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The circadian clock allows plants to actively adapt to daily environmental changes through temporal regulation of physiological traits. In response to drought stress, circadian oscillators gate ABA signalling, but the molecular mechanisms remain unknown, especially in crops. Here, we investigated the role of soybean circadian oscillators GmLCLa1, GmLCLa2, GmLCLb1 and GmLCLb2 in leaf water stress response. Under dehydration stress, the GmLCL quadruple mutant had decreased leaf water loss. We found that the dehydration treatment delayed the peak expression of GmLCL genes by 4 hr. In addition, the circadian clock in hairy roots also responded to ABA, which led to a free‐running rhythm with shortened period. Importantly, in the gmlclq quadruple mutant, diurnal expression phases of several circadian‐regulated ABA receptor, ABA catabolism and ABA signalling‐related genes were shifted significantly to daytime. Moreover, in the gmlclq mutant leaf, expression of GmPYL17, GmCYP707A, GmABI2 and GmSnRK2s was increased under water dehydration stress. In summary, our results show that GmLCLs act as negative regulators of ABA signalling in leaves during dehydration response. We investigated the molecular characteristics and the physiological function of circadian oscillators in soybean. We found the GmLCL quadruple mutant had decreased leaf water loss under dehydration stress, and GmLCLs act as negative regulators of ABA signalling in leaves during dehydration response. [ABSTRACT FROM AUTHOR]

As sessile organisms, plants perceive, respond, and adapt to the environmental changes for optimal growth and survival. The plant growth and fitness are enhanced by circadian clocks through coordination of numerous biological events. In legume species, nitrogen‐fixing root nodules were developed as the plant organs specialized for symbiotic transfer of nitrogen between microsymbiont and host. Here, we report that the endogenous circadian rhythm in nodules is regulated by MtLHY in legume species Medicago truncatula. Loss of function of MtLHY leads to a reduction in the number of nodules formed, resulting in a diminished ability to assimilate nitrogen. The operation of the 24‐h rhythm in shoot is further influenced by the availability of nitrogen produced by the nodules, leading to the irregulated nyctinastic leaf movement and reduced biomass in mtlhy mutants. These data shed new light on the roles of MtLHY in the orchestration of circadian oscillator in nodules and shoots, which provides a mechanistic link between nodulation, nitrogen assimilation, and clock function. [ABSTRACT FROM AUTHOR]

The circadian pacemaker in plants is a hierarchical multioscillator system that directs and maintains a 24‐hr oscillation required for organism homeostasis and environmental fitness. Molecular clockwork within individual tissues and organs acts cell autonomously, showing differences in circadian expression of core oscillators and their target genes; there are functional dominance and coupling in the complex regulatory network. However, molecular characteristics of organ‐specific clocks are still unknown. Here, we showed the detached shoot and root possess dynamic circadian protein–protein interactions between clock core components, periodicity in organs exhibits a difference. The period length difference between shoot and root was not remarkable in prr7‐3 and prr7‐3 prr9‐1 mutants. In addition, the phase transition curve indicated that shoot and root clock respond differently to the resetting cues of ambient temperature. PRR9 and PRR7 compensate circadian period between 22°C and 28°C in shoot, not in root. The circadian rhythms of PRR9 or PRR7 transcript accumulation showed no difference at 22°C and 28°C in shoot, but differences were observed in root. In summary, our results reveal the specificity of dynamic circadian protein–protein interactions in organ‐autonomous clocks and the critical roles of PRR9 and PRR7 in mechanisms regulating temperature compensation in aerial shoot system. We found the difference of circadian period length of dynamic circadian protein–protein interactions between shoot and root. PRR9 and PRR7 were found to contribute significantly to organ‐specific circadian periodicity maintenance and in the temperature compensation of aerial shoot clock. To the best of our knowledge, this is the first example in plants monitoring clock protein interactions in real time in individual organs. Having demonstrated the uniqueness and consistency of clock components function in aerial shoot and subterranean root, we are able to pose a variety of intriguing questions about the adaptive evolution and hierarchical coupling in the plant clock system. [ABSTRACT FROM AUTHOR]