The relationship between increased growth and resistance induced in plants by root colonizing microbes

Trichoderma spp. are effective biocontrol agents for numerous foliar and root phytopathogens, and some are also known for their abilities to enhance systemic resistance to plant diseases as well as overall plant growth. Root colonization with T. harzianum strain T22 induces large changes in the proteome of shoots of maize seedlings (Zea mays) even though T22 is present only on roots; changes also were recorded in the roots. In shoots, we identified 91 of 114 upregulated and 30 of 50 downregulated proteins. In roots, 20 upregulated and 11 downregulated proteins were found and 17 and eight, respectively, were identified. Classification of proteins differentially expressed in both shoots and roots revealed that the largest number of upregulated proteins was involved in carbohydrate metabolism; in shoots, some upregulated proteins were involved in photosynthesis. Increases in these protein classifications suggest enhanced respiratory and photosynthetic rates. These changes may be required for the enhanced growth response induced by colonization of Trichoderma following seed or soil treatments. Stress and defense related proteins that were upregulated probably are related to the enhanced resistance conferred by the Trichoderma inoculation. We suggest that Trichoderma induces both increased growth, which is mediated by an increase in photosynthetic and respiratory rates, and systemic induced resistance. These two general effects may be mediated by different elicitors.