Bacterial ACC deaminase: Insights into enzymology, biochemistry, genetics, and potential role in amelioration of environmental stress in crop plants

Abstract

Growth and productivity of crop plants worldwide are often adversely affected by anthropogenic and natural stresses. Both biotic and abiotic stresses may impact future food security and sustainability; global climate change will only exacerbate the threat. Nearly all stresses induce ethylene production in plants, which is detrimental to their growth and survival when present at higher concentrations. Consequently, management of ethylene production in plants is becoming an attractive option for countering the stress hormone and its effect on crop yield and productivity. In plants, ACC (1-aminocyclopropane-1-carboxylate) serves as a precursor for ethylene production. Soil microorganisms and root-associated plant growth promoting rhizobacteria (PGPR) that possess ACC deaminase activity regulate growth and development of plants under harsh environmental conditions by limiting ethylene levels in plants; this enzyme is, therefore, often designated as a “stress modulator.” TheACC deaminase enzyme, encoded by the AcdS gene, is tightly controlled and regulated depending upon environmental conditions. Gene regulatory components of AcdS are made up of the LRP protein-coding regulatory gene and other regulatory components that are activated via distinct mechanisms under aerobic and anaerobic conditions. ACC deaminase-positive PGPR strains can intensively promote growth and development of crops being cultivated under abiotic stresses including salt stress, water deficit, waterlogging, temperature extremes, and presence of heavy metals, pesticides and other organic contaminants. Strategies for combating environmental stresses in plants, and improving growth by introducing the acdS gene into crop plants via bacteria, have been investigated. In the recent past, some rapid methods and cutting-edge technologies based on molecular biotechnology and omics approaches involving proteomics, transcriptomics, metagenomics, and next generation sequencing (NGS) have been proposed to reveal the variety and potential of ACC deaminase-producing PGPR that thrive under external stresses. Multiple stress-tolerant ACC deaminase-producing PGPR strains have demonstrated great promise in providing plant resistance/tolerance to various stressors and, therefore, it could be advantageous over other soil/plant microbiome that can flourish under stressed environments.

Biostimulant Effect of Commercial Rhizobacteria Formulation on the Growth of Vitis vinifera L.: Case of Optimal and Water Deficit Conditions

“…This result is in agreement with the result of the rest stress indicators, such as the LRWC and total phenolic content, which were very low in these treatments. The rhizobacteria B. amyloliquefaciens and S. meliloti contained in the commercial formulations seem to enhance plant metabolism, increasing the accumulation of proline, thus creating a promoting environment that helps plants to recover more rapidly from the oxidative damage, based on the picture observed in other works [69,70].…”

Trichoderma Inoculation Alleviates Cd and Pb-Induced Toxicity and Improves Growth and Physiology of Vigna radiata (L.)

“…The ACC deaminase enzyme is released by a variety of soil microorganisms, including bacteria 51 and fungi. 52 This enzyme is essential for lowering ethylene (ET) in plants and fostering plant growth even under challenging circumstances.…”

A plant’s perception of growth-promoting bacteria and their metabolites

“…For example, some beneficial rhizobacteria can use 1-amino-cyclopropane-1-carboxylic acid (ACC) as a C and N source ( Grover et al., 2021 ; Teo et al., 2022 ) and transform it into ammonia and α-ketobutyrate, due to the possession of the enzyme 1-aminocyclopropane-1-carboxylate deaminase ( Gamalero et al., 2023 ). ACC is the precursor of ethylene, thus limiting its transformation to ethylene and its induced growth inhibition ( Shahid et al., 2023 ). Plants gain proceeds from this interaction with microorganisms to the extent that ACC has been proven to be released by plants in the rhizosphere to recruit specific bacteria able to cleave ACC ( Ali and Kim, 2018 ; Gamalero et al., 2023 ).…”