SIGNALLING PATHWAYS OF ABIOTIC STRESS RESPONSES (2) Flashcards
Explain the different systems used by plants to perceive stressful conditions. Identify which messengers are essential in the signalling pathways of different abiotic stresses.
SENSING OF MECHANICAL STIMULI
Mechanoperception is essential for responses to wind, gravity, and touch.
Opening of mechanosensitive ion channels could be due to a pulling force of the membrane caused by membrane thinning under mechanical bending.
The roots of Arabidopsis plants mutated in a mechanosensitive ion channel gene are not able to push their way from soft agar into hard agar as well as wild type plants.
TRANSDUCING THE SIGNAL OF MECHANICAL STIMULI
Current research on mechanoperception signalling indicates a role for [Ca2+] peaks and downstream elements of calcium signalling pathways.
PHOTORECEPTORS ASSOCIATED WITH EXCESS LIGHT RESPONSES
Distinct acclimations to excess light rely on the detection of different wavelengths. the same response can depend on different photoreceptors in different species.
MECHANISM OF PHOTOTROPIN LIGHT SENSING
Under blue light flavin mononucleotides (FMN) bind covalently to the LOV domains (chromophores = protein domain absorbing certain wavelengths), changing the absorbance spectrum of the photoreceptor.
FMN-bound phototropins are activated: their kinase domain is able to carry out auto-phosphorylation, and afterwards phosphorylation of other proteins to transmit the signal of blue light detection.
PHOTOTROPIN SIGNALLING AND CHLOROPLAST MOVEMENT
The signalling pathways between phototropins and actin relocation remains to be determined.
COLD SIGNALLING AND CBF TRANSCRIPTION FACTORS
Decrease in membrane fluidity (?) —»> Ca2+ channels —»> [CA2+]cyt —»>CaM, CIPK/CBL —»> ICE1 —»> CBFs —»> Cold regulated (COR) genes.
Plants that express more CBF (CBF-OE) do not need acclimation to resist frost.
Plants that express CBF (CBF-OE) shows less membrane damage upon freezing than wild type plants.
Heat shock factors control the expression of heat acclimation genes
Transgenic plants with decreased expression of heat shock factors are impaired for heat tolerance and development.
HEAT RESPONSE SIGNALLING PATHWAYS
Cellular Ca2+ concentration rapidly increases during a heat shock.
NEED TO UNDERSTAND PATHWAYS
Induction of HSPs requires ROS signal.
DPI is an inhibitor of NADP oxidases (like ROBDH)
Heat is detected through associated cellular damages
HSP1 activation by heat:
> heat induced damages in proteins
> Hsp90 associates with damaged proteins and dissociates from HSF1
> HSF1 can trimerise and become active to induce the expression of HSPs
Other chaperones are probably involved, as well as Hsp90.
Is ABA the only regulator of water stress responses?
ABA and proline accumulation of a mutant unable to synthesise ABA under water stress.
There are also ABA-independent signalling pathways for water stress acclimation.
The pathway involving the DREB2 transcription factors is used to induce the expression of stress response genes under drought, high salinity and heat, independently of ABA.
Salt stress signalling: SOS2, a multifunction kinase
The salt overly sensitive (SOS) pathway is used to maintain the Na+ concentration in the cytoplasm below toxic level.
