Effects of UVB radiation in conidia and mycelia of three model ascomycete fungi: Aspergillus fumigatus, A. nidulans e Metarhizium anisopliae

Author(s)

Érika Nascimento

• Document type: Doctoral Thesis
• Press: Ribeirão Preto.
• Institution: Universidade de São Paulo (USP). Faculdade de Ciências Farmacêuticas de Ribeirão Preto (PCARP/BC)
• Defense date: 2010-02-24

Examining board members

Gilberto Ubida Leite Braga; Regina Celia Candido; Paulo Sergio Rodrigues Coelho; Elza Tiemi Sakamoto Hojo

• Advisor: Gilberto Ubida Leite Braga

Abstract

Conidia are specialized structures produced asexually during mycelia growth of many ascomycete species. The process of conidiation involves temporal and spatial regulation of gene expression, cell specialization, intercellular communication, and formation of specific structures during fungal growth. Conidia are responsible for the reproduction, dispersal and environmental persistence of many fungal species. In pathogenic species like Aspergillus fumigatus and Metarhizium anisopliae, conidia are also responsible for host infection. One of the main environmental factors that can kill and/or damage conidia is solar UV radiation. Cyclobutane pyrimidine dimers (CPDs) are the major DNA photoproducts induced by UVB. The principal goals of the present study were to: (1) estimate the frequency of CPDs induced by sublethal doses of UVB radiation in conidial DNA of three selected ascomycetes, (2) examine correlation of CPD frequencies with germination speed, and (3) estimate the protective effect of the wild-type green conidial pigmentation on DNA in M. anisopliae var. anisopliae, (4) identify differentially expressed genes during the different phases of A. fumigatus conidiogenesis and (5) identify genes regulated by UVB radiation in A. fumigatus young mycelia. A. fumigatus, A. nidulans, and M. anisopliae conidia were exposed to 1000 mW m-2 UV irradiance for 15, 30, 60 and 90 min. Total Quaite-weighted doses were 0.9, 1.8, 3.6 and 5.4 kJ m-2, respectively. The frequencies of dimers were linear and directly proportional to the doses, with 0.215, 0.455, 0.803 and 1.628 CPDs 10 kb-1 detected at the doses of 0.9, 1.8, 3.6 and 5.4 kJ m-2 in A. fumigatus, 0.037, 0.077, 0.142 and 0.202 CPDs 10 kb-1 in A. nidulans, and 0.041, 0.085, 0.155 and 0.255 CPDs 10 kb-1 in M. anisopliae. The frequency of dimers in the M. anisopliae albino mutant DWR 180 (0.552 10 kb-1) was approximately ten times higher than of the wild-type ARSEF 23 strain (0.057 10 kb-1) after exposure to doses of 1.8 kJ m-2. DNA microarrays carrying sequence of 11,000 genes of A. fumigatus were used to compare transcriptomes of 20 h-old mycelia (initial phase of the conidiogenesis), 24 h (intermediate phase) e 25 h (final phase) with young mycelia transcriptome. Thirty-four genes displayed a statistically significant difference in expression (7 with increase and 27 with decrease mRNA expression) in 20 h-old mycelia, 101 genes (12 with increase and 89 with decrease) in 24 h-old mycelia and 76 genes (8 with increase and 68 with decrease) in 25 h-old mycelia. Some overexpressed genes (stuA ad the scytalone dehydratase gene) were previously related to specific phases of conidiogenesis but the function of most of them is unknown. Transcriptome analysis using microarrays was also used to identify genes modulated by exposures to UVB radiation (1,8 kJ m-2) in A. fumigatus young mycelia. One hundred and one differentially expressed genes were identified at the end of the exposure to UVB radiation (51 genes with increase and 50 with decrease). The radc gene displayed the higher increase in expression (approximately 16 ×). The function of most of the overexpressed genes is unknown. Four hundred and eighteen differentially expressed genes were identified 30 min after the end of exposure (51 genes with increase and 367 with decrease in expression). (AU)