关键词: 楸树, 不定根发育, 转录组, 富集分析, 激素, 差异表达基因

Abstract: [Objective] To better understand potential mechanisms involved in adventitious root (AR) formation, we performed transcriptome analysis of softwood cuttings of Catalpa bungei ‘Yu-1’ at four stages of AR formation using the Illumina sequencing method.[Method] After excision, the bases of the cuttings were dipped for 60 s in a solution with 2 g·L^-1 IBA. Samples were harvested at 0 (p0, control), 1 (p1, activation), 15 (p2, callus formation), 25 (p3, root formation) and 35 (p4, root elongation) days after cutting. Total RNAs were extracted and constructed five paired-end libraries. Libraries were sequenced on an Illumina HiSeq 2000 instrument. Raw reads were cleaned by removing adaptor sequences, empty reads, and low-quality sequences. Clean reads were assembled into non-redundant transcripts using Trinity software. Functional annotation and identification of differentially expressed genes were performed using BLASTx, RSEM, Cytoscape and MeV4.9.0. Fifteen differentially expressed unigenes were randomly selected for qPCR validation of our RNA-seq data.[Result] Following de novo assembly, 62 955 unigenes were obtained, 31 646 (50.26%) of which were annotated. A total of 11 100 differentially expressed genes (DEGs), including 10 200 unique and 900 common, were identified in four comparisons. Based on the all GO enrichment networks, cytoskeleton was only significantly enriched in the activation period, while DNA metabolic process was only significantly enriched in the callus formation. Functional annotation analysis revealed that many of these genes were involved in phenylpropanoid biosynthesis, glycolysis, and plant hormone metabolism, suggesting potential contributions to AR formation. Interestingly, the number of DEGs involved in glycolysis decreased while the number of DEGs involved in phenylpropanoid biosynthesis increased following the AR formative process. These results indicated that pathways experienced a dynamic change upon hormone stimulus to occur the corresponding AR formation.[Conclusion] It was found that crosstalk between CTK and ET promoted the callus formation and crosstalk between auxin and BRs promoted the AR elongation according to the transcriptome analysis of AR formation in softwood cuttings of the C. bungei ‘YU-1’ at four different developmental stages. Although this analysis cannot completely account for AR formation in C. bungei ‘YU-1’, it serves as a powerful tool to further explore candidate pathways and genes associated with this complex process. We expect our comprehensive transcriptional overview to prove useful in both furthering the understanding of molecular networks that regulate AR formation, and in the exploration of genes that may improve rooting rates of other trees.

Key words: Catalpa bungei, adventitious root formation, transcriptome, enrichment analysis, plant hormone, differentially expressed genes