Cloning of theArabidopsisrwm1gene for resistance toWatermelon mosaic viruspoints to a new function for natural virus resistance genes

Abstract

SUMMARYArabidopsis thaliana represents a valuable and efficient model to understand mechanisms underlying plant susceptibility to viral diseases. Here, we describe the identification and molecular cloning of a new gene responsible for recessive resistance to several isolates of Watermelon mosaic virus (WMV, genus Potyvirus) in the Arabidopsis Cvi-0 accession. rwm1 acts at an early stage of infection by impairing viral accumulation in initially infected leaf tissues. Map-based cloning delimited rwm1 on chromosome 1 in a 114-kb region containing 30 annotated genes. Positional and functional candidate gene analysis suggested that rwm1 encodes cPGK2 (At1g56190), an evolutionary conserved nucleus-encoded chloroplast phosphoglycerate kinase with a key role in cell metabolism. Comparative sequence analysis indicates that a single amino acid substitution (S78G) in the N-terminal domain of cPGK2 is involved in rwm1-mediated resistance. This mutation may have functional consequences because it targets a highly conserved residue, affects a putative phosphorylation site and occurs within a predicted nuclear localization signal. Transgenic complementation in Arabidopsis together with virus-induced gene silencing in Nicotiana benthamiana confirmed that cPGK2 corresponds to rwm1 and that the protein is required for efficient WMV infection. This work uncovers new insight into natural plant resistance mechanisms that may provide interesting opportunities for the genetic control of plant virus diseases.

Recessive Resistance to Plant Viruses: Potential Resistance Genes Beyond Translation Initiation Factors

“…When a host factor is indispensable for plant viability or is encoded by functionally redundant genes, the transient knockdown of the factor and the null mutation may produce different phenotypes (Wei et al, 2013; Xiong and Wang, 2013). Alternatively, even if a host factor plays an essential role in plant viability, a conserved amino acid substitution could confer viral resistance without an adverse effect on plant growth (Ouibrahim et al, 2014). This scenario would suggest that the substituted amino acid is critical for molecular plant–virus interaction, but not for plant viability.…”

“…A recessive allele conferring resistance to watermelon mosaic virus (WMV; Potyvirus ) has been identified in the Arabidopsis ecotype Cvi-0 and designated resistance to watermelon mosaic virus 1 ( rwm1 ) (Ouibrahim et al, 2014). Map-based cloning identified an amino acid substitution in a nuclear-encoded chloroplast phosphoglycerate kinase, cPGK2 (Ouibrahim et al, 2014).…”

“…Map-based cloning identified an amino acid substitution in a nuclear-encoded chloroplast phosphoglycerate kinase, cPGK2 (Ouibrahim et al, 2014). cPGK2 gene homologs are found in dicotyledons and monocotyledons including: Nicotiana spp., tomato, potato ( S. tuberosum ), poplar ( Populus trichocarpa ), sorghum ( Sorghum bicolor ), rice, wheat ( Triticum aestivum ), and maize.…”

“…cPGK2 gene homologs are found in dicotyledons and monocotyledons including: Nicotiana spp., tomato, potato ( S. tuberosum ), poplar ( Populus trichocarpa ), sorghum ( Sorghum bicolor ), rice, wheat ( Triticum aestivum ), and maize. Downregulation of cPGK genes in N. benthamiana compromises WMV (Ouibrahim et al, 2014) and PPV accumulation (Poque et al, 2015). Remarkably, cPGK is associated with the 3′-untranslated region of BaMV genomic RNA and is required for the efficient accumulation of BaMV in N. benthamiana (Lin et al, 2007).…”

“…The rationale for this is based on the expectation that viruses from the same genus have similar life cycles. In fact, it is known that some host factors, including eIF4Es, play a similar role in infection by different viruses from the same genus (Asano et al, 2005; Ouibrahim et al, 2014; Yang et al, 2014; Poque et al, 2015; Hashimoto et al, 2016). However, there are many exceptions that challenge this rationale (for example, see the section on eIF4Es-MEDIATED RECESSIVE RESISTANCE).…”