ACC Deaminase Producing Microorganisms in Stress Agriculture: From Hypothesis to Omics

Salt stress and drought stress can decrease the growth and productivity of agricultural crops. Plant growth-promoting bacteria (PGPB) may protect and promote plant growth at abiotic stress. The aim of this study was to search for bacterial strains that can help crops resist rises in drought and salt stresses, to improve crop seed resistance under drought and salt stresses, and to investigate the effect of bacterial strains that can help crop resist external stresses under different stress conditions. Pseudomonas DY1-3, a strain from the soil under the glacier moss community of Tien Shan No. 1, was selected to investigate its growth-promoting effects. Previous studies have shown that this strain is capable of producing ACC (1-aminocyclopropane-1-carboxylic acid) deaminase. In this experiment, multifunctional biochemical test assays were evaluated to determine their potential as PGPB and their bacterial growth-promoting properties and stress-resistant effects on maize plants were verified through seed germination experiments and pot experiments. The results showed that strain DY1-3 has good salt and drought tolerance, as well as the ability to melt phosphorus, fix nitrogen, and produce iron carriers, IAA, EPS, and other pro-biomasses. This study on the growth-promoting effects of the DY1-3 bacterial strain on maize seeds revealed that the germination rate, primary root length, germ length, number of root meristems, and vigor index of the maize seeds were increased after soaking them in bacterial solution under no-stress, drought-stress, and salt-stress environments. In the potting experiments, seedlings in the experimental group inoculated with DY1-3 showed increased stem thicknesses, primary root length, numbers of root meristems, and plant height compared to control seedlings using sterile water. In the study on the physiological properties of the plants related to resistance to stress, the SOD, POD, CAT, and chlorophyll contents of the seedlings in the experimental group, to which the DY1-3 strain was applied, were higher than those of the control group of seedlings to which the bacterial solution was not applied. The addition of the bacterial solution reduced the content of MDA in the experimental group seedlings, which indicated that DY1-3 could positively affect the promotion of maize seedlings and seeds against abiotic stress. In this study, it was concluded that strain DY1-3 is a valuable strain for application, which can produce a variety of pro-biotic substances to promote plant growth in stress-free environments or to help plants resist abiotic stresses. In addition to this, the strain itself has good salt and drought tolerance, making it an option to help crops grown in saline soils to withstand abiotic stresses, and a promising candidate for future application in agricultural biofertilizers. Full article

Transient and prolonged waterlogging stress (WS) stimulates ethylene (ET) generation in plants, but their reprogramming is critical in determining the plants’ fate under WS, which can be combated by the application of symbiotically associated beneficial microbes that induce resistance to WS. The present research was rationalized to explore the potential of the newly isolated 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing fungal endophytic consortium of Aspergillus nomiae (MA1) and Aspergillus fumigatus (MA4) on maize growth promotion under WS. MA1 and MA4 were isolated from the seeds of Moringa oleifera L., which ably produced a sufficient amount of IAA, proline, phenols, and flavonoids. MA1 and MA4 proficiently colonized the root zone of maize (Zea mays L.). The symbiotic association of MA1 and MA4 promoted the growth response of maize compared with the non-inoculated plants under WS stress. Moreover, MA1- and MA4-inoculated maize plants enhanced the production of total soluble protein, sugar, lipids, phenolics, and flavonoids, with a reduction in proline content and H₂O₂ production. MA1- and MA4-inoculated maize plants showed an increase in the DPPH activity and antioxidant enzyme activities of CAT and POD, along with an increased level of hormonal content (GA₃ and IAA) and decreased ABA and ACC contents. Optimal stomatal activity in leaf tissue and adventitious root formation at the root/stem junction was increased in MA1- and MA4-inoculated maize plants, with reduced lysigenous aerenchyma formation, ratio of cortex-to-stele, water-filled cells, and cell gaps within roots; increased tight and round cells; and intact cortical cells without damage. MA1 and MA4 induced a reduction in deformed mesophyll cells, and deteriorated epidermal and vascular bundle cells, as well as swollen metaxylem, phloem, pith, and cortical area, in maize plants under WS compared with control. Moreover, the transcript abundance of ethylene-responsive gene ZmEREB180, responsible for the induction of the WS tolerance in maize, showed optimally reduced expression sufficient for induction in WS tolerance, in MA1- and MA4-inoculated maize plants under WS compared with the non-inoculated control. The existing research supported the use of MA1 and MA4 isolates for establishing the bipartite mutualistic symbiosis in maize to assuage the adverse effects of WS by optimizing ethylene production. Full article