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GTPases are a large family of hydrolase enzymes that bind to the nucleotide guanosine triphosphate (GTP) and hydrolyze it to guanosine diphosphate (GDP). The GTP binding and hydrolysis takes place in the highly conserved P-loop "G domain", a protein domain common to many GTPases.
G proteins, also known as guanine nucleotide-binding proteins, are a family of proteins that act as molecular switches inside cells, and are involved in transmitting signals from a variety of stimuli outside a cell to its interior. Their activity is regulated by factors that control their ability to bind to and hydrolyze guanosine triphosphate (GTP) to guanosine diphosphate (GDP). When they are bound to GTP, they are 'on', and, when they are bound to GDP, they are 'off'. G proteins belong to the larger group of enzymes called GTPases.
A hormone is a class of signaling molecules in multicellular organisms that are sent to distant organs by complex biological processes to regulate physiology and behavior. Hormones are required for the correct development of animals, plants and fungi. Due to the broad definition of a hormone, numerous kinds of molecules can be classified as hormones. Among the substances that can be considered hormones, are eicosanoids, steroids, amino acid derivatives, protein or peptides, and gases.
Signal transduction is the process by which a chemical or physical signal is transmitted through a cell as a series of molecular events, most commonly protein phosphorylation catalyzed by protein kinases, which ultimately results in a cellular response. Proteins responsible for detecting stimuli are generally termed receptors, although in some cases the term sensor is used. The changes elicited by ligand binding in a receptor give rise to a biochemical cascade, which is a chain of biochemical events known as a signaling pathway.
Auxins are a class of plant hormones with some morphogen-like characteristics. Auxins play a cardinal role in coordination of many growth and behavioral processes in plant life cycles and are essential for plant body development. The Dutch biologist Frits Warmolt Went first described auxins and their role in plant growth in the 1920s. Kenneth V. Thimann became the first to isolate one of these phytohormones and to determine its chemical structure as indole-3-acetic acid (IAA). Went and Thimann co-authored a book on plant hormones, Phytohormones, in 1937.
Cytokinins (CK) are a class of plant hormones that promote cell division, or cytokinesis, in plant roots and shoots. They are involved primarily in cell growth and differentiation, but also affect apical dominance, axillary bud growth, and leaf senescence.
Gibberellins (GAs) are plant hormones that regulate various developmental processes, including stem elongation, germination, dormancy, flowering, flower development, and leaf and fruit senescence. GAs are one of the longest-known classes of plant hormone. It is thought that the selective breeding of crop strains that were deficient in GA synthesis was one of the key drivers of the "green revolution" in the 1960s, a revolution that is credited to have saved over a billion lives worldwide.
Gravitropism is a coordinated process of differential growth by a plant in response to gravity pulling on it. It also occurs in fungi. Gravity can be either "artificial gravity" or natural gravity. It is a general feature of all higher and many lower plants as well as other organisms. Charles Darwin was one of the first to scientifically document that roots show positive gravitropism and stems show negative gravitropism. That is, roots grow in the direction of gravitational pull and stems grow in the opposite direction. This behavior can be easily demonstrated with any potted plant. When laid onto its side, the growing parts of the stem begin to display negative gravitropism, growing upwards. Herbaceous (non-woody) stems are capable of a degree of actual bending, but most of the redirected movement occurs as a consequence of root or stem growth outside. The mechanism is based on the Cholodny–Went model which was proposed in 1927, and has since been modified. Although the model has been criticized and continues to be refined, it has largely stood the test of time.
Shade avoidance is a set of responses that plants display when they are subjected to the shade of another plant. It often includes elongation, altered flowering time, increased apical dominance and altered partitioning of resources. This set of responses is collectively called the shade-avoidance syndrome (SAS).
A primordium in embryology, is an organ or tissue in its earliest recognizable stage of development. Cells of the primordium are called primordial cells. A primordium is the simplest set of cells capable of triggering growth of the would-be organ and the initial foundation from which an organ is able to grow. In flowering plants, a floral primordium gives rise to a flower.
G protein-coupled receptor kinases are a family of protein kinases within the AGC group of kinases. Like all AGC kinases, GRKs use ATP to add phosphate to Serine and Threonine residues in specific locations of target proteins. In particular, GRKs phosphorylate intracellular domains of G protein-coupled receptors (GPCRs). GRKs function in tandem with arrestin proteins to regulate the sensitivity of GPCRs for stimulating downstream heterotrimeric G protein and G protein-independent signaling pathways.
Heterotrimeric G protein, also sometimes referred to as the "large" G proteins are membrane-associated G proteins that form a heterotrimeric complex. The biggest non-structural difference between heterotrimeric and monomeric G protein is that heterotrimeric proteins bind to their cell-surface receptors, called G protein-coupled receptors, directly. These G proteins are made up of alpha (α), beta (β) and gamma (γ) subunits. The alpha subunit is attached to either a GTP or GDP, which serves as an on-off switch for the activation of G-protein.
