Abstract: [Objective] The study was intended to study the gene expression profile of F1 hybrids of Populus deltoides to reveal the mechanism of hybrid vigor at the gene expression level. [Method] We sequenced the transcriptomes of three super-parent hybrids F1 (H1, H2, H3), two low-parent hybrids (L1, L2), and their parents (Q1, Q2) using high throughput sequencing. [Result] We obtained a total of 171 154 127 reads, with an average length of 200 bp and a total of 31.32 Gb size. After filtering, we aligned the clean reads to the reference genome of Populus trichocarpa and 61.89% of the clean reads could be aligned to the reference genome. The comparison between super-parent hybrids F1 and parents(H Vs Q) revealed that 342 genes were differently expressed (87 up-regulated and 255 down-regulated). We termed the different expressed gene as DEG thereafter. Meanwhile, 577 DEGs (146 up-regulated and 431 down-regulated) were identified by comparing low-parent hybrids F1 with parents(L Vs Q), and 486 DEGs (200 up-regulated and 286 down-regulated) were identified by comparison of low-parent hybrids F1 and super-parent hybrid F1(H Vs L). 377 genes that were highly related to the hybrid vigor were identified, of which 4 genes down-regulated expressed in H Vs Q, L Vs Q and H Vs L, 72 genes down-regulated expressed both in H Vs Q and L Vs Q, 129 genes differentially expressed (19 up-regulated and 110 down-regulated) both in H Vs Q and H Vs L, 170 genes differentially expressed both in L Vs Q and H Vs L. The functional analysis and pathway analysis demonstrated that there were 167, 233 and 288 DGEs could be categorized into 46, 45 and 51 functional groups, respectively. In the three main categories (cellular component, molecular function, and biological process) of the GO classification, the DEGs were mainly enriched in "catalytic activity", "amine metabolic process" and "oxidoreductase activity" etc. These activities were reported to be involved in the carbohydrate metabolism, amino acid metabolism, energy metabolism and degradation pathways and foreign substances metabolic pathways.[Conclusion] Heterosis, probably due to significant different expressions of related genes, regulates metabolic activities closely linked to growth, e.g. photosynthesis, metabolism and absorption, and thus contributes to the formation of growth advantage.

Key words: Populus deltoides, thanscriptome, differential gene expression, hybrid vigor