Loss of diel circadian clock gene cycling is a part of grape berry ripening

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Diel cycles of gene expression are thought to adapt plants to 24-h changes in environmental conditions. The circadian clock contributes to this process, but less is known about cir- cadian programs in developing reproductive organs. While model plants and controlled conditions have contributed greatly to our knowledge of circadian clock function, there is a need to better understand its role in crop plants under field conditions with fluctuating light and temperature. In this study, we investigated changes in the circadian clock dur- ing the development of grape berries of Vitis vinifera L. We found that the transcripts of circadian clock homologs had high-amplitude oscillations prior to, but not during, ripen- ing. As ripening progressed, the amplitude and rhythmic- ity of the diel oscillations decreased until most transcripts tested had no significant fluctuation over the 24-h cycle. Despite this loss of rhythmicity, the majority of circadian clock genes investigated were expressed at or near their abun- dance at the nadir of their pre-ripening oscillation although the berries remained transcriptionally active. From this, it can be concluded that cycling of the canonical circadian clock appears unnecessary for berry ripening. Our data sug- gest that changes in circadian clock dynamics during repro- ductive organ development may have important functional consequences.