Abstract
SummaryIn both Sordaria macrospora and Neurospora crassa, components of the conserved STRIPAK (striatin‐interacting phosphatase and kinase) complex regulate cell–cell fusion, hyphal network development and fruiting body formation. Interestingly, a number of Epichloë festucae genes that are required for hyphal cell–cell fusion, such as noxA, noxR, proA, mpkA and mkkA, are also required for the establishment of a mutualistic symbiotic interaction with Lolium perenne. To determine whether MobC, a homologue of the STRIPAK complex component MOB3 in S. macrospora and N. crassa, is required for E. festucae hyphal fusion and symbiosis, a mobC deletion strain was generated. The ΔmobC mutant showed reduced rates of hyphal cell–cell fusion, formed intrahyphal hyphae and exhibited enhanced conidiation. Plants infected with ΔmobC were severely stunted. Hyphae of ΔmobC showed a proliferative pattern of growth within the leaves of Lolium perenne with increased colonization of the intercellular spaces and vascular bundles. Although hyphae were still able to form expressoria, structures allowing the colonization of the leaf surface, the frequency of formation was significantly reduced. Collectively, these results show that the STRIPAK component MobC is required for the establishment of a mutualistic symbiotic association between E. festucae and L. perenne, and plays an accessory role in the regulation of hyphal cell–cell fusion and expressorium development in E. festucae.
Highlights
Mutant analysis of these components and their respective homologues [HAM-3 (PRO11), HAM-2 (PRO22), MOB-3 (MOB3), HAM-4 (PRO45), and PP2A-A and PPG-1 (PP2A subunits)] in Neurospora crassa has shown that components of the striatininteracting phosphatase and kinase (STRIPAK) complex are required for cell–cell fusion and sexual fruiting body development (Bernhards and P€oggeler, 2011; Bloemendal et al, 2010, 2012; Dettmann et al, 2013; Frey et al, 2015a,b; Fu et al, 2011; Maerz et al, 2009; Nordzieke et al, 2015; P€oggeler and K€uck, 2004; Read et al, 2012; Simonin et al, 2010)
In Sordaria, GPI1 localizes to the plasma membrane, PRO45 to the nuclear membrane, PRO45/GPI1 to mitochondria, and KIN3 and KIN24 to septal pores, whereas, in N. crassa, HAM-2 and HAM-3 localize to the nuclear envelope (Bloemendal et al, 2010; Dettmann et al, 2013; Frey et al, 2015a,b, Nordzieke et al, 2015)
A correct localization pattern of HAM-2 and HAM-3 is required for MAK-1 [cell wall integrity (CWI) pathway mitogenactivated protein (MAP) kinase] nuclear accumulation in a MAK-2 [pheromone response (PR) pathway MAP kinase]-dependent manner, as MAK-2 is required for phosphorylation of the STRIPAK component MOB3 (Dettmann et al, 2013)
Summary
The STRIPAK complex in Sordaria consists of several proteins: the striatin scaffold protein PRO11; the striatin-interacting protein PRO22; the kinase activator MOB3; the glycosylphosphatidylinisotol (GPI)-anchored protein GPI1; the serine/threonine phosphatase PP2A subunits A and C; the germinal centre kinases KIN3 and KIN23; the sarcolemmal membrane-associated protein PRO45; and several other accessory proteins (Bloemendal et al, 2012; Frey et al, 2015a,b; Nordzieke et al, 2015) Mutant analysis of these components and their respective homologues [HAM-3 (PRO11), HAM-2 (PRO22), MOB-3 (MOB3), HAM-4 (PRO45), and PP2A-A and PPG-1 (PP2A subunits)] in Neurospora crassa has shown that components of the STRIPAK complex are required for cell–cell fusion and sexual fruiting body development (Bernhards and P€oggeler, 2011; Bloemendal et al, 2010, 2012; Dettmann et al, 2013; Frey et al, 2015a,b; Fu et al, 2011; Maerz et al, 2009; Nordzieke et al, 2015; P€oggeler and K€uck, 2004; Read et al, 2012; Simonin et al, 2010). These results demonstrate that the STRIPAK complex components exhibit multiple
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