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Biological control is an environmentally friendly approach that holds promise to complement or replace chemicals to effectively protect crop plants against pests and pathogens. Environmental samples with highly diverse and competitive microbiomes that harbor antagonistic microbes with diverse modes-of-action can provide a rich source of microbial biopesticides. In the current study, bacteria isolated from rhizosphere soil and food spoilage samples were subsequently screened against various plant fungal and oomycete pathogens in growth inhibition assays. These included the new potential biocontrol bacteria Corynebacterium flavescens, Sporosarcina aquimarina and Sporosarcina saromensis with anti-fungal and antioomycete activities. Potential candidates selected by preliminary screening in plant assays were then applied to tomato, cabbage and chickpea plants to control bacterial (Pseudomonas syringae pv. tomato), fungal (Alternaria brassicicola) and oomycete (Phytophtora medicaginis) phytopathogens. Ten potential microbial biopesticides were demonstrated to be effective against these diseases, and led to significant (p < 0.05) reductions in symptoms and/or pathogen DNA compared to mock-treated diseased plants. We conclude that new and effective microbial biopesticides to control crop pathogens can be rapidly isolated from biodiverse microbiomes, where bacteria may employ these features to effectively compete against each other.

Bacteriocins are a diverse group of bacterial antimicrobial peptides (AMPs) that represent potential replacements for current antibiotics due to their novel modes of action. At present, production costs are a key constraint to the use of bacteriocins and other AMPs. Here, we report the production of bacteriocins in planta - a potentially scalable and cost-effective approach for AMP production. Nine bacteriocin genes with three different modes of action and minimal or no post-translational modifications were synthesized, cloned and used to transform Arabidopsis thaliana. To confirm bacteriocin functionality and the potential to use these plants as biofactories, Arabidopsis T3 crude leaf extracts were subjected to inhibition assays against the bacterial pathogens Clavibacter michiganensis subsp. michiganensis (Cmm) and Pseudomonas syringae pv. tomato DC3000 (Pst). Six and seven of nine extracts significantly inhibited Cmm and Pst, respectively. Three bacteriocin genes (plantaricin, enteriocin, and leucocin) were then selected for over-expression in tomato (Solanum lycopersicum). In vitro plant pathogen inhibition assays of T0, T1 and T2 transgenic tomato leaf extracts confirmed antimicrobial activity against both pathogens for all three generations of plants, indicating their potential use as stable biopesticide biofactories. Plantaricin and leucocin-expressing T2 tomato plants were resistant to Cmm, and leucocin-expressing T2 plants were resistant to Pst. This study highlights that plants can be used as biofactories for AMP production and that the expression of bacteriocins in planta may offer new opportunities for disease control in agriculture.

In the present study, we developed an efficient and reliable protocol for in vitro plant regeneration and transient gene expression in medicinal plant Artemisia annua L. For in vitro regeneration, leaf explants were cultivated in MS medium supplemented by combination of plant growth regulators including α-naphthalene-acetic acid, 6-benzyl-aminopurine, indole-3-acetic acid and 2,4-dichlorophenoxyacetic acid. The highest frequency of shoot organogenesis occurred on MS medium supplemented with 0.5 mg/l NAA plus 2 mg/l BA (86.6%) and MS medium supplemented with 1 mg/l IAA plus 2 mg/l BA (80%). Root induction was obtained on MS medium supplemented with 0.1 mg/l IBA. This is a simple, reliable, rapid and high efficient regeneration system for A. annua L. in short period via adventitious shoot induction approach. Based on the sequence of a putative sesquiterpene cyclase from A. annua , 1.7 kb fragment was amplified by PCR from Iranian variety of this plant after cDNA synthesis. Sesquiterpene cyclase gene was used for sub-cloning into pBI121 between Xba I and Sac I sites to allow the expression of the gene driven by CaMV35S promoter. The recombinant plasmids were transferred to competent cells of Agrobacterium tumefaciens strain GV 3850 for vacuum agro-infiltration. HPLC results showed 30.09% increase in atremisinin content (0.15%) in the agroinfiltrated samples (0.67%) in comparison to the control (0.51%).

In the present study, we developed an efficient protocol for in vitro plant regeneration and genetically transformed root induction in medicinal plant Artemisia aucheri Boiss. Leaf explants were cultivated in MS medium supplemented by combination of plant growth regulators including α-naphthalene-acetic acid, 6-benzyl-aminopurine, indole-3-acetic acid and 2, 4-dichlorophenoxyaceticacid. The highest frequency of shoot organogenesis occurred on MS medium supplemented with 0.05 mg/l NAA plus 2 mg/l BA (96.3 %) and MS medium supplemented with 0.5 mg/l IAA plus 2 mg/l BA (88.3 %). Root induction was obtained on MS medium supplemented with 0.5 mg/l IBA. This is a simple, reliable, rapid and high efficient regeneration system for A. aucheri Boiss in short period via adventitious shoot induction approach. Also, an efficient genetically transformed root induction for A. aucheri was developed through Agrobacterium rhizogenes-mediated transformation by four bacterial strains, A4, ATCC15834, MSU440, and A13 (MAFF-02-10266). The maximum frequency of hairy root induction was obtained using MSU440 (93 %) and ATCC15834 (89 %) bacterial strains. Hairy root lines were confirmed by PCR using the rolB gene specific primers and Southern blot analysis.

Plants are sessile organisms that face many biotic and abiotic stresses during their life cycle. They highly depend on innate immunity of cells under attack and systemic signaling enhanced by hormones from infection sites that may lead to systemic acquired resistance. Their rapid and initial responses to microbial colonization determine which physiological pathways are induced or suppressed. Pathways are controlled by kinases and key transcription factors that can result in differential expression of thousands of genes and small RNAs that may help the plant defend itself. However, virulent pathogens often mislead the plant by "hijacking" the wrong pathway that facilitates infection rather than provides resistance. More commonly, plants engage in numerous beneficial interactions with groups of soil beneficial microbes, that assist in nutrition or abiotic stress relieve, defend plants against pathogens or prime plants towards induced systemic resistance. This chapter provides an overview of the wide ranges of microbial (pathogenic and beneficial) interactions and highlights transcriptional regulatory network that allows plants to mount the appropriate responses when interacting with pathogens and/or beneficial microorganisms.