Abstract
Trichoderma is a fungal genus that includes species that are currently being used as biological control agents and/or as biofertilizers. In addition to the direct application of Trichoderma spp. as biocontrol agents in plant protection, recent studies have focused on the beneficial responses exerted on plants, stimulating the growth, activating the defenses, and/or improving nutrient uptake. The amdS gene, encoding an acetamidase of Aspergillus, has been used as a selectable marker for the transformation of filamentous fungi, including Trichoderma spp., but the physiological effects of the introduction of this gene into the genome of these microorganisms still remains unexplored. No evidence of amdS orthologous genes has been detected within the Trichoderma spp. genomes and the amdS heterologous expression in Trichoderma harzianum T34 did not affect the growth of this fungus in media lacking acetamide. However, it did confer the ability for the fungus to use this amide as a nitrogen source. Although a similar antagonistic behavior was observed for T34 and amdS transformants in dual cultures against Rhizoctonia solani, Botrytis cinerea, and Fusarium oxysporum, a significantly higher antifungal activity was detected in amdS transformants against F. oxysporum, compared to that of T34, in membrane assays on media lacking acetamide. In Trichoderma-tomato interaction assays, amdS transformants were able to promote plant growth to a greater extent than the wild-type T34, although compared with this strain the transformants showed similar capability to colonize tomato roots. Gene expression patterns from aerial parts of 3-week-old tomato plants treated with T34 and the amdS transformants have also been investigated using GeneChip Tomato Genome Arrays. The downregulation of defense genes and the upregulation of carbon and nitrogen metabolism genes observed in the microarrays were accompanied by (i) enhanced growth, (ii) increased carbon and nitrogen levels, and (iii) a higher sensitivity to B. cinerea infections in plants treated with amdS transformants as detected in greenhouse assays. These observations suggest that the increased plant development promoted by the amdS transformants was at expense of defenses.
Highlights
The fungal genus Trichoderma includes species that have the ability to antagonize, parasitize, or even kill other fungi (Lorito et al, 2010; Druzhinina et al, 2011)
Summary of the probe sets expressed differentially (FC ≥ 2 and FDR 0.10) in both amdS transformant-tomato plant interactions in comparison to control plants without Trichoderma. These probe sets were grouped into 18 different physiological processes, and their description was based on the homology with sequences of the UNIPROT database, using the BLAST algorithm and applying an E < 10−10 level
Plants treated with Trichoderma spp. may be larger and healthier and Physiological process
Summary
The fungal genus Trichoderma includes species that have the ability to antagonize, parasitize, or even kill other fungi (Lorito et al, 2010; Druzhinina et al, 2011). The molecular mechanisms involved in plant responses to Trichoderma root colonization have been explored through transcriptomic (Bailey et al, 2006; Alfano et al, 2007; Bae et al, 2011; Morán-Diez et al, 2012), proteomic (Marra et al, 2006; Segarra et al, 2007; Shoresh and Harman, 2008), and both proteomic and metabolomic (Bae et al, 2011; Brotman et al, 2012) approaches The results of these studies have confirmed the previous findings that Trichoderma is important for regulating many genes involved in plant defense against biotic and abiotic stresses, or for increasing the plant basal metabolism (i.e., photosynthetic rate or respiratory activities). This plant enhancer trait associated to Trichoderma would have more impact in agriculture than its common use as biocontrol agent (Shoresh et al, 2010)
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