Week 9 Flashcards
What cements adjacent plant cells together?
Middle Lamella
What does the cell wall/middle lamella do?
It prevents cell migration, even in embryos
What does plant developement depend on?
Patterns of cell division and cell enlargement
What connects adajcent cells?
Plasmodesmata which allows selective large molecules to go through
What are the 3 basic types of plant organs?
Stem, leaves (flowers) and roots
What are the three major tissue systems?
Dermal tissue
Ground tissue
Vascular tissue
What are the dermal tissues in plant leaves?
Upper epidermis and lower epidermis
What are the ground tissues in plant leaves?
Palisade parenchyma, bundle sheath parenchyma and spongy mesophyll
What are the vascular tissues in plant leaves?
Xylem and Phloem
What are the dermal tissues in stems?
Epidermis
What are the ground tissues in stems?
Cortex and Pith
What are the vascular tissues in stems?
Xylem and Phloem
With a vascular cambium forming a ring half way through
When did plants and animals split off from each other?
1.6 BYA
What are the similar traits of plant and animal cells?
Mitosis, meiosis, aerobic respiration etc
What was the plant progenitor like?
Autotrophic, cell wall and sessile organism
What was the animal progenitor like?
Heterotropic, lacked cell wall and can move
What is the life cycle of Arabidopsis thaliana?
Germination
Vegetative growth
Floral transition
Flowering
Maturing siliques (embryogenesis)
What are the key features of animal embryogenesis?
Morphogenic changes confinded to a breif embryonic phase
Embryogenesis generates rudimentary miniature scale modules of the adult
Lineage and mobility important in determining and maintaing cell fate (cell intrinsic information)
What are the key features of plant embryogenesis?
Embryogenesis establishes root and shoot polarity (primary meristems)
Establishes radial tissue patterning found in stems and roots
Embryo is determinate whereas subsequent development is indeterminate
Cell fate is determined by position rather than cell type (cell extrinic information)
What is the function of meristems?
Plant (stem cells) they form new cells of a plant, necessary for primary growth
Where are apical meristems found?
They are found at the tips of roots and shoots
What are different about plant stem cells in the meristem?
They retain the ability to divide and produce new cells in a indeterminate manner
What do shoot apical meristems give rise to?
Stem, leaves, flowers, fruit and seeds
What do root apical meristems give rise to?
Primary and lateral roots
What are similarities between plant and animal embryogenesis?
Developement from zygote requires control of cell proliferation and cell fate
Asymmetric cell divisions in the zygote generates cells that undergo distinct devlopmental patterns
Cell fate is controlled by transcription factors that then regulate the expression of specific genes
What are the 2 type of cells that first divide in plant embryos?
Apical and basal cells
What is the protoderm?
Thin outer layer of meristem cells in plant embryos and the growing points of roots and stems
What is the cotyledon?
Leaf cells inside the embryo
What are periclincal cell divisions?
New cell walls form parallel to the tissue surface
What are anticlinal cell divisions?
New cell walls at 90 degrees to the tissue surface
What does the apical cell form?
Apical cell is always on top and will form an embryo
What does the basal cell form?
It is always on the bottom and will always form the suspensor (umbilical cord for plants)
What is the structure of the 8-cell plant embryo?
2 cell Apical embryo region
2 cell Central embryo region
1 cell Hypophysis
1 cell suspensor
What structure of a seedling?
Cotyledons
Shoot apical meristem
Hypocotyl
Primary root which has quiescent center root cap
Who defined the term morphogen?
Alan Turing
What is morphogen?
“form-generating substance”
What is the french flag model?
Different cell fates therefore gene expression are determined by the concentrations of different morphogens
What does position-dependant signalling need?
1- A cue that signifies positions within the developing structure (morphogen)
2- Individual cells must be able to ‘read’ this positional cue
3- Cells must have the capacity to respond to this manner
What is an example of plant morphogens?
Auxin
What does the mutant gurke mean for a plant?
Severly impacts apical formation
What does the mutant fackel?
The central region is gone
What does the mutant monopteros?
The basal region is gone
What does the mutant gnom?
The terminal region has gone
What is monopteros?
A transciption facotor that respondes to auxin (auxin response factor (ARF))
What are lateral meristems?
They are vascular combium and cork cambium which are necessary for secondary growth
What are axillary meristems?
They are formed at the node between the stem and the leaves
What are the 3 functions of the 3 layers in a shoot apex?
Layer 1 - generates epidermis
Layer 2 and 3 - Generate internal tissues
What is the structure of the upper part of the shoot apex?
Shoot apical meristem which is flanked by the leaf primordium
What does the peripheral zone develop into?
The leaf primordia
What does the rib zone develop into?
Structural cells of the stem
How many stem cells does the central zone of the shoot apical meristem in A.thaliana have?
50 stem cells
What does cytohistological staining show?
That the SAM is comprised of distinct cellular layers and functional zones
What happens some stem cells out of the central zone?
They get pushed out into the peropheral zone and rapidally divide to form new organs
This also happens with the central zone with stem tissues
What are the 3 layers and their function in Arabidopsis SAM?
