Elaine M. Tobin | |
---|---|
Born | Elaine Munsey December 23, 1944 |
Education | Oberlin College, Harvard University |
Known for | Circadian clock in plants |
Partner(s) | Allan J. Tobin, [1] J. Philip Thornber [2] |
Scientific career | |
Institutions | University of California, Los Angeles |
Elaine Munsey Tobin (born December 23, 1944, Louisville, Kentucky) [3] is a professor of molecular, cell, and developmental biology at the University of California, Los Angeles (UCLA). [4] Tobin is recognized as a Pioneer Member of the American Society of Plant Biologists (ASPB). [5]
Tobin studies how phytochrome photoreceptors interact with the circadian clock in plants, in particular circadian oscillator proteins and the ways in which feedback loops are regulated through gene expression. [4] Tobin identified one of the first two components of the circadian clock in plants, the dawn expressed transcription factor CCA1. [6] [7] Her lab also showed that CCA1 was necessary for phytochrome response in Arabidopsis thaliana [8] and that one type of regulation involves the phosphorylation of CCA1 by the protein kinase CK2. [7] [9]
Elaine Munsey was born in Louisville, Kentucky on December 23, 1944. [3] Her family had immigrated from Odessa and Lithuania. [1] Munsey's interests included science, mathematics and basketball. She attended the 1960 Democratic National Convention as a volunteer working for Adlai Stevenson II's presidential campaign. While in high school, she also participated in civil rights marches and heard Martin Luther King Jr. speak in Louisville. [1] She graduated from Seneca High School in Louisville in 1962. [10]
She earned her Bachelor of Arts degree from Oberlin College in 1966, majoring in chemistry. [3] After graduation, she spent a summer as an Appalachian Volunteer, working as a community organizer in Wolfe County, Kentucky, as part of Lyndon Johnson's War on Poverty. [1]
She was accepted into the Biology Department at Stanford. She took classes in plant physiology with Winslow Briggs, worked in his laboratory, and transferred to Harvard when Briggs took a professorship there. In 1968 she married Allan J. Tobin. They spent a year at the Weizmann Institute of Science in Israel, where Elaine Tobin worked with plant geneticist Ezra Galun. [1] After returning to North America, she completed her Ph.D. in Biology at Harvard University in 1972. [3] She later married J. Philip Thornber. [2]
In 1973 Tobin went to Brandeis University, where she did postdoctoral work with Attila Klein, on the influence of light on the development of plants. In 1975 she was hired in the Biology Department at University of California, Los Angeles (UCLA). Support was sparse, but she was able to get funding for basic research on plants from the National Institutes of Health (NIH). She was able to obtain laboratory space previously used by retiring professor Karl Hamner. [11]
As a student with Winslow Briggs, Tobin had been introduced to the effects of phytochrome on flowering and to the work of Karl Hamner on circadian rhythms and flowering. [1] Circadian rhythms in plants help them to coordinate with external light/dark cycles. Anticipating dawn, dusk, and seasonal day length allows plants to more effectively regulate both daily and seasonal activities, including the movement of leaves and petals, the opening of stomata for photosynthesis, stem growth, and the development of flowers. [12]
Tobin first used Lemna gibba (duckweed) and later Arabidopsis thaliana (cress) as model plant systems to study light regulation of gene expression in plants, examining interactions between phytochrome photoreceptors, genes, and circadian rhythms. [13] Tobin was able to isolate poly(A) RNA from duckweed, expose slab gels to x-ray film, and show that while some mRNAs decreased in light, others increased. [13]
In 1984, postdoctoral student Jane Silverthorne and Tobin demonstrated that photoreceptors in plants could affect the transcription of specific genes. Light-harvesting chlorophyll a/b-binding (LHCB) protein sequences from Lemna gibba were low in darkness but could be rapidly and reversibly restored by light exposure. [13] Tobin's group also demonstrated phytochrome regulation of LHCB proteins (also known as cab genes) in Arabidopsis. [13] [14] [15] By growing duckweed heterotrophically in the dark, and exposing it briefly to red and far-red light, Tobin demonstrated the effects of phytochromes on plant growth and transcription in rcbs genes. [16]
In a series of experiments beginning in 1993, Tobin's lab described DNA-binding activity with an affinity for LHCB in plant cells. Using a DNA fragment, they screened the Arabidopsis expression library, and cloned a protein with relevant binding activity, which they named CCA1. They showed that Circadian Clock Associated 1 (CCA1) was necessary for phytochrome response in Arabidopsis thaliana. [8] Reports on the activity of CCA1 and a closely related gene (LHY) from George Coupland were submitted together to Cell in 1998. [1] The two genes were the first two components of the circadian clock or central oscillator mechanism in plants to be identified. [6] [7] Among many other studies of the regulation and function of CCA1, Tobin has determined that one method of clock regulation involves the phosphorylation of CCA1 by the protein kinase CK2. [17]
Elaine M. Tobin retired from teaching in 2014. [1]
A circadian rhythm, or circadian cycle, is a natural oscillation that repeats roughly every 24 hours. Circadian rhythms can refer to any process that originates within an organism and responds to the environment. Circadian rhythms are regulated by a circadian clock whose primary function is to rhythmically co-ordinate biological processes so they occur at the correct time to maximise the fitness of an individual. Circadian rhythms have been widely observed in animals, plants, fungi and cyanobacteria and there is evidence that they evolved independently in each of these kingdoms of life.
