Proteomic analysis of soybean [Glycine max (L.) Meer.] seeds during imbibition at chilling temperature

Many of the world’s important crops such as soybean are now widely distributed, beyond their original zones of natural selection and chilling temperature is one of the major abiotic environmental factors which limit their growth and yield. Various molecular mechanisms, underlying chilling stress and plant responses are yet to be discovered. Chilling temperatures impart maximum damage to the soybean seeds, sown in wet soils, during imbibition, causing poor germination rate, reduced seedling emergence, decreased seedling vigor, and ultimately severe loss in yield. Here we report the changes in proteome of soybean seeds exposed to low temperature (4°C) during imbibition in a known chilling-resistant soybean cultivar Z22, using two-dimensional gel electrophoresis (2-DE) and Matrix-Assisted Laser Ionization Time of Flight Mass Spectrometry (MALDI-TOF/MS). Total 40 protein spots were differentially expressed in response to low temperature, in which, 25 protein spots were up-regulated and fifteen protein spots were down-regulated. According to the search in primary databases, these proteins were a part of many metabolic pathways including, cell defense, energy, protein synthesis, cell growth/division, storage, transcription and transport. To investigate the change in mRNA levels during imbibition at 4°C, quantitative RT-PCR of nine up-regulated protein genes was carried out, which clearly demonstrated an increase in the transcript levels of five genes, whereas no change was observed for other four genes. Results of this study provide some invaluable insights about the response of soybean seeds to low temperature imbibition which include; (1) alcohol dehydrogenase I and RAB21 might contribute in decreasing the effect of anoxia, resulting from water up-take during imbibition, (2) stress-related proteins such as LEA and GST24 probably played a pivotal role in confronting low temperature stress and (3) expression of some crucial enzymes (malate dehydrogenase and phosphoenolpyruvate carboxylase) involved in TCA cycle was enhanced, which might be beneficial for seeds, in stress conditions during germination.