Week 13 L2: Plant Development - KNOX and ARP genes Flashcards
What are KNOX1 genes?
encode TF that important for identity of organs. help maintain the meristem in an indeterminate growth.
necessary for SAM formation in arabidopsis
Where are the KNO1 genes expressed?
meristem
Where are KNOX1 genes not expressed?!
peripheral zone to form primary organs
What happens when KNOX1 gene is expressed in maize?
meristem markers are excluded from lateral primordia
What is an example of KNOX1 gene ?
STM1
How does a plant differ in mutant STM gene?
plant will be shootmeristemmless thus have an absence of true leaf formation
What is STM?
shootmeristemless mutant
What do KNOX1 genes stimulate?
cytokinin synthesis
What are cytokinins?
any of a number of plant hormones that influence growth and the stimulation of cell division.
Regulate shoot meristem size, leaf primordia number, and leaf and shoot growth.
Keeps meristem in that interderminate state
What does cytokinin biosythetic gene encode?
IPT - isopentenyl transferase
What is the role of IPT?
It is a biosynthetic enzyme.
In a mutant STM1, plant cannot express leaves or little leave formation as they are not dividing much. To counteract this, IPT can induce CK syntheisis.
Where is IPT gene expressed?
Is expressed at the STM promoter at the SAM and rescues mutant.
What is STM?
A TF that induces expression of an IPT gene and thus leaf formation.
What is the effect of overexpression of KNOX genes in the meristem?
increase intermitancy and complexity in lateral organs.
What does the leaf look like in maize with KNOX-OE?
makes knots + extra growth
Where are the KNOX genes expressed?
are undifferenciated in the central zone.
What are cells in the peripheral zone called?
founder cells
What are founder cells?
specified by their position at. the meristem periphery.
morphologically indistinguishable from surrounding cells at this stage but comprise different sets of genes.
What is turned off in founder cells?
KNOX1 genes off an other genes are turned on.
What happens once founder cells are activated?
increase cell division and start making a bulge that can be visually seen.
Then further growth and differentiation produce a leaf.
What is the order of events for lateral organ formation in the founder cells?
specification –> founder cells –> activation –> organ primordium –> growth and differentiation –> organ
How do leaf primordium become a leaf rather than part of the meristem?
1) KNOX genes are not expressed there (in the peripheral)
2) founder cells in the primordia are functionally distinct from the cells in the meristem.
3) They become determinate- growth stops once leaf is formed
What does determinate mean?
Once a leaf forms a leaf it is done and won’t become anything else .
What is the example of primordium specific genes?
ARP genes
What do the ARP genes promote?
growth, differentiation and determinacy
What do the ARP genes encode?
MYB transcription factors.
What genes confere with determinacy?
ARP genes
Where are ARP genes expressed?
cell leaf primordia
lateral organs
What is the mutant type of plant for ARP gene?
as1 mutant
What does the as1 mutant lead to?
increased leaf complexity and indeterminacy
What gene has a similar outcome to KNOX-OE?
as1
What is the relationship between ARP and KNO1 genes?
they are mutually antagonistic.
Have distinct boundaries
The 2 classes of TF are mutually repressive. Help establish a separate identity for emerging leaf primordium.
What establishes the boundary?
has a distinct expression profile which help modulate the identity of both.
Mobile elements such as miRNAs which are gong to help control the spatial expression of these genes.
What would the expression pattern of AS1 in an stm1 mutant?
stm is a dwarf plant
What happens if we lose as1?
We get KNOX genes expressed where they shouldn’t be in the leaf.
What happens if we lose KNOX?
We get as1 being expressed where it shouldn’t be
