The Plant Growth-Promoting Fungus Aspergillus ustus Promotes Growth and Induces Resistance Against Different Lifestyle Pathogens in Arabidopsis thaliana

Abstract

To deal with pathogens, plants have evolved sophisticated mechanisms including constitutive and induced defense mechanisms. Phytohormones play important roles in plant growth and development, as well as in the systemic response induced by beneficial and pathogen microorganisms. In this work, we identified an Aspergillus ustus isolate that promotes growth and induces developmental changes in Solanum tuberosum and Arabidopsis thaliana. A. ustus inoculation on A. thaliana and S. tuberosum roots induced an increase in shoot and root growth, and lateral root and root hair numbers. Assays performed on Arabidopsis lines to measure reporter gene expression of auxin-induced/ repressed or cell cycle controlled genes (DR5 and CycB1, respectively) showed enhanced GUS activity, when compared with mock-inoculated seedlings. To determine the contribution of phytohormone signaling pathways in the effect elicited by A. ustus, we evaluated the response of a collection of hormone mutants of Arabidopsis defective in auxin, ethylene, cytokinin, or abscisic acid signaling to the inoculation with this fungus. All mutant lines inoculated with A. ustus showed increased biomass production, suggesting that these genes are not required to respond to this fungus. Moreover, we demonstrated that A. ustus synthesizes auxins and gibberellins in liquid cultures. In addition, A. ustus induced systemic resistance against the necrotrophic fungus Botrytis cinerea and the hemibiotrophic bacterium Pseudomonas syringae DC3000, probably through the induction of the expression of salicylic acid, jasmonic acid/ethylene, and camalexin defense-related genes in Arabidopsis.

Beneficial Interactions in the Rhizosphere

“…Aspergillus ustus does promote plant growth and can synthesize auxins and gibberellins. However, it was also able to promote plant growth in hormone defective mutants (auxin, ethylene, cytokinine or abscisic acid), and thus Aspergillus has other mechanisms that might be more important than hormone production (Salas-Marina et al 2011 ). Trichoderma has ACC deaminase activity, similar to what was described for PGPR above, and silencing of that gene decreased root elongation promotion of the mutants on canola seedlings (Viterbo et al 2010 ).…”

“…Trichoderma , Fusarium , Penicillium , Phoma and Pythium (Shoresh et al 2010 ;Trillas and Segarra 2009 ). Aspergillus ustus induced systemic resistance against Botrytis and Pseudomonas syringae , probably via jasmonic acid, salicylic acid, ethylene and camalexin defense related genes (Salas-Marina et al 2011 ). Trichoderma in tomato up regulates SA and this appears to be related to stronger JA response after Botrytis cinerea infection (Tucci et al 2011 ).…”

Ecologically Different Fungi Affect Arabidopsis Development: Contribution of Soluble and Volatile Compounds

“…In particular, plant growth-promoting rhizobacteria (PGPR; [4]) and rhizospheric fungi (PGPF [5]) are able to promote plant growth and development thanks to direct and indirect mechanisms. Indirect mechanisms include improved mineral nutrition through mineral solubilisation or disease suppression, whereas direct mechanisms involve production of phytohormones and volatile organic compounds (VOCs) [6]. Many PGPR strains can release volatile mixtures that stimulate plant growth [7].…”

“…Plant growth and development may be influenced by the interaction with either beneficial or pathogenic microorganisms [3,6]. For example, several non-mutualistic PGPR modify plant root architecture by increasing primary root length, lateral root number, length and density, or root hair formation [8–12].…”

Isolation and Characterization of Mercury Resistant <i>Trichoderma</i> Strains from Soil with High Levels of Mercury and Its Effects on <i>Arabidopsis thaliana</i> Mercury Uptake

“…This antagonism involves competition for nutrients and space, the production of antibiotics and the induction of systemic resistance in plants [10]. For the last two decades Trichoderma isolates have been used extensively in biological control and their influ-Advances in Microbiology ence on several microbial populations has been extensively investigated [9].…”