Proteomic and Transcriptomic Analyses of Agave americana in Response to Heat Stress

Plants with Crassulacean acid metabolism must cope with severe environmental stresses including heat-limited, water-limited, and CO2-limited environments throughout their life cycles in arid or semiarid habitats. Heat stress affects the rate of photosynthesis and related thermotolerance in many plants. To elucidate the mechanism(s) of heat tolerance and the role(s) of stromal proteomes in the heat-tolerant plant Agave americana, stromal proteins were extracted from heat-stressed and control plants and subjected to a novel proteomics approach using a Multidimensional Protein Identification Technology (MudPIT) and followed by mass spectrometry. Several differentially expressed stromal proteins were identified under heat stress, and their subcellular localization, as well as their biological and molecular functions, was determined in silico. A total of 58 stromal proteins that play important roles in photosynthesis, defense, plastid metabolic functions, hormonal biosynthesis, stress signal perception, and transduction were identified. Expression of both nuclear-encoded and chloroplast-encoded proteins was reduced under heat stress, suggesting that plants must have undergone disruption of major physiological and metabolic pathways at high temperature stress. Similarly, relative transcript levels of 16 selected stromal genes were analyzed in heat-stressed plants at 3 different temperatures and compared to those of control plants. Both MudPIT and real-time polymerase chain reaction analyses indicated that several proteins/genes were either upregulated or downregulated under heat stress. As there was no correlation between some transcriptomic and proteomics data, this suggested that posttranslational modifications must play some roles in plant thermotolerance and adaptation to high temperatures.