Abstract
BackgroundPhytophthora species secrete cytoplasmic effectors from a family named Crinkler (CRN), which are characterised by the presence of conserved specific domains in the N- and C-terminal regions. P. parasitica causes disease in a wide range of host plants, however the role of CRN effectors in these interactions remains unclear. Here, we aimed to: (i) identify candidate CRN encoding genes in P. parasitica genomes; (ii) evaluate the transcriptional expression of PpCRN (Phytophthora parasitica Crinkler candidate) during the P. parasitica interaction with Citrus sunki (high susceptible) and Poncirus trifoliata (resistant); and (iii) functionally characterize two PpCRNs in the model plant Nicotiana benthamiana.ResultsOur in silico analyses identified 80 putative PpCRN effectors in the genome of P. parasitica isolate ‘IAC 01/95.1’. Transcriptional analysis revealed differential gene expression of 20 PpCRN candidates during the interaction with the susceptible Citrus sunki and the resistant Poncirus trifoliata. We have also found that P. parasitica is able to recognize different citrus hosts and accordingly modulates PpCRNs expression. Additionally, two PpCRN effectors, namely PpCRN7 and PpCRN20, were further characterized via transient gene expression in N. benthamiana leaves. The elicitin INF-1-induced Hypersensitivity Response (HR) was increased by an additive effect driven by PpCRN7 expression, whereas PpCRN20 expression suppressed HR response in N. benthamiana leaves. Despite contrasting functions related to HR, both effectors increased the susceptibility of plants to P. parasitica.ConclusionsPpCRN7 and PpCRN20 have the ability to increase P. parasitica pathogenicity and may play important roles at different stages of infection. These PpCRN-associated mechanisms are now targets of biotechnological studies aiming to break pathogen’s virulence and to promote plant resistance.
Highlights
Phytophthora species secrete cytoplasmic effectors from a family named Crinkler (CRN), which are characterised by the presence of conserved specific domains in the N- and C-terminal regions
Candidate Crinkler (CRN) effectors of P. parasitica (PpCRN) Here, we explored the available genomes of P. parasitica deposited under the international project “Phytophthora parasitica genome initiative” database to obtain the genome data of P. parasitica isolates from different hosts and geographic origins, to study the CRN effectors
The conserved LxLFLAK motif was identified in several PpCRN candidates from distinct P. parasitica genomes, but it showed a variation in terms of quantity and sequence diversity from one genome to another (Fig. 1)
Summary
Phytophthora species secrete cytoplasmic effectors from a family named Crinkler (CRN), which are characterised by the presence of conserved specific domains in the N- and C-terminal regions. P. parasitica causes disease in a wide range of host plants, the role of CRN effectors in these interactions remains unclear. The pathogen’s attack strategy relies on the secretion of effector proteins that functionally modulate the interaction with the host plant at early times of infection and Phytophthora is a genus of oomycete that forms a group of eukaryotic microorganisms classified within Stramenopiles, which are notable plant pathogens, affecting a wide variety of plants, and causing an extensive damage in natural and cultivated ecosystems [6]. Phytophthora spp. can cause several diseases in citrus depending on the plant tissue that is infected, with root rot and trunk gummosis [10, 11]. Citrus gummosis disease is considered one of the most serious diseases affecting citrus industry worldwide, causing significant economic losses in several regions [12]
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