Abstract
Bipolaris oryzae is the causal agent of brown leaf spot disease in rice, and its asexual spore (conidium) formation is known to be induced by near-ultraviolet (NUV) irradiation. In order to reveal the photomorphogenic response and to identify new genes upregulated by NUV irradiation, suppression subtractive hybridization (SSH) was carried out in B. oryzae. To confirm the differential gene expression in NUV-irradiated mycelia, quantitative real-time PCR (qRT-PCR) analysis was performed among 301 genes arbitrarily chosen from 1170 cDNA clones. The expression of 46 genes (named NUV01 to NUV46) was found to be significantly enhanced (>4-fold) by NUV irradiation. Sequence analysis revealed that 23 out of the 46 sequences (50%) showed significant matches to known fungal genes. The 46 genes were categorized as either BLR1-dependent or BLR1-independent expression groups using the BLR1-deficient mutant, which presumably lacks the blue/UVA-absorbing photoreceptor. This finding demonstrates that NUV irradiation can induce gene regulation, and that this response may be mediated by both a blue/UVA-absorbing photoreceptor and an as-yet-unidentified photoreceptor in B. oryzae.
Highlights
Fungal life is greatly modulated by light, as observed in processes such as pigment biosynthesis, the formation of reproductive structures, phototropism, and so on [1] [2]
To reveal the mechanisms underlying the photomorphogenic response to NUV irradiation in B. oryzae, we focused on the regulatory genes induced by NUV irradiation, and reported that NUV irradiation enhanced the expression of the novel NUV-inducible gene (UVI-1) [8], three melanin biosynthesis genes [9]-[11], the BMR1 gene encoding a transcriptional factor for these melanin biosynthesis genes [12], and the photolyase gene [13]
We previously reported that NUV irradiation enhances the expression of a novel NUV-inducible gene (UVI-1) [8], three melanin biosynthesis genes [9]-[11], the BMR1 gene encoding a transcriptional factor for these melanin biosynthesis genes [12], and a photolyase gene [13]
Summary
Fungal life is greatly modulated by light, as observed in processes such as pigment biosynthesis, the formation of reproductive structures, phototropism, and so on [1] [2]. Blue light is most effective in fungal photomorphogenesis such as that in Neurospora crassa and Trichoderma atroviride, whereas red light and near-ultraviolet (NUV; 300 - 400 nm) can be effective for the induction of conidiation in Aspergillus nidulans [3] and Bipolarisoryzae [4] [5], respectively. The molecular bases of fungal photoreceptors as well as of photomorphogenesis by blue and red light have been widely studied, as detailed in a number of published reviews [2] [6] [7]. Suppression subtractive hybridization (SSH) is a method based on suppressive PCR that allows the creation of subtracted cDNA libraries for the identification of genes differentially expressed in response to different experimental conditions. We report 46 newly identified genes that were upregulated by NUV irradiation in B. oryzae using SSH methods
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