Poster: Plant-pathogen interactions

Abs # 522: Pathogen induced, nonclassical secretion of the mannitol metabolizing enzyme mannitol dehydrogenase (MTD) in plants.

Presenter:	Williamson, John D, john_williamson@ncsu.edu
Authors	Williamson, John D (A)   Pharr, Mason  (A)   Zamski, Eli  (B)
Affiliations:	(A): Department of Horticultural Science, North Carolina State University (B): Department of Agricultural Botany, The Hebrew University of Jerusalem, Israel

The sugar alcohol mannitol and its catabolic enzyme mannitol dehydrogenase (MTD) have well-characterized roles in photosynthesis, osmoprotection and metabolism. There is now growing evidence that indicates both also play a role in host-pathogen interactions. Mannitol is an antioxidant, and current research in both plants and animals suggests that fungal pathogens secrete mannitol to suppress active oxygen-mediated host defenses. Our work further suggests that plants counter this by making MTD to catabolize mannitol of fungal origin. For this to be an effective defense the plant’s pathogen-induced MTD must be co-localized with pathogen-produced mannitol. Previous work in this and other labs, however, showed that pathogen-secreted mannitol was likely extracellular, while MTD in healthy plants was cytosolic. Here we will present the results of immunolocalization analyses, together with blot and chemical analysis of proteins secreted by cultured cells, that now shown that an anti-MTD serum cross-reacting protein rapidly appears in the extracellular space of pathogen-induced plants in the absence of cell lysis. As there is no recognizable Golgi/ER transport sequence in celery MTD or in any of its identified homologs, this implies that MTD is secreted by a Golgi-independent (i.e. nonclassical) secretion mechanism in response to pathogen attack. While several stress and pathogen-induced nonclassical secretion mechanisms have been described in animals, none has been characterized in plants.