Abstract
Bridging cellular reproduction and survival is essential for all life forms. Aspergillus fungi primarily reproduce by forming asexual spores called conidia, whose formation and maturation is governed by the central genetic regulatory circuit BrlA→AbaA→WetA. Here, we report that WetA is a multi-functional regulator that couples spore differentiation and survival, and governs proper chemical development in Aspergillus flavus. The deletion of wetA results in the formation of conidia with defective cell walls and no intra-cellular trehalose, leading to reduced stress tolerance, a rapid loss of viability, and disintegration of spores. WetA is also required for normal vegetative growth, hyphal branching, and production of aflatoxins. Targeted and genome-wide expression analyses reveal that WetA exerts feedback control of brlA and that 5,700 genes show altered mRNA levels in the mutant conidia. Functional category analyses of differentially expressed genes in ΔwetA RNA-seq data indicate that WetA contributes to spore integrity and maturity by properly regulating the metabolic pathways of trehalose, chitin, α-(1,3)-glucan, β-(1,3)-glucan, melanin, hydrophobins, and secondary metabolism more generally. Moreover, 160 genes predicted to encode transcription factors are differentially expressed by the absence of wetA, suggesting that WetA may play a global regulatory role in conidial development. Collectively, we present a comprehensive model for developmental control that bridges spore differentiation and survival in A. flavus.
Highlights
Coordination of cellular reproduction and survival is fundamental to the existence and propagation of all living organisms
BlastP analysis against eight previously characterized WetA amino acid sequences reveals that A. flavus WetA has 99%, 61%, 57%, 53%, 53%, 68%, and 35% aa identity with WetA of A. oryzae, A. fumigatus, A. nidulans, Penicillium chrysogenum, P. digitatum, Beauveria bassiana, and Fusarium graminearum, respectively
Phylogenetic analysis revealed that A. flavus WetA is nested within a clade that contains the A. oryzae, A. nidulans, P. digitatum, and P. chrysogenum WetA sequences, while B. bassiana WetA clusters with the F. graminearum sequence
Summary
Coordination of cellular reproduction and survival is fundamental to the existence and propagation of all living organisms. From the simplest single cell organisms to complex multicellular plants and animals, regulatory and signalling systems have evolved to ensure that future viability of the reproductive cells. Fungi primarily reproduce through spore propagation; fungal spores are adapted for dispersal and are resistant to desiccation, heat, oxidative and UV stresses, properties which render them very capable of establishing infections [1]. Fungal sporulation involves coordinated control of morphological, physiological, and metabolic (chemical) developmental processes. The genus Aspergillus includes several organisms that are commonly found in the human environment. The widely distributed Aspergillus flavus is an opportunistic
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