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PLANTS INTERACTING WITH OTHER ORGANISMS

Plant-Derived Sucrose Is a Key Element in the Symbiotic Association between Trichoderma virens and Maize Plants^1,[C],[W]

Department of Plant Pathology and Microbiology, Texas A&M University, College Station, Texas 77843

Fungal species belonging to the genus Trichoderma colonize the rhizosphere of many plants, resulting in beneficial effects such as increased resistance to pathogens and greater yield and productivity. However, the molecular mechanisms that govern the recognition and association between Trichoderma and their hosts are still largely unknown. In this report, we demonstrate that plant-derived sucrose (Suc) is an important resource provided to Trichoderma cells and is also associated with the control of root colonization. We describe the identification and characterization of an intracellular invertase from Trichoderma virens (TvInv) important for the mechanisms that control the symbiotic association and fungal growth in the presence of Suc. Gene expression studies revealed that the hydrolysis of plant-derived Suc in T. virens is necessary for the up-regulation of Sm1, the Trichoderma-secreted elicitor that systemically activates the defense mechanisms in leaves. We determined that as a result of colonization of maize (Zea mays) roots by T. virens, photosynthetic rate increases in leaves and the functional expression of tvinv is crucial for such effect. In agreement, the steady-state levels of mRNA for Rubisco small subunit and the oxygen-evolving enhancer 3-1 were increased in leaves of plants colonized by wild-type T. virens. We conclude that during the symbiosis, the sucrolytic activity in the fungal cells affects the sink activity of roots, directing carbon partitioning toward roots and increasing the rate of photosynthesis in leaves. A discussion of the role of Suc in controlling the fungal proliferation on roots and its pivotal role in the coordination of plant-microbe associations is provided.

² Present address: Department of Synthetic Biology and Bioenergy, J. Craig Venter Institute, 9704 Medical Center Drive, Rockville, MD 20850.

The author responsible for distribution of materials integral to the findings presented in this article in accordance with the policy described in the Instructions for Authors (www.plantphysiol.org) is: Charles M. Kenerley (c-kenerley{at}tamu.edu).

^[C] Some figures in this article are displayed in color online but in black and white in the print edition.

^[W] The online version of this article contains Web-only data.

www.plantphysiol.org/cgi/doi/10.1104/pp.109.141291

^* Corresponding author; e-mail c-kenerley{at}tamu.edu.

Received May 12, 2009; accepted August 5, 2009; published August 12, 2009.