Differential Effects of Day/Night Cues and the Circadian Clock on the Barley Transcriptome.

The circadian clock is a complex transcriptional network that regulates gene expression in anticipation of the day/night cycle and controls agronomic traits in plants. However, in crops, how the internal clock and day/night cues affect the transcriptome remains poorly understood. We analyzed the diel and circadian leaf transcriptomes in the barley (Hordeum vulgare) cultivar 'Bowman' and derived introgression lines harboring mutations in EARLY FLOWERING3 (ELF3), LUX ARRHYTHMO1 (LUX1), and EARLY MATURITY7 (EAM7). The elf3 and lux1 mutants exhibited abolished circadian transcriptome oscillations under constant conditions, whereas eam7 maintained oscillations of ≈30% of the circadian transcriptome. However, day/night cues fully restored transcript oscillations in all three mutants and thus compensated for a disrupted oscillator in the arrhythmic barley clock mutants elf3 and lux1 Nevertheless, elf3, but not lux1, affected the phase of the diel oscillating transcriptome and thus the integration of external cues into the clock. Using dynamical modeling, we predicted a structure of the barley circadian oscillator and interactions of its individual components with day/night cues. Our findings provide a valuable resource for exploring the function and output targets of the circadian clock and for further investigations into the diel and circadian control of the barley transcriptome.

Osmotic stress at the barley root affects expression of circadian clock genes in the shoot.

The circadian clock is an important timing system that controls physiological responses to abiotic stresses in plants. However, there is little information on the effects of the clock on stress adaptation in important crops, like barley. In addition, we do not know how osmotic stress perceived at the roots affect the shoot circadian clock. Barley genotypes, carrying natural variation at the photoperiod response and clock genes Ppd-H1 and HvELF3, were grown under control and osmotic stress conditions to record changes in the diurnal expression of clock and stress-response genes and in physiological traits. Variation at HvELF3 affected the expression phase and shape of clock and stress-response genes, while variation at Ppd-H1 only affected the expression levels of stress genes. Osmotic stress up-regulated expression of clock and stress-response genes and advanced their expression peaks. Clock genes controlled the expression of stress-response genes, but had minor effects on gas exchange and leaf transpiration. This study demonstrated that osmotic stress at the barley root altered clock gene expression in the shoot and acted as a spatial input signal into the clock. Unlike in Arabidopsis, barley primary assimilation was less controlled by the clock and more responsive to environmental perturbations, such as osmotic stress.

Connections between circadian clocks and carbon metabolism reveal species-specific effects on growth control.

The plant circadian system exists in a framework of rhythmic metabolism. Much has been learned about the transcriptional machinery that generates the clock rhythm. Interestingly, these components are largely conserved between monocots and dicots, but key differences in physiological and developmental output processes have been found. How the clock coordinates carbon metabolism to drive plant growth performance is described with a focus on starch breakdown in Arabidopsis. It is proposed that clock effects on plant growth and fitness are more complex than just matching internal with external rhythms. Interesting recent findings support that the products of photosynthesis, probably sucrose, in turn feeds back to the clock to set its rhythm. In this way, the clock both controls and is controlled by carbon fluxes. This has an interesting connection to stress signalling and water-use efficiency, and it is now known that the clock and abscisic acid pathways are reciprocally coordinated. These processes converge to drive growth in a species-specific context such that predictions from the Arabidopsis model to other species can be restricted. This has been seen from phenotypic growth studies that revealed that dicot shoot growth is rhythmic whereas monocot shoot growth is continuous. Taken together, emerging evidence suggests reciprocal interactions between metabolism, the circadian clock, and stress signalling to control growth and fitness in Arabidopsis, but transferability to other species is not always possible due to species-specific effects.

Temporomandibular joint involvement in children with juvenile idiopathic arthritis.

OBJECTIVE: To determine the rate of temporomandibular joint (TMJ) involvement and find factors associated with TMJ arthritis in a single-center cohort of patients with juvenile idiopathic arthritis (JIA). METHODS: Retrospective analysis of all patients with JIA visiting the rheumatology clinic between January 1, 2005, and December 31, 2006. Followup information was included until August 2008. A diagnosis of TMJ arthritis was based on clinical rheumatological and/or radiological findings. RESULTS: After a mean followup time for JIA of 4.6 years (range 0.08-14.17), 86/223 patients (38.6%) had developed TMJ arthritis. The rate of TMJ involvement differed significantly among JIA subtypes (p = 0.0016), with 61% in extended oligoarticular, 52% in polyarticular rheumatoid factor (RF)-negative, 50% in psoriatic, 36% in systemic, 33% in polyarticular RF-positive, 33% in persistent oligoarticular, 30% in unclassified JIA, and 11% in enthesitis-related arthritis. The rate of TMJ involvement in our cohort was statistically significantly lower for patients who were HLA-B27-positive (p = 0.0002). In a multivariate analysis, the association of the following factors was confirmed: JIA subtype (p = 0.0001), a higher erythrocyte sedimentation rate (ESR) at diagnosis (p = 0.0038), involvement of joints of the upper extremity (p = 0.011), the absence of HLA-B27 (p = 0.023), and younger age at onset of JIA (p = 0.050). CONCLUSION: In our cohort of children with JIA, the overall rate of TMJ involvement was 38.6%. Patients with certain JIA subtypes, a higher ESR at disease onset, involvement of upper extremity joints, and younger age at diagnosis were more likely to develop TMJ arthritis. The presence of HLA-B27 seemed to be protective.