Abstract
False smut of rice, caused by Ustilaginoidea virens (Cooke) Takahashi (teleomorph: Villosiclava virens), is one of the most important diseases affecting rice worldwide. Agrobacterium tumefaciens-mediated transformation was used to identify functional genes in U. virens. In this study, we selected a single-copy insertion mutant T133 with deficiency in producing conidia by screening the T-DNA insertion mutant library of U. virens. The UvPRO1-deletion mutant was successfully obtained after cloning the targeted gene by analysis of the T-DNA insert site of mutant T133. Further research showed that the UvPRO1 mutant was reduced in growth rate and could not produce conidia in PSB medium, while sensitivities to sodium dodecyl sulfate, Congo red, and hyperosmotic stress increased. Moreover, the UvPRO1 deletion mutant hyphae could extend along the surface of spikelets at 1–3 dpi, but mycelia became shriveled and completely lost the ability to infect spikelets at 4 dpi. The relative expression level of UvPRO1 at 8 dpi was more than twice as high as that at 1–2 dpi. These results suggest that UvPRO1 plays a critical role in hyphal growth and conidiation, as well as in stress response and pathogenesis. These findings provide a novel mode of action for the PRO1 protein in fungi and improve the understanding of the function of UvPRO1 in the life cycle of U. virens.
Highlights
False smut of rice, caused by Ustilaginoidea virens (Cooke) Takahashi, is a minor disease that has been present in the major rice-growing areas of Asia, Africa, and America for some time (Deng, 1989; Savary et al, 2000; Ashizawa et al, 2010)
T-DNA flanking sequences were recovered from these mutants by amplifying genomic DNA sequences flanking T-DNA insertions of transformants with TAIL-PCR and inverse PCR (Supplementary Table 1)
In the presence of 30–70 mg/L Congo red (CR), similar results to growth assays with sodium dodecyl sulfate (SDS) were obtained, in that UvPRO1-27 mutant displayed a slower radial growth rate than the wild-type or C UvPRO1-27 (Figure 6C). These results suggested that the UvPRO1 mutant had increased sensitivity to CR and SDS
Summary
False smut of rice, caused by Ustilaginoidea virens (Cooke) Takahashi (teleomorph: Villosiclava virens), is a minor disease that has been present in the major rice-growing areas of Asia, Africa, and America for some time (Deng, 1989; Savary et al, 2000; Ashizawa et al, 2010). Compared with other important diseases such as rice blast and bacterial leaf blight, studies on the interaction of the false smut pathogen and the rice host at the molecular level are few. Fan et al (2015) used time-course microscopic and transcriptional approaches to investigate host responses to U. virens infection, and the results implied that U. virens may hijack rice nutrient reservoir systems to successfully colonize rice floral organs and to form false smut balls Compared with other important diseases such as rice blast and bacterial leaf blight, studies on the interaction of the false smut pathogen and the rice host at the molecular level are few. Sun et al (2013) reported the genome sequence of U. virens and predicted possible effectors. Zhang et al (2008) characterized the first MAPK protein from U. virens and verified that UVMK1 is a homolog of Magnaporthe grisea PMK1. Rao et al (2014) cloned a homolog of HOG1 from U. virens and measured transcript levels of UvHog under salinity conditions, suggesting that UvHog may be involved in the specific response to salt stress. Fan et al (2015) used time-course microscopic and transcriptional approaches to investigate host responses to U. virens infection, and the results implied that U. virens may hijack rice nutrient reservoir systems to successfully colonize rice floral organs and to form false smut balls
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