Abstract
Slow germination speed caused by low temperature stress intensifies the risk posed by adverse environmental factors, contributing to low germination rate and reduced production of rapeseed. The purpose of this study was to understand the transcriptional regulation mechanism for rapid germination of rapeseed. The results showed that seed components and size do not determine the seed germination speed. Different temporal transcriptomic profiles were generated under normal and low temperature conditions in genotypes with fast and slow germination speeds. Using weight gene co-expression network analysis, 37 823 genes were clustered into 15 modules with different expression patterns. There were 10 233 and 9111 differentially expressed genes found to follow persistent tendency of up- and down-regulation, respectively, which provided the conditions necessary for germination. Hub genes in the continuous up-regulation module were associated with phytohormone regulation, signal transduction, the pentose phosphate pathway, and lipolytic metabolism. Hub genes in the continuous down-regulation module were involved in ubiquitin-mediated proteolysis. Through pairwise comparisons, 1551 specific upregulated DEGs were identified for the fast germination speed genotype under low temperature stress. These DEGs were mainly enriched in RNA synthesis and degradation metabolisms, signal transduction, and defense systems. Transcription factors, including WRKY, bZIP, EFR, MYB, B3, DREB, NAC, and ERF, are associated with low temperature stress in the fast germination genotype. The aquaporin NIP5 and late embryogenesis abundant (LEA) protein genes contributed to the water uptake and transport under low temperature stress during seed germination. The ethylene/H2O2-mediated signal pathway plays an important role in cell wall loosening and embryo extension during germination. The ROS-scavenging system, including catalase, aldehyde dehydrogenase, and glutathione S-transferase, was also upregulated to alleviate ROS toxicity in the fast germinating genotype under low temperature stress. These findings should be useful for molecular assisted screening and breeding of fast germination speed genotypes for rapeseed.
Highlights
Seed germination is a crucial developmental stage in the life cycle of plants, beginning with the uptake of water by the quiescent dry seeds and ending with the protrusion of radicle through the seed coat[1,2]
Utilizing the weighted gene co-expression network analysis[37,38], the present study highlights the power of transcriptome analysis to elucidate specific network regulation of germination processes and to detect potential candidate genes involved in fast germination of rapeseed (Brassica napus L.) under low temperature stress
The results showed that there was a significant variation in germination speed under low temperature stress, and the mean germination time (MGT) ranged from 2.16 to 5.89 d for rapeseed
Summary
Seed germination is a crucial developmental stage in the life cycle of plants, beginning with the uptake of water by the quiescent dry seeds and ending with the protrusion of radicle through the seed coat[1,2]. Germination speed decreases at temperatures below the optimal germination range (20–25 °C) for rapeseed (Brassica napus L.)[15] This delay of germination intensifies the adverse effects of other abiotic factors on germination, lowering the final seedling emergence rate and limiting the ability of plants to produce a high seed yield[16]. Candidate genes controlling seed germination and vigor in Brassica napus L. have been identified by genome-wide association mapping[31]; studies on gene regulatory networks related to fast germination under low temperature stress remain rare[32,33,34]. Utilizing the weighted gene co-expression network analysis[37,38], the present study highlights the power of transcriptome analysis to elucidate specific network regulation of germination processes and to detect potential candidate genes involved in fast germination of rapeseed (Brassica napus L.) under low temperature stress
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