR to TuMV JPN 1, but not complete immunity or extreme resistance.

The Effects of Turnip Mosaic Virus Infections on the Deposition of Secondary Cell Walls and Developmental Defects in Arabidopsis Plants Are Virus-Strain Specific

“…Thus, not only the different subcellular behavior of the P3 protein, but also the different impact of the infections on plant development and/or SCW formation discussed in this paper happen. Non-host resistance range also differs between strains (Sardaru et al, 2018), and recent important differences have been recently described for the interaction of the P1 viral protein with the host protein G3BP-2, leading to relevant differences in the formation of stress granules (Reuper and Krenz, 2021). How these relevant differences in the biology of intimate interactions with the host should be taken into account for the taxonomical differentiation between strains of viral species, will need to be considered in the future.…”

Association between flower stalk elongation, anArabidopsisdevelopmental trait, and the subcellular location and movement dynamics of the nonstructural protein P3 ofTurnip mosaic virus

“…All these P3‐mediated processes are influenced by determinants in the P3 C‐terminal region. We also recently identified a molecular motif within this region as determinant of the apparent nonhost resistance of Ethiopian mustard to the JPN 1 isolate (Sardaru et al ., 2018). All these findings provided an adequate context for P3 comparisons of two TuMV isolates (UK1 and JPN 1) having differential effects on Arabidopsis development.…”

Resistance to Turnip Mosaic Virus in the Family Brassicaceae

“…In analyzing the resistance phenotype to TuMV in Ethiopian mustard, with infection by a pathotype 1 strain (UK1) of TuMV and apparent non-infection by a pathotype 7 isolate (JPN1), the resistance was associated with restricted systemic movement and absence of symptoms. The restricted vs. resistance-breaking phenotype mapped to the C-terminal region of the P3 protein, with a major determinant being amino acids 1099 and 1100 of the polyprotein, equivalent to amino acids 279 and 280 of the P3 protein (Sardaru et al, 2018). These changes in phenotype may be due, in part, to the same amino acid pairs (Lys-Met vs. Thr-Ile) at positions 279 and 280, respectively, appearing to be involved in the ability to infect radish (Suehiro et al, 2004), with Thr-Ile leading to restricted infection of Ethiopian mustard, and Lys-Met leading to the inability to infect radish.…”