L11- maintenance of acquired immunity

Question 1

how long does priming of SA (salicylic acid)- inducuible defence genes last

Answer 1

it is long lasting
tested pathogen on primed BABA Arabidopsis, pathogen infection was 28 days after vaccine, there was strong resistance post-vaccine. plants were still primed after 28 days

this was the same result when looking at JA (jasmonic acid) vaccine after 3 weeks JA priming increased resistance. The VSP2 gene was activated and showed clear priming pattern, however PDF12 repressed responsiveness post JA priming this was due to the memory of priming retained in only one branch in JA pathway, the PDF1.2 defence gene is antagonistic to the VSP2 pathway

Question 2

what is epigenetic trait

Answer 2

heritable trait passed down via cell division, meiosis or mitosis that cannot be explained by variation in DNA sequence

Question 3

has epigenetic traits been seen in plants

Answer 3

sort of, progeny of infected plant (infected with Pst DC3000) would show individuals with higher resistance, it was also found they were more resistant to other biotrophic pathogens not just the specific one, progeny showed a much stronger response to salicylic acid

Question 4

what evidence was seen for epigenetic mechanism

Answer 4

DNA methylation is complex, and is tightly regulated by transposons (jumping mobile DNA), these can be quite damaging if not silenced. methylated DNA signals for tight compaction of chromatin, dna is tight compacted so transcriptional machinery does not have access, too much tight chromatin can spread into neighbouring genes and be harmful- so important to be balanced, this ROS1 enzyme is responsible for removing methylation

so the easiest way to check is dna methylation homeostasis is involved in acquired heritable resistance is to use knock out machinery in these genes. knockout mutation in ros1 did not effect experiment via growth so was tested, it was found mutants progeny had high levels of infection this is due to hyper-methylation (ROS1 prevents methylation so without it get more)

heritable acquired immunity only occurs when parental plants experience significant growth penalty

Question 5

what was found in eprigenetic recombinant inbred lines

Answer 5

epigenetic recombinant inbred lines (epiRILs) varying in DDM1(dwarf plant mutant, reduced methylation at transposons) -dependent DNA methylation, they express epigenetic resistance, they had 123 identical lines that varied in dna demethylation, reduced methylation correlated with heritable resistance

lines that were very resistance, showed normal growth phenotype compared to parent that was stunted

Question 6

is it possible to create epigenetic modified disease resistant crops

Answer 6

lettuce has 50x more TEs then arabidopsis, mutants in DNA methylation machinery are more likely to be lethal and/or more sterile in lettuce, generation of crop epiRILS require fine tuning of the level of DNA hypo-methylation. active removal of DNA demethylation by ros1 is important for induced resistance.

Question 7

what is the estradiol inducible at ROS1 construct

Answer 7

this is a molecular genetic tool, its a transformation vector, where gene coding for ROS1 is fused to YFB, drivin by LEXA promotor. When you these transgenic plants with estradiol it acitvates the estradiol receptors activate binds LEXA promotor

the estradiol-induced AtROS1:YFP expression elicits long-lasting IR to biotrophic pathogens, this is via hypo methylation, reduced dna methylation

• this also effects plant growth, there is only a reduced growth rate in the first few days after estradiol vaccine