Microbial enzyme, 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase: An elixir for plant under stress.

Ethylene, being deleterious to plant in some instances like stress, is essential for ripening of fruits, overcoming seed dormancy and initiation of germination, however, ethylene can inhibit root elongation post germination. For plants, 1-aminocyclopropane-1-carboxylic acid (ACC) serves as precursor of ethylene however, for microbes ACC acts as chemoattractant. This establishes a scenario in the rhizosphere where, ACC utilizing microbes dominate the rhizospheric microbiome. A dynamic equilibrium of ACC concentration exists among root, rhizosphere, and bacterium; for such microbes ACC serves as source of nutrition for which they produce an enzyme ACC deaminase (ACCD) which in turn also benefits plants by reducing the levels of ACC and thereby reducing ethylene production in root. The basic function of ACCD is to degrade ACC in to α-ketobutyrate and ammonia, which is then absorbed by bacteria and plants, respectively. The reservoir of ACC in plants is huge, which on experiencing any sort of biotic and abiotic stress is converted to ethylene. Ethylene when overproduced in this way under stress, suddenly induces plant death. The rationale of using microbes with ACCD activity is, sought to decrease the magnitude of ethylene produced in plant under stresses. Because of such phenomenon of ethylene reduction in plant by the rhizospheric microbes, their use in agriculture has a unique stature as it benefits the agrarian society by sustaining high yields even during stress. This review emphasizes to portray the various aspects of ACCD producing microbes. • Increased ethylene level can cause damage to plant growth and health. • ACC oxidase catalyzes final step of ethylene synthesis. • Ammonia and α-ketobutyrate decreases ethylene levels in host plants. • LRP - ACC and glycerol phosphoryldiester phosphodiesterase complex regulates acdS. [ABSTRACT FROM AUTHOR]