Plant development Flashcards
(102 cards)
1
Q
What is a defining feature of plants?
A
Plants are sessile and cannot move.
2
Q
What is developmental plasticity in plants?
A
The ability of plants to alter their development in response to local environmental conditions.
3
Q
What are the two types of apical meristems in plants?
A
- Shoot apical meristem (SAM) * Root apical meristem (RAM)
4
Q
What do shoot apical meristems (SAM) produce?
A
- Stems * Leaves * Flowers * Branches
5
Q
What do root apical meristems (RAM) produce?
A
The branching root system.
6
Q
How are plant cells arranged?
A
Plant cells are laid down in a rigid cell wall matrix, almost brick-like.
7
Q
What is the role of patterns of cell division in plant tissues?
A
They create orderly arrangements of cell files and layers.
8
Q
What are anticlinal cell divisions?
A
Cell divisions that are orthogonal to an existing layer of cells, keeping daughter cells in the same layer.
9
Q
What are periclinal cell divisions?
A
Cell divisions that are parallel to a layer, creating new layers.
10
Q
What is Arabidopsis thaliana?
A
A model plant for studying development, known for its genetic analysis.
11
Q
What is the generation time for Arabidopsis thaliana?
A
A single plant can produce 5,000-10,000 seeds in as short as 6 weeks.
12
Q
What is the size of the Arabidopsis genome?
A
125 Mb of DNA with 25,498 identified proteins.
13
Q
What percentage of the Arabidopsis genome is made up of transposable elements?
A
14%.
14
Q
What are the two stages of plant development?
A
- Embryonic stage * Post-embryonic stage
15
Q
What is embryogenesis?
A
The initial growth and divisions of a fertilized cell to form the embryo.
16
Q
What is the protoderm stage in embryogenesis?
A
The stage where transverse divisions produce a single outer layer of cells.
17
Q
What characterizes the heart stage embryo?
A
Proliferation of cells in the upper half gives rise to cotyledon primordia.
18
Q
What is the function of meristems?
A
They are organized cellular structures capable of indeterminate growth.
19
Q
How do Arabidopsis flowers develop?
A
From floral meristems which produce various floral organs.
20
Q
What determines cell fate in plants?
A
It can be influenced by cell position within the tissue or the lineage of the parent cell.
21
Q
What is cell ablation?
A
A method where individual cells are killed to observe the effects on development.
22
Q
How does Arabidopsis respond to cell ablation?
A
Neighboring cells compensate for the lost cell, indicating positional cues play a significant role.
23
Q
What are developmental defects in Arabidopsis caused by?
A
Mutations induced by chemical or ionizing mutagens or random insertion of foreign DNA.
24
Q
What are the two major classes of embryo mutants in Arabidopsis?
A
- Disrupted organogenesis * Lacking body segments
25
What does the FASS gene affect?
It is required for proper microtubule dynamics and accurate positioning of cell walls.
26
What role does auxin play in plant development?
It coordinates the initiation and maintenance of growth in plants.
27
What do MONOPTEROS and BODENLOS mutants affect?
They regulate auxin-mediated gene expression.
28
What is the significance of the GNOM gene?
It encodes a protein required for proper secretion and localization of auxin efflux transporters.
29
True or False: Precise cell division is required for proper pattern formation in plants.
False.
30
What role do hormones play in plant growth?
Hormones regulate many aspects of plant growth, such as cell division and developmental processes.
31
What is auxin and its significance in plants?
Auxin, such as indole acetic acid (IAA), controls cell elongation and the formation of vascular tissue, and is pivotal for apical-basal polarity.
32
What determines plant cell fate?
Positional information is the major determinant of plant cell fate, rather than lineage.
33
How does auxin influence cell polarity in plant tissues?
Auxin controls cell polarity through selective traffic of influx and efflux transporters.
34
What is the core mechanism for nuclear auxin responses?
It involves binding of auxin to SCFTIR1/AFB ubiquitin ligase and AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) substrate proteins.
35
What happens to Aux/IAA proteins when auxin binds?
Their ubiquitination and degradation release AUXIN RESPONSE FACTOR (ARF) transcription factors from inhibition.
36
How is auxin synthesized in plants?
Auxin is synthesized from tryptophan in two steps via TAAs and YUCCA enzymes.
37
What is the function of the AUX1 gene?
The AUX1 gene encodes an influx carrier; loss of this gene confers resistance to the herbicide 2,4-D.
38
What is the role of PIN1 gene in auxin transport?
PIN1 encodes a specific auxin efflux carrier; loss of its activity results in a 'pin-like' structure with loss of lateral organs.
39
Where is the PIN1 protein localized in plant cells?
PIN1 is localized at the basal side of cells in the center of the root.
40
What is the impact of auxin flux at the root tip?
Auxin flux is redirected upwards, controlling cell elongation and bending of the root.
41
What are the key components of auxin signal reception?
The TRANSPORT INHIBITOR RESISTANT (TIR) F-box proteins, AUXIN/INDOLE-3-ACETIC ACID (Aux/IAA) transcriptional coregulators, and AUXIN RESPONSE FACTORs (ARFs).
