Untitled Deck Flashcards
What is the function of the HRL1 gene in Arabidopsis thaliana?
HRL1 encodes AtPPT1, essential for metabolite transport between organelles and regulates ROS homeostasis, pathogen defense, and programmed cell death in plants.
AtPPT1 stands for phosphoenolpyruvate/phosphate translocator 1.
How do plants defend themselves against pathogens?
Plants use multiple immune strategies, including:
* Physical barriers (cell walls, cuticles)
* Reactive oxygen species (ROS) production
* Hormonal signaling (salicylic acid (SA), jasmonic acid (JA), and ethylene (ET))
* Systemic acquired resistance (SAR)
* Pathogenesis-related (PR) gene activation
Each of these strategies plays a crucial role in enhancing plant immunity.
What is the role of reactive oxygen species (ROS) in plant defense?
ROS act as signaling molecules that trigger hypersensitive response (HR)-like cell death to limit pathogen spread, but excessive ROS can cause tissue damage.
Excessive ROS accumulation is particularly notable in hrl1 mutants.
How was the HRL1 gene cloned?
HRL1 was identified using positional cloning combined with EMS mutagenesis, mapping the mutation and sequencing candidate genes.
EMS stands for ethyl methanesulfonate, a chemical used for mutagenesis.
What happens when HRL1 is overexpressed?
Overexpression leads to disrupted ROS homeostasis, excessive immune signaling, and potential growth defects due to overactive defense responses.
What is the significance of Coenzyme Q10 in plant defense?
Coenzyme Q10 is involved in electron transport and ROS balance, influencing immune responses and oxidative stress.
What effect does the hrl1 mutation have on the plant?
- Increased ROS levels
- Enhanced resistance to Pseudomonas syringae
- Growth defects (stunted growth)
- Pre-activated systemic acquired resistance (SAR)
What role does the mitochondrial electron transport chain play in ROS production?
The mitochondrial electron transport chain produces ROS as a byproduct of ATP synthesis; disruptions can lead to excessive ROS accumulation.
What happens when HRL1 is knocked out completely?
- Reduced ROS accumulation
- Weakened immune responses
- Increased susceptibility to pathogens
How was the function of HRL1 confirmed through genetic complementation?
Researchers reintroduced the wild-type HRL1 gene into hrl1 mutants, restoring normal ROS levels and improving growth.
What is a transgenic animal?
A transgenic animal is one whose genome has been changed to carry a gene from another species or to use genome editing techniques.
What was the first successful transgenic animal?
The first successful transgenic animal is a mouse.
What are the three primary approaches used to create transgenic animals?
- DNA microinjection
- Gene transfer into gametes
- Somatic cell nuclear transfer (SCNT)
What is the purpose of using vectors in transgenesis?
Vectors are used to increase the probability of gene expression by carrying foreign DNA.
What is the most effective transgenic marker currently used?
Fluorescent Protein
What is sperm-mediated gene transfer (SMGT)?
Sperm-mediated gene transfer is a technique where sperm carries exogenous DNA into the fertilized ovum, integrating it into the embryo’s genome.
What is one of the main ethical concerns regarding transgenesis?
Manipulation of embryos can have a negative impact on animal welfare.
How is transgenic technology applied in agriculture?
- Greater prolificacy and reproductive performance
- High feed consumption and growth rate
- Improved carcass composition
- Improved milk production and/or composition
- Increased disease resistance
What is xenotransplantation?
Xenotransplantation is the transfer of foreign organs into humans, such as humanized pig organs.
What is the success rate of somatic cell nuclear transfer (SCNT)?
0.5 to 5%
What is the main advantage of in planta transformation methods over conventional in vitro methods?
Extremely heterogeneous in their modes of action and types of organs targeted for stable transformation.
Which plant species is most commonly transformed using the floral dip method?
Arabidopsis thaliana
What are the two main steps involved in generating stable plant transformants?
- Transformation of the plant cells
- Development of the cell into a whole plant
What is the primary target of the floral dip method in Arabidopsis?
The female reproductive tissues, the ovules.
