Oxygenated Fatty Acids with Anti-rice Blast Fungus Activity in Rice Plants

Abstract Background MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression at the post-transcriptional level in eukaryotes. In rice, MIR7695 expression is regulated by infection with the rice blast fungus Magnaporthe oryzae with subsequent down-regulation of an alternatively spliced transcript of natural resistance-associated macrophage protein 6 (OsNramp6). NRAMP6 functions as an iron transporter in rice. Results Rice plants grown under high iron supply showed blast resistance, which supports that iron is a factor in controlling blast resistance. During pathogen infection, iron accumulated in the vicinity of M. oryzae appressoria, the sites of pathogen entry, and in cells surrounding infected regions of the rice leaf. Activation-tagged MIR7695 rice plants (MIR7695-Ac) exhibited enhanced iron accumulation and resistance to M. oryzae infection. RNA-seq analysis revealed that blast resistance in MIR7695-Ac plants was associated with strong induction of defense-related genes, including pathogenesis-related and diterpenoid biosynthetic genes. Levels of phytoalexins during pathogen infection were higher in MIR7695-Ac than wild-type plants. Early phytoalexin biosynthetic genes, OsCPS2 and OsCPS4, were also highly upregulated in wild-type rice plants grown under high iron supply. Conclusions Our data support a positive role of miR7695 in regulating rice immunity that further underpin links between defense and iron signaling in rice. These findings provides a basis to better understand regulatory mechanisms involved in rice immunity in which miR7695 participates which has a great potential for the development of strategies to improve blast resistance in rice.

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The Role of Silicon in Preventing Appressorial Penetration by the Rice Blast Fungus

Phytopathology ◽

10.1094/phyto-98-9-1038 ◽

2008 ◽

Vol 98 (9) ◽

pp. 1038-1044 ◽

Cited By ~ 52

Author(s):

T. Hayasaka ◽

H. Fujii ◽

K. Ishiguro

Keyword(s):

Silica Gel ◽

Rice Blast ◽

Rice Blast Fungus ◽

Leaf Epidermis ◽

Adaxial Surface ◽

Rice Plants ◽

Blast Fungus ◽

Spray Inoculation ◽

Rice Leaves

To test the hypothesis that silicon (Si) confers resistance against appressorial penetration of the rice blast fungus, the proportion of appressorial penetration into the leaf epidermis to total appressoria formed was compared among rice plants amended with various rates of silica gel to those plants nonamended. The amounts of Si in the youngest leaves were consistent with the amounts of silica gel applied to the rice plants. Relative Si levels on the adaxial surface of leaves as detected by energy dispersive X-ray analysis also increased with the amounts of silica gel applied. Based on light microscopic observation of the adaxial surface of rice leaves, the proportion of appressorial penetration was reduced by increasing amounts of silica gel applied and increased with the length of period after spray inoculation. Consequently, these results strongly support the hypothesis and suggest that Si in the leaf epidermis may confer resistance against appressorial penetration. Meanwhile, the number of lesions per leaf also decreased with the amount of Si applied, while only a certain part of penetrated appressoria could become sporulating susceptible lesions. This suggests that Si also confers physiological resistance against blast infection after the penetration.

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OsNAC111, a Blast Disease–Responsive Transcription Factor in Rice, Positively Regulates the Expression of Defense-Related Genes

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-03-14-0065-r ◽

2014 ◽

Vol 27 (10) ◽

pp. 1027-1034 ◽

Cited By ~ 35

Author(s):

Naoki Yokotani ◽

Tomoko Tsuchida-Mayama ◽

Hiroaki Ichikawa ◽

Nobutaka Mitsuda ◽

Masaru Ohme-Takagi ◽

...

Keyword(s):

Transcription Factor ◽

Transgenic Rice ◽

Transcriptional Activation ◽

Rice Blast ◽

Rice Blast Fungus ◽

Blast Disease ◽

Pr Genes ◽

Rice Plants ◽

Blast Fungus ◽

Transgenic Rice Plants

Plants respond to pathogen attack by transcriptionally regulating defense-related genes via various types of transcription factors. We identified a transcription factor in rice, OsNAC111, belonging to the TERN subgroup of the NAC family that was transcriptionally upregulated after rice blast fungus (Magnaporthe oryzae) inoculation. OsNAC111 was localized in the nucleus of rice cells and had transcriptional activation activity in yeast and rice cells. Transgenic rice plants overexpressing OsNAC111 showed increased resistance to the rice blast fungus. In OsNAC111-overexpressing plants, the expression of several defense-related genes, including pathogenesis-related (PR) genes, was constitutively high compared with the control. These genes all showed blast disease-responsive expression in leaves. Among them, two chitinase genes and one β-1,3-glucanase gene showed reduced expression in transgenic rice plants in which OsNAC111 function was suppressed by a chimeric repressor (OsNAC111-SRDX). OsNAC111 activated transcription from the promoters of the chitinase and β-1,3-glucanase genes in rice cells. In addition, brown pigmentation at the infection sites, a defense response of rice cells to the blast fungus, was lowered in OsNAC111-SRDX plants at the early infection stage. These results indicate that OsNAC111 positively regulates the expression of a specific set of PR genes in the disease response and contributes to disease resistance.

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Identification and Characterization of 2′-Deoxyuridine from the Supernatant of Conidial Suspensions of Rice Blast Fungus as an Infection-Promoting Factor in Rice Plants

Molecular Plant-Microbe Interactions ◽

10.1094/mpmi-07-10-0172 ◽

2011 ◽

Vol 24 (5) ◽

pp. 519-532 ◽

Cited By ~ 3

Author(s):

Sugihiro Ando ◽

Yuko Sato ◽

Hideyuki Shigemori ◽

Takafumi Shimizu ◽

Kazunori Okada ◽

...

Keyword(s):

Rice Blast ◽

Chemical Structure ◽

Rice Blast Fungus ◽

Conidial Suspension ◽

Rice Plants ◽

Blast Fungus ◽

Plant Pathogen Interactions ◽

Identification And Characterization ◽

Compatible Interactions

We previously detected infection-promoting activity in the supernatant of the conidial suspension (SCS) of the rice blast fungus. In the present study, a molecule carrying the activity was purified and identified as 2′-deoxyuridine (dU). The infection-promoting activity of dU was strictly dependent on its chemical structure and displayed characteristics consistent with those of the SCS. Notably, the activity of dU was exclusively detected during interactions between rice and virulent isolates of the fungus, the number of susceptible lesions in leaf blades was increased by dU, and nonhost resistance in rice plants was not affected by treatment with dU. In addition, the expression of pathogensis-related genes, accumulation of H2O2, and production of phytoalexins in rice in response to inoculation with virulent fungal isolates was not suppressed by dU. The infection-promoting activity of dU was not accompanied by elevated levels of endogenous abscissic acid, which is known to modify plant-pathogen interactions, and was not detected in interactions between oat plants and a virulent oat blast fungus isolate. Taken together, these results demonstrate that dU is a novel infection-promoting factor that acts specifically during compatible interactions between rice plants and rice blast fungus in a mode distinct from that of toxins and suppressors.

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