42
What role do TIR1/AFB proteins play in auxin perception?
They promote auxin responses and are incorporated into a SCFTIR1/AFB complex.
43
What is the domain architecture of TIR1/AFB proteins?
They contain an F-box domain and a leucine-rich-repeat (LRR) domain for auxin binding.
44
What is the function of Aux/IAA proteins?
Aux/IAA proteins act as corepressors to prevent auxin-responsive transcription.
45
What is the function of the EAR motif in Aux/IAA proteins?
It mediates interaction with TOPLESS (TPL) corepressor.
46
What is the role of histone deacetylases (HDACs) in auxin response?
HDACs remove acetyl groups from histones, leading to a more compact chromatin state and reduced DNA accessibility.
47
What are the classes of ARF proteins?
Class A (transcriptional activators) and Classes B and C (transcriptional repressors).
48
What is the significance of the glutamine-rich domain in Class A ARFs?
It is crucial for their classification as transcriptional activators.
49
Fill in the blank: Auxin induces primary response genes known as _______.
AUX/IAAs, GH3s, and SAURs.
50
What is the importance of the TGTCTC motif in auxin response?
It confers auxin responsiveness when duplicated or coupled to another promoter element.
51
What is the function of the SWITCH/SUCROSE NONFERMENTING (SWI/SNF) complexes?
They alter the occupancy or positioning of nucleosomes to change DNA accessibility.
52
True or False: The specificity of auxin responses is critical for triggering multiple distinct responses during plant development.
True.
53
What is the role of ARF dimers in binding sites?
ARF dimers can bind with high affinity to adjacent inverted binding sites, influenced by their spacing
## Footnote
This selectivity is more pronounced in vivo than in vitro
54
What happens to A-ARFs under low auxin conditions?
A-ARFs act as repressors and bind with a repressive cofactor, Aux/IAA
## Footnote
This binding recruits TPL
55
What is the function of IAA in the auxin pathway?
IAA acts as a molecular glue that allows TIR1/AFB to sequester Aux/IAA away from A-ARFs
## Footnote
This process enables A-ARFs to become transcriptional activators
56
What are the three conserved domains in ARF proteins?
* N-terminal DNA-binding domain (DBD)
* Middle region (MR)
* C-terminal Phox and Bem1 (PB1) domain
## Footnote
Each domain has distinct functions in DNA binding and protein interactions
57
What does the B3 domain in ARF proteins do?
The B3 domain allows ARFs to bind DNA motifs called Auxin Response Elements (AuxREs)
## Footnote
This is crucial for ARF's role in transcription regulation
58
How do ARFs affect transcription once bound to chromatin?
ARFs can either repress or activate transcription through their middle region (MR)
## Footnote
This dual function is essential for auxin response
59
What is the significance of feedback control in auxin transport?
Feedback control prevents excessive auxin response by regulating auxin transport and biosynthesis
## Footnote
For example, PIN and YUC genes are transcriptionally regulated by auxin levels
60
What is the role of the GNOM gene in Arabidopsis embryogenesis?
GNOM regulates the traffic of membrane vesicles and is required for proper PIN1 localization
## Footnote
Mutant gnom embryos show a loss of apical-basal polarity
61
What triggers the initiation of the root meristem in Arabidopsis?
The targeted flux of auxin triggers degradation of the Aux/IAA protein BDL, releasing MP (ARF5)
## Footnote
This activates target genes for root meristem initiation
62
What is the function of PIN proteins in auxin transport?
PIN proteins are auxin efflux carriers that facilitate polar transport of auxin
## Footnote
They are essential for gravitropism and root development
63
True or False: A-ARFs mainly act as transcriptional repressors.
False
## Footnote
A-ARFs primarily act as transcriptional activators under high auxin conditions
64
Fill in the blank: ARF proteins can _______ to alter their activity or DNA-binding specificity.
[interact with cofactors]
65
How do auxins affect endocytosis?
Auxins inhibit endocytosis and can reverse the effects of substances that block exocytosis
## Footnote
This regulation helps maintain the localization of PIN proteins
66
What is the evolutionary significance of ARFs in land plants?
ARFs likely originated in a common ancestor to land plants and algal sisters, diverging into three classes: A, B, and C
## Footnote
These classes are functionally distinct and conserved across land plants
67
What roles do A- and B-class ARFs play in plant development?
* A-ARFs: transcriptional activators
* B-ARFs: transcriptional repressors
## Footnote
These functions are crucial for regulating auxin responses
68
What is the relationship between auxin and root meristem initiation?
Auxin dynamics and feedback loops are critical for the specification of the root meristem during embryogenesis
## Footnote
Changes in auxin levels influence cell fate decisions
69
What is the role of PIN3 in auxin transport?
PIN3 acts as a gravity-controlled switch, directing auxin to the lower surface of a tilted root.
70
How does auxin concentration affect cell elongation in roots?
A higher concentration of auxin will inhibit cell elongation on the lower side of the root, causing it to bend towards the vertical.
71
What happens when PIN2 is lost in roots?
Loss of PIN2 causes a loss of the gravitropic response.
72
How does auxin affect cell expansion in shoots?
