AUTHOR=Domínguez Sara , Rubio M. Belén , Cardoza Rosa E. , Gutiérrez Santiago , Nicolás Carlos , Bettiol Wagner , Hermosa Rosa , Monte Enrique 

TITLE=Nitrogen Metabolism and Growth Enhancement in Tomato Plants Challenged with Trichoderma harzianum Expressing the Aspergillus nidulans Acetamidase amdS Gene

JOURNAL=Frontiers in Microbiology

VOLUME=7

YEAR=2016

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2016.01182

DOI=10.3389/fmicb.2016.01182

ISSN=1664-302X

ABSTRACT=<p><italic>Trichoderma</italic> 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 <italic>Trichoderma</italic> 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 <italic>amdS</italic> gene, encoding an acetamidase of <italic>Aspergillus</italic>, has been used as a selectable marker for the transformation of filamentous fungi, including <italic>Trichoderma</italic> spp., but the physiological effects of the introduction of this gene into the genome of these microorganisms still remains unexplored. No evidence of <italic>amdS</italic> orthologous genes has been detected within the <italic>Trichoderma</italic> spp. genomes and the <italic>amdS</italic> heterologous expression in <italic>Trichoderma harzianum</italic> 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 <italic>amdS</italic> transformants in dual cultures against <italic>Rhizoctonia solani, Botrytis cinerea</italic>, and <italic>Fusarium oxysporum</italic>, a significantly higher antifungal activity was detected in <italic>amdS</italic> transformants against <italic>F. oxysporum</italic>, compared to that of T34, in membrane assays on media lacking acetamide. In <italic>Trichoderma</italic>-tomato interaction assays, <italic>amdS</italic> 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 <italic>amdS</italic> transformants have also been investigated using <italic>GeneChip Tomato Genome Arrays</italic>. 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 <italic>B. cinerea</italic> infections in plants treated with <italic>amdS</italic> transformants as detected in greenhouse assays. These observations suggest that the increased plant development promoted by the <italic>amdS</italic> transformants was at expense of defenses.</p>