Inhibition Mechanism of Caffeine in Tea Pathogenic Fungi Botryosphaeria Dothidea and Colletotrichum Gloeosporioides

Abstract Background Caffeine acts as an antifungal agent; however, its underlying inhibition mechanism remains unclear. To investigate variations in caffeine antifungal activity, this study was evaluate the inhibition mechanisms of caffeine on phytopathogens Botryosphaeria dothidea and Colletotrichum gloeosporioides through transcriptomic analysis, which causes leaf necrosis and anthracnose on tea leaves, respectively.Results Our in vitro results shows that the antifungal activity of caffeine quite different between B. dothidea and C. gloeosporioides. Furthermore, microscopic observation and bioactivity assay results proved that caffeine destroyed the fungal protective layers (cell wall and cell membrane) and subcellular organelles. The transcriptomes of these two fungi exposed to different caffeine concentrations were analyzed by high-throughput sequencing and the results showed that caffeine repressed gene expression involved in the pathways of mRNA surveillance, ribosome biogenesis in eukaryotes, aminoacyl-tRNA biosynthesis, etc. Particularly, caffeine affected gene expression in melanin biosynthesis in C. gloeosporioides, resulting in the disturbances of melanin production and fungal pathogenicity. Manually infected tea leaves showed melanin pigment was important to appressorium development and fungal infection by histopathological observation and fungal biomass quantification. Besides, C. gloeosporioides successfully enters into the host tissue even plant could build multilayer defenses against the fungus, this might be due to the variation in pathogen targets and quantities of secondary metabolites by the host cells.Conclusions Overall, our findings indicate that caffeine in the environment can reduce the fungal growth and physiological activities. However, the genome-wide expression showed different transcriptional profiles between these fungal isolates. Thus, we believe that target of the caffeine varied among isolates and melanin may play a major role in fungus caffeine tolerance. Further in-depth research required to conclude this hypothesis.