Compounds in rice plants protect the plant from competitors by suppressing growth in competing plants

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Many plants naturally produce chemicals to defend against microbial and insect attack, and to compete with other plants that grow nearby. “Allelopathy” is the production and release of a chemical by one organism that is either detrimental or beneficial to another organism.

Allelopathic varieties of rice (Oryza sativa) produce a compound known as momilactone B when growing near an agricultural weed called barnyard grass. Enzymes in allelopathic rice synthesize momilactones, which support the rice crop’s success by suppressing the growth of barnyard grass and other weeds. The exact mechanism by which momilactone B suppresses competing plants is still being uncovered. Current research indicates that the allelopathic compound negatively affects metabolic processes and reactions needed for the synthesis of cellular components in the competing plants.

Growing allelopathic varieties of rice and other crop plants could reduce the use of agricultural chemicals. Conventional pesticides frequently harm non-target organisms and lose effectiveness when resistant pest populations arise. Plant compounds, however, are less likely to promote resistance and can even feed soil microorganisms, thereby potentially enhancing populations of beneficial microbes in soil. This is analogous to the effects that taking probiotics or eating yogurt have on the human gut microbiome. Using plant compounds to mimic this natural process of stimulating soil microbial growth could make crop systems less vulnerable to weed competition and pathogens.

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References

“These results imply that allelopathic rice seedlings can sense certain allelochemicals [plant compounds] released by E. crus-galli [barnyard grass] into the soil, and respond by increased production of allelochemicals inhibitory to E. crus-galli.” (Kong et al. 2006:48)

Journal article
Allelochemicals released by rice roots and residues in soilPlant and SoilAugust 11, 2006
Kong CH, Li HB, Xu XH, Wang P

“The rice diterpenoid momilactones provide an example of natural products for which correlative biochemical evidence has been obtained for a role in allelopathy. Here, we apply reverse genetics, using knock-outs of the relevant diterpene synthases [enzymes] … to demonstrate that rice momilactones are involved in allelopathy, including suppressing growth of the widespread rice paddy weed, barnyard grass (Echinochloa crus-galli). Thus, our results not only provide novel genetic evidence for natural product-mediated allelopathy, but also furnish a molecular target for breeding and metabolic engineering of this important crop plant.” (Xu et al. 2011:570)

Journal article
Genetic evidence for natural product-mediated plant-plant allelopathy in rice (Oryza sativa)New PhytologistNovember 12, 2011
Xu M, Galhano R, Wiemann P, Bueno E, Tiernan M, Wu W, Chung I-M, Gershenzon J, Tudzynski B, Sesma A, Peters RJ

“Mechanistic understanding of specific plant metabolites and pathogen effectors that trigger, like vaccines in animals, the adaptive immune response of soils may provide practical means to engineer the indigenous soil microbiome for enhancing plant health and securing future crop yields.” (Raaijmakers and Mazzola 2016:1393)

Journal article
Soil immune responsesScienceJune 17, 2016
Raaijmakers JM, Mazzola M

Journal article
Biological activities of rice allelochemicals momilactone A and BJournal of Rice ResearchSeptember 16, 2013
Kato-Noguchi H, Ota K

Journal article
Momilactone sensitive proteins in Arabidopsis thalianaNatural Product CommunicationsMarch 1, 2015
Kato-Noguchi H, Kitajima S

Book section
Allelopathy in the search for natural herbicide modelsAllelopathy: Organisms, Processes, and InteractionsDecember 9, 1994
Macias FA

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Living System/s

Organism
Oryza sativa

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