XAP5 CIRCADIAN TIMEKEEPER regulates ethylene responses in aerial tissues of Arabidopsis

Department of Plant Biology, College of Biological Sciences, University of California, Davis, California 95616, USA.
Plant physiology (Impact Factor: 6.84). 02/2011; 155(2):988-99. DOI: 10.1104/pp.110.164277
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The phytohormone ethylene differentially regulates plant architecture and growth in both a light- and nutrient-dependent fashion. The modulation of plant development by ethylene in response to both external and internal signals can also generate tissue-specific differential responses. Here, we report that XAP5 CIRCADIAN TIMEKEEPER (XCT) is involved in blue light-dependent ethylene responses in the aerial tissues of Arabidopsis (Arabidopsis thaliana) seedlings. XCT was first identified as a circadian clock mutant with a short free-running period. The xct mutation also causes sugar-specific hypocotyl growth defects, in which mutants are short in blue light when grown on a sucrose-rich medium but tall when grown on sucrose-deficient medium. Our data suggest that the hypocotyl defects in blue light are not directly caused by defects in clock or light signaling but rather by enhanced ethylene responses. In blue light, xct mutants have a more active ethylene response pathway and exhibit growth phenotypes similar to the constitutive ethylene signaling mutant constitutive triple response1 (ctr1). xct mutants also have reduced ethylene emission, analogous to plants that have lost CTR1 function. Genetic analysis suggests that XCT negatively regulates ethylene responses downstream of ETHYLENE-INSENSITIVE3 in aerial tissues. However, XCT is not required for all ethylene-mediated processes, such as the inhibition of root growth. Thus, XCT acts downstream of a major transcriptional regulator in an organ-specific manner, playing an environment-dependent role in the regulation of plant growth.

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Available from: Filip Vandenbussche, Mar 19, 2014
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    • "e to ethylene emissions . Ethylene signaling components , such as EIN3 , also display a similar oscil - latory pattern of expression in response to light and sugar availability ( Yanagisawa et al . , 2003 ; Lee et al . , 2006 ) . XAP5 CIRCADIAN TIMEKEEPER ( XCT ) is also involved in blue light - dependent ethylene responses in Arabidopsis shoots ( Ellison et al . , 2011 ) . The expression of ABA - and JA - responsive genes also oscil - lates diurnally ( Mizuno and Yamashino , 2008 ) . The genes impli - cated in the synthesis of geranylgeranyl diphosphate ( GGDP ) , an intermediate metabolite in isoprenoids synthesis , which leads to the production of chlorophylls , carotenoids , tocopherols , ABA and G"
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    Frontiers in Plant Science 04/2015; 6:255. DOI:10.3389/fpls.2015.00255 · 3.95 Impact Factor
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    • "At2g21150 encodes a nuclear localized protein, XCT, that is highly conserved across species (Martin-Tryon and Harmer, 2008). XCT was first isolated from a genetic screen for mutants with altered circadian clock running (Martin-Tryon and Harmer, 2008) and later shown to be involved in ethylene signaling (Ellison et al., 2011). "
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    ABSTRACT: Small RNAs (sRNAs) play important regulatory roles in various aspects of plant biology. They are processed from double-stranded RNA precursors by Dicer-like (DCL) proteins. There are three major classes of sRNAs in Arabidopsis: DCL1-dependent microRNA (miRNA), DCL3-dependent heterochromatic siRNA (hc-siRNA) and DCL4-dependent trans-acting siRNA (ta-siRNA). We have previously isolated a mutant with compromised miRNA activity, cma33. Here we show CMA33 encodes a nuclear localized protein XCT (XAP5 CIRCADIAN TIMEKEEPER). The cma33/xct mutation led to reduced accumulation of not only miRNAs but also hc-siRNAs and ta-siRNAs. Intriguingly, we found that the expression of DCL1, DCL3 and DCL4, but not other genes in the sRNA biogenesis pathways, was decreased in cma33/xct. Consistent with this, the occupancy of Pol II at DCL1, DCL3 and DCL4 genes was reduced upon the loss of CMA33/XCT. Collectively, our data suggest that CMA33/XCT modulates sRNA production through regulating the transcription of DCLs. Copyright © 2015 The Author. Published by Elsevier Inc. All rights reserved.
    Molecular Plant 03/2015; 8(8). DOI:10.1016/j.molp.2015.03.002 · 6.34 Impact Factor
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    • "Accumulation was performed for 24 h starting on day 7. Measurements were performed as described in Ellison et al. (2011). Data presented are from at least three independent biological repeats (sealed container with c. 100 seedlings). "
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    ABSTRACT: The vegetative development of plants is strongly dependent on the action of phytohormones. For over a century, the effects of ethylene on plants have been studied, illustrating the profound impact of this gaseous hormone on plant growth, development and stress responses. Ethylene signaling is under tight self-control at various levels. Feedback regulation occurs on both biosynthesis and signaling. For its role in developmental processes, ethylene has a close and reciprocal relation with auxin, another major determinant of plant architecture. Here, we discuss, in view of novel findings mainly in the reference plant Arabidopsis, how ethylene is distributed and perceived throughout the plant at the organ, tissue and cellular levels, and reflect on how plants benefit from the complex interaction of ethylene and auxin, determining their shape. Furthermore, we elaborate on the implications of recent discoveries on the control of ethylene signaling.
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