The daily timing of circadian (Х24-h) controlled activity in many animals exhibits seasonal adjustments, responding to changes in photoperiod (day length) and temperature. In Drosophila melanogaster, splicing of an intron in the 3 untranslated region of the period (per) mRNA is enhanced at cold temperatures, leading to more rapid daily increases in per transcript levels and earlier "evening" activity. Here we show that daily fluctuations in the splicing of this intron (herein referred to as dmpi8) are regulated by the clock in a manner that depends on the photoperiod (day length) and temperature. Shortening the photoperiod enhances dmpi8 splicing and advances its cycle, whereas the amplitude of the clock-regulated daytime decline in splicing increases as temperatures rise. This suggests that at elevated temperatures the clock has a more pronounced role in maintaining low splicing during the day, a mechanism that likely minimizes the deleterious effects of daytime heat on the flies by favoring nocturnal activity during warm days. Light also has acute inhibitory effects, rapidly decreasing the proportion of dmpi8-spliced per transcript, a response that does not require a functional clock. Our results identify a novel nonphotic role for phospholipase C (no-receptor-potential-A [norpA]) in the temperature regulation of dmpi8 splicing.Circadian rhythms are driven by cellular oscillators known as clocks or pacemakers and are an important aspect of the temporal organization observed in a wide range of organisms from bacteria to humans (11,12). These clocks exhibit free-running (self-sustaining) periods of Х24 h in the absence of environmental cues. Nonetheless, an important adaptive feature of circadian oscillators is that they are synchronized (entrained) by daily changes in environmental modalities, most notably visible light and ambient temperature.Light is almost certainly the predominant entraining agent in nature. Under natural conditions the light-dark (LD) cycle aligns the phases of clocks and evokes daily adjustments in the approximately 24-h endogenous periods of these oscillators such that they precisely match the 24-h solar day. The duration of day length (photoperiod) can modify the temporal alignment between a circadian rhythm and local time (22). A physiologically relevant advantage of this inherent flexibility of clocks is that the daily distributions of physiological and behavioral rhythms are not rigidly locked to local time but can be adjusted for seasonal changes in day length.Despite the obvious importance of photoperiod, ambient temperature is also a key environmental modality regulating the timing of circadian rhythms (50). This makes intuitive sense, because in temperate latitudes seasonal changes in day length are also accompanied by predictable changes in average daily temperatures. Thus, circadian clocks play an important role in endowing organisms with the ability to anticipate daily and seasonal changes in environmental conditions, resulting in physiological and behavioral rhythms that occu...

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Summary Sleep:wake cycles break down with age, but the causes of this degeneration are not clear. Using a Drosophila model we addressed the contribution of circadian mechanisms to this aged-induced deterioration. We found that in old flies free-running circadian rhythms (behavioral rhythms assayed in constant darkness) have a longer period and an unstable phase before they eventually degenerate. Surprisingly, rhythms are weaker in light:dark cycles and the circadian-regulated morning peak of activity is diminished under these conditions. On a molecular level, aging results in reduced amplitude of circadian clock gene expression in peripheral tissues. However, oscillations of the clock protein PERIOD (PER) are robust and synchronized among different clock neurons, even in very old, arrhythmic flies. To improve rhythms in old flies, we manipulated environmental conditions, which can have direct effects on behavior, and also tested a role for molecules that act downstream of the clock. Coupling temperature cycles with a light:dark schedule or reducing expression of protein kinase A (PKA) improved behavioral rhythms and consolidated sleep. Our data demonstrate that a robust molecular time-keeping mechanism persists in the central pacemaker of aged flies, and reducing PKA can strengthen behavioral rhythms.

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MicroRNA-mediated post-transcriptional regulations are increasingly recognized as important components of the circadian rhythm. Here we identify microRNA let-7, part of the Drosophila let-7-Complex, as a regulator of circadian rhythms mediated by a circadian regulatory cycle. Overexpression of let-7 in clock neurons lengthens circadian period and its deletion attenuates the morning activity peak as well as molecular oscillation. Let-7 regulates the circadian rhythm via repression of CLOCKWORK ORANGE (CWO). Conversely, upregulated cwo in cwo-expressing cells can rescue the phenotype of let-7-Complex overexpression. Moreover, circadian prothoracicotropic hormone (PTTH) and CLOCKregulated 20-OH ecdysteroid signalling contribute to the circadian expression of let-7 through the 20-OH ecdysteroid receptor. Thus, we find a regulatory cycle involving PTTH, a direct target of CLOCK, and PTTH-driven miRNA let-7.

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Rhizobia-legume symbiosis is an important type of plant-microbe mutualism; however, the establishment of this association is complicated and can be affected by many factors. The soybean rhizosphere has a specific microbial community, yet whether these organisms affect rhizobial nodulation has not been well investigated. Here, we analyzed the compositions and relationships of soybean rhizocompartment microbiota in three types of soil. First, we found that the rhizosphere community composition of soybean varied significantly in different soils, and the association network between rhizobia and other rhizosphere bacteria was examined. Second, we found that some rhizosphere microbes were correlated with the composition of bradyrhizobia and sinorhizobia in nodules. We cultivated 278 candidate Bacillus isolates from alkaline soil. Finally, interaction and nodulation assays showed that the Bacillus cereus group specifically promotes and suppresses the growth of sinorhizobia and bradyrhizobia, respectively, and alleviates the effects of saline-alkali conditions on the nodulation of sinorhizobia as well as affecting its colonization in nodules. Our findings demonstrate a crucial role of the bacterial microbiota in shaping rhizobia-host interactions in soybean, and provide a framework for improving the symbiotic efficiency of this system of mutualism through the use of synthetic bacterial communities.