Atypical RXLR effectors are involved in Phytophthora cactorum pathogenesis

Abstract

RXLR effectors are pathogenic factors secreted from oomycetes to manipulate the immunity of the host. Typical RXLR effectors contain an RXLR-dEER motif at the N-terminus, whereas atypical RXLRs show variations on this motif. The oomycete Phytophthora cactorum is known to infect over 200 plant species, resulting in significant agricultural economic losses. Although genome-wide identification and functional analyses of typical RXLRs from P. cactorum have been performed, little is known of atypical PcaRXLRs. Here, we identified RXLRs, both typical and atypical, in P. cactorum and compared them with those of other oomycete pathogens. Fewer RXLRs were identified in P. cactorum compared with other Phytophthora species, possibly due to fewer duplication events of RXLRs. In contrast, the percentage of atypical RXLRs was higher in P. cactorum than in other species, suggesting significant roles in P. cactorum pathogenesis. Analysis of RXLR gene expression showed that most were transcribed, suggesting their functionality. Transient expression of two atypical RXLRs in Nicotiana benthamiana showed that they induced necrosis dependent on host SGT1 and HSP90. Furthermore, two additional atypical RXLRs suppressed the defense response in N. benthamiana and promoted P. cactorum infection. These results demonstrate the vital role of atypical RXLRs in P. cactorum and provide valuable information on their evolutionary patterns and interactions with host plants.