Proteomic analysis of rubber trees uncovers a systemic response to white root rot disease

Abstract

White root rot disease caused by Rigidoporus microporus (Sw.) Overeem is a disastrous root disease found in rubber trees (Hevea brasiliensis). It significantly reduces natural rubber production and triggers plant death. In the early stages of infection, the aboveground parts of the diseased plant are still healthy. However, by the time that disease symptoms are apparent, it is too late for the plant to recover. Thus, this study aims to understand the systemic response of rubber trees during root infection by using 2D-PAGE coupled with LC-MS/MS. The root system of rubber tree clone RRIM600 was inoculated with R. microporus for 50 days and the stems were then collected for analysis. The results indicate that fungal infection of underground rubber tree parts can trigger changes in the proteome profile of asymptomatic aboveground parts. Fifteen protein spots were found to be differentially expressed between pathogen-inoculated and mock-inoculated plants. Nine spots were significantly changed after infection (p < 0.05). Small heat shock proteins were the major group of stress-related proteins that were significantly down-regulated after infection. Moreover, the hydrogen cyanide releasing enzymes, antioxidant enzymes and photosynthesis associated proteins were down-regulated in the stems of infected trees. The down-regulation of several proteins that are involved in the stress defense response contributed to white root rot disease susceptibility of the RRIM600 clone. This research contributes to a better understanding of the mechanisms behind rubber tree systemic responses to white root rot disease, and the candidate proteins that may be useful in rubber trees breeding programs.