The Late Elongated Hypocotyl gene (LHY), is an oscillating gene found in plants that functions as part of their circadian clock. LHY encodes components of mutually regulatory negative feedback loops with Circadian Clock Associated 1 (CCA1) in which overexpression of either results in dampening of both of their expression. This negative feedback loop affects the rhythmicity of multiple outputs creating a daytime protein complex.[1] LHY was one of the first genes identified in the plant clock, along with TOC1 and CCA1. LHY and CCA1 have similar patterns of expression, which is capable of being induced by light.[2] Single loss-of-function mutants in both genes result in seemingly identical phenotypes, but LHY cannot fully rescue the rhythm when CCA1 is absent, indicating that they may only be partially functionally redundant. Under constant light conditions, CCA1 and LHY double loss-of-function mutants fail to maintain rhythms in clock-controlled RNAs.[3]
The circadian clock in plants has completely different components to those in the animal, fungus or bacterial clocks. The plant clock does have a conceptual similarity to the animal clock in that it consists of a series of interlocking transcriptional feedback loops. The genes involved in the clock show their peak expression at a fixed time of day. The peak expression of the CCA1 and LHY genes occurs at dawn, and the peak expression of the TOC1 gene occurs roughly at dusk. CCA1/LHY and TOC1 proteins repress the expression of each others genes. The result is that as CCA1/LHY protein levels start to reduce after dawn, it releases the repression on the TOC1 gene, allowing TOC1 expression and TOC1 protein levels to increase. As TOC1 protein levels increase, it further suppresses the expression of the CCA1 and LHY genes. The opposite of this sequence occurs overnight to re-establish the peak expression of CCA1 and LHY genes at dawn.
CCA1 is generally a more significant component of this oscillator. Light induces its transcription, and mRNA levels peak at dawn along with LHY.[4] CCA1 and LHY associate to inhibit transcription of the Evening Complex (EC) proteins: ELF4, ELF3 and LUX, which suppresses their accumulation until dusk when LHY and CCA1 protein levels are at their lowest. Four primary pseudo-response regulator proteins (PRR9, PRR7, PRR5 and TOC1/PRR1) perform the majority of interactions with other proteins within the circadian oscillator, and another (PRR3) that has limited function. These genes are all paralogs of each other, and all repress the transcription of CCA1 and LHY at various times throughout the day.
Plants that have lost function of LHY and CCA1 lose the ability to stably maintain circadian rhythm and other output phenomena. In one study, such plants showed photoperiod- insensitive early flowering under long- day (16 hours of light/ 8 hours of dark) conditions and short day (8 hours of light, 16 hours of dark conditions), and arrhythmicity under constant light conditions.[5] However they retain some circadian function in light/dark cycles, showing that Arabidopsis circadian clock is not completely dependent on CCA1 and LHY activity.[6] Plants with non-functioning LHY and CCA1 show a wavy leaf phenotype in constant light conditions. Mutants also have increased vascular pattern complexity in their leaves, with more areoles, branch points and free ends than wild-type Arabidopsis.[5]
The function of LHY was initially demonstrated by a group in the Steve Kay lab, including Andrew Millar.[7]
^Lu, S. X., and S. M., Andronis. "CIRCADIAN CLOCK ASSOCIATED1 and LATE ELONGATED HYPOCOTYL Function Synergistically in the Circadian Clock of Arabidopsis" Plant Physiology Vol. 150. (2009): 834–843.
^Green, RM. "Loss of the circadian clock-associated protein 1 in Arabidopsis results in altered clock-regulated gene expression." Proc Natl Acad Sci U S A. Vol. 96. (1999)
^Kangisser, Shlomit, Esther Yakir, and Rachel M. Green. "Proteasomal regulation of the CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) stability is part of the complex control of CCA1" Plant Signaling & Behavior Vol. Volume 8, Issue 3. (2013)
^ abAihara, Kohei, and Satoshi Naramoto. "Increase in vascular pattern complexity caused by mutations in LHY and CCA1 in Arabidopsis thaliana under continuous light" Plant Biotechnology Vol. 31. (2014): 43-47.