Layer 1 - anticlinal cell divisions - epidermal
Layer 2 - anticlinal cell divisions
Layer 3 - anticlinal and periclinal
What does WUSCHEL do?
Promotes cell division in SAM (mutants do not produce SAM)
What is WUSHEL?
A homeoox transcription factor, induces transcription of genes necessary for SAM function
What are clavata3 mutants like?
Clavata3 mutants make meristem bigger and WUSCHEL expression pattern changed
What is the function of clavata3?
Inhibit meristem growth and controls wuschel expression
What is clavata3?
A small extracellular protein (ligand)
What is CLV1?
A receptor kinase: CLV3 is a ligand for CLV1
What is the function of CLV1?
Also necessary to inhibit meristematic growth
What happens if a plant is mutnat in CLV1?
Has the same phenotyoe of enlarged meristem as CLV3
What is the role of cell-extrinsic informaiton in meristem maintenance?
WUSCHEL induces transcription of genes
WUSCHEL acts non-cell autonomously - produced in L3 below the SAM (short range stimulator)
WUSCHEL induce expression of CLV3 in L1 and L2 cells of the SAM
CLV3 also acts non-cell autonomously (Long range inhibitor)
CLV1 expressing cells can regulate WUSCHEL expression in response to CLV3
CLV1 expression is confinded to a small region of cells where WUS is also expressed
What is the function of STM?
Suppresses cell differentiation (shoot promeristem does form in stm mutants)
What is the function of AS1?
Promotes leaf development
What is the difference between root apical meristem and shoot apical meristem?
Similiar but shoot apical meristem induced induced by root cap
What is the function of Quiescent center?
Organisisng centre in the shoot apical meristem
What gene in the root apical meristem determines stem cell fate?
WOX5
What is the function of the peptide CLE40?
Regulates stem cell fate and WOX5
How do transcription factors help the developmental pathway of plants?
Transcription factors determine cell, tissue and organ identity
What controls developmental pathway?
Developmental pathways are controlled by networks of interacting genes. These networks are regulated by transcription factors
How do transcription factors contribute to the patterning process?
The movement of transcription factors can contribute to the patterning process
What regulates cell development?
Development is regulated by cell-to-cell signalling
What determines a cell’s fate?
It is determined by position, not clonal history (cell extrinsic information)
In WT Arabidopsis roots have is the patterning of cells?
They have distinct radial patterning of cell layers
In WT Arabidopsis roots what gives rise to specific cell files?
The defined plane of cell division in stem cells gives rise to specific cells
What way to cells mostly grow in roots?
Anticlinal
What happens during the begining of periclinal devision?
Cortical endodermal intial (stem cell) divides to form a mother endodermal cell which divides forming cortical cell
What are two genes that control root developement in Arabidopsis?
SHORTROOT (SHR) (1 cell layer that is only cortex)
SCARECROW (SCR) (1 cell layer that is cortex + endodermal)
What happens if you have a mutation in SHR and SCR?
This results in slow growing roots that lack distinct endodermal and cortical cells
What do both SHR and SCR encode for?
They both encode for GRAS transcription factors
What happens if periclinal cell division fails in stem cells?
This cell division fails to produce two cell types (this what happens in scr and shr mutants)
What happens in transcriptional fusion?
A recombinant gene was constructed
The cellular transcription pattern can be determined following UV illumination of longitudinal sections
What are the two points used in locating the expression of SHR?
A SHR promoter and a green fluescent protein (GFP)
In translational fusion the SHR gene is in between the promoter and GFP
What happens in translational fusion?
A recombinant gene was constructed
Translation of the mRNA produces a chimeric protein
The cellular location of the protein can be determined
Where does the transcriptional fusion (where expressed) of the SHR promoter occur?
GFP fusion shows SHR is transctibed in cells of the vascular cylinder (stele)
Where does the translational fusion (where is protein) of the SHR promoter occur?
GFP fusions show that the protein is also located in the vascular cylinder but can also be found in the adjacent endodermal cell layer and the QC
What does the location of SHR trancription and translation mean about SHR protein?
SHR is a non-cell autonomous protein (it can move between cells)
What did scientist find out about with translational fusion of SCR?
They SCR protein is expressed in a single cell layer in roots - the endodermis, but not the cortex
What did scientist find out about with translational fusion of SCR in shr mutant?
SCR expression is weak in the endodermal cell layer when SHR is absent
What did scientist find out about SCR through translational factors in transgenuc Arabidopsis and shr mutant?
SHR expression stimulates SCR
What happens to SHR when it is first transcribed?
SHR synthesised in stele cells moves in both directions across the nuclear pore complex (this accounts for the diffuse appearance of GFP in stele cells)
How does SHR leaves the stele cells?
SHR moves through the plasmadesmata to neighbouring cells
What happens to the SHR when it enters the neighbouring cell?
The SHR is modified which prevents further transport throught the plasmadesmata
What happens to the SHR after it has been modified?
SHR activtaes SCr which intiates endodermal cell development
What is required in the same cell to specify endodermal characters?
