Sociedade Brasileira de Espectrometria de Massas – BrMASS
Natural Products (PN)
Increased Virulence Factor of Fungal Banana Pathogen
Mycosphaerella fijiensis: Generation of Singlet Molecular Oxygen
by Melanin and Melanin Biosynthesis Intermediates
Fernanda M. Prado1, Miguel J. Beltrán-García2, Marilene S. Oliveira1, David
Ortiz-Mendoza2, Alexsandra C. Scalfo1, Adalberto P. Junior3, Marisa H. G.
Medeiros1 and Paolo Di Mascio1
[email protected]
1
Instituto de Química da Universidade de São Paulo, Departamento de
Bioquímica, São Paulo, Brasil. 2Departamento de Química-ICET, Universidad
Autónoma de Guadalajara, Guadalajara, México. 3Faculdade de Ciências
Farmacêuticas, Universidade de São Paulo, Departamento de Tecnologia
Bioquímico-Farmacêutica, São Paulo, Brasil.
The fungus Mycosphaerella fijiensis causes the banana black Sigatoka. Black
Sigatoka costs billions of dollars annually by lost fruit yielding as well as by the use of
excessive amounts fungicides. In many tropical and subtropical countries, the fruit
losses are considered a food security issue (1). High genetic variability, fungicide
resistance and aggressiveness characterize this fungus. Fungal strains that accumulate
dark pigment are more aggressive for the banana leaf tissue than those with less or no
pigment content. This pigment could be a 1,8-dihydroxynaphthalene melanin (DHNmelanin), a typically fungal melanin (2). For plant fungal pathogens, melanin
contributes to virulence by allowing tissue invasion, inactivation of the defence system
and possibly cell death. In this work, we suggest that melanin synthetized by M.
fijiensis is an increased virulence factor through the generation of singlet molecular
oxygen (1O2) (3). We demonstrated the generation of 1O2 through monomol light
emission at 1270 nm from melanin of mycelia and melanin secreted into culture media
irradiated with a Nd:YAG laser at 532 nm. The analyses of mycelia and culture media
by SEM analysis, ultraviolet/infrared absorption spectrophotometry and MALDI-TOF
mass spectrometry demonstrated that this pigment content is 1,8dihydroxynaphthalene-melanin (DHN-melanin), a polymeric melanin. Using melanin
biosynthesis inhibitors (tricyclazol and pyroquilon), we identified many melanin
biosynthesis intermediates by HPLC-MS/MS. Our results demonstrated that fungal
source of 1O2 could be DHN-melanin and melanin biosynthesis intermediates. The 1O2
generated by M. fijiensis probably acts as a virulence factor of two ways: first, it
protects fungus from oxidative attack of plant and second, indirectly it causes necrotic
death of plant cells.
(1) Churchill, A. C.; Mol Plant Pathol. 2011, 12(4), 307-28.
(2) Kogej, T. et al, FEMS Microbiology Letters 2004, 232, 203-209.
(3) Suzukawa A. A. et al, Free Radic. Biol. Med. 2012, 52(9), 1945-1953.