Abstract
Aspergillus flavus and its main secondary metabolite AFB1 pose a serious threat to several important crops worldwide. Recently, it has been reported that some PHD family transcription factors are involved in the morphogenesis and AFB1 biological synthesis in A. flavus, but the role of Cti6, a PHD domain containing protein in A. flavus, is totally unknown. The study was designed to reveal the biological function of Cti6 in the fungus by deletion of cti6, and its two domains (PHD and Atrophin-1) through homologous recombination, respectively. The results showed that Cti6 might up-regulate the mycelium growth, conidiation, sclerotia formation and AFB1 biological synthesis of A. flavus by its PHD domain, while Atrophin-1 also improved the conidiation of the fungus. The qRT-PCR analysis showed that Cti6 increased the conidiation of the fungus through AbaA and BrlA mediated conidiation pathway, triggered the formation of sclerotia by orthodox sclerotia formation pathway, and improved the production of AFB1 by orthodox AFB1 synthesis pathway. Crops models analysis showed that A. flavus Cti6 plays vital role in colonization and the production of AFB1 on the host grains mainly via PHD domain. Bioinformatics analysis showed Cti6 is conservative in Aspergillus spp., and mCherry mediated subcellular localization showed that most Cti6 accumulated in the nuclei, which reflected that Cti6 performed its important biological function in the nuclei in Aspergillus spp.. The results of the current study elucidate the roles of PHD domain containing proteins in the mechanism of the infection of crops by A. flavus, and provided a novel target for effectively controlling the contamination of Aspergillus spp. to crops.
Highlights
As a soil saprophyte worldwide, the notorious Aspergillus flavus colonizes many important crops, such as corn, peanut and cotton, and the threat of the pathogen to the life of immunosuppressed patients through aspergillosis is just second to A. fumigatus (Amaike and Keller 2011; Hedayati et al 2007; Tsui et al 2011)
Cti6 is more conserved among Aspergillus spp., the lowest similarity is between A. flavus and A. nidulans (68.55% Identity, 100% Query Cover) in the cladogram
A PHD and a Atrophin-1 domain were found from the Cti6 homologs of both A. flavus and A. oryzae, and only PHD domain could be found in all 10 homologous proteins (Fig. 1b)
Summary
As a soil saprophyte worldwide, the notorious Aspergillus flavus colonizes many important crops, such as corn, peanut and cotton, and the threat of the pathogen to the life of immunosuppressed patients through aspergillosis is just second to A. fumigatus Hedayati et al 2007; Tsui et al 2011) This pathogenic fungus causes aflatoxicosis to animal and human through the contamination of crop and feed by its most toxic secondary metabolites among known mycotoxins: aflatoxins (including aflatoxin B1, B2, G1 and G2) (Amaike and Keller 2011; Tumukunde et al 2020). Our previous study revealed that the PHD family transcription factors are involved in the morphogenesis and aflatoxin biological synthesis in A. flavus, which showed that the PHD family transcription factor Rum represses conidiation, increases sclerotia formation and aflatoxin biological synthesis, up-regulates amylase activity of A. flavus, and involves in the colonization of the pathogenic fungus on crop kernels (Hu et al 2018). The current study was conducted to reveal the functions of Cti in the virulence of A. flavus, and to find a new target for the early control of the contamination of the pathogenic fungus
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