Research article

Calcium-mediated perception and defense responses activated in plant cells by metabolite mixtures secreted by the biocontrol fungus Trichoderma atroviride

Lorella Navazio^1* , Barbara Baldan^1* , Roberto Moscatiello¹ , Anna Zuppini¹ , Sheridan L Woo² , Paola Mariani¹ and Matteo Lorito²

¹  Dipartimento di Biologia, Università di Padova, Via U. Bassi 58/B, 35131 Padova, Italy

²  Dipartimento di Arboricoltura, Botanica e Patologia Vegetale, Università di Napoli "Federico II", Via Università 100, 80055 Portici (NA), Italy

author email corresponding author email* Contributed equally

BMC Plant Biology 2007, 7:41doi:10.1186/1471-2229-7-41

Published:	30 July 2007

Abstract

Background

Calcium is commonly involved as intracellular messenger in the transduction by plants of a wide range of biotic stimuli, including signals from pathogenic and symbiotic fungi. Trichoderma spp. are largely used in the biological control of plant diseases caused by fungal phytopathogens and are able to colonize plant roots. Early molecular events underlying their association with plants are relatively unknown.

Results

Here, we investigated the effects on plant cells of metabolite complexes secreted by Trichoderma atroviride wild type P1 and a deletion mutant of this strain on the level of cytosolic free Ca²⁺ and activation of defense responses. Trichoderma culture filtrates were obtained by growing the fungus alone or in direct antagonism with its fungal host, the necrotrophic pathogen Botrytis cinerea, and then separated in two fractions (>3 and <3 kDa). When applied to aequorin-expressing soybean (Glycine max L.) cell suspension cultures, Trichoderma and Botrytis metabolite mixtures were distinctively perceived and activated transient intracellular Ca²⁺ elevations with different kinetics, specific patterns of intracellular accumulation of reactive oxygen species and induction of cell death. Both Ca²⁺ signature and cellular effects were modified by the culture medium from the knock-out mutant of Trichoderma, defective for the production of the secreted 42 kDa endochitinase.

Conclusion

New insights are provided into the mechanism of interaction between Trichoderma and plants, indicating that secreted fungal molecules are sensed by plant cells through intracellular Ca²⁺ changes. Plant cells are able to discriminate signals originating in the single or two-fungal partner interaction and modulate defense responses.