Transcriptome and digital gene expression analysis of herbaceous peony (Paeonia lactiflora Pall.) to screen thermo-tolerant related differently expressed genes

Herbaceous peony (Paeonia lactiflora Pall.) is easily injured by heat stress (HS), which greatly restricts its application and promotion. In this study, the thermo-tolerance of three representative P. lactiflora cultivars had been firstly assessed. 'Zifengyu' was identified as the thermo-tolerant cultivar with relatively lower values and smaller variations in malondialdehyde, hydrogen peroxide (H2O2) and proline contents under HS. Subsequently, their transcriptomes were sequenced by RNA sequencing (RNA-seq) technology to construct a complete database. 81,599 unigenes were obtained, and 34,940 unigenes had been annotated. Moreover, through digital gene expression analysis of thermo-tolerant 'Zifengyu' and moderately thermo-tolerant 'Hongyanzhenghui', 161 heat stress response genes had been screened involving heat shock protein genes, plant hormone signal transduction related genes, fatty acid synthesis genes, reactive oxygen species-scavenging genes and secondary metabolites related genes. And the effectively and timely response of these genes to HS could endow thermo-tolerance to 'Zifengyu'. Among these genes, 11 key thermo-tolerant related genes whose expressions were all significantly up-regulated in 'Zifengyu' and 'Hongyanzhenghui' during development and the former possessed higher levels could be regarded as the candidate genes, including isoprene synthase gene, 2 peroxidase genes, 3-oxoacyl-acyl carrier protein reductase gene (FabG), 3 transcription factor genes (bHLH, NAC and WRKY), HSP20 and 3 HSP70. These results could provide a better understanding of heat stress response in P. lactiflora, and pave for the breeding of thermo-tolerant cultivars.