L12- indirect ecological defence Flashcards
how do maize use aboveground trophic interactions with beneficial insects
in maize when it is attacked by larvae of Egyptian cotton wool, they release volatile blend- this includes green leaf volatiles, aromatic volatiles and terpenoid volatiles
volatiles play important role in recruiting parasitic wasps that lay eggs in caterpillar that kills them off
how does maize use belowground tritrophic interactions with nematodes
when maize is attacked by western corn rootworm, root emit e-beta-carphylene, this recruits pathogenic nematodes that infect the larvae of rootworm
what are the steps for plants recruiting soil microbes
step 1-
attack by pathogen or herbivore, trigger local and systemic signals that activate root immunity
step 2-
change in root exudation profiles of primary and secondary metabolites
step 3-
selection and/or recruitment of beneficial root microbes, resulting in altered root microbiome activities
step 40
the altered micro-biome antagonises pathogens and herbivores via ISR, direct antagonism, parasitism, or nutrient competition.
what did the phylochip anaylsis show
the phylochip (glass device with taxonomic testing for bacterial microbes) analysis of soils from defence elicited Arabidopsis, looked at unplanted soil, soil with healthy Arabidopsis plant and then soil with plants with 4 different treatments - methyl jasminate (MeJA), salicyclic acid, and biological stresses; botrytis cinerea (necrotrophic fungus), and hpa (downy midlew, biotrophic)
found that stress treatments resulted in different community structures in soil, the downy mildew treatment had the largest effect, the microbial species that were acquired were , stenotrophomanas sp, xanthomonas sp, microbacterium sp gram negative bacteria were found to have been acquired through the treated plants
the three species were tested on semi sterile soil to see effect of bacteria on growth and disease resistance, found that spore production of hpa was minimally reduced in the presence of the different species but it was significantly reduced when all three bacteria were present, found that growth was also significantly increased in the presence of all three species
the last experiment tested hpa infected Arabidopsis, compared unplanted soils and treated soil. they used infected soil for a second planting. found that spore production was decreased when soil was already exposed to downy mildew (hpa), innoculation of hpa condition soil to disease suppresion so second planted plants became more resistant.
what do roots of young maize exude
high quantities of the benzoxazinoid DIMBOA
around day 7 of maize growth had super high quantities of DIMBOA the secondary metabolite.
DIMBOA had already been found to be exuded from the leaf cells into intercellular space upon attack by aphids or colonisation of necrotising fungi northern leaf blight, it acts as an aboveground defence metabolite against pests and disease, when under attack compounds are hydrolysed to form toxic compounds
looked at effect of DIMBOA when under such high quantities which is found in root, looked at the beneficial rise in beneficial rhizobacterium called pseudomonas k24 that loves rhizophore of wheat.
Found under higher quantities of DIMBOA, high qunatities of DIMBOA had little effect on conc of pseudomonas (must be very tolerant), however pathogen a.tumerfaciens was dramatically reduced
looked into cells of pseudomonas k24 that had biologically realistic conc of DIMBOA added and then looked at the effect on genes, small faction of genes were highly uprated, found the group of genes evolved to break down aromatic compounds, this explains how it is so tolerant and colonised rhizophere to maize. found three genes that were highly upregulated were critical for positive chemotaxis in pseudomonas putida (moving towards a specific chemical), this suggested that maize was crying out for help from p.putida,
what was the differential effect of mutations affecting DIMBOA production on PGPR root colonisation
looked at 4 maize strains
-wild type
- igl single mutant, produces 90% DIMBOA
- single bx mutant, strongly reduced DIMBOA
- double mutant - completely impacted DIMBOA production
found that pseudomonas putida strongly colonised in the wild type, igl single mutant (nearly wildtype) showed substantial colonisation, in single bx mutant there was very little colonisation, double mutant could barely find any presence of species
the results of this experiment was replicated by using non-sterile agri soil and introducing P.putida. and planting igl single mutant and double mutant and studied the rhizophere, there was no difference in number of colonies, but found that double mutant caused signifcant difference in P.putida colonisation specifically.
what were the impacts of mutations in the BX pathway on the rhizosphere microbiome
looked at wildtype maize, bx1 (complete knockout of downstream benzoxazinoid components, bx2 (upstream mutation), and bx6 (downstream mutation which is responsible for the conversion of DIBOA into DIMBOA)
found bx6 accumulate more DIBOA then DIMBOA, subtle change in composition of benzoxazinoids. bx1 and bx2 accumulated little benzoaxazinoids.
found that OTU (different taxonomic units), 113 different beneficial bacteria were affected by at least one bx mutation, some bacteria were more common in wildtype and so tolerable of benzoxazinoids and species that were more common in mutant so potentially killed/harmed by benzoxazinoids
- very few operational taxonomic units differed between wt and dx6 so, DIBOA (accumulate in bx6 mutant) has a similar function is DIMBOA, led to finding of MBOA which is a resilient stable compound, exudation of MBOA and benzoxazinoids had a legacy effect of pest suppression, future plants grown in conditioned soil that homed the mutants (less benzoaxinoids) were more susceptible
