Abstract
Early circadian studies in plants by de Mairan and de Candolle alluded to a regulation of circadian clocks by humidity. However, this regulation has not been described in detail, nor has its influence on physiology been demonstrated. Here we report that, under constant light, circadian humidity oscillation can entrain the plant circadian clock to a period of 24 h probably through the induction of clock genes such as CIRCADIAN CLOCK ASSOCIATED 1. Under simulated natural light and humidity cycles, humidity oscillation increases the amplitude of the circadian clock and further improves plant fitness-related traits. In addition, humidity oscillation enhances effector-triggered immunity at night possibly to counter increased pathogen virulence under high humidity. These results indicate that the humidity oscillation regulates specific circadian outputs besides those co-regulated with the light-dark cycle.
Highlights
Circadian studies in plants by de Mairan and de Candolle alluded to a regulation of circadian clocks by humidity
To test whether humidity is a regulator of the plant circadian clock, we first examined the influence of daily humidity oscillation on plant physiology
We found that WT plants accumulated more biomass and flowered earlier under oscillating humidity than under 70% relative humidity (RH) and that these effects were dependent on core clock genes (Fig. 1c, d)
Summary
Circadian studies in plants by de Mairan and de Candolle alluded to a regulation of circadian clocks by humidity. Humidity oscillation enhances effector-triggered immunity at night possibly to counter increased pathogen virulence under high humidity These results indicate that the humidity oscillation regulates specific circadian outputs besides those co-regulated with the light-dark cycle. PRR1, better known as TIMING OF CAB EXPRESSION 1 (TOC1), is an evening-phased TF, which, together with CCA1 and LHY, forms the core feedback loop[8,9] This CCA1/LHYTOC1 core loop is further connected with the morning loop (i.e., PRR5, PRR7 and PRR9) and the evening loop (i.e., PRR3, EARLY FLOWERING 3, EARLY FLOWERING 4, LUX ARRHYTHMO and GIGANTEA) to create the complex architecture of the plant circadian clock[8]. Our study reveals that in the absence of light and temperature cues, air humidity entrains the plant circadian clock probably through high humidity-mediated induction of CCA1; whereas, in the presence of light-dark cycles, oscillating air humidity increases the amplitude of clock genes, further improves plant fitness-related traits and enhances resistance against evening-inoculated pathogens. This study demonstrates humidity oscillation as a regulator of the circadian clock and shows its specific impacts on plant physiology
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