Reversible cytoplasmic rearrangements precede wall apposition, hypersensitive cell death and defense-related gene activation in potato/Phytophthora infestans interactions

Abstract

Abstract.We used video microscopy techniques as a tool for live examination of the dynamic aspects of plant/fungus interactions. Early, dynamic responses of epidermal midrib cells of leaves from a potato cultivar (Solanum tuberosum L. cv. Datura) carrying resistance gene R1 to Phytophthora infestans (race 1: compatible interaction, race 4: incompatible interaction) were monitored. Similar responses were observed in both types of interaction, ranging from no visible reaction of invaded plant cells to hypersensitive cell death. The overall defense response of each individual cell exhibited a highly dynamic behavior that appeared to be tightly coordinated with the growth of the fungus. Initial localized reactions, including major rearrangements within the cytoplasm, occurred directly at the fungal penetration site, where rapid apposition of autofluorescent material and callose took place. If fungal invasion stopped at this stage, the host cell restored its normal cytoplasmic activity and survived. Hypersensitive cell death occurred only when fungal growth had proceeded to the formation of a clearly identifiable haustoriurn. In such cases, cytoplasm and nucleus conglomerated around the intracellular fungal structure, followed by a sudden collapse of the whole conglomerate and an instantaneous collapse of the fungal haustorium. Only small quantitative differences between the compatible and incompatible interactions of the two fungal races were observed for these early responses of epidermal cells. In the incompatible interaction, a slightly larger number of epidermal cells responded to fungal attack. More pronounced quantitative differences between compatible and incompatible interactions occurred upon fungal invasion of the mesophyll. These differences in the number of responding cells were not reflected at the level of gene expression: the spatial and temporal activation patterns of two defense-related genes, encoding phenylalanine ammonia-lyase and pathogenesis-related protein 1, were similar in both types of interaction.Dedicated to Professor Peter Sitte, Freiburg, Germany, on the occasion of his 65th birthday Abbreviations: PAL = phenylalanine ammonia-lyase; PR 1 = pathogenesis-related protein 1; FITC = fluorescein isothiocyanateCorrespondence to: Elmon Schmelzer; FAX: 49 (221) 5062313

The Potato Late Blight Pathogen Phytophthora infestans and Other Pathogenic Oomycota

“…This finding is in agreement with the cytological studies of Freytag et al (1994), who observed hypersensitive reacting mesophyll cells not only in incompatible but also compatible interactions and suggested that the difference between compatibility and incompatibility is due to comparatively small quantitative difference in the number of mesophyll cells that respond hypersensitively. How these quantitative differences are determined and what the function of putative race-specific elicitors or suppressors is in this process is unclear.…”

“…Characteristically, the anticlinal walls of epidermal cells are penetrated by the penetration hyphae and often the cells next to stomatal guard cells are the target sites for penetration. Hyphal structures are formed in the epidermal cell from which the mycelium grows, initially intercellularly, while intracellular haustoria are formed in the mesophyll cell layer (Coffey and Gees 1991;Freytag et al 1994).…”

“…Little is known about the genetic and molecular basis of virulence/avirulence in P. infestans. Spielman et al (1989Spielman et al ( , 1990 (Freytag et al 1994). Whether this small quantitative difference is related to differences in the amount of race-specific elicitor or suppressor produced at a certain site in the infected tissues in unknown.…”

The hypersensitive response and the induction of cell death in plants

“…The timing of these events has been precisely established using video microscopy during an incompatible interaction between Phytophthora infestans and potato. Only 26 s are necessary for plant cell collapse and death, and death of the fungus follows 20 s later (Freytag et al, 1994). Such rapid responses could make detection of intermediate steps almost impossible using fixed tissues.…”

Knocking on the heaven’s wall: pathogenesis of and resistance to biotrophic fungi at the cell wall

“…Formation of these cell wall appositions (CWAs) or papillae is usually accompanied by a co-localised accumulation of phenolics and reactive oxygen species [2][3][4][5][6]. The complex process of sub-cellular cell wall remodelling is tightly linked to the rapid disassembly and subsequent focal reassembly of the plant cytoskeleton at fungal entry sites, which is indicative of a pathogen-triggered cell polarisation [6][7][8][9]. There has been a long-standing controversy, however, over whether CWAs function in disease resistance or facilitate the entry of fungal pathogens into host cells by providing a structural collar for the intruder.…”