OsWRKY97, an Abiotic Stress-Induced Gene of Rice, Plays a Key Role in Drought Tolerance.

Drought stress is one of the major causes of crop losses. The WRKY families play important roles in the regulation of many plant processes, including drought stress response. However, the function of individual WRKY genes in plants is still under investigation. Here, we identified a new member of the WRKY families, OsWRKY97, and analyzed its role in stress resistance by using a series of transgenic plant lines. OsWRKY97 positively regulates drought tolerance in rice. OsWRKY97 was expressed in all examined tissues and could be induced by various abiotic stresses and abscisic acid (ABA). OsWRKY97-GFP was localized to the nucleus. Various abiotic stress-related cis-acting elements were observed in the promoters of OsWRKY97. The results of OsWRKY97-overexpressing plant analyses revealed that OsWRKY97 plays a positive role in drought stress tolerance. In addition, physiological analyses revealed that OsWRKY97 improves drought stress tolerance by improving the osmotic adjustment ability, oxidative stress tolerance, and water retention capacity of the plant. Furthermore, OsWRKY97-overexpressing plants also showed higher sensitivity to exogenous ABA compared with that of wild-type rice (WT). Overexpression of OsWRKY97 also affected the transcript levels of ABA-responsive genes and the accumulation of ABA. These results indicate that OsWRKY97 plays a crucial role in the response to drought stress and may possess high potential value in improving drought tolerance in rice.

Antifungal activity of endophytic Bacillus safensis B21 and its potential application as a biopesticide to control rice blast.

Endophytic bacteria are potential biocontrol agents for the control of fungal diseases. Here, an endophyte strain, B21, was isolated from Osmanthus fragrans Lour. fruits and identified as Bacillus safensis by analysis of its 16S rDNA gene sequence and its biochemical and physiological characteristics. The culture filtrate showed antifungal activity against Magnaporthe oryzae, which causes rice blast disease, and the IC50 of the methanol extract was 15.56 µg/mL, which was significantly lower than that of carbendazim (25.16 µg/mL). The antifungal activity of the methanol extract was stable at a wide range of pH values (1-9) and temperatures (40-100 °C). Two antifungal compounds were isolated by organic extraction, silica gel column chromatography and high-performance liquid chromatography (HPLC). Based on electrospray ionization mass spectrometry (ESI-MS) and nuclear magnetic resonance spectrometry (NMR) analyses, the structures of the antifungal compounds were identified as iturin A2 and iturin A6. Additionally, the hyphae treated with iturin (iturin A2 or iturin A6) could be stained with the fluorescent dye propidium iodide (PI), indicating that these two compounds inhibited the growth of hyphae by changing the hyphal membrane permeability. In field experiments, spray treatment with fermentation broth resulted in a lower disease index than treatment with carbendazim, as did the culture filtrate. The results suggest that strain B21 and its bioactive compounds have the potential to be developed into a biopesticide for the biocontrol of rice blast.

The isolation of the antagonistic strain Bacillus australimaris CQ07 and the exploration of the pathogenic inhibition mechanism of Magnaporthe oryzae.

Biological control as a promising method to combat plant disease has gained public attention in recent years. In the present study, we isolated 12 strains resistant to Magnaporthe oryzae from western Sichuan subalpine soil. Among them, CQ07 exhibited remarkable activity against M. oryzae. The result of 16S rRNA sequence analysis revealed that CQ07 is approximately 99% similar to Bacillus australimaris. The sterilized culture filtrate of CQ07 inhibited the growth of M. oryzae, which motivated us to deduce the influence of CQ07 on the pathogenicity of M. oryzae. As shown by experimentation, sterilized culture filtrate (10 µl/ml) of CQ07 can delay and even suppress the germination of conidia and prevent the formation of appressorium in vitro and in vivo. In addition, by simulative field tests, the spraying of conidia suspension diluted with sterilized culture filtrate of CQ07 reduced infection of rice blast. To better control rice blasts, understanding the infection mechanism of M. oryzae and inhibiting the mechanism of the antagonistic strain is of great importance.

Isolation and evaluation of endophytic Bacillus tequilensis GYLH001 with potential application for biological control of Magnaporthe oryzae.

Biological control is a promising measure in the control of plant disease. In the present study, we isolated 13 endophytic strains from Angelica dahurica. Among them, an endophytic strain which was named GYLH001 exhibited remarkable activity against Magnaporthe oryzae. 16S rRNA sequence analysis, biochemical and physiological proved that it is Bacillus tequilensis. The sterilized culture filtrate of GYLH001 can inhibit the growth of M.oryzae, which suggests the presence of secondary metabolites. Proved by experiment, GYLH001 can produce cellulase, protease, gelatinase, indole-3-acetic acid and 1-amino-cyclopropane-1-carboxylate deaminase. In addition, the temperature experiment showed that secondary metabolites produced by GYLH001 had good thermal stability. They can remain activity even heated at 100°C for 30 min. They also had good acid-resistance in heavily acidic condition. But under alkaline condition, the antifungal effect decreased significantly. By simulative field tests, the spraying of GYLH001 spore solution could prevent and treat rice blast. Through continuous separation and purification of sterilized culture filtrate and identification by mass spectrometry, the molecular weight of an active substance is 364.26. In the control of rice blast, B. tequilensis GYLH001 has potential as a biological control agent in agriculture.