Principles In Plant Development Flashcards
Angiosperm development
- low degree of tissue specialisation
- high degree of tissue plasticity
- organogenesis occurs throughout life @ meristems
- rigid cell walls; morphogenesis occurs by differential growth, not cell movement
- permanently rooted; and environment profoundly affects development
- no permanent germline
Can predicable fate maps be determined?
- Clonal analysis
- The each spikelet pair is derived from a single cell
- looking for patterns of shared mutation (e.g. virescence)
Induce sectors in mature maize embryo
- irradiation creates random change
- where is it?
Sector size in mature maize plant
- grow the plants (1000s)
- 18 leaves, tassel and ear
- score where the green sectors are in the field
- no compartments, overlap
- no rigid fate map; plasticity
‘Fate map’ of embryonic maize meristem
- first 5 leaves initiated @ embryogenesis
- probability map
Assess growth plasticity
1) grow
2) remove leaves
3) place apex back in culture
4) count leaves that form
- plastic: more meristems would form
- time-shift assay
Are cells “used up” in the meristem?
- “depleted” meristem produces entire set of leaves
- probability, but not predictability
Is cellular differentiation lineage or position dependent?
Good q!
Maize leaf anatomy
- C4
- bundle sheath + mesophyll cells
white deficiency and ring chromsomes
- a more contrived sector analysis
- ring chromosomes contain wt gene copy (spontaneous loss during mitosis)
- homozygous mutation on autosome: cells are white
Sectors of chlorophyll fluorescence
- where is the white tissue in the cross-section?
Sector types
- sectors are undermine about lineage relationships in leaf (3 layers)
- indicates timing of mutation
Distinct cell types share a cell lineage
- one internal cell divides to form a middle layer
- middle layer forms all BS and mesophyll cells
- positional
Indeterminate growth
Shoot/root
Determinate growth
Leaf, lateral root, floral organ
What regulates the switch from indeterminate to determinate growth?
Knotted1 gain of function promoter mutation in maize (Kn1)
Kn1
- “knots” of indeterminate growth on the leaf due to ectopic expression
GOF
- dominant genes can’t tell you what a gene is necessary for
- you need a LOF recessive gene
Kn1 expression
- in meristem, not leaves
- isn’t switched off
- causes aberrant division
KNOX in Arabidopsis
- 35S constitutive promoter
- KNAT1 = ortholog
- Homeobox
- LOF: shootmeristemless
Sufficiency experiments
Express a gene ectopically
KNAT1
- ectopic expression gives extra division; lobing
What regulates organ formation?
Auxin gradients
Auxin gradients in organ primordia
- auxin responsive DR5 pro motor driving fluorescent reporter gene expression
- watch organogenesis
- proto-leaves maxima
NPA on organs
- no leaves
- PIN-like fluorescence
Discrete auxin foci allow
Organ formation
PIN proteins
- mutants = pin
- localise to one side, outgrowth direction
To what extent to changes in cell division planes alter morphogenesis?
tangled maize mutants have aberrant cell divisions
tangled
- ‘messy’ epidermal cells
- leaves feel papery
Quantify division plane direction in tangled mutants
- transverse divisions are completely random
tangled morphology
- normal shape
- smaller, crinklier
- supracelullar control to balance/check
To what extent to cells act cell-autonomously?
- Sector induction in Kn1 mutant maize plants
- does Kn1 only act where it is expressed?
Sector induction in Kn1 mutant maize plants
- genetic mosaic analysis; removing a gene product
- wt: green
- homozygous recessive: white
- irradiate and look for white sectors
Sector types in Kn1
- knots on epidermis correlate with expression of mutant allele in central leaf domain
- gene is only sufficient to make knots if it is expressed in middle layer
- TFs move cell-> cell via plasmodesmata
Kn1 TFs and plasmodesmata
- usually: 2kDa limit
- these are 60
- mechanism unknown
Accumulation of Kn1 gene products
- Ab localisation
- protein, but not mRNA accumulates in the epidermis
- not expressed here
Confirming Kn1 protein mobility
- fuse to a fluorescent tag and object: moves out
- control tag stays in
Root development in legumes
- changes in presence of bacteria and fungi
Root development in legumes process
- molecular signals initiate the interactions
- plant root exudates: flavonoids, strigolactone
- Rhizobia: nod factor
- fungi: myc factor
- root redifferentiates at site of perception into nodules
Nodules
- Complex vascular network
- pops of bacteria
nod factors
- bind to cell-surface RLKs
- ligand recognises binding domain
RLKs
- ligand binding activated internal kinase domain
- downstream phosphorylation
- most interacts w / environmental cues
Downstream of RLKs (NFR115)
- membrane depolarisation due to early ion fluxes
- root tip swelling
- SYMRK induces calcium fluctuations/relocalisation/spiking (RLK, MLK cascades)
- TF induction for new developmental programme
- root hair curling, NIN activation
- infection thread formation
- nodule organogenesis
Gametophyte
- multicellular
- contains gametes
Ovule
- somatic tissue
- megaspore mother cell specification
- meiosis: haploid tetrad (3x degenerate)
- remaining divide mitotically to form 8x nuclei
- one doesn’t divide: 7 cells
- this is the multicellular gametophyte
Anther
- microscopic mother cell goes thru meiosis to form tetrad
- mitosis forms pollen grains
- 2x sperm nuclei
- 1x degenerative cell
Genes that restrict sporophyte no to remain discrete
- lead to more mega/microspore mother cells
- small peptides
- RLKs
- specified cell initiates a communication cascade w/ neighbouring cells to inhibit them from becoming mother cells
What distinguishes germline from somatic tissues?
- neighbour differentiation
- epigenetic marks on megaspore mother cell goes
Epigenetic marks on megaspore mother cell
- total heterochromatin volume >
- H8 mother cell specification
- H1 neighbouring cells
