Abstract
Bipolaris oryzae is the causal agent of brown spot disease in rice and produces the dark pigment melanin. We isolated and characterized T4HR1 gene encoding 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN) reductase, which converted 1,3,6,8-THN to scytalone in the melanin biosynthesis from B. oryzae. A sequence analysis showed that the T4HR1 gene encoded a putative protein of 268 amino acids showing 50% - 99% sequence identity to other fungal 1,3,6,8-THN reductases. Targeted disruption of the T4HR1 gene showed a different phenotype of mycelial color due to an accumulation of shunt products compared to those of wild-type on PDA plates using tricyclazole as a melanin biosynthesis inhibitor. A quantitative real-time PCR analysis showed that the expression of T4HR1 transcripts was enhanced by near-ultraviolet (NUV) irradiation and regulated by transcriptional factor BMR1, similar to three other melanin biosynthesis genes (polyketide synthase gene [PKS1], scytalone dehydratase gene [SCD1], and 1,3,8-THN reductase gene [THR1]) in the melanin biosynthesis of B. oryzae. These results suggested that common transcriptional mechanisms could regulate the enhanced gene expression of these melanin biosynthesis genes by NUV irradiation in B. oryzae.
Highlights
Melanin is a dark-pigmented polymer that protects organisms against environmental stress, and its production is widespread in the fungal kingdom [1]-[3]
We have identified polyketide synthase gene (PKS1) [17], scytalone dehydratase gene (SCD1) [18], and 1,3,8-THN reductase gene (THR1) [19] in B. oryzae and observed that the expression of these melanin biosynthesis genes was enhanced by near-ultraviolet (NUV: 300 - 400 nm) irradiation
We demonstrated that the expression of the T4HR1 was enhanced by NUV irradiation and was dependent on the transcription factor BMR1, which was similar to the expressions of three other melanin biosynthesis genes in B. oryzae
Summary
Melanin is a dark-pigmented polymer that protects organisms against environmental stress, and its production is widespread in the fungal kingdom [1]-[3]. Melanin accumulates in fungal cell walls and has been believed to confer tolerance to environmental stresses such as UV radiation [4]-[7]. DHN-melanin biosynthesis in B. oryzae starts with a polyketide synthaseusing acetate as a precursor (Figure 1). A hydroxynaphthalene reductase converts 1,3,6,8-tetrahydroxynaphthalene (1,3,6,8-THN) to scytalone. 1,3,8-THN reductase converts the 1,3,8-THN to vermelone, which is further dehydrated to 1,8-DHN. We have identified polyketide synthase gene (PKS1) [17], scytalone dehydratase gene (SCD1) [18], and 1,3,8-THN reductase gene (THR1) [19] in B. oryzae and observed that the expression of these melanin biosynthesis genes was enhanced by near-ultraviolet (NUV: 300 - 400 nm) irradiation. The 1,3,6,8-THN reductase gene has not yet been identified and characterized in B. oryzae, 1,3,6,8-THN reductase genes have been identified and characterized in Magnaporthe grisea [20] [21], Colletotrichum orbiculare [22], Sordaria macrospora [23], and Cochliobolus heterostrophus [24]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
