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Background: Salinity is a major threat to the agriculture industry due to the negative impact of salinity stress on crop productivity. In the present study, we isolated rhizobacteria and evaluated their capacities to promote crop growth under salt stress conditions. Results: We isolated rhizospheric bacteria from sand dune flora of Pohang beach, Korea, and screened them for plant growth-promoting (PGP) traits. Among 55 bacterial isolates, 14 produced indole-3-acetic acid (IAA), 10 produced siderophores, and 12 produced extracellular polymeric and phosphate solubilization. Based on these PGP traits, we selected 11 isolates to assess for salinity tolerance. Among them, ALT29 and ALT43 showed the highest tolerance to salinity stress. Next, we tested the culture filtrate of isolates ALT29 and ALT43 for IAA and organic acids to confirm the presence of these PGP products. To investigate the effects of ALT29 and ALT43 on salt tolerance in soybean, we grew seedlings in 0 mM, 80 mM, 160 mM, and 240 mM NaCl treatments, inoculating half with the bacterial isolates. Inoculation with ALT29 and ALT43 significantly increased shoot length (13%), root length (21%), shoot fresh and dry weight (44 and 35%), root fresh and dry weight (9%), chlorophyll content (16–24%), Chl a (8–43%), Chl b (13–46%), and carotenoid (14–39%) content of soybean grown under salt stress. Inoculation with ALT29 and ALT43 also significantly decreased endogenous ABA levels (0.77-fold) and increased endogenous SA contents (6–16%), increased total protein (10–20%) and glutathione contents, and reduced lipid peroxidation (0.8–5-fold), superoxide anion (21–68%), peroxidase (12.14–17.97%), and polyphenol oxidase (11.76–27.06%) contents in soybean under salinity stress. In addition, soybean treated with ALT29 and ALT43 exhibited higher K+ uptake (9.34–67.03%) and reduced Na+ content (2–4.5-fold). Genes involved in salt tolerance, GmFLD19 and GmNARK, were upregulated under NaCl stress; however, significant decreases in GmFLD19 (3–12-fold) and GmNARK (1.8–3.7-fold) expression were observed in bacterial inoculated plants. Conclusion: In conclusion, bacterial isolates ALT29 and ALT43 can mitigate salinity stress and increase plant growth, providing an eco-friendly approach for addressing saline conditions in agricultural production systems. [ABSTRACT FROM AUTHOR]

Waterlogging stress (WS) induces ethylene (ET) and polyamine (spermine, putrescine, and spermidine) production in plants, but their reprogramming is a decisive element for determining the fate of the plant upon waterlogging-induced stress. WS can be challenged by exploring symbiotic microbes that improve the plant's ability to grow better and resist WS. The present study deals with identification and application of 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase-producing fungal endophyte Trichoderma asperellum (strain MAP1), isolated from the roots of Canna indica L., on wheat growth under WS. MAP1 positively affected wheat growth by secreting phytohormones/secondary metabolites, strengthening the plant's antioxidant system and influencing the physiology through polyamine production and modulating gene expression. MAP1 inoculation promoted yield in comparison to non-endophyte inoculated waterlogged seedlings. Exogenously applied ethephon (ET synthesis inducer) and 1-aminocyclopropane carboxylic acid (ACC; ET precursor) showed a reduction in growth, compared to MAP1-inoculated waterlogged seedlings, while amino-oxyacetic acid (AOA; ET inhibitor) application reversed the negative effect imposed by ET and ACC, upon waterlogging treatment. A significant reduction in plant growth rate, chlorophyll content, and stomatal conductance was noticed, while H2O2, MDA production, and electrolyte leakage were increased in non-inoculated waterlogged seedlings. Moreover, in comparison to non-inoculated waterlogged wheat seedlings, MAP1-inoculated waterlogged wheat exhibited antioxidant–enzyme activities. In agreement with the physiological results, genes associated with the free polyamine (PA) biosynthesis were highly induced and PA content was abundant in MAP1-inoculated seedlings. Furthermore, ET biosynthesis/signaling gene expression was reduced upon MAP1 inoculation under WS. Briefly, MAP1 mitigated the adverse effect of WS in wheat, by reprogramming the PAs and ET biosynthesis, which leads to optimal stomatal conductance, increased photosynthesis, and membrane stability as well as reduced ET-induced leaf senescence. [ABSTRACT FROM AUTHOR]

Fungal endophytes are known to secrete a large array of secondary metabolites (phenols, flavonoids, indole acetic acid (IAA) etc.) that facilitate crops under stress conditions. Considering this, a potent plant growth promoting endophyte (SXSp1) from the spines and leaves of Solanum xanthocarpum L. has been isolated. The isolated strain ably secreted high quantities of indole-3-acetic acid, phenols and flavonoids. Also, it exhibited phosphate solubilization, siderophore and had 2,2 diphenyl-1-picrylhydrazyl (DPPH) scavenging activity. The SXSp1 also resisted the salinity stress up to 150 mM. LC/MS analysis of SXSp1 culture filtrate (CF) revealed the presence of p-hydroxyl benzoic acid, diadzein, genistien, myricetin and caffeoyl-D-glucose. Moreover, the inoculation of maize plants with SXSp1 significantly (P=0.05) promoted the chlorophyll and carotenoid contents, root and shoot lengths, plant fresh and dry weights, catalase and peroxidase activities, proline, phenolics, flavonoids and relative water contents (RWCs) under salinity. More interestingly, SXSp1-associated plants showed lower endogenous abscisic acid (ABA) and higher endogenous IAA contents that helped the plants to resist salinity stress up to 100 mM. After sequencing, internal transcribed spacer (ITS) regions (ITS1 and ITS4) and phylogenetic analysis, the SXSp1 was identified as Meyerozyma caribbica. [ABSTRACT FROM AUTHOR]

Contamination of agricultural land with heavy metal is a serious biological and environmental issue. Such threat can be challenged by exploring the plant symbiotic microbes that can improve plant growth through phyto-hormones secretion and chromate chelation. In the current study, chromate resistant rhizospheric Staphylococcus arlettae strain MT4 was isolated from the rhizosphere of Malvestrum tricuspadatum L. The strain showed potential to secrete phytohormones and plant growth promoting secondary metabolites under induced chromate stress, making it a best suitable candidate in chromate stress alleviation. Moreover, the rhizobacterium MT4 significantly promoted the net assimilation and relative growth rate of sunflower grown in the presence of chromate (100 ppm). Chromate stress alleviation strategy of MT4 strain was three-fold. MT4 alleviated chromate stress and promoted the sunflower growth by suppressing the chromate intake by the host, modulating phytohormones and strengthening of the host's antioxidant system. The improved antioxidant system was confirmed by noticing lower ROS accumulation and improved ROS scavenging, lower peroxidase activity and higher accumulation of phenols and flavonoids. • Staphylococcus arlettae MT4 significantly promotes net assimilation and relative growth rate of Cr stressed sunflower. • MT4 associated seedlings had reduced uptake and higher reduction of Cr. • Strong antioxidant system of MT4 associated seedlings immuned them to grow healthy under Cr stress. [ABSTRACT FROM AUTHOR]