EG 3&4

Question 1

what is the basic workflow of MAP kinase pathway

Answer 1

-contributes to the relaying of an extracellular signal to intracellular compartments (like nucleus)
-involves sequential activity of 3 kinases (MAPK3, MAPK2, MAPK)
-results in the phosphorylation of regulatory proteins

Question 2

explain the conclusion carried out with Botrytis cinerea on mpk3 and mpk6 mutants

Answer 2

known that PAD3 expression was a normal response to B. cinerea,
-concluded that functional MPK3 and MPK6 are required for activation of PAD3 in response to B. cinerea
-also concluded that WRKY33 needs to be phosphorylated (on a serine) by MPK3/6 to activate PAD3 expression

Question 3

what are reactive oxygen species (ROS)

Answer 3

-highly reactive forms of oxygen with at least 1 unpaired electron in their orbitals -meaning they react very easily with other molecules and oxidise them through accepting an electron from the molecules they react with

Question 4

where can ROS be produced

Answer 4

mitochondria, peroxisomes, chloroplasts

Question 5

what cellular components do ROS react with

Answer 5

proteins, DNA and RNA, lipids

Question 6

ROS levels are closely regulated, what happens at low and high levels

Answer 6

at low levels ROS act as signalling molecules, at high levels ROS burst and cause cell death

Question 7

how does Ca2+ act as a secondary messenger

Answer 7

Ca2+ relays signals arising from stresses or developmental processes through changes in intracellular concentration of Ca2+

Question 8

what does Ca2+ dependent signalling involve/depend on

Answer 8

depends on Ca2+ sensor proteins (such as Calmodulin and Ca2+ dependent kinases) which are proteins that bind Ca2+

Question 9

what happens in Ca2+ dependent signalling following sensor protein binding

Answer 9

after binding these proteins interact with and activate or phosphorylate other proteins (target proteins being transcription factors, other kinases, enzymes)

Question 10

what are some physical changes involved in defence response of plants

Answer 10

callose deposition which is synthesized in cell wall around the site of infection, stomatal closure

Question 11

what are secondary metabolites

Answer 11

-organic molecules that are not involved in normal growth, development, reprod
-heterogeneous chemicals
-quickly synthesized around infection site
-general antimicrobial activity
-mechanism of action is unclear: membrane disruption and/or pathogen cell death

Question 12

what is a tested example of secondary metabolites against disease

Answer 12

phytoalexins tested against fungus Alternaria brassicicola, showed disease much stronger in absence of phytoalexins

Question 13

what do plant hormones do

Answer 13

they regulate development and responses to environmental factors by binding to a receptor triggering a signalling cascade resulting in change of gene expression

Question 14

what are examples of plant hormones that play a role in plant defence - and their lifestyles (trophs)

Answer 14

salicylic acid (SA - a biotroph and a hemibiotroph), jasmonic acid (JA - a necrotroph and hemitbioroph), ethylene (which is a gas - necrotroph)

Question 15

what are the 2 pathways of SA biosynthesis

Answer 15

ICS1 dependent in the chloroplast (95%), PAL dependent in the cytosol (5%)

Question 16

following experiments what gene was discovered to be important for SA biosynthesis and with what conclusions

Answer 16

ICS1 gene, concluded that plants lacking functional ICS1 produce little free and conjugated SA, thus are more susceptible to fungal growth (and other pathogens)

Question 17

can SA be modified

Answer 17

yes, yields diverse SA derivatives (salicylates) with different functions

Question 18

what does SA signalling lead to and what gene/receptor is heavily involved

Answer 18

leads to gene expression, NPR1 is the receptor of SA and activates the response genes to SA making NPR1 essential to SA mediated responses to biotrophic pathogens

Question 19

what are some SA response genes and what they do

Answer 19

ICS1 (early, increases SA levels), NPR1 (early, further activation of SA response genes), WRKY (early, transcription factors), PR1, PR5, BGL2

Question 20

what are PR genes

Answer 20

pathogenesis related genes, encode for hydrolytic enzymes, cell wall modifying enzymes, antimicrobial peptides, components of signalling pathways, PR genes are stored in vacuoles or outside cells

Question 21

what is the NPR1 work flow in SA signalling

Answer 21

-NPR1 forms oligomers through disulphide bridges of cys residues and other NPR1s
-once a pathogen is detected these oligomers dissociate and NPR1s are drawn inside the nucleus where they otherwise cannot enter
-here the NPR1s react with transcription factors which together activate the SA-responsive defence genes