Time of day-dependent variations of immune system parameters are ubiquitous phenomena in immunology. The circadian clock has been attributed with coordinating these variations on multiple levels; however, their molecular basis is little understood. Here, we systematically investigated the link between the circadian clock and rhythmic immune functions. We show that spleen, lymph nodes, and peritoneal macrophages of mice contain intrinsic circadian clockworks that operate autonomously even ex vivo. These clocks regulate circadian rhythms in inflammatory innate immune functions: Isolated spleen cells stimulated with bacterial endotoxin at different circadian times display circadian rhythms in TNF-␣ and IL-6 secretion. Interestingly, we found that these rhythms are not driven by systemic glucocorticoid variations nor are they due to the detected circadian fluctuation in the cellular constitution of the spleen. Rather, a local circadian clock operative in splenic macrophages likely governs these oscillations as indicated by endotoxin stimulation experiments in rhythmic primary cell cultures. On the molecular level, we show that >8% of the macrophage transcriptome oscillates in a circadian fashion, including many important regulators for pathogen recognition and cytokine secretion. As such, understanding the cross-talk between the circadian clock and the immune system provides insights into the timing mechanism of physiological and pathophysiological immune functions.adrenalectomy ͉ LPS ͉ IL-6 ͉ microarray ͉ TNF-␣ A 24-h periodicity in the environment has led to the evolution of molecular circadian clocks in organisms ranging from cyanobacteria to humans. Circadian rhythms display a near 24-h period and persist even in the absence of external timing information. In mammals, a small hypothalamic region, the suprachiasmatic nucleus (SCN), has been identified as the master pacemaker regulating circadian rhythms in physiology, metabolism, and behavior (1). Recent evidence shows that also peripheral organs such as liver, heart, kidney, skin, and even cultured cell lines contain circadian oscillators. Although the SCN probably sets the phase of these peripheral clocks (by as yet unknown means), recent reports implicate peripheral clocks in the regulation of local physiology (2-4). The fundamental mechanism of rhythm generation is cell autonomous and highly conserved in SCN and peripheral cells: Interlocked transcriptional/translational feedback loops involving clock genes, such as Per1-3, Cry1-2, Clock, Bmal1, and Rev-Erb␣ create oscillations on the molecular level (reviewed in ref. 2).In the immune system, many functions and parameters have been described to be time-of-day dependent, e.g., lymphocyte proliferation (5), natural killer (NK) cell activity (6), humoral immune response (7), rhythms in absolute and relative numbers of circulating white blood cells and their subsets (8), cytokine levels (9), and serum cortisol (10) (reviewed in ref. 11). In addition, time-of-day variation in susceptibility to infection (12), cour...

In a screen for potential mediators of brassinosteroid (BR) e¡ects, the EXORDIUM (EXO) protein was identi¢ed as a regulator of BR-responsive genes. The EXO gene was characterized as a BR-up-regulated gene. EXO overexpression under the control of the 35SCaMV promoter resulted in increased transcript levels of the BR-up-regulated KCS1, Exp5, N N-TIP, and AGP4 genes, which likely are involved in the mediation of BR-promoted growth. 35S: :EXO lines grown in soil or in synthetic medium showed increased vegetative growth in comparison to wild-type plants, resembling the growth phenotype of BRtreated plants. Thus, the EXO protein most likely promotes growth via the modulation of gene expression patterns.

Asr genes are exclusively found in the genomes of higher plants. In many species, this gene family is expressed under abiotic stress conditions and during fruit ripening. The encoded proteins have nuclear localisation and consequently a transcription factor function has been suggested. Interestingly, yeast-one-hybrid experiments revealed that a grape ASR binds to the promoter of a hexose transporter gene (VvHT1). However, the role of these proteins in planta is still elusive. By using a reverse genetics approach in potato we found that modification of Asr1 expression has no incidence on the aerial phenotype of the plant but exerts a dramatic effect in tuber. Asr1 antisense potatoes displayed decreased tuber fresh weight whereas Asr1 overexpressors had a diminished number of tubers. Moreover, overexpression lines showed lower transcript levels of a plasma membrane hexose transporter and a concomitant decrease in glucose content in parenchyma cells of potato tubers. On the same hand glucose uptake rate was also reduced in one of the overexpressing lines. It thus seems likely that Asr1 is involved in the control of hexose uptake in heterotrophic organs. In addition, the transgenic plants were characterized by several other changes in steady state metabolite levels. Results presented here support a role for ci21A/Asr1 in glucose metabolism of potato tuber.

Asr (for ABA, stress, ripening) genes are exclusively found in the genomes of higher plants, and the encoded proteins have been found localized both to the nucleus and cytoplasm. However, before the mechanisms underlying the activity of ASR proteins can be determined, the role of these proteins in planta should be deciphered. Results from this study suggest that ASR is positioned within the signaling cascade of interactions among glucose, abscisic acid, and gibberellins. Tobacco (Nicotiana tabacum) transgenic lines with reduced levels of ASR protein showed impaired glucose metabolism and altered abscisic acid and gibberellin levels. These changes were associated with dwarfism, reduced carbon dioxide assimilation, and accelerated leaf senescence as a consequence of a fine regulation exerted by ASR to the glucose metabolism. This regulation resulted in an impact on glucose signaling mediated by Hexokinase1 and Snf1-related kinase, which would subsequently have been responsible for photosynthesis, leaf senescence, and hormone level alterations. It thus can be postulated that ASR is not only involved in the control of hexose uptake in heterotrophic organs, as we have previously reported, but also in the control of carbon fixation by the leaves mediated by a similar mechanism.