Primavera otoño 2020 (Año LXIII Núms. 122-123)

horizontes@pucpr.edu Año LXIV Núm. 124-125 horizontes PRIMAVERA / OTOÑO 2021 PUCPR 67 defenses against abiotic stress and improves its growth. Kong et al. (2015) demonstrated that ACC deaminase reduced plant ethylene levels and enhanced its antioxidant defense system. ACC deaminase is often associated with reduced water-logging stress levels as a side-effect because of its interaction with the plant roots. ACC deaminase application has shown a reduction in chlorophyll content, overall growth rate, and stomatal conductance in waterlogging stress-treated plants (Rauf et al., 2021). This bacterial enzyme shows promise in counteracting abiotic stress, boosting the overall plant’s beneficial effects, and enhancing its survivability. Plant methionine is the precursor to the ethylene metabolic route of in plants. Rhizobium spp. use this metabolic route. Nascimento et al. (2016) confirmed that ethylene biosynthesis occurred via a methionine-dependent pathway where methionine was converted to S-adenosyl methionine (SAM) by the enzyme SAM synthase. Subsequently, the SAMwas converted to ACC by the enzyme ACC synthase that was later converted to ethylene by the enzyme ACC oxidase. Notably, the limiting step in plant ethylene biosynthesis was the conversion of SAM to ACC. Changing this limiting factor with a more straightforward alternate metabolic route could prove vital in reducing plant ethylene levels. Subramanian et al. (2015) revealed that ACC’s conversion into a-ketobutyrate and ammonia by the enzyme ACC deaminase reduced plant stress by controlling ethylene levels. They revealed that ACC’s conversion into a-ketobutyrate and ammonia by the enzyme ACC deaminase reduced plant stress by controlling ethylene levels. The structural gene encoded for ACC deaminase has been identified as acdS, alongside its regulatory gene known as acdR. Lemaire et al. (2015) discovered that the acdS gene’s location varies in different species, including in transferable elements such as plasmids. These genes are part of the microorganism’s dispensable genome, explaining their variable locations. Checcucci et al. (2017) discovered that samples underwent extensive horizontal gene transfer, playing a substantial role in shaping acdS phylogeny. Exogenous genes have a horizontal transference predisposition. Srinivasan et al. (2017) confirmed that the acdS gene expressed exogenously and enhanced plant tolerance to abiotic stress. Plasmids are small extrachromosomal DNA molecules found within a cell separated from chromosomal DNA. Plasmids are used in genetic engineering to amplify a gene of interest and in molecular cloning as a vector. DNA plasmid molecules are capable of independent replication. Fernández-Llamosas et al. (2020) developed the pSEVA237acdS plasmid, which represented a new genetic tool to provide an additional PGP (plant growth-promoting) trait in those PGPB (plant growth-promoting bacteria) lacking ACC deaminase activity. The plasmid fostered plant production even under stressful conditions such as cultivation in polluted soils. Li et al. (2015) designed primers based on the differentiation between ACC deaminase homologs for specific amplification of partial acdS genes from a wide range of bacteria. They amplified the E295 and L322 residues identified as crucial positions for differentiating ACC deaminase from homologs and designed degenerate primers (sequences with several bases) for specific amplification of the acdS gene. These residues may prove vital for the isolation, transformation, and insertion of the acdS genes into plants. Identification and evaluation of the acdS genes were conducted using a sterile DS salt minimal medium (Jung et al., 2018). The researchers isolated the gene of interest via DNA extraction and purification and used a