| Summary: | Upon infection plant pathogens secrete a large amount of effector molecules into the host plant. These effectors are thought to aid the infection processes by fending off the plant’s defence and modifying its transcriptional machinery to benefit the pathogen. This is true for Phytophthora capsici an oomycete pathogen of many important crops including tomato and cucumber. We identified and characterised CRN effectors in P. capsici. With 84 putative effectors composed of 29 different effector domains, the CRNs form a large and diverse class. CRN domain expansion is likely to have occurred in the peronosporales lineage of oomycetes (to which P. capsici belongs), though CRNs can be identified in all oomycetes sequenced to date. We show that CRN effectors are upregulated during infection and as expected by their diverse sequences, appear to have different dynamics. Even though all CRNs localise to the plant nucleus, suggesting involvement in key regulatory processes of the host, their subnuclear localisations differ. We confirm that one CRN, CRN12_997 is targeting a tomato TCP transcription factor. This transcription factor plays crucial roles in development, but is also involved in defence responses. CRN12_997 alters TCP localisation by dissociating it from the chromatin-associated fraction of the cell and thus prevents it function. Additionally we have identified putative targets for three other CRNs. Again these targets, including glyceraldehyde 3’phostphate dehydrogenase, Fibrillarin 2 and histone H4, indicate the potential involvement of CRNs in altering transcription machinery of the host plant; all targets can be linked to transcriptional complexes in plants. We conclude that CRNs are likely to play an important role in the infection process. The study of CRN effectors will provide insight into infection mechanisms and may also help to unravel networks involved in plant regulation and development.
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