Plant Signalling 1

Question 1

Plant development

‘plastic’?

Answer 1

From a single-celled zygote:

• cell division and differentiation
• no cell migration, just expansion

Meristem cell retain character throughout life

‘Plastic’ development: largely determined by environmental factors promoting biochemical, physiological and developmental adaptation

Question 2

Meristems

Answer 2

Plant stem cells that can differentiate into different types of cells. Main types are:

• Shoot Apical Meristems (SAM)
• Root Apical Meristem (RAM)
• Auxillary meristems (repressed by SAM normally)
• Lateral root meristems

Question 3

Unable to flee danger, plants fight danger (herbivores)

Answer 3

• Produce poisonous/unpleasant-tasting compounds
• regrows parts that are eaten

Similar to animals, they perceive external stimuli and bring about cellular response via signalling pathways

Question 4

Plant hormones

Answer 4

Act autonomously, transported to different parts of plant to bring various cellular responses.

• Hormones and their signalling pathways interact (complex systems) to regulate growth/development
• Small organic molecules and peptides that are locally produced and regulated with local and distant targets

Examples:

• Auxins, cytokinins, ethylene, abscisic acid, Gibberellins
• Also NO and Jasmonates

Question 5

Jasmonates structure and roles

Answer 5

Fatty-acid derived signal molecules analogous to prostaglandins in animal cells
- derived from membrane lipids, pressed through Beta-oxidation

Role in plants:

• Reproductive development
• Stress response to UV, insects, microbes, temperature etc….

Question 6

Role of Jasmonates in defence against insects (herbivores)

Answer 6

1) Insects wound plant by eating (insect-derived elicitors detected)
2) Jasmonic acid (JA) produced
3) JA triggers gene expression for local and systemic responses
- production of volatiles to attract parasitoids and prime defences of nearby plants
- up-regulate production of proteinase inhibitors to block insect digestive capabilities

Question 7

Jasmonate Biosynthesis

Answer 7

Begins in chloroplast:
- cleavage of a-linolenic acid from chloroplast phospholipids (FA-derived)

Continues in peroxisome:

• Beta-oxidation produces JA
• The OPDA enters the peroxisome via the COMATOSE ABC transporter (active transport + ion trapping): proven through mutants accumulating less JA than wt

JA conjugation in the cytoplasm:
- conjugate to various molecules to form various derivates (aka oxylipins)

Question 8

Understanding JA’s roles thanks to mutants

Answer 8

1) the opr3, fad3,7,8 triple mutant:
- males were sterile, susceptible to disease
- rescued by application of JA (proves mutation in JA production)

2) Coi1 mutants are insensitive to coronatine toxin used to screen for mutants:
- male sterile and insect attack can’t be rescued by JA application (mutation prevents response to JA)
- Coi1 normally encodes an F-box protein functioning within the ubiquitin pathway for protein degradation

Question 9

Ubquitin conjugation pathway

Answer 9

E1 activates Ub, E2 transfers Ub to target protein, E3 provides specificity for Ub-protein binding and finally degraded by 26S proteosome

• Coi1 = F-box protein component of multi-subunit SCF type E3 ligase

Question 10

Jasmonate’s mechanism of activating gene expression

Answer 10

JAZ proteins = transcriptional repressors on JA response genes

• JA-Ile (isoleucine) levels increase from stimulus activation (herbivory) promoting interaction between JAZ repressors and SCFcoi1
• JAZ repressor is ubiquitinated and degraded allowing response gene to be expressed