In Addition to Damaging the Plasma Membrane, Phenolic Monoterpenoid Carvacrol can Bind to Minor Groove of DNA of Phytopathogenic Fungi to Potentially Control Tea Leaf Spot Caused by Lasiodiplodia theobromae

Carvacrol expresses a wide range of biological activities, but the studies of its mechanisms focused on bacteria, mainly involving the destruction of the plasma membrane. In this study, carvacrol exhibited strong antifungal activities against several phytopathogenic fungi and determined a novel antifungal mechanism against Lasiodiplodia theobromae. RNA sequencing indicated that many genes of L. theobromae hyphae were predominately induced by carvacrol, particularly those involved in replication and transcription. Hyperchromic, hypsochromic, and bathochromic effects in the UV-visible absorption spectrum were observed following titration of calf thymus DNA (ctDNA) and carvacrol, which indicated the formation of a DNA–carvacrol complex. Circular dichroism (CD) spectroscopy indicated the response of DNA to carvacrol was similar to 4’, 6-diamidino-2-phenylindole (DAPI), but different from that of ethidium bromide (EB), implying the ionic bonds between carvacrol and ctDNA. Fluorescence spectrum (FS) analysis indicated that carvacrol quenched the fluorescence of double-stranded DNA more than single-stranded DNA, indicating that carvacrol mainly bound to double-stranded DNA. A displacement assay showed that carvacrol reduced the fluorescence intensity of the DNA–DAPI complex through competing with DAPI, but this did not occur for DNA–EB. FS assay revealed that carvacrol bound to AAA sequence on the minor groove of ds-oligonucleotides. The hydroxyl of carvacrol was verified to bind to ctDNA through a comparative test in which structural analogs of carvacrol, including thymol, 4-ethyl-1,2-dimethyl, etc. were analyzed. The current study indicated carvacrol can destruct plasma membranes and bind to the minor groove of DNA, which inhibited the fungal proliferation by disturbing the stability of dsDNA.