Submitted to: Zeitschrift Fur Naturforschung
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2010
Publication Date: 4/1/2010
Citation: Chou, J., Huang, Y. 2010. Differential expression of thaumatin-like proteins in sorghum infested with greenbugs. Zeitschrift Fur Naturforschung. 65c(3-4):271-276. Interpretive Summary: Induced resistance in plants is part of the host defense mechanisms against various biotic and abiotic stresses including pest insects. Thaumatin-like proteins (TLPs), known as pathogenesis-related class 5 proteins (PR-5), has been reported in range of plant species and are often associated with response to abiotic stress and pathogen attack. In this study, expression of thaumatin-like protein was analyzed in resistant and susceptible sorghum varieties against greenbug aphid. The activity of thaumatin-like protein was determined at various time-points following aphid infestation using the real-time polymerase chain reaction (RT-PCR). The results showed that the expression levels of the TLP were increased in response to greenbug feeding and the increased levels were time-dependent. In susceptible line the TLP's transcripts increased several thousand folds at 120 hours post infestation (hpi), while for the two resistant sorghum lines its expression increased less than one hundred folds compared to the controls. The highly aphid-induced TLP activity in all sorghum lines, especially in susceptible ones, suggested that in addition to the role of TLP in host defense there were complex host defense mechanisms operating in sorghum plants during host response to greenbug infestation.
Technical Abstract: This study was designed to quantitatively analyze the expression of thaumatin-like protein (TLP) at the transcriptional level in different sorghum lines when they were infested with greenbug. Three sorghum lines, Tx7000, PI550607, and PI550610, were used. RNAs were isolated from the different sorghum lines that were infested with greenbugs at different infestation times. The resultant mRNA was reverse transcribed into cDNA and the RT-PCR products were separated by agarose gel. Then, real-time PCR data were analyzed in comparison of the TLP gene expression with the beta-actin gene as a reference. The expression levels of the TLP gene were also compared between samples. The results showed that the transcripts of the TLP were induced by greenbug feeding and the increased levels were time-dependent. In the susceptible line, the TLP's transcripts increased several thousand-fold at 120 hours post infestation (hpi), while for the two resistant sorghum lines the TLP expression level increased less than one hundred-fold compared to the controls. This is the first demonstration that thaumatin-like proteins are involved in plant defense response against insects.