Novel sesquiterpenes and polyketides from the fungi Corynespora sp. YG-11 and Penicillium rubens YG-2 promote tobacco growth and enhance its stress resistance

The deterioration of tobacco (Nicotiana tabacum L.) quality and yield is caused by abiotic stress (temperature, salt, heavy metals, etc.) and biotic stress (plant pathogens). The growth-promoting and stress resistance-enhancing compounds were isolated from endophytic fungi Corynespora sp. YG-11 and Penicillium rubens YG-2, both derived from tobacco tissue culture seedlings. One unprecedented sesquiterpene-cyclohexenone hybrid skeleton, corynecaserpene A (1), seventeen undescribed sesquiterpenes， corynecaserpenes B-R (2-18), a novel alkaloid, corynecapenoid A (19), and three known compounds (24-25, and 29) from Corynespora sp. Four unreported polyketides, peniciruketides A-D (20-23), and three known compounds (26-28) from Penicillium rubens. The chemical structures were conclusively elucidated by spectroscopic analysis, ECD calculation, DP4 + analysis, Mosher’s method, and single-crystal X-ray diffraction (SXRD). The growth-promoting and stress resistance-enhancing activities of the compounds on tobacco seedlings were evaluated, and the results indicated that cyclohexenoneterpene F (27) exerted a significant growth-promoting effect on the shoot and root lengths of tobacco seedlings in the absence of stress. Corynecaserpene F (6) and fumiparaphine B (29) showed prominent stress-mitigating activity in tobacco seedlings under abiotic stresses (salt, low temperature), and corynecaserpenes B (2), J (10) and peniciruketide A (20) exhibited a significant alleviating effect on both abiotic stresses and biotic stress (plant pathogen) in tobacco seedlings. Additionally, cyclohexenoneterpene F (27) exhibited significant antifungal activity against Cladosporium sp., showing a mycelial growth inhibition rate of 68% at 30 μg/mL. The structure-activity relationship of the compounds regarding their growth-promoting activity on tobacco seedlings were discussed.