Quantitative gene expression for Aux, Atp, and DGAT1 genes affected with Bacillus subtilis, Rhizobium, Azospirillum, Burkholderia bacteria, and Trichoderma harzianum and Arbuscular mycorrhizal fungus in olive (Cv.Shammi)

Background: Olive cultivation holds significant agricultural importance. Elucidating the molecular responses of olive seedlings to microbial inoculation can inform strategies to enhance growth and productivity. This study investigated the expression of three key genes—auxin (OeAUX), adenosine triphosphate (OeATP), and diacylglycerol acyltransferases (OeDGAT1)—in Shami olive seedlings following treatment with bacterial and fungal inoculants. Methods: Seedlings were inoculated with bacterial suspensions (Bacillus subtilis, Rhizobium, Azospirillum, and Burkholderia) and fungal suspensions (Trichoderma harzianum and Arbuscular mycorrhizal fungi). Results: Bacillus subtilis and Burkholderia significantly upregulated OeAUX expression, while fungal treatments induced slight but significant increases. For OeATP, Rhizobium and B. subtilis induced substantial overexpression (113.509- and 91.350-fold, respectively). Notably, Arbuscular mycorrhizal fungi elicited a profound 3427.107-fold increase in OeATP expression. The highest OeDGAT1 expression was observed with B. subtilis treatment, while Burkholderia, Azospirillum, and Arbuscular mycorrhizal fungi also induced significant upregulation. Conclusion: Specific microbial inoculants significantly modulate the expression of growth- and energy-related genes in olive seedlings. Bacillus subtilis consistently enhanced the expression of all three genes, while Arbuscular mycorrhizal fungi exerted a particularly strong impact on OeATP. These findings indicate the potential of targeted microbial applications to improve olive seedling development through the modulation of key molecular pathways.