Abstract
Circadian clocks improve plant fitness in a rhythmic environment. As each cell has its own circadian clock, we hypothesized that sets of cells with different functions would have distinct rhythmic behaviour. To test this, we investigated whether different organs in field-grown sugarcane follow the same rhythms in transcription. We assayed the transcriptomes of three organs during a day: leaf, a source organ; internodes 1 and 2, sink organs focused on cell division and elongation; and internode 5, a sink organ focused on sucrose storage. The leaf had twice as many rhythmic transcripts (>68%) as internodes, and the rhythmic transcriptomes of the internodes were more like each other than to those of the leaves. Among the transcripts expressed in all organs, only 7.4% showed the same rhythmic pattern. Surprisingly, the central oscillators of these organs — the networks that generate circadian rhythms — had similar dynamics, albeit with different amplitudes. The differences in rhythmic transcriptomes probably arise from amplitude differences in tissue-specific circadian clocks and different sensitivities to environmental cues, highlighted by the sampling under field conditions. The vast differences suggest that we must study tissue-specific circadian clocks in order to understand how the circadian clock increases the fitness of the whole plant.
Highlights
The circadian clock is an endogenous signaling network that allows organisms to adapt to rhythmically changing environments
The grass PRRs consist of TIME FOR CAB EXPRESSION1 (TOC1), PRR37, PRR73, PRR59, and PRR95, and it is not clear whether they have the same functions as their Arabidopsis counterparts, even though they are capable of complementing Arabidopsis mutations[13,14]
We harvested leaf +1 (L1), a source organ, and two sink organs: internodes 1 and 2 (I1), organs focused on cell division and cell elongation that includes the shoot apical meristem; and internode 5 (I5), an organ focused on sucrose accumulation
Summary
The circadian clock is an endogenous signaling network that allows organisms to adapt to rhythmically changing environments. The Input Pathways detect entraining cues that keep the circadian clock continuously synchronized to the environment In plants, these cues include light, temperature, and sugar levels[6,7,8]. (Arabidopsis), one loop, called the morning loop, starts with the light induction of CIRCADIAN CLOCK ASSOCIATED1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) at dawn. Most research to date on plant circadian rhythms has been done under controlled conditions, inside a growth room or growth chamber. Two plant species have had their rhythmic transcripts identified in field conditions: rice and pineapple[21,22,23,24] To better understand how the plant circadian clock regulates transcription under natural conditions in different organs, we measured transcription in three organs of field-grown sugarcane grown during the day. We found that the rhythmic transcripts of the L1, I1, and I5 are widely specialized and likely to respond differently to environmental cues
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