Abstract:
Phytophthora cinnamomi is a plant pathogenic oomycete that causes Phytophthora root rot
of avocado (PRR). Currently, there is a limited understanding of the molecular interactions
underlying this disease. Other Phytophthora species employ an arsenal of effector proteins
to manipulate host physiology, of which the RxLR effectors contribute to virulence by interfering with host immune responses. The aim of this study was to identify candidate RxLR
effectors in P. cinnamomi that play a role in establishing PRR, and to infer possible functions
for these effectors. We identified 61 candidate RxLR genes which were expressed during
infection of a susceptible avocado rootstock. Several of these genes were present in multiple copies in the P. cinnamomi genome, suggesting that they may contribute to pathogen fitness. Phylogenetic analysis of the manually predicted RxLR protein sequences revealed 12
P. cinnamomi RxLRs that were related to characterised effectors in other Phytophthora
spp., providing clues to their functions in planta. Expression profiles of nine more RxLRs
point to possible virulence roles in avocado–highlighting a way forward for studies of this
interaction. This study represents the first investigation of the expression of P. cinnamomi
RxLR genes during the course of avocado infection, and puts forward a pipeline to pinpoint
effector genes with potential as virulence determinants, providing a foundation for the future
functional characterization of RxLRs that contribute to P. cinnamomi virulence in avocado.
