L10- Onset of acquired immunity

Question 1

why is BABA-IR in aradbidopsis, a model system for studying mechanisms of acquired immunity

Answer 1

it shows priming’s effect on increased effectiveness of innate immunity, baso plant vaccine
it does this in two ways
- priming of early-acting cell wall defence
- priming of late acting SA-dependent defences

however also shows side effects which reduces its ability to be used for crops widely, that plants that are heavily primed have reduced growth, also cant be sprayed on leaves due to the wax layer

Question 2

what is the ibi1 mutant
what did it show about IBI1 protein

Answer 2

Impaired in Baba-induced Immunity
hypersensitive to BABA-induced stress

these plants are more greatly negatively effected by BABA priming, they also do not show the benefits of BABA priming
-hypersensitive to side effects, no benefits of priming

this is because IBI1 encodes an Asp-tRNA synthetase, these enzymes play role in translation of RNA into proteins, this one particularly ligated t-RNA and L-Asp to aspartic acid to proteins (idrk)

r form of BABA, R-BABA is very similar to L-asp protein, IBI1 binds to R-BABA and activates function of priming.

Question 3

how can IBI1 mutants are more suseptible to BABA negatives

Answer 3

if it prevents binding, then it causes upstream accumulation of uncharged tRNA, this means something is wrong with amino acid homeostasis

GCN2 is a protein kinases that controls uncharged tRNA, if their is too much it phosphorylates proteins EIF2alpha, when phosphorylated it inactivates translation, and so causes stress and prevents growth

Question 4

can you enhance IBI1 (BABA receptor) expressions

Answer 4

enhancing IBI1 boosts induced resitance and increased tolerance to BABA-induced stress (negatives of BABA),

tests show (increased IBI1) mutants will grow more then WT when treated with BABA under no disease tolerance, and there is (even more) increased resistance in mutants then wt when treated with BABA and under disease pressure

Question 5

what is the four stage model of IBI1 downstream signalling

Answer 5

shows that protein move from the endoplasmic reticulum and into cytoplasm ready to start defence.

• this movement is increased when treated with BABA, further increases if under attack from mildew, and this increase is even greater aided if plant is under attack from mildew and primed with BABA

this has been proved using yeast-two hybrid screen and then through bimolecular fluorescence complementation

Question 6

what does VOZs do during BABA-IR

Answer 6

VOZ1 and VOZ2 regulate SA-independent priming of cell wall defence, if you knock out these transcription factors, you partially compromise BABA induced resistance

but there is no effect on late SA-dependent defence, this shows why there is still partial defence during this mutant knockout

Question 7

why does mildew work on ABA signalling

Answer 7

downy mildew activates the abscisic acid signalling, this tricks plant into thinking its under abiotic stress, however the VOZ1/2 gene redirect this by counteracting signal and stop ABA-induced tolerance gene and into early PTI gene and callose defence

Question 8

what did a screening for less toxic analogous of R-BABA show

Answer 8

less toxic R-BABA still induce resistance, but some strains didnt induce resistance that well

R-beta-homoserine, is a strain that still induced defence, without toxic effects on plant growth, however, RBH is not perceived by IBI1and operates through different pathways potentially working through the JA/ET-dependent defence pathway and not BABA-induced resistance this was found by using a forward genetic screen,Found that RBH did not work via the same receptor RBH works on the JA/ET dependent defences as opposed to BABA which primes for SA dependent defence, but both prime for cell wall defences

through an IR assay found RBH immune mutants had mutant LHT1 gene, this gene is an amino acid transporter- these mutants that could not use RBH had no resistance to pathogens, but mutants that overexpressed this there were increased resistance- LHT is cellular transporter of RBH. Found that LHT1 knockouts had reduced accumulation of RBH and so no induced resistance, but in overexpression of LHT1 line there was more accumulation of RBH then control, so less RBH to reach full immunity this is associated with increased accumulation of RBH (vaccine). The overexpression of LHT1 line, progressive inhibition of growth to the point at 5 millimolar plant started dying off. repeated experiment with presence of L-alanine which is a protogenetic amino acid in for LHT1 transported, this could outcompete toxic effect of RBH, found out it was toxic, and Arabidopsis has a limited native uptake, artificial increase to this shows phytotoxicity. Tested if BABA was also transported by LHT1. LHT1knockout mutants severely compromised in resistance against downy mildew, supports LHT1 transports BABA. Overexpression also causes plant death. So LHT1 transports both baba and RBH. A yeast strain that contained 10 mutations in amino acid transports was used to show that when the mutant had LHT1 addition it start to accumulate alanine

despite structural similarity and that they share the same transporter, they act through complete different pathways, this could be used via combined vaccines, this is being done/studied in very low conc