G alpha subunits are one of the three types of subunit of guanine nucleotide binding proteins, which are membrane-associated, heterotrimeric G proteins.
Peptide signaling plays a significant role in various aspects of plant growth and development and specific receptors for various peptides have been identified as being membrane-localized receptor kinases, the largest family of receptor-like molecules in plants. Signaling peptides include members of the following protein families.
Guanine nucleotide-binding protein G(t) subunit alpha-3, also known as gustducin alpha-3 chain, is a protein subunit that in humans is encoded by the GNAT3 gene.
In biology, phototropism is the growth of an organism in response to a light stimulus. Phototropism is most often observed in plants, but can also occur in other organisms such as fungi. The cells on the plant that are farthest from the light contain a hormone called auxin that reacts when phototropism occurs. This causes the plant to have elongated cells on the furthest side from the light. Phototropism is one of the many plant tropisms, or movements, which respond to external stimuli. Growth towards a light source is called positive phototropism, while growth away from light is called negative phototropism. Negative phototropism is not to be confused with skototropism, which is defined as the growth towards darkness, whereas negative phototropism can refer to either the growth away from a light source or towards the darkness. Most plant shoots exhibit positive phototropism, and rearrange their chloroplasts in the leaves to maximize photosynthetic energy and promote growth. Some vine shoot tips exhibit negative phototropism, which allows them to grow towards dark, solid objects and climb them. The combination of phototropism and gravitropism allow plants to grow in the correct direction.
In molecular biology, the auxin binding protein family is a family of proteins which bind auxin. They are located in the lumen of the endoplasmic reticulum (ER). The primary structure of these proteins contains an N-terminal hydrophobic leader sequence of 30-40 amino acids, which could represent a signal for translocation of the protein to the ER. The mature protein comprises around 165 residues, and contains a number of potential N-glycosylation sites. In vitro transport studies have demonstrated co-translational glycosylation. Retention within the lumen of the ER correlates with an additional signal located at the C terminus, represented by the sequence Lys-Asp-Glu-Leu, known to be responsible for preventing secretion of proteins from the lumen of the ER in eukaryotic cells.
Feronia, also known as FER or protein Sirene, is a recognition receptor kinase found in plants. FER plays a significant part in the plant immune system as a receptor kinase which assists in immune signaling within plants, plant growth, and plant reproduction. FER is regulated by the Rapid Alkalinization Factor (RALF). FER regulates growth in normal environments but it is most beneficial in stressful environments as it helps to initiate immune signaling. FER can also play a role in reproduction in plants by participating in the communication between the female and male cells. FER is found in and can be studied in the organism Arabidopsis thaliana.
Niko Geldner is a German-Swiss biologist specialised in the study of Plant Cell and Developmental Biology. He is a full professor and the director of the plant cell biology laboratory at the University of Lausanne.
Ethylene signaling pathway is a signal transduction in plant cells to regulate important growth and developmental processes. Acting as a plant hormone, the gas ethylene is responsible for promoting the germination of seeds, ripening of fruits, the opening of flowers, the abscission of leaves and stress responses. It is the simplest alkene gas and the first gaseous molecule discovered to function as a hormone.
References
- ↑ "New Distinguished professors honored at fall reception, 2013" https://college.unc.edu/2013/11/22/profs2013/
- ↑ "Past Presidents". American Society of Plant Biologists. Retrieved 30 May 2023.
- ↑ Jones, A.M., L.L. Melhado, T.-H.D. Ho, C.J. Pearce, and N.J. Leonard (1984) Azido Auxins: Photoaffinity labeling of auxin-binding proteins in maize coleoptile with tritiated 5-azidoindole-3- acetic acid. Plant Physiol 75:1111-1116
- ↑ Jones, A.M., M.A. Venis (1989) Photoaffinity labeling of auxin-binding proteins in maize. Proc. Natl. Acad. Sci. USA 86:6153-6156
- ↑ Ullah, H. Chen, J. G., Young, J., Im, K-H., Sussman, MR., Jones, AM (2001) Modulation of cell proliferation by heterotrimeric G-protein in Arabidopsis. Science 292: 2066-2069
- ↑ Jones, A. M. , Im, K-H., Savka, M., Wu, M-J., DeWitt, N.G., Shillito, R. Binns, A. (1998) Auxin-dependent cell expansion mediated by overexpressed auxin-binding protein 1. Science 282: 1114-1117.
- ↑ Chen, J, Ullah, H., Young, J.C., Sussman, M.R., Jones, A.M (2001) ABP1 is required for organized cell elongation and division in Arabidopsis embryogenesis. Genes and Development 15:902-911.
- ↑ Jones, A M (2001) Programmed cell death in development and defense. Plant Physiol. 125: 94-97
- ↑ Urano, D Chen, J-G Botella, JR and Jones AM (2013) Heterotrimeric G protein signaling in the plant kingdom. Open Biology Mar 27;3(3):120186. doi: 10.1098/rsob.120186