Emerging seedlings respond to environmental conditions such as light and temperature to optimize their establishment. Seedlings grow initially through elongation of the hypocotyl, which is regulated by signaling pathways that integrate environmental information to regulate seedling development. The hypocotyls of Arabidopsis (Arabidopsis thaliana) also elongate in response to sucrose. Here, we investigated the role of cellular sugar-sensing mechanisms in the elongation of hypocotyls in response to Suc. We focused upon the role of SnRK1, which is a sugar-signaling hub that regulates metabolism and transcription in response to cellular energy status. We also investigated the role of TPS1, which synthesizes the signaling sugar trehalose-6-P that is proposed to regulate SnRK1 activity. Under light/dark cycles, we found that Suc-induced hypocotyl elongation did not occur in tps1 mutants and overexpressors of KIN10 (AKIN10/SnRK1.1), a catalytic subunit of SnRK1. We demonstrate that the magnitude of Suc-induced hypocotyl elongation depends on the day length and light intensity. We identified roles for auxin and gibberellin signaling in Suc-induced hypocotyl elongation under short photoperiods. We found that Suc-induced hypocotyl elongation under light/dark cycles does not involve another proposed sugar sensor, HEXOKINASE1, or the circadian oscillator. Our study identifies novel roles for KIN10 and TPS1 in mediating a signal that underlies Suc-induced hypocotyl elongation in light/dark cycles.
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© 2015 Kusakina et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Circadian clocks regulate many aspects of plant physiology and development that contribute to essential agronomic traits. Circadian clocks contain transcriptional feedback loops that are thought to generate circadian timing. There is considerable similarity in the genes that comprise the transcriptional and translational feedback loops ofthe circadian clock in the plant Kingdom. Functional characterisation of circadian clock genes has been restricted to a few model species. Here we provide a functional characterisation of the Hordeum vulgare (barley) circadian clock genes Hv CIRCADIAN CLOCK ASSOCIATED 1(HvCCA1) and Hv PHOTOPERIODH1, which are respectively most similar to Arabidopsis thaliana CIRCADIAN CLOCK ASSOCIATED 1 (AtCCA1) and PSEUDO RESPONSE REGULATOR 7 (AtPRR7). This provides insight into the circadian regulation of one of the major crop species of Northern Europe. Through a combination of physiological assays of circadian rhythms in barley and heterologous expression in wild type and mutant strains of A. thaliana we demonstrate that HvCCA1 has a conserved function to AtCCA1. We find that Hv PHOTOPERIOD H1 has AtPRR7-like functionality in A. thaliana and that the effects of the Hv photoperiod h1 mutation on photoperiodism and circadian rhythms are genetically separable.
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The circadian clock is an endogenous 24h oscillator regulating many critical biological processes in plants. One of the key characteristics of the circadian clock is that it is buffered against temperature, maintaining an approximately 24h rhythm over a broad physiological temperature range. Here, we tested temperature-buffering capacity of the circadian clock across a number of Arabidopsis accessions using several circadian clock reporters: leaf movement, CCA1:LUC and LHY:LUC. We found that leaf movement was the best temperature buffered circadian output. On the other hand, when temperature increases, circadian rhythms of CCA1 and LHY transcription shorten considerably across all accessions, indicating that the clock driving expression of CCA1 and LHY is not perfectly buffered. This feature might be crucial to plants growing in a constantly changing environment, and here, we provide insight into the importance of period shortening to plant growth performance and the benefits of a flexible clock.© 2013 The Authors.
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Correct circadian regulation increases plant productivity, and photosynthesis is circadian-regulated. Here, we discuss the regulatory basis for the circadian control of photosynthesis. We discuss ca ndidate mechanisms underpinning circadian oscillations of light harvesting and consider how the circadian clock modulates CO 2 fixation by Rubisco. We show that new techniques may provide a platform to better understand the signalling pathways that couple the circadian clock with the photosynthetic apparatus. Finally, we discuss how understanding circadian regulation in model systems is underpinning research into the impact of circadian regulation in crop species.© 2013 Springer Science+Business Media Dordrecht.
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