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Results for “Signal Transduction/genetics/physiology”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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10 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2003

The ARG1-LIKE2 gene of Arabidopsis functions in a gravity signal transduction pathway that is genetically distinct from the PGM pathway

The arl2 mutants of Arabidopsis display altered root and hypocotyl gravitropism, whereas their inflorescence stems are fully gravitropic. Interestingly, mutant roots respond like the wild type to phytohormones and an inhibitor of polar auxin transport. Also, their cap columella cells accumulate starch similarly to wild-type cells, and mutant hypocotyls display strong phototropic responses to lateral light stimulation. The ARL2 gene encodes a DnaJ-like protein similar to ARG1, another protein previously implicated in gravity signal transduction in Arabidopsis seedlings. ARL2 is expressed at low levels in all organs of seedlings and plants. arl2-1 arg1-2 double mutant roots display kinetics of gravitropism similar to those of single mutants. However, double mutants carrying both arl2-1 and pgm-1 (a mutation in the starch-biosynthetic gene PHOSPHOGLUCOMUTASE) at the homozygous state display a more pronounced root gravitropic defect than the single mutants. On the other hand, seedlings with a null mutation in ARL1, a paralog of ARG1 and ARL2, behave similarly to the wild type in gravitropism and other related assays. Taken together, the results suggest that ARG1 and ARL2 function in the same gravity signal transduction pathway in the hypocotyl and root of Arabidopsis seedlings, distinct from the pathway involving PGM.

NASA Discipline Plant Biology↗
NASA NTRS2002

Mutations in the gravity persistence signal loci in Arabidopsis disrupt the perception and/or signal transduction of gravitropic stimuli

Gravity plays a fundamental role in plant growth and development, yet little is understood about the early events of gravitropism. To identify genes affected in the signal perception and/or transduction phase of the gravity response, a mutant screen was devised using cold treatment to delay the gravity response of inflorescence stems of Arabidopsis. Inflorescence stems of Arabidopsis show no response to gravistimulation at 4 degrees C for up to 3 h. However, when gravistimulated at 4 degrees C and then returned to vertical at room temperature (RT), stems bend in response to the previous, horizontal gravistimulation (H. Fukaki, H. Fujisawa, M. Tasaka [1996] Plant Physiology 110: 933-943). This indicates that gravity perception, but not the gravitropic response, occurs at 4 degrees C. Recessive mutations were identified at three loci using this cold effect on gravitropism to screen for gravity persistence signal (gps) mutants. All three mutants had an altered response after gravistimulation at 4 degrees C, yet had phenotypically normal responses to stimulations at RT. gps1-1 did not bend in response to the 4 degrees C gravity stimulus upon return to RT. gps2-1 responded to the 4 degrees C stimulus but bent in the opposite direction. gps3-1 over-responded after return to RT, continuing to bend to an angle greater than wild-type plants. At 4 degrees C, starch-containing statoliths sedimented normally in both wild-type and the gps mutants, but auxin transport was abolished at 4 degrees C. These results are consistent with GPS loci affecting an aspect of the gravity signal perception/transduction pathway that occurs after statolith sedimentation, but before auxin transport.

NASA Discipline Plant Biology↗
NASA NTRS1997

Rapid systemic up-regulation of genes after heat-wounding and electrical stimulation

