Comparative genomic and transcriptomic analyses of the Fuzhuan brick tea-fermentation fungus Aspergillus cristatus.

Yongyi Ge,Yongfeng Liu,Xinyu Zhang,Kevin D Hyde,Xiuxiu Ren,Yongxiang Liu,Yumei Tan,Zuoyi Liu,Yuchen Wang

doi:10.1186/s12864-016-2637-y

Abstract

BackgroundAspergillus cristatus is the dominant fungus involved in the fermentation of Chinese Fuzhuan brick tea. Aspergillus cristatus is a homothallic fungus that undergoes a sexual stage without asexual conidiation when cultured in hypotonic medium. The asexual stage is induced by a high salt concentration, which completely inhibits sexual development. The taxon is therefore appropriate for investigating the mechanisms of asexual and sexual reproduction in fungi. In this study, de novo genome sequencing and analysis of transcriptomes during culture under high- and low-osmolarity conditions were performed. These analyses facilitated investigation of the evolution of mating-type genes, which determine the mode of sexual reproduction, in A. cristatus, the response of the high-osmolarity glycerol (HOG) pathway to osmotic stimulation, and the detection of mycotoxins and evaluation of the relationship with the location of the encoding genes.ResultsThe A. cristatus genome comprised 27.9 Mb and included 68 scaffolds, from which 10,136 protein-coding gene models were predicted. A phylogenetic analysis suggested a considerable phylogenetic distance between A. cristatus and A. nidulans. Comparison of the mating-type gene loci among Aspergillus species indicated that the mode in A. cristatus differs from those in other Aspergillus species. The components of the HOG pathway were conserved in the genome of A. cristatus. Differential gene expression analysis in A. cristatus using RNA-Seq demonstrated that the expression of most genes in the HOG pathway was unaffected by osmotic pressure. No gene clusters associated with the production of carcinogens were detected.ConclusionsA model of the mating-type locus in A. cristatus is reported for the first time. Aspergillus cristatus has evolved various mechanisms to cope with high osmotic stress. As a fungus associated with Fuzhuan tea, it is considered to be safe under low- and high-osmolarity conditions.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-016-2637-y) contains supplementary material, which is available to authorized users.

Highlights

Aspergillus cristatus is the dominant fungus involved in the fermentation of Chinese Fuzhuan brick tea
We investigated the relationship between the highosmolarity glycerol (HOG) pathway and osmotic pressure, verified the safety of A. cristatus under low- and high-osmotic pressure conditions, and established the evolutionary patterns of the mating-type genes through genome sequencing and RNA-Seq transcriptomic data from A. cristatus at two developmental stages
Fumonisin B1 was detected at 0.17 and 0.15 ppm at low and high osmolarities, respectively. This is lower than the standard (2 ppm) set by the US Food and Drug Administration (FDA) [46] (Additional file 2: Figure S2). These data suggest that the strain is safe under low- and Conclusions Comparison of the Mating-typing gene (MAT) loci of A. cristatus with those of other Aspergillus species revealed that the evolution of the A. cristatus MAT locus differs from those of other Aspergillus species

Summary

Introduction

Aspergillus cristatus is the dominant fungus involved in the fermentation of Chinese Fuzhuan brick tea. De novo genome sequencing and analysis of transcriptomes during culture under high- and low-osmolarity conditions were performed. These analyses facilitated investigation of the evolution of mating-type genes, which determine the mode of sexual reproduction, in A. cristatus, the response of the highosmolarity glycerol (HOG) pathway to osmotic stimulation, and the detection of mycotoxins and evaluation of the relationship with the location of the encoding genes. Various fungal taxa are important during the production of Fuzhuan brick tea, which is produced under controlled temperature and moisture conditions [4]. Aspergillus cristatus is the dominant taxon, termed the “Golden Flower Fungus” because of its yellow cleistothecium colour (Fig. 1) [5]

Methods

Results

Conclusion