Transcriptome Sequencing Analysis of Birch (Betula platyphylla Sukaczev) under Low-Temperature Stress

Low temperature is one of the common abiotic stresses that adversely affect the growth and development of plants. In this study, we used RNA-Seq to identify low-temperature-responsive genes in birch and further analyzed the underlying molecular mechanism. Birch seedlings were treated by the low temperature (6 degrees C) for 0, 1, 1.5, 2, 2.5, and 3 h, respectively. A total of 3491 genes were differentially expressed after low-temperature stress. Gene Ontology (GO) and Kyoto Encyclopedia of Gene and Genomes (KEGG) functional enrichment analysis were performed for the differentially expressed genes (DEGs). GO analysis indicated that 3491 DEGs were distributed into 1002 categories, and these DEGs were enriched in "cell process", "metabolic process", and "stimulus response", under the "biological process" category; in "organelles" and "cell components", under the "cell component" category; and in "catalytic activity" and "adhesion", under the "molecular function" category. The KEGG enrichment indicated that 119 DEGs were involved in Ca2+ and plant hormone signal transduction; 205 DEGs were involved in secondary metabolic processes, such as lipid metabolism and phenylpropanoid biosynthesis pathway; and 20 DEGs were involved in photosynthesis. In addition, a total of 362 transcription factors (TFs) were differentially expressed under low-temperature stress, including AP2/ERF, C2H2, MYB-HB-like, WRKY, bHLH, WD40-like, and GRAS families. Gene Bpev01.c0480.g0081 (calmodulin-like CML38), Bpev01.c1074.g0005 (calmodulin-like CML25), Bpev01.c1074.g0001 (Calcium-binding EF-hand family protein), Bpev01.c2029.g0005 (calmodulin-like protein), Bpev01.c0154.g0008 (POD), Bpev01.c0015.g0143 (N-acetyl-1-glutamate synthase), and Bpev01.c0148.g0010 (branched chain amino acid transferase) were up-regulated at a high level, under low-temperature stress.