By timing many diel rhythmic events, circadian clock provides an adaptive advantage for higher plants. Meanwhile, circadian clock displays plasticity and can be entrained by the external environmental cues and internal factors. However, whether cellular energy status can regulate circadian clock is largely unknown in higher plants. The evolutionarily conserved TOR (target of rapamycin) signaling among eukaryotic organisms has been implicated as an integrator for cellular nutrient and energy status. Here, we demonstrated that chemically blocking electron transport chain of mitochondrial can lengthen the circadian period. Similarly, chemical inhibition of TOR activity by Torin 1, a specific inhibitor for TOR kinase, and knockdown of TOR transcript levels significantly elongate the circadian period as well. Our findings imply that TOR signaling may mediate energy status-regulated circadian clock in plants, and the reciprocal regulation between the circadian clock and TOR signaling might be an evolutionary mechanism for fitness and adaptation in plants.

Circadian pace is modulated by light intensity, known as the Aschoff’s rule, with largely unrevealed mechanisms. Here we report that photoreceptor CRY2 mediates blue light input to the circadian clock by directly interacting with clock core component PRR9 in blue light dependent manner. This physical interaction dually blocks the accessibility of PRR9 protein to its co-repressor TPL/TPRs and the resulting kinase PPKs. Notably, phosphorylation of PRR9 by PPKs is critical for its DNA binding and repressive activity, hence to ensure proper circadian speed. Given the labile nature of CRY2 in strong blue light, our findings provide a mechanistic explanation for Aschoff’s rule in plants, i.e., blue light triggers CRY2 turnover in proportional to its intensity, which accordingly releasing PRR9 to fine tune circadian speed. Our findings not only reveal a network mediating light input into the circadian clock, but also unmask a mechanism by which the Arabidopsis circadian clock senses light intensity.

The serum amyloid A (sAA) is a common sensitive indicator for the diagnosis of infectious diseases, and sAA levels are increased in pneumonia. However, the detailed molecular mechanism is unknown. Previous studies have demonstrated the participation of Toll-like receptor (TLR) 2 and its downstream protein activator protein-1 (AP-1) in inflammatory lung injury. This study aimed to investigate the effect of sAA on LPS-induced BEAS-2B cells injury and uncover the possible mechanism. The human bronchial epithelial cell line BEAS-2B was exposed to sAA with or without lipopolysaccharide (LPS) treatment, then cell viability, inflammation and apoptosis were evaluated. The effects of TLR2 knockout on sAA + LPS-treated BEAS-2B cells were also determined. Results revealed that sAA treatment reduced cell viability in a concentration-dependent manner and the effect of 500 nM sAA on cell viability was approximately equivalent to LPS. The levels of inflammatory cytokines including tumor necrosis factor (TNF)-α, interleukin (IL)-1β, IL-8, monocyte chemotactic protein (MCP)-1 and IL-6 as well as cell apoptosis and expression of proteins related to apoptosis were significantly increased upon sAA or LPS stimulation. The expression of TLR2 and AP-1 was also elevated in cells challenged with sAA or LPS. Besides, sAA and LPS co-treatment further enhanced the actions of LPS. However, the knockdown of TLR2 obviously blunted the effects of LPS and sAA co-treatment on cell viability, inflammation and apoptosis. Taken together, our results revealed that sAA could exert an enhanced effect on LPS-induced BEAS-2B cells injury via promoting TLR2/AP-1 expression.