Comparative Proteomic Analysis of <i>Brassica napus</i> in Response to Drought Stress

Drought is one of the most widespread stresses leading to retardation of plant growth and development. We examined proteome changes of an important oil seed crop, canola (<i>Brassica napus</i> L.), under drought stress over a 14-day period. Using iTRAQ LC–MS/MS, we identified 1976 proteins expressed during drought stress. Among them, 417 proteins showed significant changes in abundance, and 136, 244, 286, and 213 proteins were differentially expressed in the third, seventh, 10th, and 14th day of stress, respectively. Functional analysis indicated that the number of proteins associated with metabolism, protein folding and degradation, and signaling decreased, while those related to energy (photosynthesis), protein synthesis, and stress and defense increased in response to drought stress. The seventh and 10th-day profiles were similar to each other but with more post-translational modifications (PTMs) at day 10. Interestingly, 181 proteins underwent PTMs; 49 of them were differentially changed in drought-stressed plants, and 33 were observed at the 10th day. Comparison of protein expression changes with those of gene transcription showed a positive correlation in <i>B. napus</i>, although different patterns between transcripts and proteins were observed at each time point. Under drought stress, most protein abundance changes may be attributed to gene transcription, and PTMs clearly contribute to protein diversity and functions.