Submitted to: Plant Biology
Publication Type: Peer reviewed journal
Publication Acceptance Date: 4/3/2006
Publication Date: 7/5/2006
Citation: Ji, J., Scott, M.P., Bhattacharyya, M.K. 2006. Light is essential for degradation of ribulose-1,5-biphosphate carboxylase-oxygenase large subunit during sudden death syndrome development in soybean. Plant Biology. 8:597-605. Interpretive Summary: Soybean sudden death syndrome (SDS) is a disease that reduces the yield of soybeans yields in 10 states. A toxin produced by a fungal pathogen causes infected plants to die. In order to control this disease, it is important to understand the moleculuar mechanisms causing the disease symptoms. We determined that the leaves of plants exposed to the toxin are killed by an accumulation of reactive oxygen species and we demonstrated the feasability of isolating the toxin. This will allow us to characterize the SDS toxin molecularly. This information will facilitate development of plants that are resistant to the disease, benefiting soybean producers by increasing yields.
Technical Abstract: Fusarium solani f. sp. glycines (Fsg) has been reported to produce at least two phytotoxins. Cell-free Fsg-culture filtrates containing phytotoxins have been shown to develop foliar sudden death syndrome (SDS) in soybean. We have investigated the changes in protein profiles of diseased leaves caused by cell-free Fsg-culture filtrates prepared from Fsg isolates. Two-dimensional sodium dodecyl sulfate-polyacrylamide gel electrophoresis (PAGE) was conducted to investigate the protein profiles of diseased and healthy leaves. An approximately 55 kDa protein was found to be degraded in diseased leaves. Matrix-assisted laser desorption-ionization time-of-flight mass spectrometric analyses and database search revealed that the degraded protein is the ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) large subunit which is involved in carbon assimilation and photorespiration. This result was confirmed by western blotting experiments. We have shown that light is essential for degradation of Rubisco large subunit by cell-free Fsg-culture filtrates. Cell-free Fsg-culture-induced degradation of Rubisco large subunit was accompanied by accumulation of reactive oxygen species under light conditions. Terminal deoxynucleotidyl transferase-mediated nick-end labeling experiments suggested that programmed cell death was initiated in leaves of seedlings fed with cell-free Fsg culture-filtrates. The degradation of Rubisco large subunit, accumulation of free radicals and programmed cell death also occurred in leaves of seedlings fed with active anion-exchange column fractions prepared from cell-free Fsgculture filtrates. These results suggest that in presence of light Fsg-culture filtrates containing phytotoxins cause degradation of Rubisco large subunit and accumulation of free radicals, and thereby, initiate programmed cell death leading to foliar SDS development in soybean.