Dawn and Dusk Set States of the Circadian Oscillator in Sprouting Barley (Hordeum vulgare) Seedlings

The plant circadian clock is an internal timekeeper that coordinates biological processes with daily changes in the external environment. The transcript levels of clock genes, which oscillate to control circadian outputs, were examined during early seedling development in barley (Hordeum vulgare), a model for temperate cereal crops. Oscillations of clock gene transcript levels do not occur in barley seedlings grown in darkness or constant light but were observed with day-night cycles. A dark-to-light transition influenced transcript levels of some clock genes but triggered only weak oscillations of gene expression, whereas a light-to-dark transition triggered robust oscillations. Single light pulses of 6, 12 or 18 hours induced robust oscillations. The light-to-dark transition was the primary determinant of the timing of subsequent peaks of clock gene expression. After the light-to-dark transition the timing of peak transcript levels of clock gene also varied depending on the length of the preceding light pulse. Thus, a single photoperiod can trigger initiation of photoperiod-dependent circadian rhythms in barley seedlings. Photoperiod-specific rhythms of clock gene expression were observed in two week old barley plants. Changing the timing of dusk altered clock gene expression patterns within a single day, showing that alteration of circadian oscillator behaviour is amongst the most rapid molecular responses to changing photoperiod in barley. A barley EARLY FLOWERING3 mutant, which exhibits rapid photoperiod–insensitive flowering behaviour, does not establish clock rhythms in response to a single photoperiod. The data presented show that dawn and dusk cues are important signals for setting the state of the circadian oscillator during early development of barley and that the circadian oscillator of barley exhibits photoperiod-dependent oscillation states

Gene silencing by RNA interference in the ectoparasitic mite, Psoroptes ovis

Abstract The presence of components of the RNA interference (RNAi) pathway in Psoroptes ovis, an ectoparasitic mite responsible for psoroptic mange, was investigated through interrogation of the P. ovis genome. Homologues of transcripts representing critical elements for achieving effective RNAi in the mite, Tetranychus urticae and the model organisms Caenorhabditis elegans and Drosophila melanogaster were identified and, following the development of a non-invasive immersion method of double stranded RNA delivery, gene silencing by RNAi was successfully demonstrated in P. ovis. Significant reductions in transcript levels were achieved for three target genes which encode the Group 2 allergen (Pso o 2), mu-class glutathione S-transferase (PoGST-mu1) and beta-tubulin (Poβtub). This is the first demonstration of RNAi in P. ovis and provides a mechanism for mining transcriptomic and genomic datasets for novel control targets against this economically important ectoparasite

Studies of thrips migratory flights in Israel

Blue sticky traps on 3.0 m high poles were used to determine the characteristics of Thrips tabaci and Frankliniella occidentalis migratory flight in Israel from 2003 to 2007. In an open area, both thrips species were caught from March to November. The dominant species was T. tabaci except during the spring. About 70% of the thrips were caught below 1.0 m above ground. Trapping height appears to reflect thrips’ concentration gradient in the air because it was not affected by setting up the poles over a sticky surface. From April to September the westerly sea breezes usually exceed 10 km/h from late morning to twilight time. As a result, about 85% and 10% of the thrips were caught in the morning and at dusk, respectively. When we used similar traps mounted on wind vanes, at 1.0 m above ground 70% of the thrips were caught on the leeward side. Thus, it appears that thrips fly mainly upwind during their migration. Indeed, while most prevailing winds are from the west, most thrips were caught on the eastern side of the poles (40–50%) and the fewest on the western side (10–20%). This information may be used to focus monitoring and control of these thrips in time and space