Regulations of capsaicin synthesis in Capsicum annuum L. by Penicillium resedanum LK6 during drought conditions

• Gibberellins producing Penicillium resedanum LK6 increased the plant growth and biomass of Capsicum annuum L. during drought.
• Active association of endophyte increased the fruit yield and capsaicin contents during drought.
• Phenylalanine ammonia-lyase and Capsaicin synthase mRNA expressions were higher in endophyte-interaction than control.
• Symbiosis of endophyte reduced ROS production while increased antioxidant enzymes to counteract drought stress.

We investigated the influence of endophytic fungal association (Penicillium resedanum LK6) on the growth, yield and capsaicin biosynthesis of Capsicum annuum L. under drought stress. Exposure to drought stress for three weeks retarded the growth of non-inoculated control plants by significantly reducing shoot length, leaf area, chlorophyll content, flower number and pepper fruit yield. Conversely, the active association of endophyte with host-plants significantly increased these plant growth and yield parameters. The drought-induced oxidative stress was pronounced in control plants. This was revealed by the increased production of superoxide anions and reduced activities of peroxidase, catalase and polyphenol oxidase in control plants as compared to plants with endophytic-symbiosis. The capsaicin content in pepper fruit was significantly higher in endophyte-associated plants than control under drought. The capsaicin biosynthesis-related mRNA expressions of Phenylalanine ammonia-lyase and Capsaicin synthase were two-fold higher in endophyte-infected plants than control under drought stress. Fungal endophytes increased host-plant growth and its yield during stress by activating the essential constituents of phenylpropanoid pathways. This indicates that increased synthesis of secondary metabolites can increase plant's abiotic stress tolerance.