Functional characterization of candidate co-factor genes involved in A-to-I mrna editing in fusarium graminearum
Adenosine-to-Inosine (A-to-I) mRNA editing is a post-transcriptional modification of specific sites within the mRNA that has only recently been observed in filamentous fungi. In the wheat scab fungus Fusarium graminearum, this phenomenon has shown to be facilitated by FgTad2 and FgTad3, homologs of Adenine Deaminase Acting on tRNA (ADAT). Interestingly, these two proteins are constitutively expressed in all different life stages, in contrast to only the sexual stage-specific nature of A-to-I mRNA editing in F. graminearum. To understand the molecular mechanisms regulating this process, six candidate co-factor genes were identified which interact with FgTad2 and/or FgTad3, specifically during sexual reproduction. Deletion mutants of four candidate co-factor genes were successfully generated. All four mutants displayed normal asexual development of F. graminearum, but four mutants also altered sexual function. Those four mutant led to formation of morphologically normal perithecia and ascospores, but the perithecia failed to discharge ascospores. More interestingly, in FGSG_10943 deletion mutant, most of these ascospores germinated precociously within the perithecium. I also observed, that among the candidate co-factor genes which are specifically expressed during sexual reproduction, FGSG_10943 was significantly upregulated during the later stage of sexual development. This gene is restricted in nature to only a few orders of fungi in the class Sordariomycetes that form dark pigmented ascocarps, particularly Hypocreales and Glomerellales. Taken together, these results indicate that the four candidate co-factor genes are dispensable for vegetative growth of the fungus and involved in ascospore discharge. FGSG_10943 appears to be involved in autoinhibition of ascospores inside the perithecia and interact with FgTad2 during sexual reproduction to mediate A-to-I mRNA editing in F. graminearum.