When one leaf of a tomato plant is electrically-stimulated or heat-wounded, proteinase inhibitor genes are rapidly up-regulated in distant leaves. The identity of the systemic wound signal(s) is not yet known, but major candidates include hormones transmitted via the phloem or the xylem, the electrically-stimulated self-propagating electrical signal in the phloem (the action potential, AP), or the heat-wound-induced surge in hydraulic pressure in the xylem evoking a local change in membrane potential in adjacent living cells (the variation potential, VP). In order to discriminate between these signals we have adopted two approaches. The first approach involves applying stimuli that evoke known signals and determining whether these signals have similar effects on the "model" transcripts for proteinase inhibitors (pin) and calmodulin (cal). Here we show that a heat wound almost invariably evokes a VP, while an electrical stimulation occasionally evokes an AP, and both of these signals induce accumulation of transcripts encoding proteinase inhibitors. The second approach involves identifying the array of genes turned on by heat-wounding. To this end, we have constructed a subtractive library for heat-wounded tissue, isolated over 800 putatively up-regulated clones, and shown that all but two of the fifty that we have analyzed by Northern hybridization are, indeed, up-regulated. Here we show the early kinetics of up-regulation of three of these transcripts in the terminal (4th) leaf in response to heat-wounding the 3rd leaf, about 5 cm away. Even though these transcripts show somewhat different time courses of induction, with one peaking at 30 min, another at 15 min, and another at 5 min after flaming of a distant leaf, they all exhibit a similar pattern, i.e., a transient period of transcript accumulation preceding a period of transcript decrease, followed by a second period of transcript accumulation.

NASA Discipline Plant Biology↗
NASA NTRS2002

Molecular aspects of stress-gene regulation during spaceflight

Spaceflight-associated stress has been the topic of investigation since the first terrestrial organisms were exposed to this unique environment. Organisms that evolved under the selection pressures of earth-normal environments can perceive spaceflight as a stress, either directly because gravity influences an intrinsic biological process, or indirectly because of secondary effects imparted by spaceflight upon environmental conditions. Different organisms and even different organs within an organism adapt to a spaceflight environment with a diversity of tactics. Plants are keenly sensitive to gravity for directed development, and are also sensitive to other stresses associated with closed-system spaceflight environments. Within the past decade, the tools of molecular biology have begun to provide a sophisticated evaluation of spaceflight-associated stress and the genetic responses that accompany metabolic adaptation to spaceflight.

manned↗
NASA NTRS1997

The ethylene signal transduction pathway in Arabidopsis

The gaseous hormone ethylene is an important regulator of plant growth and development. Using a simple response of etiolated seedlings to ethylene as a genetic screen, genes involved in ethylene signal transduction have been identified in Arabidopsis. Analysis of two of these genes that have been cloned reveals that ethylene signalling involves a combination of a protein (ETR1) with similarity to bacterial histidine kinases and a protein (CTR1) with similarity to Raf-1, a protein kinase involved in multiple signalling cascades in eukaryotic cells. Several lines of investigation provide compelling evidence that ETR1 encodes an ethylene receptor. For the first time there is a glimpse of the molecular circuitry underlying the signal transduction pathway for a plant hormone.

NASA Discipline Plant Biology↗
NASA NTRS1997

The ethylene response pathway in Arabidopsis

The simple gas ethylene influences a diverse array of plant growth and developmental processes including germination, senescence, cell elongation, and fruit ripening. This review focuses on recent molecular genetic studies, principally in Arabidopsis, in which components of the ethylene response pathway have been identified. The isolation and characterization of two of these genes has revealed that ethylene sensing involves a protein kinase cascade. One of these genes encodes a protein with similarity to the ubiquitous Raf family of Ser/Thr protein kinases. A second gene shows similarity to the prokaryotic two-component histidine kinases and most likely encodes an ethylene receptor. Additional elements involved in ethylene signaling have only been identified genetically. The characterization of these genes and mutants will be discussed.

Non-NASA Center↗
NASA NTRS1996

Life in a changing world: TCH gene regulation of expression and responses to environmental signals

The Arabidopsis TCH genes were discovered as a consequence of their marked upregulation of expression in response to seemingly innocuous stimuli such as touch. Further analyses have indicated that these genes are upregulated by a variety of diverse stimuli. Understanding the mechanism(s) and factors that control TCH gene regulation will shed light on the signaling pathways that enable plants to respond to changing environmental conditions. The TCH proteins include calmodulin, calmodulin-related proteins and a xyloglucan endotransglycosylase. Expression analyses and localization of protein accumulation indicate that the potential sites of TCH protein function include expanding cells and tissues under mechanical strain. We hypothesize that the TCH proteins may collaborate in cell wall biogenesis.