A circadian clock, or circadian oscillator, also known as one’s internal alarm clock is a biochemical oscillator that cycles with a stable phase and is synchronized with solar time.
Cryptochromes are a class of flavoproteins found in plants and animals that are sensitive to blue light. They are involved in the circadian rhythms and the sensing of magnetic fields in a number of species. The name cryptochrome was proposed as a portmanteau combining the chromatic nature of the photoreceptor, and the cryptogamic organisms on which many blue-light studies were carried out.
Florigens are proteins capable of inducing flowering time in Angiosperms. The prototypical florigen is encoded by the FT gene and its orthologs in Arabidopsis and other plants. Florigens are produced in the leaves, and act in the shoot apical meristem of buds and growing tips.
The repressilator is a genetic regulatory network consisting of at least one feedback loop with at least three genes, each expressing a protein that represses the next gene in the loop. In biological research, repressilators have been used to build cellular models and understand cell function. There are both artificial and naturally-occurring repressilators. Recently, the naturally-occurring repressilator clock gene circuit in Arabidopsis thaliana and mammalian systems have been studied.
In molecular biology, an oscillating gene is a gene that is expressed in a rhythmic pattern or in periodic cycles. Oscillating genes are usually circadian and can be identified by periodic changes in the state of an organism. Circadian rhythms, controlled by oscillating genes, have a period of approximately 24 hours. For example, plant leaves opening and closing at different times of the day or the sleep-wake schedule of animals can all include circadian rhythms. Other periods are also possible, such as 29.5 days resulting from circalunar rhythms or 12.4 hours resulting from circatidal rhythms. Oscillating genes include both core clock component genes and output genes. A core clock component gene is a gene necessary for to the pacemaker. However, an output oscillating gene, such as the AVP gene, is rhythmic but not necessary to the pacemaker.
The frequency (frq) gene encodes the protein frequency (FRQ) that functions in the Neurospora crassa circadian clock. The FRQ protein plays a key role in circadian oscillator, serving to nucleate the negative element complex in the auto regulatory transcription-translation negative feedback-loop (TTFL) that is responsible for circadian rhythms in N. crassa. Similar rhythms are found in mammals, Drosophila and cyanobacteria. Recently, FRQ homologs have been identified in several other species of fungi. Expression of frq is controlled by the two transcription factors white collar-1 (WC-1) and white collar-2 (WC-2) that act together as the White Collar Complex (WCC) and serve as the positive element in the TTFL. Expression of frq can also be induced through light exposure in a WCC dependent manner. Forward genetics has generated many alleles of frq resulting in strains whose circadian clocks vary in period length.
Timing of CAB expression 1 is a protein that in Arabidopsis thaliana is encoded by the TOC1 gene. TOC1 is also known as two-component response regulator-like APRR1.
Circadian Clock Associated 1 (CCA1) is a gene that is central to the circadian oscillator of angiosperms. It was first identified in Arabidopsis thaliana in 1993. CCA1 interacts with LHY and TOC1 to form the core of the oscillator system. CCA1 expression peaks at dawn. Loss of CCA1 function leads to a shortened period in the expression of many other genes.
Steve A. Kay is a British-born chronobiologist who mainly works in the United States. Dr. Kay has pioneered methods to monitor daily gene expression in real time and characterized circadian gene expression in plants, flies and mammals. In 2014, Steve Kay celebrated 25 years of successful chronobiology research at the Kaylab 25 Symposium, joined by over one hundred researchers with whom he had collaborated with or mentored. Dr. Kay, a member of the National Academy of Sciences, U.S.A., briefly served as president of The Scripps Research Institute. and is currently a professor at the University of Southern California. He also served on the Life Sciences jury for the Infosys Prize in 2011.
