P-286 - Genomic and transcriptomic analyses on NLR immune receptors in parasitic plants

Parasitic plants connect their vasculatures with host plants to obtain water and nutrients. Recent genomic studies have shown a significant shrinkage in intracellular immune receptors, nucleotide-binding leucine-rich repeat receptors (NLRs), in parasitic plants. We hypothesized that the NLR contraction contributed to establishing the intimate plant–plant interaction because activated NLRs trigger cell death in response to non-self molecules. Therefore, we surveyed NLR conservation in nine parasitic plants from three orders. Our NLR annotation found a tendency of decreased NLR copy numbers in parasitic plants along with increased their host dependency. Moreover, Toll/Interleukin-1 receptor (TIR)-NLRs and some downstream genes were convergently lost in obligate parasitic species among the examined parasitic lineages. In addition, we analyzed the expression patterns of NLR signaling components in a model parasitic plant, Phtheirospermum japonicum, and found that most differentially expressed NLRs were transcriptionally suppressed during host infection compared with the roots growing without a host. Interestingly, we also found a low expression level of PjPAD4, one of the TIR-NLR downstream genes, during host invasion. Our data suggest that genomic and transcriptomic downregulation of NLR signaling may have an important role in establishing adequate parasitism without autoactivating immune responses.