NASA Discipline Plant Biology↗
NASA NTRS1990

Characterization and distribution of a maize cDNA encoding a peptide similar to the catalytic region of second messenger dependent protein kinases

Maize (Zea mays) roots respond to a variety of environmental stimuli which are perceived by a specialized group of cells, the root cap. We are studying the transduction of extracellular signals by roots, particularly the role of protein kinases. Protein phosphorylation by kinases is an important step in many eukaryotic signal transduction pathways. As a first phase of this research we have isolated a cDNA encoding a maize protein similar to fungal and animal protein kinases known to be involved in the transduction of extracellular signals. The deduced sequence of this cDNA encodes a polypeptide containing amino acids corresponding to 33 out of 34 invariant or nearly invariant sequence features characteristic of protein kinase catalytic domains. The maize cDNA gene product is more closely related to the branch of serine/threonine protein kinase catalytic domains composed of the cyclic-nucleotide- and calcium-phospholipid-dependent subfamilies than to other protein kinases. Sequence identity is 35% or more between the deduced maize polypeptide and all members of this branch. The high structural similarity strongly suggests that catalytic activity of the encoded maize protein kinase may be regulated by second messengers, like that of all members of this branch whose regulation has been characterized. Northern hybridization with the maize cDNA clone shows a single 2400 base transcript at roughly similar levels in maize coleoptiles, root meristems, and the zone of root elongation, but the transcript is less abundant in mature leaves. In situ hybridization confirms the presence of the transcript in all regions of primary maize root tissue.

NASA Program Space Biology↗
NASA NTRS2000

Developmental evolutionary biology of the vertebrate ear: conserving mechanoelectric transduction and developmental pathways in diverging morphologies

This brief overview shows that a start has been made to molecularly dissect vertebrate ear development and its evolutionary conservation to the development of the insect hearing organ. However, neither the patterning process of the ear nor the patterning process of insect sensory organs is sufficiently known at the moment to provide more than a first glimpse. Moreover, hardly anything is known about otocyst development of the cephalopod molluscs, another triploblast lineage that evolved complex 'ears'. We hope that the apparent conserved functional and cellular components present in the ciliated sensory neurons/hair cells will also be found in the genes required for vertebrate ear and insect sensory organ morphogenesis (Fig. 3). Likewise, we expect that homologous pre-patterning genes will soon be identified for the non-sensory cell development, which is more than a blocking of neuronal development through the Delta/Notch signaling system. Generation of the apparently unique ear could thus represent a multiplication of non-sensory cells by asymmetric and symmetric divisions as well as modification of existing patterning process by implementing novel developmental modules. In the final analysis, the vertebrate ear may come about by increasing the level of gene interactions in an already existing and highly conserved interactive cascade of bHLH genes. Since this was apparently achieved in all three lineages of triploblasts independently (Fig. 3), we now need to understand how much of the morphogenetic cascades are equally conserved across phyla to generate complex ears. The existing mutations in humans and mice may be able to point the direction of future research to understand the development of specific cell types and morphologies in the formation of complex arthropod, cephalopod, and vertebrate 'ears'.

Non-NASA Center↗
NASA NTRS1999

Root gravitropism: a complex response to a simple stimulus?

Roots avoid depleting their immediate environment of essential nutrients by continuous growth. Root growth is directed by environmental cues, including gravity. Gravity sensing occurs mainly in the columella cells of the root cap. Upon reorientation within the gravity field, the root-cap amyloplasts sediment, generating a physiological signal that promotes the development of a curvature at the root elongation zones. Recent molecular genetic studies in Arabidopsis have allowed the identification of genes that play important roles in root gravitropism. Among them, the ARG1 gene encodes a DnaJ-like protein involved in gravity signal transduction, whereas the AUX1 and AGR1 genes encode proteins involved in polar auxin transport. These studies have important implications for understanding the intra- and inter-cellular signaling processes that underlie root gravitropism.

Review, Tutorial↗