Magnaporthe oryzae CK2 Accumulates in Nuclei, Nucleoli, at Septal Pores and Forms a Large Ring Structure in Appressoria, and Is Involved in Rice Blast Pathogenesis

Abstract

Magnaporthe oryzae (Mo) is a model pathogen causing rice blast resulting in yield and economic losses world-wide. CK2 is a constitutively active, serine/threonine kinase in eukaryotes, having a wide array of known substrates, and involved in many cellular processes. We investigated the localization and role of MoCK2 during growth and infection. BLAST search for MoCK2 components and targeted deletion of subunits was combined with protein-GFP fusions to investigate localization. We found one CKa and two CKb subunits of the CK2 holoenzyme. Deletion of the catalytic subunit CKa was not possible and might indicate that such deletions are lethal. The CKb subunits could be deleted but they were both necessary for normal growth and pathogenicity. Localization studies showed that the CK2 holoenzyme needed to be intact for normal localization at septal pores and at appressorium penetration pores. Nuclear localization of CKa was however not dependent on the intact CK2 holoenzyme. In appressoria, CK2 formed a large ring perpendicular to the penetration pore and the ring formation was dependent on the presence of all CK2 subunits. The effects on growth and pathogenicity of deletion of the b subunits combined with the localization indicate that CK2 can have important regulatory functions not only in the nucleus/nucleolus but also at fungal specific structures such as septa and appressorial pores.

Conserved Eukaryotic Kinase CK2 Chaperone Intrinsically Disordered Protein Interactions

“…To aid in interpreting the results, we made a functional classification of the interacting proteins. The pulldown was, as expected based on our previous study, overrepresented for proteins known to be present in nucleoli and at septa (4).…”

“…Identification of potential septal and nucleolar and other substrates for MoCK2 by GFP-CKa pulldown and investigation of whether these proteins contain a CK2 phosphorylation unfolding motif. The CK2 localization pattern suggested that CK2 may have substrates associated with septa and nucleolar function (4). To explore this, we performed coimmunoprecipitation to identify proteins interacting with CK2, using GFP-CKa as a bait, and, in addition to the bait, identified 1,505 proteins (Data Set S1).…”

“…are named a1, a2, b1, and b2 (3), whereas several other fungi, including M. oryzae, only contain one CKa (4). CK2 has been shown to phosphorylate a large number of proteins (1,2,5), and it seems to be involved in many cellular processes (5).…”

“…We previously argued when we studied CK2 localization and involvement in pathogenesis (4) that filamentous fungi are better models than yeasts for investigating eukaryotic cellular functions involved in cell-cell communication. We showed that the M. oryzae CK2 holoenzyme (MoCK2) accumulates in the nucleolus and that it localizes in structures near septal pores and assembles to form a large ring structure perpendicular to the appressorium penetration pore (4).…”

OmicsDB::Pathogens - A database for exploring functional networks of plant pathogens

“…Plant pathogens have until now had little representation in these databases. Electronic resources for Fusarium graminearum eFG (Liu et al, 2013) a model species in plant pathology (Zhang et al, 2019), contains functional annotation as well as annotations of transcription factors and curated and predicted pathogenic genes for fusarium. PHI-base (Urban et al, 2017) is a great resource for curated Pathogen-Host Interactions but is manually curated and thus limited in size.…”