LUX or Phytoclock1 (PCL1) is a gene that codes for LUX ARRHYTHMO, a protein necessary for circadian rhythms in Arabidopsis thaliana. LUX protein associates with Early Flowering 3 (ELF3) and Early Flowering 4 (ELF4) to form the Evening Complex (EC), a core component of the Arabidopsis repressilator model of the plant circadian clock. The LUX protein functions as a transcription factor that negatively regulates Pseudo-Response Regulator 9 (PRR9), a core gene of the Midday Complex, another component of the Arabidopsis repressilator model. LUX is also associated with circadian control of hypocotyl growth factor genes PHYTOCHROME INTERACTING FACTOR 4 (PIF4) and PHYTOCHROME INTERACTING FACTOR 5 (PIF5).
Andrew John McWalter Millar, FRS, FRSE is a Scottish chronobiologist, systems biologist, and molecular geneticist. Millar is a professor at The University of Edinburgh and also serves as its chair of systems biology. Millar is best known for his contributions to plant circadian biology; in the Steve Kay lab, he pioneered the use of luciferase imaging to identify circadian mutants in Arabidopsis. Additionally, Millar's group has implicated the ELF4 gene in circadian control of flowering time in Arabidopsis. Millar was elected to the Royal Society in 2012 and the Royal Society of Edinburgh in 2013.
Pseudo-response regulator (PRR) refers to a group of genes that regulate the circadian oscillator in plants. There are four primary PRR proteins that 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 Circadian Clock Associated 1 (CCA1) and Late Elongated Hypocotyl (LHY) at various times throughout the day. The expression of PRR9, PRR7, PRR5 and TOC1/PRR1 peak around morning, mid-day, afternoon and evening, respectively. As a group, these genes are one part of the three-part repressilator system that governs the biological clock in plants.
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. 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. 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.
Transcription-translation feedback loop (TTFL) is a cellular model for explaining circadian rhythms in behavior and physiology. Widely conserved across species, the TTFL is auto-regulatory, in which transcription of clock genes is regulated by their own protein products.
Carla Beth Green is an American neurobiologist and chronobiologist. She is a professor in the Department of Neuroscience and a Distinguished Scholar in Neuroscience at the University of Texas Southwestern Medical Center. She is the former president of the Society for Research on Biological Rhythms (SRBR), as well as a satellite member of the International Institute for Integrative Sleep Medicine at the University of Tsukuba in Japan.
Dmitri Nusinow is an American chronobiologist who studies plant circadian rhythms. He was born on November 7, 1976, in Inglewood, California. He currently resides in St. Louis, and his research focus includes a combination of molecular, biochemical, genetic, genomic, and proteomic tools to discover the molecular connections between signaling networks, circadian oscillators, and specific outputs. By combining these methods, he hopes to apply the knowledge elucidated from the Arabidopsis model to other plant species.
EARLY FLOWERING 3 (ELF3) is a plant-specific gene that encodes the hydroxyproline-rich glycoprotein and is required for the function of the circadian clock. ELF3 is one of the three components that make up the Evening Complex (EC) within the plant circadian clock, in which all three components reach peak gene expression and protein levels at dusk. ELF3 serves as a scaffold to bind EARLY FLOWERING 4 (ELF4) and LUX ARRHYTHMO (LUX), two other components of the EC, and functions to control photoperiod sensitivity in plants. ELF3 also plays an important role in temperature and light input within plants for circadian clock entrainment. Additionally, it plays roles in light and temperature signaling that are independent from its role in the EC.
The chlorophyll a/b-binding protein gene, otherwise known as the CAB gene, is one of the most thoroughly characterized clock-regulated genes in plants. There are a variety of CAB proteins that are derived from this gene family. Studies on Arabidopsis plants have shed light on the mechanisms of biological clocks under the regulation of CAB genes. Dr. Steve Kay discovered that CAB was regulated by a circadian clock, which switched the gene on in the morning and off in the late afternoon. The genes code for proteins that associate with chlorophyll and xanthophylls. This association aids the absorption of sunlight, which transfers energy to photosystem II to drive photosynthetic electron transport.
Stacey Harmer is a chronobiologist whose work centers on the study of circadian rhythms in plants. Her research focuses on the molecular workings of the plant circadian clock and its influences on plant behaviors and physiology. She is a professor in the Department of Plant Biology at the University of California, Davis.