RNA-Seq解析cAMP促进禾谷镰孢菌DON毒素产生的分子基础

 禾谷镰孢菌(Fusarium graminearum)引起的小麦赤霉病(Fusarium head blight)不仅造成小麦产量损失,而且病菌在侵染过程中会释放大量真菌毒素,导致小麦籽粒污染,严重威胁人畜健康。实验室前期研究发现外源添加环磷酸腺苷(cAMP)可以促进禾谷镰孢菌脱氧雪腐镰孢菌烯醇毒素(Deoxynivalenol, DON)产生,但其分子机制尚不清楚。本研究利用转录组分析了cAMP处理后禾谷镰孢菌基因的表达情况,探究了cAMP促进DON毒素合成的潜在机制。研究发现响应cAMP处理的差异表达基因有4 470个,其中1 818个基因上调,2 652个基因下调。负责DON毒素合成TRI基因簇的所有基因在cAMP处理下均上调表达,表明cAMP通过诱导TRI基因簇表达促进DON毒素合成。进一步分析了cAMP下游依赖性蛋白激酶A(PKA)的敲除突变体Δpka的转录组数据,发现几乎所有TRI基因簇基因均下调表达,并且cAMP处理上调表达而Δpka突变体中下调表达的基因中显著富集真菌毒素代谢相关的基因,该结果进一步表明cAMP通过PKA通路调控DON毒素合成。此外,cAMP处理后,可诱导DON毒素产生的γ-氨基丁酸(gamma-aminobutyric acid, GABA)合成相关基因上调表达,而GABA分解相关基因下调表达。这表明禾谷镰孢菌可通过调节细胞内的GABA水平促进DON毒素合成。

RNA-Seq analysis reveals the molecular mechanism of enhanced DON production by cAMP-treatment in Fusarium graminearum

Fusarium head blight caused by Fusarium graminearum is a devastating disease on wheat. It not only causes yield loss of wheat, but also seriously threatens the health of human and livestock due to production of many mycotoxins that contaminate grains by the pathogens during infection. Previous study revealed that exogenous addition of cyclic adenosine monophosphate (cAMP) could promote the production of DON in F. graminearum, but the underlying mechanism is unclear. To reveal the molecular mechanism, in this study, we used RNA-Seq to analyze the gene expression of F. graminearum under the treatment of exogenous cAMP. The results showed that 1 818 and 2 652 genes were specifically up-regulated and down-regulated in the cAMP-treated samples, respectively. All the TRI genes in the TRI-cluster that responsible for the synthesis of DON, were significantly up-regulated, suggesting that cAMP promotes DON production by inducing the expression of TRI genes in F. graminearum. Furthermore, we performed RNA-Seq analysis of the Δcpk1 knockout mutant of protein kinase A. The results showed that all the TRI genes in the TRI-cluster were significantly down-regulated in the Δcpk1 mutant. Mycotoxin metabolism related genes were enriched in the genes up-regulated in cAMP-treated samples but down-regulated in the Δcpk1 mutant, confirming that cAMP regulates DON production via PKA pathway. In addition, genes related to biosynthesis of gamma aminobutyric acid (GABA), an inducer of DON production, were up-regulated while genes related to GABA degradation were down-regulated in the cAMP-treated samples. These results reveal that the DON production is modulated by the GABA level in F. graminearum.