Physiological Response Characteristics And Transcriptomic Comparsion Of Two Eucalyptu Trees Under Low Temperature Stress

Natural distribution and cultivated areas of Eucalyptus were limited by low temperature stress which is one of the natural disasters in all of the world. Therefore, studies on response mechanisms of plants to low-temperature stress are very important, not only been a guide to prologue and cultivation but also helps to breed the cold-tolerance plants. The intact seedling of E.urophylla×E.grandis and E. dunnii were exposed to low-temperature, and the morphological characteristics, physiological characteristics and as well as transcriptomic comparsion of both Eucalyptus under low temperature stress were investigated. The results are as follows:1) The activities of SOD and the content of CAT in both species increased under low-temperature stress, it indicated that the anti-oxidative systems played an important role in potentiating cold-tolerance of plant and limiting the production of free radicals to protect membrane integrity. E.dunnii showed a better adaptability for low-temperature stress with higher SOD and CAT activity and lower MDA content than E.urophylla×E.grandis, suggesting E.dunnii has a better low-temperature resistance than E. urophylla×E.grandi.2) The expression profile of transcriptome were significantly different between E.dunnii and E.urophylla×E.grandis. Four cDNA libraries were constructed from the leaves of E. dunnii and E.urophylla×E.grandis exposed to low-temperature for varying lengths of time and were evaluated by RNA-Seq analysis. The final assembly generated101,325transcripts (≥200bp) with an average length of1,134bp and N50of1,946bp, representing114.9Mb of Eucalyptus transcriptome. Among these transcripts,64,590transcripts (63.74%) were annotated by6functional databases. After removing the background differential transcripts of two genotypes, we found8,154Differently Expressed Unigenes (DEUs), suggesting these transcripts might be associated with the genotype-specific molecular responses to low-temperature. While these genotype-specific uigenes were performed functional clustering analysis, the results showed that the GO term of’Response to stress’was markedly enriched under low-temperature. In addition,253transcription factors, such as the members of NAC, MYB families, and68protein kinases were identified in these8,154genotype-specific transcripts, which indicated the upstream regulatory elements also attended the response of low-temperature stress.3) The low-temperature resistance was related to the regulation of transcription factor in E.dunnii. plantlets were exposed at4℃for0h,3h,6h,12h and24h, and cDNA libraries were carried out for transcriptome sequencing. The final optimized assembly generated205,325transcripts with an average length of1,701bp and N50of2,627bp, representing349.38Mb of the E. dunnii transcriptome. Among these transcripts,134,358transcripts (65.4%) were annotated in the Nr database using the Blast2GO software. According to the differential analysis results (Log2FC=1, FDR<0.5), we obtained11,395,11,908,11,901,12,671,8,935,10,641,11,843,9,531,11,489and10,230DETs (Differentially Expressed Transcripts) among10data sets,0h vs3h,0h vs6h,0h vs12h,0h vs24,3h vs6h,3h vs12h,3h vs24h,6h vs12h,6h vs24h,12h vs24h. Most transcripts were up-regulated as the cold stress prolonging, suggesting that these transcripts may be involved in the response to cold stress. Besides, the cold-relevant GO categories, such as ’Response to stress’ and Translational initiation’, were remarkedly enriched the GO terms. A total of586Contigs involving in transcription factor activity and169Contigs related to protein kinase activity were identified, which were classified into65types of transcription factors and8types of protein kinases based on their domains, respectively.4) Established a relatively complete transcriptome database of Eucalyptus responding to low-temperature. The assembly of the Eucalyptus gene index and the transcripts classification performed in this study will serve as useful genomic resources for the genetic improvement of Eucalyptus plants and also provide insights into the molecular mechanisms of cold-tolerance in E. dunnii.