Higher levels of auxin stimulate cell expansion, causing the shoot to bend in the opposite direction.
73
What is the effect of synthetic auxin on undifferentiated tissue?
Application of synthetic auxin causes the formation of differentiated vascular cells.
74
What disrupts the pattern and connectivity of vasculature in Arabidopsis leaves?
Auxin transport inhibitors disrupt the pattern and connectivity of vasculature.
75
What does the expression of the ATHB-8 gene reflect during leaf development?
The expression of ATHB-8 is progressively refined during leaf development, reflecting canalisation of auxin transport.
76
What is canalisation in the context of auxin transport?
Canalisation involves a provascular cell attracting slightly more auxin than its neighbouring cells, enhancing its polar auxin transport capacity.
77
What is the role of CAMEL in auxin transport?
CAMEL modulates auxin-mediated PIN trafficking and polarity through the phosphorylation of PIN proteins.
78
What does the CANAR protein do in relation to CAMEL?
CANAR functions as a negative regulator of CAMEL by diminishing its autophosphorylation and reducing its kinase activity towards PIN1.
79
How do plant cells adjacent to a wound respond?
They re-differentiate to repair disrupted tissue and form a bypass around the broken connection.
80
What are the main functions of the shoot apical meristem (SAM)?
The SAM produces lateral organs, stem tissues, and regenerates itself.
81
What two processes must be balanced in the shoot apical meristem?
(i) Maintenance of undifferentiated stem cells, (ii) Commitment of cells towards differentiation.
82
What are the three zones of the shoot apical meristem?
* Central zone (CZ)
* Peripheral zone (PZ)
* Rib zone (RZ)
83
What does the CLAVATA1 gene encode?
CLAVATA1 encodes a receptor kinase protein expressed in the shoot meristem.
84
What is the role of the CLAVATA3 gene?
CLAVATA3 encodes a secreted peptide ligand for the CLV1/CLV2/CRN receptor complexes.
85
What happens in clavata mutant plants?
They exhibit enlarged shoot meristems and flowers with increased numbers of organs.
86
What is the function of the WUSCHEL gene?
WUSCHEL is required for stem cell identity in the shoot meristem.
87
What is the relationship between WUSCHEL and CLAVATA genes?
They establish a negative feedback loop regulating meristem maintenance.
88
How does WUSCHEL activity regulate CLAVATA3 expression?
WUS forms homodimers that negatively regulate CLV3 expression in the central meristem.
89
What is the role of the ERECTA-like family of receptors?
They restrict meristem width in the signaling pathway.
90
What is the role of ERECTA-like (ERL) receptors in the meristem?
ERL receptors restrict meristem width and are expressed throughout the meristem.
## Footnote
ERL receptors interact with EPFL ligands, which are expressed in the periphery of the meristem.
91
What do EPFL ligands do in relation to CLV3 and WUS expression?
EPFL ligands inhibit the expression of WUS and CLV3 in the periphery of the SAM, confining them to the center.
## Footnote
This mechanism establishes stem cell positioning along the radial axis.
92
Define phyllotaxy.
Phyllotaxy is the arrangement of leaves on a stem, which can be opposite, whorled, or alternate.
## Footnote
Most species exhibit alternate leaves, forming a spiral pattern.
93
What is the Fibonacci or 'golden' angle in phyllotaxy?
The angle between successive leaves on a stem is often about 137.5 degrees, known as the Fibonacci angle.
94
Who proposed that plant development mechanisms might explain spiral phyllotaxy?
Wilhelm Hofmeister proposed that each new primordium develops on the tip of the growing stem in the spot that is farthest from older primordia.
95
What phenomenon did Douady and Couder demonstrate with their experiment involving droplets?
They showed that droplets added to a magnetized surface would form a spiral pattern based on repulsion and attraction forces.
96
How does auxin influence primordium formation in plants?
Auxin concentration must reach a critical value for a new primordium to form, with inflow stimulating growth and depleting surrounding areas.
97
Fill in the blank: Auxin flux and accumulation can trigger genetic responses through interaction with _______ and ARF proteins.
Aux/IAA
98
What is the function of the MONOPTEROS (MP) ARF transcription factor?
MP elevates the expression of auxin transporters and recruits adjacent cells to form a focus for auxin traffic and cytoskeletal polarity.
99
What are the take-home messages regarding plant development?
1. Plant body plans are flexible and built through local interactions.
2. Auxin is a mobile informational molecule.
3. Auxin triggers specific genetic responses via Aux/IAA and ARF pathways.
4. Genetic responses can trigger coordinated behavior in adjacent cells.
5. Competition for auxin can cause lateral inhibition and spatial patterning.
6. PIN-mediated transport of auxin regulates growth balance across tissues.
100
True or False: WUS can form heterodimers with members of the HAIRY MERISTEM (HAM) family.
True
101
What happens to CLV3 expression in the ham1.2.3 mutant?
CLV3 expression increases and moves from the central zone to the organizing center.
102
What is the significance of WUS-STM heterodimers?
WUS-STM heterodimers enhance the stability of WUS binding to the CLV3 promoter, promoting its expression in the central zone.
