Dehydration-responsive alterations in the chloroplast proteome and cell metabolomic profile of rice reveals key stress adaptation responses

Chloroplast is a semi-autonomous organelle in plants and other photosynthetic eukaryotes, playing a fundamental role of regulating photosynthesis. It is also responsible for sustaining essential biosynthetic reactions including synthesis of amino acids, fatty acids and terpenes. Photosynthesis, the conversion of light energy into chemical energy, serves as the sensor of environmental changes and augments different cellular functions to initiate adaptive responses. However, the molecular processes and regulatory mechanisms of dehydration tolerance adopted by chloroplast remain largely unknown. To gain a better understanding of dehydration response, a chloroplast proteome map of rice was developed. Four-week-old rice seedlings were subjected to dehydration by withholding water for 9 d, and the magnitude of dehydration-induced damage to the chloroplast was monitored. The iTRAQ-based quantitative proteome analysis led to the identification of 40 differentially regulated proteins (DRPs). The DRPs were presumably involved in a wide array of metabolic processes including chloroplast energy metabolism, photosynthesis and defense response. Furthermore, dehydration-induced changes in the metabolite profile and network analysis revealed a high abundance of branched chain amino acids and sugar that might reduce osmotic potential, thereby protecting cellular integrity. The proteomics approach revealed altered status of major photosynthesis related proteins, while cell metabolite profile demonstrated alteration of tricarboxylic acid cycle intermediates, indicating dehydration-triggered alterations in ATP production and energy metabolism. Altogether, these results demonstrated that the global regulation of chloroplast proteome is intimately linked to cellular metabolic rewiring of adaptive responses, which may favor genetic manipulation of crop species for better adaptation.