What is the pollen-tube pathway transformation method?
A method that applies exogenous donor DNA onto the severed style of the recipient plant, transported via the pollen tube to the ovary.
What is the role of Agrobacterium in in planta transformation?
Agrobacterium is a biological vector that introduces DNA for in planta transformation.
What is the main limitation of the floral dip method in terms of offspring?
The generation of hemizygous offspring and a narrow range of species amendable to the method.
What is the purpose of using morphogenic regulators in plant transformation?
To deliver developmental regulators to recipient plants for identifying normal transgenic shoots.
What is the significance of the shoot apical meristem in in planta transformation?
It is a primary target for introducing genetic material, allowing stable integration of transgenes into the plant germline.
What is the main advantage of using the pollen-tube pathway method?
No regeneration step and fast preparation.
What are the three key signaling molecules involved in Arabidopsis defense against pathogens?
- Salicylic acid (SA)
- Jasmonic acid (JA)
- Ethylene (ET)
What is the primary characteristic of the hrl1 mutant in Arabidopsis?
Characterized by spontaneous necrotic lesions, accumulation of reactive oxygen species, and enhanced resistance to pathogens.
How does the hrl1 mutation affect resistance to virulent bacterial and oomycete pathogens?
It leads to enhanced resistance, suppressing the growth of these pathogens.
What role does salicylic acid play in systemic acquired resistance (SAR)?
SA is a key endogenous signal required for the expression of the SA-dependent defense signaling pathway.
How does ethylene (ET) signaling influence systemic PR-1 expression in hrl1?
ET signaling contributes to PR-1 expression, but its effect is weaker than SA.
What effect does the coi1 mutation have on lesion formation in hrl1 plants?
Coi1 limits the severity of cell death in hrl1, necessary for sensitivity to coronatine and jasmonates.
How do SA and jasmonic acid (JA) signaling pathways interact in regulating PDF1.2 expression?
SA suppresses PDF1.2; in hrl1, high SA levels inhibit JA-dependent responses.
What molecular marker is used to indicate ET/JA-responsive defense gene activation?
PDF1.2 is a widely used marker for ET/JA-dependent defense responses.
How does the presence of the nahG gene affect the defense responses in hrl1 plants?
NahG converts SA to an inactive catechol, blocking SAR onset and abolishing PR gene expression.
What is the significance of AtrbohD expression in hrl1 mutant?
AtrbohD encodes a major subunit of NADPH oxidase complex and induces HR.
What is the primary characteristic of the Arabidopsis hrl1 mutant?
Spontaneous HR-like lesions due to excessive ROS accumulation.
How does hrl1 affect hypersensitive response (HR) cell death against avirulent pathogens?
hrl1 mutants exhibit enhanced HR cell death due to hyperactivated defense.
What effect does preexisting systemic acquired resistance (SAR) have on HR cell death in hrl1?
Pre-existing SAR limits HR cell death, preventing excessive damage.
Which genetic modifications can reverse the suppressed HR phenotype in hrl1?
Mutating NPR1 restores HR cell death, indicating SAR’s limiting role.
What experimental evidence supports that SAR induction can suppress HR in wild-type plants?
Pre-inducing SAR reduces HR lesion size and limits cell death.
Why was electrolyte leakage measured in this study?
Electrolyte leakage indicates cell membrane damage during HR, with increased leakage showing enhanced cell death.
What was the effect of dexamethasone (Dex)-induced AvrRpt2 expression in hrl1 plants?
hrl1 plants showed exaggerated HR cell death upon AvrRpt2 induction.
How does PR-1 expression respond to pathogen infection in hrl1 plants?
PR-1 is constitutively upregulated in hrl1, indicating pre-activated defense.
How did the hrl1 npr1 and hrl1 nahG mutants differ in their HR responses?
hrl1 npr1: Increased HR cell death; hrl1 nahG: Reduced HR lesions due to low SA levels.
What is the proposed biological significance of SAR-mediated suppression of HR?
Prevents excessive cell death, ensuring defense mechanisms do not compromise plant growth.
