Week 13 L3: Plant Development - Branching Flashcards
What is an axillary bud?
the precursor of a branch or lateral shoot.
Formed at the junction between a leaf and the stem.
What are axillary buds?
Axillary meristems
What is an axillary meristem?
Can go on and form branches
What does activation of axillary meristems lead to?
more shoots
What are the axillary shoots?
side shoots
What is the structure of the axillary side shoots?
mimic that of the main stem
Do all buds form flowers?
no, not all buds flower
What determines if a bud will form a flower?
if it becomes active or not is highly regulated, dictates whether the plant is an ultra-branched plant or a plant with no branching
What is the difference between teosinte and modern corn?
their degree of branching
What type of corn has more branching?
ancestral maize (teosinte)
How would you describe a plant with limited branching with a clear central stem?
apically dominant over axillary shoots
apical dominance
What is the traditional view of what causes apical dominance?
an inhibitory signal from the shoot tip
How do we know that apical dominance is due to a signal in the shoot tip?
Decapitate the shoot tip and get bud outgrowth
inhibition relieved
Why is it advantageous to grow buds when root tip is decapitated?
If an animal eats the top of the plant, it can have a plan B.
Is decapitation followed by bud growth an example of canalise trait?
NO, it is an example of plasticity. As the environment changes, the plant adapts
Changing their architecture in response
How do you inhibits a decapitated plant from branching? Initially thought
Add auxin to the tip
no bud outgrowth
How was auxin as an axillary branch inhibitor proven wrong?
auxin application does not suppress axillary branching in max mutants
What is a max3 mutant?
multiple axillary branches mutant
How was it found that shoot and root suppress branching in max3?
a reciprocal experiment
a max3 shoot with a WT root
a max3 root with a WT shoot
What was concluded from the reciprocal experiment?
the branch controlling signal can be made in either tissue and can move from root to shoot
What is the hormone responsible for axillary bud inhibition?
strigalactone (SL)
What is strigalactone?
a biosynthetic signalling component.
caretenoid-derived plant hormone
How was strigalactone known?
From various pathogens which infect plants and plants themselves.
What is the effect of strigalactone in max1?
SL treatment repressed axillary bud outgrowth in mutants. As the inhibitory SL is added so branch growth is less that max 1 with control.
What is the relationship between strigolactone and auxin?
auxin up-regulates SL synthesis
Are SLs conservered?
YES
What hormones promote shoot outgrowth?
cytokinin in the meristem
How does auxin regulate strigolactone?
stimulates CCD7 AND CCD8 to activate SL which inhibits bud growth
How does auxin inhibit cytokinin?
it inhibits IPT which usually stimulates cytokinin to stimulate bud growth
How does auxin inhibit cytokinin?
it inhibits IPT which usually stimulates cytokinin to stimulate bud growth
Does auxin directly inhibit bud growth too?
yes
Where is auxin located?
shoot tip SAM
Where is strigolactone located?
Root tip meristem
Where is cytokinin located?
root rip meristem
What abiotic factors inhibit branching?
low light
high density
What abiotic factors promote branching?
sugars and fertiliser
What are other repressor mutants in plants for shoot branching?
BRC 1 and 2
What kind of mutants is ycc1?
auxin over-producing mutant
What are all the mutant types of branching?
brc1
yyc1
max1
How do you set up a qPCR experiment?
BRC1 gene with an endogenous control gene between species.
Allow to compare genotypes between individuals
e.g. ACTIN8
What is the purpose of the qPCR?
compare levels of BRC1 in brc-1, max mutants and ycc1
What were the levels of BRC1 mRNA in max mutants?
low, as the mutant of max is defective in the strigolactone gene so will be branching. Thus low levels of branching inhibitory gene (low BRC1)
What are levels of BRC1 in yyc1 branching mutants like?
ycc1 overproduce auxin so will have very little branching this high levels of BRC1 which inhibits branching
What does a BRC mutant cause to plant branching?
Highly branched
What does this tell us about hormone signalling pathways?
The hormone signalling pathways signalling the expression of these genes in the axillary but and that is correlating to whether that bud is active or not.
What causes apical dominance in maize?
up-regulation of single gene, teosinte branched 1 (Tb1), encoding a TCP transcription factor - an orthologue of branched1/2 in arabidopsis.
What are the similar mutants in arabidopsis and maize which cause a decrease in branching?
maize: Tb1 mutant
arab: BRC1 mutant
Why does the upregulation of Tb1 mutant cause an apical architecture?
As it encodes TCP TF which acts like BRC1&2 to decrease axillary branching and cause an apical structure.
growth and little branching
What are the inhibitoey branching hormones?
MAIZE: Tb1
Arab: BRC1/2
What does a plant look like which has a mutant version of Tb1/BRC1?
Lots of leaves
BEACUSE the mutant hormones are not repressing branching.
