Large-scale identification of genes involved in septal pore plugging in multicellular fungi

Abstract

Multicellular filamentous fungi have septal pores that allow cytoplasmic exchange, and thus connectivity, between neighboring cells in the filament. Hyphal wounding and other stress conditions induce septal pore closure to minimize cytoplasmic loss. However, the composition of the septal pore and the mechanisms underlying its function are not well understood. Here, we set out to identify new septal components by determining the subcellular localization of 776 uncharacterized proteins in a multicellular ascomycete, Aspergillus oryzae. The set of 776 uncharacterized proteins was selected on the basis that their genes were present in the genomes of multicellular, septal pore-bearing ascomycetes (three Aspergillus species, in subdivision Pezizomycotina) and absent/divergent in the genomes of septal pore-lacking ascomycetes (yeasts). Upon determining their subcellular localization, 62 proteins were found to localize to the septum or septal pore. Deletion of the encoding genes revealed that 23 proteins are involved in regulating septal pore plugging upon hyphal wounding. Thus, this study determines the subcellular localization of many uncharacterized proteins in A. oryzae and, in particular, identifies a set of proteins involved in septal pore function.

Fungal transglutaminase domain–containing proteins are involved in hyphal protection at the septal pore against wounding

“…Three proteins with the ID AO090023000250 (SppB), AO090102000549 (budding yeast Cyk3), and AO090005001528 (budding yeast Png1) were identified. SppB plays a key role in septal pore plugging upon wounding ( Mamun et al ., 2023 ). Cyk3 is involved in the formation and progression of cleavage furrows during cytokinesis in yeast ( Onishi et al ., 2013 ).…”

“…The accumulation of SppB to the septal pore did not occur abruptly but progressively within a few minutes after wounding (Supplemental Figure S3C). The N-terminal disordered region of SppB is essential for its accumulation to the septal pore ( Mamun et al ., 2023 ). To determine the regions responsible for the hyphal protective function in SppB, truncation analysis was performed.…”

“…Several SPP proteins ( Mamun et al ., 2023 ) and a septal pore-accumulating (SpaA) protein (gene ID: AO090020000030), which was newly identified in this study, accumulate to the septal pore upon hyphal wounding, similar to SppB. The molecular mechanism of the septal pore accumulation has not been determined.…”

“…Considering these dynamic regulations, our understanding of the underlying molecular mechanisms is limited. In a previous study, we identified several septal pore plugging (SPP) proteins using a combination of bioinformatics, large-scale localization, and functional analysis ( Mamun et al ., 2023 ). Notably, SppB containing the TGc domain showed wound-induced accumulation to the septal pore and exhibited function in hyphal protection upon wounding ( Mamun et al ., 2023 ).…”

Aspergillus SUMOylation mutants have normal dynein function but exhibit chromatin bridges

“…Syncytia are separated by a cross wall-like structure called the septum, whose formation is triggered by the septationinitiation network (SIN), but it does not necessarily couple with nuclear division, which differs from septation/cytokinesis in yeasts (Kim et al, 2006;Kim et al, 2009;Krapp et al, 2004;Wolfe and Gould, 2005). In filamentous fungi, each septum contains a septal pore, which allows some intercompartmental exchanges during interphase, and the septal pore in A. nidulans closes during mitosis using a NimA-kinase-involved mechanism (Shen et al, 2014), which differs from the Woronin-body-mediated septal-pore-sealing in response to hyphal injury (Jedd and Chua, 2000;Mamun et al, 2023;Shen et al, 2014;Songster et al, 2023;Steinberg et al, 2017;Tenney et al, 2000). It is not clear whether chromatin bridges prevent the sealing of septal pores during mitosis in A. nidulans.…”