The meiosis‐specific APC activator FgAMA1 is dispensable for meiosis but important for ascosporogenesis in Fusarium graminearum

Abstract

Ascospores are the primary inoculum in Fusarium graminearum . Interestingly, 70 of its genes have premature stop codons (PSC) and require A-to-I editing during sexual reproduction to encode full-length proteins, including the ortholog of yeast Ama1, a meiosis-specific activator of APC/C. In this study, we characterized the function of FgAMA1 and its PSC editing. FgAMA1 was specifically expressed during sexual reproduction. The Fgama1 mutant was normal in growth and perithecium formation but defective in ascospogenesis. Instead of forming four-celled, uninucleate ascospores, Fgama1 mutant produced oval, single-celled, binucleated ascospores by selfing. Some mutant ascospores began to bud and underwent additional mitosis inside asci. Expression of the wild-type or edited FgAMA1 but not the uneditable allele complemented Fgama1 . In the Fgama1 x mat-1-1 outcross, over 60% of the asci had eight Fgama1 or intermediate (elongated but single-celled) ascospores, suggesting efficient meiotic silencing of unpaired FgAMA1 . Deletion of FgPAL1 , one of the genes upregulated in Fgama1 also resulted in defects in ascospore morphology and budding. Overall, our results showed that FgAMA1 is dispensable for meiosis but important for ascospore formation and discharge. In F. graminearum , whereas some of its targets are functional during meiosis, FgAma1 may target other proteins that function after spore delimitation.

FgPal1 regulates morphogenesis and pathogenesis in Fusarium graminearum

“…In a previous study, FgPAL1 (FGSG_08726) was found to be upregulated in the Fgama1 mutant and important for ascosporogenesis (Hao et al, 2019). FgPAL1 is orthologous to PAL1 of S. cerevisiae and encodes a 521 amino acid (aa) protein with a conserved PAL1 domain at the C-terminal region.…”

“…Interestingly, 70 genes have premature stop codons (PSCs) that require A-to-I editing to encode full-length functional proteins in F. graminearum. Several genes with PSC editing events are known to be important for ascospore formation or release, including PUK1, AMD1 and FgAMA1 (Liu et al, 2016;Cao et al, 2017;Hao et al, 2019).…”

“…Mature perithecia are melanized and contain asci with eight four‐celled ascospores. In each developing ascus, the diploid nucleus formed after karyogamy goes through meiosis and one round of post‐meiotic mitosis before the delimitation of eight ascospores (Nakayashiki, 2005; Hao et al ., 2019). The nucleus in each developing ascospores then undergoes two more rounds of mitosis and cytokinesis before the formation of four‐celled ascospores with one nucleus per compartment.…”

“…graminearum . Several genes with PSC editing events are known to be important for ascospore formation or release, including PUK1 , AMD1 and FgAMA1 (Liu et al ., 2016; Cao et al ., 2017; Hao et al ., 2019).…”

The ‘pears and lemons’ protein UvPal1 regulates development and virulence of Ustilaginoidea virens

“…Pal1p was reported to be present at the initial stage of endocytosis to and interact with Ede1p, but was not required for bulk-or receptor-mediated endocytosis in S. cerevisiae (Carroll et al, 2012). In F. graminearum, deletion of FgPAL1 resulted in defects in fungal development, such as vegetative growth, perithecial formation and ascospore morphology (Hao et al, 2019). Although there have been studies in a few fungi, the function of Pal1 proteins is still largely unknown in fungal pathogens.…”