Doctor of Philosophy (PhD)


Plant Pathology and Crop Physiology

Document Type



Asian soybean rust, caused by Phakopsora pachyrhizi, is an emerging disease in the continental U. S. and resistant commercial varieties have not been reported. In an effort to understand the interactions during rust infection of soybean, protein profile changes were examined over a 14-day period in soybean leaves of one susceptible commercial line (Pioneer 93M60) with or without soybean rust inoculation using proteomics in this study. Forty protein spots differentially expressed after rust inoculation were identified and fourteen of them were recovered and sequenced. These included proteins involved in plant defense, stress, metabolism, and other biological processes. During the time-course of rust infection, several proteins were significantly induced as early as 10 hai, such as pathogenesis-related protein 10 (PR10) and cytosolic glutamine synthetase. PR10 and chalcone isomerase 1 (CHI1), putative plant defense proteins, were further examined using quantitative real-time PCR (qRT-PCR). CHI1 transcript, the most abundant among three CHIs, was highly induced by soybean rust infection at 10 hai. Transcript level of PR10 was also significantly induced at 10 hai, 6 and 8 dai. We found that two accessions (PI417089A and PI567104B) showed consistent immune response to a Louisiana soybean rust isolate using both detached leaf assay and greenhouse inoculation after screening of 12 accessions. Fungal biomass, determined using qRT-PCR, increased significantly at 2 days after infection in susceptible lines, whereas no or little increase was detected in the resistant lines. Protein profiles of these two resistant and two susceptible lines (PI548631 and 93M60) were compared to find proteins involved in host resistance at the molecular level. Eight and 15 proteins were identified as up-regulated spots at 1 day after rust infection in both resistant accessions after comparing to the susceptible lines, PI548631 and 93M60, separately. Sixteen spots were sequenced, and they belonged to plant defense, signaling, and photosynthesis. We found that most up-regulated protein spots were identified as potential plant defense-related proteins in this study using proteomics and proteomics approach may be an effective means to identify novel proteins potentially involved in host resistance.



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Committee Chair

Chen, Zhi-Yuan/CZ-Y