SCR and SHR are both needed
Why are both SCR and SHR needed to specify endodermal characters?
SCR and SHR proteins form a heterodimer complex that switches on expression of endodermal genes
What are produced from the shoot apical meristem?
All the above ground structures like flowers, caline leaves and rosette leaves
What is the floral transition?
The switch from vegetative to reproductive devlopment (inflorescence meristem)
What factors can influence floral transtion?
Age
Photoperiod
Vernalisation
Ambient temperature
Gibberelin
Light quality
Abiotic stress
Sucrose
What is vernalisation?
The requirement for cold period before flowering
What is the FT gene?
The flowering locus which can measure day length
Which couple of proteins are cruicial for all flowering cues (floral intergrators)?
FT, SOC1 and LFY
What is the function of SOC1 and LFY?
Are floral intergraters which can analyse all factors and decide whether or not to flower
What is the function or floral intergrators?
They activate the meristem indentity genes on the position where the floral meristem will form
Which genes are the floral meristem identity genes?
LFY, AP1 (CAL)
What happens in lfy mutant plants?
They become bushier as they start the process of forming meristem but quickily can not continue so they make branches with leaves on it. They may make something like a flower but it will be enclosed and look mutated
What happens in ap1 mutants?
They get further along than lfy plants but they still can’t form leaves. When they start to flower flowers instead or petals they start trying to form new flowers ie stalks. They constantly make meristematic tissue
What happens when you have an ap1/cal double mutant?
This produces inflorescene meristems instead of floral meristems, which looks like cauliflower. This is a huge meristem
What activates genes for floral organ development?
Meristem identity genes activate genes downstream needed for floral organ development
What are the 4 different type of floral organs?
Stamen
Carpel
Petal
Sepal
What are the two parts of the stamen?
Anther and Filament
What are the 3 parts of the carpel?
Stigma, style and ovary
Where is the petal always located compared to the sepal?
Always in between 2 sepals
What is the step of floral developement
Bulges form on the sides of the meristem which will become flowers
What happens when the bulge moves away from the meristem?
It becomes more developement forming a sepal and then the other organs will slowly form within it until it opens
What is field 1 for flower schematic diagrams?
Field 1: Sepals and petals
What is field 2 for flower schematic diagrams?
Petals and stamens
What is field 3 for flower schematic diagrams?
Stamens and carpels
What part of the flower organ labelled as whorls?
Whorl 1: sepals
Whorl 2: petals
Whorl 3: stamens
Whorl 4: carpels
What did they find about mutants in flower developement?
They impacted 2 consectutive whorls ie a field
What parts of a flower where impacted with a deficiens mutant?
The petals and stamens (field 1)
What parts of a flower where impacted with a plena mutant?
The stamens and carpels (field 3)
What does the apetala2-2 mutant in arabiposis flower look like?
Only Petals and stamen (impacted petal and sepal)
What does the pistillata2 mutant in arabiposis flower look like?
Only sepal and carpel (similar to deficiens)
What does the agamous1 mutant in arabiposis flower look like?
Only petals and sepal (similar to plena)
What is the ABC-model of flower developement?
3 classes of activity:A, B and C function
Each of the ABC function encompasses 2 whorls
A and C function mutually repress each other
Which whorls goes to each letter?
A: Whorl 1 and 2
B: Whorl 2 and 3
C: Whorl 3 and 4
What is the relationship between A and C?
They mutually repress each other, they are mutually exclusive. If one isnt produce then the other is produced ie no A means every cell will produce C
Where are class A genes expressed?
They start through out the bulge but eventually move to the outside for petal and sepal development
Where are class B genes expressed?
They are expressed in a ring the centre of the bud but are expressed later
Where are class C genes expressed?
They are expressed in the centre where the stamens and carpels form
What is the genes underlying class A?
APETALA1 & 2
What is the genes underlying class B?
APETALA3/ PISTILLATA
What is the genes underlying class C?
AGAMOUS
What happens in a plant with a quadruble mutant of Ap1, ap2, ap3/pi, Ag?
Ectopic expression of these genes in leaves did not lead to homeotic transformations ino floral organs. Same pattern as a flower but its all leaves
What are E class genes?
They are genes needed in every cell for flower development, meaning the model is ABCE
What happens in a plant with ectopic expression of A, B and E genes?
This gives rise to petals
What is gene E?
SEPALLATA1-4 (floral meristem identity genes)
What do most ABCE genes encode for?
MADS-domain transcription factors
What do the MADS-domain transcription factors do?
These bind to DNA in dimers. The dimers can also form tetradimers
What is the structures of MADS-domain transcription factor?
MADS box domain ——– intervening region-/-coiled-coil domain —- Nonconserved carboxy-terminal domain
What is the name of the overal region of the MADS transcription factors, not including the MADS box domain?
The protein-protein interaction
What is the ‘floral quartet model’
Different tetramers in different organs eg for petal it has the A class gene, the B class genes and the E class genes
What is the function of the ABCE genes?
They regulate hundreds of genes, with a regulatory network downstream of the ABCE-proteins is complex
