| Sclerotinia sclerotiorum (Lib.) de Bary has host range comprises at least75families and278genera including more than400plant species, it is a devastatingnecrotrophic fungal plant pathogen of many agriculture crops including sunflower,soybean, oilseed rape, edible dry bean, chickpea, dry pea, lentils and monocotyledonsuch as onion and tulip. Taxonomically this fungus is a homothallic ascomycetebelonging to the family Sclerotiniaceae of the order Helotiales. Developmentally, ahallmark of this and related fungi is the production of hardy multicellular sclerotiaformed from the aggregation of vegetative hyphae and enclosed by a melanized rindlayer. These structures play a significant role in the survival and persistence ofinfectious propagules in agriculture fields. Sclerotia can survive under harshbiological and physical environments including low temperature, microbially activesoils, and dry environments for several years. Under suitable environmentalconditions, sclerotia germinate either into vegetative hyphae (myceliogenicgermination) or into apothecia (carpogenic germination), with the latter releasinglarge quantities of ascospores that initiate new disease cycles. With its adaptationsfor long-term survival and pathogenicity on a broad range of hosts, S. sclerotiorum isone of the most challenging agricultural pathogens to manage and causes largeglobal economic losses annually.The development and carpogenic germination of sclerotia involves severaldistinct stages and is affected by numerous exogenous factors such as photoperiod,temperature, oxygen concentration, ambient pH, mechanical factors and nutrients. Atthe same time, this process is also tightly regulated by intrinsic genetic factors.Independent and cross-talking pathways have been shown to be involved in sclerotium development; in particular, phosphorylative relay involving AMP cyclase,ERK-like mitogen-activated protein kinase and Ser/Thr phosphatases type2A and2B, and represention a transitional structure spanning asexual and sexualdevelopment during the S. sclerotiorum development. In this study, we isolated twotranscriptional factors Ss-Nsd1and Ss-Fox1from the S. sclerotiorum, and we reporton the regulatory functions of the S. sclerotiorum GATA-type IVb zinc-fingertranscription factor Ss-Nsd1and Ss-Fox1in these processes. Ss-Nsd1is orthologousto the Aspergillus nidulans NsdD (never in sexual development) proteins.TheSs-nsd1gene showed a strong UV-A light-dependent and tissue-specific transcriptaccumulation in stipe and early developing apothecium tissues. The Ss-nsd1deletionmutant strains (ΔSs-nsd1) produced phialides and phialospores promiscuously inboth vegetative culture and within sclerotia. In striking contrast, phialosporedevelopment occurred only on the sclerotium surface in the wild type. Loss ofSs-nsd1function affected sclerotium structural integrity and disrupted ascogoniaformation during conditioning for carpogenic germination. As a consequence,apothecium development was abolished. The Ss-nsd1deletion mutants were alsodefective in compound appressorium formation. However, the Ss-fox1is a Forkheadprotein family coding gene. In sum, We functionally and characterized the Ss-nsd1and Ss-fox1genes by gene deletion and demonstrate that the Ss-nsd1functionssimilarly as its ascomycete orthologs nsdD gene in balancing sexual and asexualdevelopments by both negatively regulating phialospore (spermatia) formation andpositively regulating sclerotium, compound appressorium and apotheciumdevelopment， however the Ss-fox1deletion mutant strains (ΔSs-fox1) affectapothecia development in S. sclerotiorum.Further study is for Ss-nsd1and Ss-fox1genes linking signaling pathways anddownstream genes have the potential to increase understanding of the common andunique pathways adopted for varying sexual and asexual development in filamentousfungi. |
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