^Alabadi, David, and Marcelo J. Yanovsky. "Critical Role for CCA1 and LHY in Maintaining Circadian Rhythmicity in Arabidopsis" Current Biology Vol. 12(9). (2002): 757–761.
The LateElongatedHypocotyl gene (LHY), is an oscillating gene found in plants that functions as part of their circadian clock. LHY encodes components...
loop consists of CCA1 (Circadian and Clock-Associated 1) and LHY (LateElongatedHypocotyl), which encode closely related MYB transcription factors that regulate...
induces its transcription, and mRNA levels peak at dawn along with LateElongatedHypocotyl (LHY). CCA1 and LHY associate to inhibit transcription of the Evening...
Arabidopsis thaliana in 2001 and included two MYB transcription factors, LATEELONGATEDHYPOCOTYL (LHY), CIRCADIAN CLOCK ASSOCIATED 1 (CCA1), and TIMING OF CAB EXPRESSION...
below for more information. LHY – The LHY gene, also known as the LateElongatedHypocotyl gene, is a gene found in plants that encodes components of mutually...
are pushed above ground. The hypocotylelongates while the epicotyl remains the same in length. In this way, the hypocotyl pushes the cotyledon upward...
morning clock factors CIRCADIAN CLOCK ASSOCIATED 1 (CCA1) and LATEELONGATEDHYPOCOTYL (LHY) to specifically inhibit the transcription of evening-expressed...
identified in plants, CRY1 and CRY2, which regulate the inhibition of hypocotyl elongation in response to blue light. Cryptochromes control stem elongation...
Joanna Putterill, Isabelle A. Carré, and George Coupland. "The lateelongatedhypocotyl mutation of Arabidopsis disrupts circadian rhythms and the photoperiodic...
The EE may be bound by Circadian Clock Associated 1 (CCA1) and LateElongatedHypocotyl (LHY) proteins to suppress expression of LUX. The LUX ARRHYTHMO...
primordia at the apex, and will become the shoot upon germination. The hypocotyl, the embryonic axis below the point of attachment of the cotyledon(s)...
[citation needed] Stem tubers generally start off as enlargements of the hypocotyl section of a seedling, but sometimes also include the first node or two...
germination takes place above the ground. In epigeal germination, the hypocotylelongates and forms a hook, pulling rather than pushing the cotyledons and...
between the grafted tissues. Research conducted in Arabidopsis thaliana hypocotyls has shown that the connection of phloem takes place after three days of...
catalyzed in the hypocotyls of juvenile sunflower seedlings while heliotropic bending in the shoot apex does not start occurring until the later developmental...
embryo has five major components including the shoot apical meristem, hypocotyl, root meristem, root cap, and cotyledons. Unlike the embryonic development...
be distorted if the infection is intense. Black and elongated lesions can girdle the hypocotyls and kill seedlings. On the leaves, scattered small dark-green...
activity in the lateral root primordium and the transition zone between the hypocotyl and the root. Seedlings were harvested every day for a week and stained...
as well as growing conditions influence the extent of branching. The elongated and serrated leaves reach lengths of 10–15 cm (3.9–5.9 in) and widths...
central circuit of interacting transcription factors in the Arabidopsis hypocotyl". eLife. 3. doi:10.7554/eLife.03031. PMC 4075450. PMID 24867218. Marín-de...
observed as soon as the seedling has emerged. Above ground, the hypocotylelongates as the plant reaches upward for light. Underground, the roots grow...
epigeal emergence, in which the hypocotylelongates and becomes arched in the soil. As the hypocotyl continues to elongate, it pulls the cotyledons upward...
develop from nodes of prostrate stems of some plant species, or from the hypocotyl rather than from the radicle of a germinating monocotyledon. adventive...
inhibits COP1 activity and allows transcription factors such as ELONGATEDHYPOCOTYL 5 (HY5) to accumulate. HY5 is a basic leucine zipper (bZIP) factor...
short primary root and hypocotyl develop – the cotyledon is raised above the soil surface on a long petiole. From the hypocotyl and upper part of the primary...
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