Proteomic analysis of drought stress in important agricultural crops

As global climate changes, more floods, droughts and severe heat waves have been seen in recent decades. An adequate water supply is vital for plant growth. Thus, droughts have become one of the biggest threats accompanying global climate change. To feed the fast growing world population and overcome the impacts of drought stress, development of cereal crops tolerant to water deficit, and understanding the molecular mechanisms of drought stress response, is required. As such, we have investigated rice and wheat plants exposed to drought stress using proteomic approaches coupled with other physiological measurements. Initially, two rice landraces with contrasting drought tolerance were exposed to drought conditions followed by 3 days of re-watering. Mature leaves were harvested from plants from each treatment for protein extraction and subsequent shotgun proteomic analysis, with validation of selected proteins by western blotting. Gene Ontology (GO) annotations of differentially expressed proteins provide insights into the metabolic pathways that are involved in drought stress resistance. Our data indicate that IAC1131 appears to be better able to cope with stressful conditions by up-regulating a suite of stress and defence response related proteins. Nipponbare, in contrast, lacks the range of stress responses shown by the more stress tolerant variety, and responds to drought stress by initiating a partial shutdown of chlorophyll biosynthesis in an apparent attempt to preserve metabolic resources. In addition to the mature rice leaves, the shoot growth zones of IAC1131 and Nipponbare were dissected at each time point for mitotic analysis and protein extraction, and subsequent quantitative proteomic analysis. Gene Ontology (GO) annotations of differentially expressed proteins provided insights into differential responses of the growing zones of Nipponbare and IAC1131 to drought stress. IAC1131 sustained more mitotic cells during the drought cycle by up-regulating a suite of proteins involved in DNA replication, cellular component organization and meristem maintenance. In contrast, Nipponbare had a greatly reduced proportion of dividing cells and lacked the range of proteomic responses shown by the drought tolerant variety. In order to expand this thesis to include other cereal crops in addition to rice, we chose to investigate the effects of short and long term drought stress on young wheat seedlings. Four-day old wheat seedlings were exposed to 10 and 20 days drought stress followed by 3 and 7 days of re-watering. Proteomic analysis indicated a decline in abundance of proteins related to photosynthesis, carbohydrate metabolism, and energy metabolism. In addition, an increased abundance of proteins related to stress and defence were identified. After recovery, the abundance of the stress responsive proteins returned partially or completely to that of the control plants, suggesting they perform important functional roles in drought-specific response. Altogether, this study provided valuable fundamental insights into molecular mechanisms of drought stress response in both rice and wheat, and produced valuable knowledge for future molecular assisted breeding in these and other cereal crops.