The work being carried out in our laboratory is aimed at understanding several aspects of the circadian system of plants.
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1. Post translational regulation of CCA1 and LHY CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATE ELONGATED HYPOCOTYL (LHY) are single MYB transcription factors and key components of the plant oscillator. Despite the fact that CCA1 and LHY have been found in representatives of all groups in the plant kingdom, their regulation, particularly at the post-translational level, is still poorly understood. Our research objectives are to identify and characterize CCA1 and LHY interacting proteins (the CCA1/LHY interactome), to study their role in controlling CCA1/LHY activity and the circadian oscillator. |
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2. Circadian regulation of stomata Stomata allow gas exchange between the interior of the plant and its environment. Opening and closing of the stomata is driven by changes in the turgor pressure of the guard cells and is regulated by the circadian system. We have developed techniques that allow us to study circadian rhythms in individual cells and shown that Arabidopsis stomatal guard cells have circadian systems that are significantly different from those of the surrounding leaf cells. We are currently exploring the mechanisms and significance of the unique stomatal guard cell circadian clock. |
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3. The adaptive advantages of circadian systems
It has been suggested that having an endogenous circadian system enables an organism to anticipate periodic environmental changes and adapt its physiological and developmental states accordingly, thus conferring a fitness advantage. However there is, to date, only limited evidence supporting the assumption that having a circadian system can increase fitness and therefore be adaptive.
It has been suggested that having an endogenous circadian system enables an organism to anticipate periodic environmental changes and adapt its physiological and developmental states accordingly, thus conferring a fitness advantage. However there is, to date, only limited evidence supporting the assumption that having a circadian system can increase fitness and therefore be adaptive.
Arabidopsis
We are using an evolutionary approach to examine the adaptive significance of a functional circadian system. By crossing Arabidopsis plants containing mutations that cause changes in circadian rhythms, we have created a population of plants with genetic variance for circadian rhythmicity. We showed that plants with endogenous rhythms that more closely match the environmental T-cycle are fitter, producing relatively more viable offspring in the F3 population. Thus, having a circadian clock that matches with the environment is adaptive in Arabidopsis.
We are using an evolutionary approach to examine the adaptive significance of a functional circadian system. By crossing Arabidopsis plants containing mutations that cause changes in circadian rhythms, we have created a population of plants with genetic variance for circadian rhythmicity. We showed that plants with endogenous rhythms that more closely match the environmental T-cycle are fitter, producing relatively more viable offspring in the F3 population. Thus, having a circadian clock that matches with the environment is adaptive in Arabidopsis.
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Barley
We are also interested in understanding the circadian system in food crops. In a collaboration with Dr. Seth Davis and Dr Maria Von Korff (Max Planck Institute for Plant Breeding Research, Cologne), Dr. Munqez Shtaya (An-Najah University, Nablus), Dr. Eyal Fridman (Vulcani Institute) and Dr. Moshe Kiflaw (Ben Gurion University) we have shown that there is variability for circadian traits in wild barley lines. We are analyzing circadian rhythms in populations of wild barley from a widely different eco-geographical locations in the Southern Levant part of the Fertile Crescent, an area with a high proportion of the total genetic variation of wild barley to determine how different environmental parameters may exert selection on circadian rhythms. |
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Pines
By contrast with angiosperms, the circadian system in gymnosperms is still poorly understood. Circadian genes have been identified in several species including Norway spruce, Douglas-fir (Pseudotsuga menziesii) and Japanese cedar (Cryptomeria japonica) and their expression shown to oscillate in diel (daily light/dark) conditions. Surprisingly though, a study on Norway spruce, found that the trees rapidly became arrhythmic in constant conditions. It is possible that gymnosperms may have less complex oscillators than those of angiosperms resulting in rapidly dampened timers that are less resilient to outside noise. However, given that circadian rhythms are almost ubiquitous amongst eukaryotic organisms, it seems unlikely that gymnosperms are completely arrhythmic. We are starting to test whether there are conditions in which pine trees may show circadian rhythms. |
