Abstract
Aspergillus flavus is a saprophytic soil fungus that poses a serious threat worldwide as it contaminates many food and feed crops with the carcinogenic mycotoxin called aflatoxin. This pathogen persists as sclerotia in the soil which enables fungal survival in harsh environmental conditions. Sclerotia formation by A. flavus depends on successful cell communication and hyphal fusion events. Loss of LaeA, a conserved developmental regulator in fungi, abolishes sclerotia formation in this species whereas overexpression (OE) of laeA results in enhanced sclerotia production. Here we demonstrate that sclerotia loss and inability to form heterokaryons in A. flavusΔlaeA is mediated by homologs of the Neurospora crassa ham (hyphal anastomosis) genes termed hamE-I in A. flavus. LaeA positively regulates ham gene expression and deletion of hamF, G, H, or I phenocopies ΔlaeA as demonstrated by heterokaryon and sclerotia loss and reduced aflatoxin synthesis and virulence of these mutants. Deletion of hamE showed a less severe phenotype. hamE-I homologs are positively regulated by the clock controlled transcription factor ADV-1 in N. crassa. Similarly, the ADV-1 homolog NosA regulates hamE-I expression in A. flavus, is required for sclerotial development and is itself positively regulated by LaeA. We speculate that a putative LaeA>NosA>fusion cascade underlies the previously described circadian clock regulation of sclerotia production in A. flavus.
Highlights
Most plant pathogenic fungi have developed both asexual and sexual modes of reproduction with specific roles in life and disease cycles
Sclerotia are overwintering structures formed through extensive hyphal fusion events and in A. flavus their formation is associated with aflatoxin synthesis
Following leads from studies showing a requirement of LaeA (Lae1) for sclerotia production (Kale et al, 2008; Amaike and Keller, 2009; Schumacher et al, 2015), we present our findings supporting a model where LaeA regulation of a cell fusion cascade underscores a critical cellular mechanism required for sclerotial formation in fungi
Summary
Most plant pathogenic fungi have developed both asexual and sexual modes of reproduction with specific roles in life and disease cycles. A critical developmental stage of several plant pathogenic fungi is formation of the survival structure, the sclerotium. Multicellular structures visible by the eye that are formed by branching and fusion of interwoven hyphae (Erental et al, 2008). There are three overlapping stages in the development of sclerotia: initiation, when hyphae begin to fusion together to form small, discrete initials; development, the sclerotial size enlarges with white coloration; and maturation, the surface becomes pigmented and harder (Willetts and Bullock, 1992). The longevity of sclerotia in agricultural soils is a concern in crop protection and contributes to outbreaks of disease by sclerotial fungi (Coley-Smith and Cooke, 1971)
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
