Question

when plants are attacked by pathogens, they can alter their root secretions to recruit beneficial microbes from the surrounding soil —a phenomenon termed the \cry for help\ response. roeland berendsen and colleagues at utrecht university investigated this mechanism in arabidopsis thaliana infected with the downy mildew pathogen hyaloperonospora arabidopsidis. the researchers observed that foliar infection triggered significant changes in root exudate composition, particularly an increase in the secretion of certain organic acids and amino acids, and that specific beneficial bacteria—including species of stenotrophomonas, xanthomonas, and microbacterium—became enriched in the rhizosphere of infected plants. based on these observations, berendsen and colleagues hypothesize that the altered root exudate profiles directly mediate the selective recruitment of these protective bacteria, which subsequently confer enhanced disease resistance to the host plant. 12 mark for review which finding, if true, would most directly support the hypothesis by berendsen and colleagues? a arabidopsis plants grown in sterilized soil showed significantly greater susceptibility to hyaloperonospora arabidopsidis infection than plants grown in natural soil containing diverse microbial communities. b application of the specific organic acids and amino acids identified in infected-plant exudates to the soil surrounding healthy arabidopsis plants resulted in enrichment of stenotrophomonas, xanthomonas, and microbacterium similar to that observed in pathogen-infected plants. c the beneficial bacteria enriched in the rhizosphere of infected arabidopsis plants were found to produce antimicrobial compounds effective against hyaloperonospora arabidopsidis in laboratory cultures. d compared with healthy arabidopsis plants, pathogen-infected plants exhibited significantly higher expression of genes associated with jasmonic acid and salicylic acid signaling pathways in root tissues.

Explanation:

The hypothesis is that altered root exudate (specific organic acids and amino acids) mediates recruitment of protective bacteria. Option B directly tests this by applying those exudate components to healthy plants and seeing if the same bacteria are enriched, which supports the causal link between exudates and bacterial recruitment. Option A compares sterilized vs natural soil (not direct on exudate - bacteria link), C focuses on bacteria's antimicrobial action (not recruitment by exudates), D looks at gene expression (not related to exudate - bacteria recruitment).

Answer:

B. Application of the specific organic acids and amino acids identified in infected - plant exudates to the soil surrounding healthy Arabidopsis plants resulted in enrichment of Stenotrophomonas, Xanthomonas, and Microbacterium similar to that observed in pathogen - infected plants.