Expression of T4HR1, a 1,3,6,8-Tetrahydroxynaphthalene Reductase Gene Involved in Melanin Biosynthesis, Is Enhanced by Near-Ultraviolet Irradiation in Bipolaris oryzae

摘要

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.