Intracellular kynurenine promotes acetaldehyde accumulation, further inducing the apoptosis in soil beneficial fungi Trichoderma guizhouense NJAU4742 under acid stress

In this study, the growth of fungi Trichoderma guizhouense NJAU4742 was significantly inhibited under acid stress, and the genes related to acid stress were identified based on transcriptome analysis. Four genes including tna1, adh2/4, and bna3 were significantly up-regulated. Meanwhile, intracellular hydrogen ions accumulated under acid stress, and ATP synthesis was induced to transport hydrogen ions to maintain hydrogen ion balance. The enhancement of glycolysis pathway was also detected, and a large amount of pyruvic acid from glycolysis was accumulated due to the activity limitation of PDH enzymes. Finally, acetaldehyde accumulated, resulting in the induction of adh2/4. In order to cope with stress caused by acetaldehyde, cells enhanced the synthesis of NAD(+) by increasing the expression of tna1 and bna3 genes. NAD(+) effectively improved the antioxidant capacity of cells, but the NAD(+) supplement pathway mediated by bna3 could also cause the accumulation of kynurenine (KYN), which was an inducer of apoptosis. In addition, KYN had a specific promoting effect on acetaldehyde synthesis by improving the expression of eno2 gene, which led to the extremely high intracellular acetaldehyde in the cell under acidic stress. Our findings provided a route to better understand the response of filamentous fungi under acid stress.

Automated summary

This study found that the growth of Trichoderma guizhouense NJAU4742 fungi was significantly inhibited under acid stress. Transcriptome analysis identified genes related to acid stress, including tna1, adh2/4, and bna3, which were significantly up-regulated. Under acid stress, intracellular hydrogen ions accumulated, and ATP synthesis was induced for hydrogen ion transport to maintain balance. Enhanced glycolysis and accumulation of pyruvic acid were also observed. The accumulation of acetaldehyde induced the expression of adh2/4. To cope with acetaldehyde stress, cells increased the expression of tna1 and bna3 genes to enhance NAD(+) synthesis. However, the NAD(+) supplement pathway mediated by bna3 could lead to the accumulation of kynurenine (KYN), an inducer of apoptosis. Additionally, KYN specifically promoted acetaldehyde synthesis by improving eno2 gene expression, resulting in high intracellular acetaldehyde under acidic stress. These findings contribute to a better understanding of the response of filamentous fungi under acid stress.