In fluorescent pseudomonads, the Gac/Rsm signal transduction pathway controls secondary metabolism to suppress of fungal root pathogens via the expression of regulatory small RNAs (sRNAs). Because of its high cost, this pathway needs to be turned off in response to environmental stress. However, little is known about its underlying molecular mechanisms. In this study, it has been demonstrated that Lon protease negatively regulated the Gac/Rsm cascade in Pseudomonas protegens. It has also been shown that the alarmone ppGpp (guanosine tetraphosphate) appears to be essential for sustaining epiphytic fitness and biocontrol activity of P. protegens.
Pathogenicity, morphological and genetic aspects of fungi isolated from seven gramineous plants with blast disease in the southern Tohoku region were studied. Spores had the typical form of Pyricularia. Most isolates did not form lesions on rice, but all were pathogenic to the host of origin. On the basis of toxin production and a phylogenetic tree based on the rDNA-ITS sequence of the isolates, the fungi isolated from plants in the grass genera Lolium, Erichloa, Panicum and Setaria were identified as Pyricularia oryzae, but are unlikely to serve as inoculum to cause rice blast disease.
A simple paper-disc method was developed to prepare DNA from a large number of samples of Pyricularia oryzae for polymerase chain reaction (PCR)-based analyses such as simple-sequence repeat analysis was developed by testing variables such as culture period, drying the culture, buffer volume and centrifugation for extracting DNA, and stability after storage. Mycelium from a single-spore isolate in the center of a plate of oatmeal–0.5% w/v sucrose–1.6% (w/v) agar is allowed to grow onto paper discs (ø 6 mm) on the plates. After 7 days at 26°C, the mycelium-permeated discs are dried in a dessicator, placed in 200 µl Tris-EDTA buffer (10 mM Tris·HCl, 1 mM EDTA, pH 8.0) in a microtube, and vortexed for ca. 2 s. After the preparation is centrifuged at 21,500×g for 30 min at 4°C, 1 µl of the supernatant with the fungal DNA can be used as the template to detect genomic and mitochondrial genes using PCR or the preparation can be stably stored at 4°C for 8 weeks.