Deep sequencing analysis of transcriptomes in Aspergillus flavus in response to resveratrol

Abstract

Background: Resveratrol has been reported as a natural phytoalexin that inhibits infection or the growth of certain fungi including Aspergillus flavus. Our previous research revealed that aflatoxin production in A. flavus was reduced in medium with resveratrol. To understand the molecular mechanism of the A. flavus response to resveratrol treatment, the high-throughput paired-end RNA-Seq was applied to analyze the transcriptomic profiles of A. flavus.

Results: In total, 366 and 87 genes of A. flavus were significantly up- and down- regulated, respectively, when the fungus was treated with resveratrol. Gene Ontology (GO) functional enrichment analysis revealed that 48 significantly differentially expressed genes were involved in 6 different terms. Most genes in the aflatoxin biosynthetic pathway genes cluster (#54) did not show a significant change when A. flavus was treated with resveratrol, but 23 of the 30 genes in the #54 cluster were down-regulated. The transcription of aflA and aflB was significantly suppressed under resveratrol treatment, resulting in an insufficient amount of the starter unit hexanoate for aflatoxin biosynthesis. In addition, resveratrol significantly increased the activity of antioxidative enzymes that destroy radicals, leading to decreased aflatoxin production. Moreover, stuA, fluG, flbC, and others genes involved in mycelial and conidial development were down-regulated, which disrupted the cell's orderly differentiation and blocked conidia formation and mycelia development. The transcripts of laeA and veA were slightly inhibited by resveratrol, which may partly decrease aflatoxin production and depress conidia formation.

Conclusions: Resveratrol can affect the expression of A. flavus genes that are related to developmental and secondary metabolic processes, resulting in decreased aflatoxin production and conidia formation and could also cause abnormal mycelia development. These results provide insight into the transcriptome of A. flavus in response to resveratrol and a new clew for further study in regulation of aflatoxin biosynthesis in A. flavus.

Fig. 1

Mycelioid colony of A. flavus cultured on solid A & M medium. AM (Control), resveratrol was not added to the A&M medium. AM-Res (Treatment), resveratrol was added to the A&M medium (3.0 μg/mL). The mycelioid colony diameter of A. flavus in the AM-Res was similar to that in the AM, but the number of A. flavus conidia in the AM was greater than that in the AM-Res

Fig. 2

Vegetative mycelia of A. flavus cultured in liquid A & M medium. AM (Control), resveratrol was not added to the A&M medium. AM-Res (Treatment), resveratol was added to the A&M medium (3.0 μg/mL)

Fig. 3

Classification of raw reads. Raw reads including clean reads (blue), adapter sequences (purple), reads containing undefined nucleotides (N’s) (red), and low-quality reads (green) generated from Illumina RNA-sequencing (RNA-seq)

Fig. 4

Distribution of reads mapped to genome regions. The genic distribution of reads from mRNA-seq of A. flavus (AF2202) mapped to exons (blue), introns (red), and intergenic regions (green)

Fig. 5

Quantitative real-time PCR validations of the up-regulated and down-regulated genes characterized by RNA-seq. log₂(fold change) = log₂(AM-Res/AM)