Cloning of the Arabidopsis rwm1 gene for resistance to Watermelon mosaic virus points to a new function for natural virus resistance genes

SUMMARYArabidopsis thaliana represents a valuable and efficient model to understand mechanisms underlying plantsusceptibility to viral diseases. Here, we describe the identification and molecular cloning of a new generesponsible 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 accumulationin initially infected leaf tissues. Map-based cloning delimited rwm1 on chromosome 1 in a 114-kb regioncontaining 30 annotated genes. Positional and functional candidate gene analysis suggested that rwm1encodes cPGK2 (At1g56190), an evolutionary conserved nucleus-encoded chloroplast phosphoglyceratekinase with a key role in cell metabolism. Comparative sequence analysis indicates that a single amino acidsubstitution (S78G) in the N-terminal domain of cPGK2 is involved in rwm1-mediated resistance. This muta-tion may have functional consequences because it targets a highly conserved residue, affects a putativephosphorylation site and occurs within a predicted nuclear localization signal. Transgenic complementationin Arabidopsis together with virus-induced gene silencing in Nicotiana benthamiana confirmed that cPGK2corresponds to rwm1 and that the protein is required for efficient WMV infection. This work uncovers newinsight into natural plant resistance mechanisms that may provide interesting opportunities for the geneticcontrol of plant virus diseases.Keywords: Potyvirus, phosphoglycerate kinase, resistance gene, Arabidopsis, Watermelon mosaic virus.INTRODUCTIONPathogens have evolved specialized tactics to invadeplants, bypass or overcome host defences, and reroute cel-lular functions to their own benefits. These features areespecially true for viruses that are obligate intracellularparasites. Because of their limited gene repertoires, virusescompletely rely on the use of host factors to perform infec-tion. In this scheme, the absence or mutation of a singlehost factor, also called a susceptibility factor, may lead toplants being fully or partially resistant to viruses (Trunigerand Aranda, 2009). The characterization of such suscepti-bility factors is therefore of particular interest to providemechanistic insights into plant–virus interactions and alsoto identify potential targets for improved disease manage-ment (Pavan et al., 2010).A large number of viruses have been demonstrated toinfect the model plant Arabidopsis thaliana (hereafter Ara-bidopsis) under standard laboratory conditions (Ouibrahimand Caranta, 2013). This offers a unique opportunity toexploit this versatile plant model to decipher the moleculardialogue between plants and viruses. Reverse genetics inArabidopsis has led to the identification of several host fac-tors involved in viral infection processes. For example, themembrane-associated TOM1 and TOM3 proteins arerequired for efficient multiplication of Tobacco mosaicvirus (TMV) and were initially identified by screening Ara-bidopsis EMS-mutagenized populations for altered infec-tion phenotypes (Yamanaka et al., 2002). Other essentialhost factors have been discovered from studies that were