RNA Interference-Mediated Repression of Cell Wall Invertase Impairs Defense in Source Leaves of Tobacco

• Published in: Plant physiology (Bethesda) 2008-07, Vol.147 (3), p.1288-1299
• Main Authors: Essmann, Jutta, Schmitz-Thom, Ina, Schön, Hardy, Sonnewald, Sophia, Weis, Engelbert, Scharte, Judith
• Format: Article
• Language: English
• Subjects: Adenosine diphosphate; beta-Fructofuranosidase - metabolism; Biological and medical sciences; Carbohydrate Metabolism; Carbohydrates; Cell biochemistry; Cell Death; Cell physiology; Cell Wall - metabolism; Enzymes; Fundamental and applied biological sciences. Psychology; Glucans - metabolism; Hexoses; Hexoses - metabolism; Host-Parasite Interactions; Hydrogen peroxide; Infections; Leaves; Mesophyll cells; Molecular Sequence Data; Nicotiana - enzymology; Nicotiana - microbiology; Nicotiana - physiology; Nicotiana tabacum; Pathogens; Photosynthesis; Phytophthora - physiology; Phytophthora nicotianae; Plant cells; Plant Diseases - microbiology; Plant Leaves - metabolism; Plant physiology and development; Plants; Plants Interacting with Other Organisms; Plants, Genetically Modified - physiology; RNA Interference; Sucrose - metabolism; Sugars; Tobacco; Transgenic plants
• ISSN: 0032-0889; 1532-2548
• DOI: 10.1104/pp.108.121418

The significance of cell wall invertase (cwINV) for plant defense was investigated by comparing wild-type tobacco (Nicotiana tabacum) Samsun NN (SNN) with plants with RNA interference (RNAi)-mediated repression of cwINV (SNN::cwINV). In source leaves of SNN::cwINV, the activity of cwINV was repressed by about 90%. Sucrose export and apoplastic carbohydrate levels were significantly reduced, while photosynthesis and dark respiration exhibited little or no change. Activities of sucrose synthase and phosphofructokinase were depressed moderately, while ADP-glucose pyrophosphorylase was diminished greatly. Yet, the content of cytosolic/vacuolar carbohydrates was not significantly lower, which correlated with the absence of phenotypic effects in SNN::cwINV under normal growing conditions. By contrast, defense-related processes in primary metabolism and hypersensitive cell death were impaired and delayed in correlation with repression of cwINV. The increase in cwINV observed in source leaves of the resistant wild type following infection with Phytophthora nicotianae was absent in SNN::cwINV. Also, defense-related callose deposition at cell-to-cell interfaces, the related decline in sugar export, and accumulation of apoplastic carbohydrates were reduced and delayed. Expression of pathogenesis-related proteins and increase in phenylalanine ammonia-lyase and glucose-6-phosphate dehydrogenase activities were alleviated. Formation of hydrogen peroxide and development of hypersensitive lesions were weak and heterogeneous, and the pathogen was able to sporulate. We conclude that in photosynthetically active leaves of the apoplastic phloem loader, tobacco cwINV plays an essential role for acquisition of carbohydrates during plant-pathogen interactions and that the availability of these carbohydrates supports the onset of the hypersensitive reaction and ensures successful defense.