Week 13 L3: Plant Development - Branching

Question 1

What is an axillary bud?

Answer 1

the precursor of a branch or lateral shoot.

Formed at the junction between a leaf and the stem.

Question 2

What are axillary buds?

Answer 2

Axillary meristems

Question 3

What is an axillary meristem?

Answer 3

Can go on and form branches

Question 4

What does activation of axillary meristems lead to?

Answer 4

more shoots

Question 5

What are the axillary shoots?

Answer 5

side shoots

Question 6

What is the structure of the axillary side shoots?

Answer 6

mimic that of the main stem

Question 7

Do all buds form flowers?

Answer 7

no, not all buds flower

Question 8

What determines if a bud will form a flower?

Answer 8

if it becomes active or not is highly regulated, dictates whether the plant is an ultra-branched plant or a plant with no branching

Question 9

What is the difference between teosinte and modern corn?

Answer 9

their degree of branching

Question 10

What type of corn has more branching?

Answer 10

ancestral maize (teosinte)

Question 11

How would you describe a plant with limited branching with a clear central stem?

Answer 11

apically dominant over axillary shoots

apical dominance

Question 12

What is the traditional view of what causes apical dominance?

Answer 12

an inhibitory signal from the shoot tip

Question 13

How do we know that apical dominance is due to a signal in the shoot tip?

Answer 13

Decapitate the shoot tip and get bud outgrowth

inhibition relieved

Question 14

Why is it advantageous to grow buds when root tip is decapitated?

Answer 14

If an animal eats the top of the plant, it can have a plan B.

Question 15

Is decapitation followed by bud growth an example of canalise trait?

Answer 15

NO, it is an example of plasticity. As the environment changes, the plant adapts

Changing their architecture in response

Question 16

How do you inhibits a decapitated plant from branching? Initially thought

Answer 16

Add auxin to the tip

no bud outgrowth

Question 17

How was auxin as an axillary branch inhibitor proven wrong?

Answer 17

auxin application does not suppress axillary branching in max mutants

Question 18

What is a max3 mutant?

Answer 18

multiple axillary branches mutant

Question 19

How was it found that shoot and root suppress branching in max3?

Answer 19

a reciprocal experiment

a max3 shoot with a WT root
a max3 root with a WT shoot

Question 20

What was concluded from the reciprocal experiment?

Answer 20

the branch controlling signal can be made in either tissue and can move from root to shoot

Question 21

What is the hormone responsible for axillary bud inhibition?

Answer 21

strigalactone (SL)

Question 22

What is strigalactone?

Answer 22

a biosynthetic signalling component.

caretenoid-derived plant hormone

Question 23

How was strigalactone known?

Answer 23

From various pathogens which infect plants and plants themselves.

Question 24

What is the effect of strigalactone in max1?

Answer 24

SL treatment repressed axillary bud outgrowth in mutants. As the inhibitory SL is added so branch growth is less that max 1 with control.

Question 25

What is the relationship between strigolactone and auxin?

Answer 25

auxin up-regulates SL synthesis

Question 26

Are SLs conservered?

Answer 26

YES

Question 27

What hormones promote shoot outgrowth?

Answer 27

cytokinin in the meristem

Question 28

How does auxin regulate strigolactone?

Answer 28

stimulates CCD7 AND CCD8 to activate SL which inhibits bud growth

Question 29

How does auxin inhibit cytokinin?

Answer 29

it inhibits IPT which usually stimulates cytokinin to stimulate bud growth

Question 30

How does auxin inhibit cytokinin?

Answer 30

it inhibits IPT which usually stimulates cytokinin to stimulate bud growth

Question 31

Does auxin directly inhibit bud growth too?

Answer 31

yes

Question 32

Where is auxin located?

Answer 32

shoot tip SAM

Question 33

Where is strigolactone located?

Answer 33

Root tip meristem

Question 34

Where is cytokinin located?

Answer 34

root rip meristem

Question 35

What abiotic factors inhibit branching?

Answer 35

low light | high density

Question 36

What abiotic factors promote branching?

Answer 36

sugars and fertiliser

Question 37

What are other repressor mutants in plants for shoot branching?

Answer 37

BRC 1 and 2

Question 38

What kind of mutants is ycc1?

Answer 38

auxin over-producing mutant

Question 39

What are all the mutant types of branching?

Answer 39

brc1 yyc1 max1

Question 40

How do you set up a qPCR experiment?

Answer 40

BRC1 gene with an endogenous control gene between species. Allow to compare genotypes between individuals e.g. ACTIN8

Question 41

What is the purpose of the qPCR?

Answer 41

compare levels of BRC1 in brc-1, max mutants and ycc1

Question 42

What were the levels of BRC1 mRNA in max mutants?

Answer 42

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)

Question 43

What are levels of BRC1 in yyc1 branching mutants like?

Answer 43

ycc1 overproduce auxin so will have very little branching this high levels of BRC1 which inhibits branching

Question 44

What does a BRC mutant cause to plant branching?

Answer 44

Highly branched

Question 45

What does this tell us about hormone signalling pathways?

Answer 45

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.

Question 46

What causes apical dominance in maize?

Answer 46

up-regulation of single gene, teosinte branched 1 (Tb1), encoding a TCP transcription factor - an orthologue of branched1/2 in arabidopsis.

Question 47

What are the similar mutants in arabidopsis and maize which cause a decrease in branching?

Answer 47

maize: Tb1 mutant arab: BRC1 mutant

Question 48

Why does the upregulation of Tb1 mutant cause an apical architecture?

Answer 48

As it encodes TCP TF which acts like BRC1&2 to decrease axillary branching and cause an apical structure. growth and little branching

Question 49

What are the inhibitoey branching hormones?

Answer 49

MAIZE: Tb1 Arab: BRC1/2

Question 50

What does a plant look like which has a mutant version of Tb1/BRC1?

Answer 50

Lots of leaves | BEACUSE the mutant hormones are not repressing branching.