ATR2Cala2fromArabidopsis-infecting downy mildew requires 4 TIR-NLR immune receptors for full recognition

Abstract

SummaryArabidopsisCol-0 RPP2A and RPP2B confer recognition ofArabidopsisdowny mildew (Hyaloperonospora arabidopsidis[Hpa]) isolate Cala2, but the identity of the recognized ATR2Cala2effector was unknown.To revealATR2Cala2, an F2population was generated from a cross betweenHpa-Cala2 andHpa-Noks1. We identified ATR2Cala2as a non-canonical RxLR-type effector that carries a signal peptide, a dEER motif, and WY domains but no RxLR motif. Recognition ofATR2Cala2and its effector function were verified by biolistic bombardment, ectopic expression andHpainfection.ATR2Cala2is recognized in accession Col-0 but not in Ler-0 in which RPP2A and RPP2B are absent. InATR2Emoy2andATR2Noks1alleles, a frameshift results in an early stop codon. RPP2A and RPP2B are essential for the recognition of ATR2Cala2. Stable and transient expression ofATR2Cala2under 35S promoter inArabidopsisandNicotiana benthamianaenhances disease susceptibility.Two additional Col-0 TIR-NLR (TNL) genes (RPP2CandRPP2D) adjacent toRPP2AandRPP2Bare quantitatively required for full resistance toHpa-Cala2.We comparedRPP2haplotypes in multipleArabidopsisaccessions and showed that all 4 genes are present in all ATR2Cala2-recognizing accessions.