Global transcriptomics identification and analysis of transcriptional factors in different tissues of the paper mulberry.

BACKGROUND: The paper mulberry (Broussonetia papyifera) is one of the multifunctional tree species in agroforestry system and is also commonly utilized in traditional medicine in China and other Asian countries. To identify the transcription factors (TFs) and comprehensively understand their regulatory roles in the growth of the paper mulberry, a global transcriptomics TF prediction and the differential expression analysis among root, shoot and leaf were performed by using RNA-seq. RESULTS: Results indicate that there is 1, 337 TFs encoded by the paper mulberry and they belong to the 55 well-characterized TF families. Based on the phylogenetic analysis, the TFs exist extensively in all organisms are more conservative than those exclusively exist in plant and the paper mulberry has the closest relationship with the mulberry. According to the results of differential expression analysis, there are 627 TFs which exhibit the differential expression profiles in root, shoot and leaf. ARR-Bs, ARFs, NACs and bHLHs together with other root-specific and highly expressed TFs might account for the developed lateral root and unconspicuous taproot in the paper mulberry. Meanwhile, five TCPs highly expressed in shoot of the paper mulberry might negatively regulate the expression of 12 LBDs in shoot. Besides, LBDs, which could directly or indirectly cooperate with ARFs, bHLHs and NACs, seem to be the center knot involving in the regulation of the shoot development in the paper mulberry. CONCLUSIONS: Our study provides the comprehensive transcriptomics identification of TFs in the paper mulberry without genome reference. A large number of lateral organ growth regulation related TFs exhibiting the tissue differential expression may entitle the paper mulberry the developed lateral roots, more branches and rapid growth. It will increase our knowledge of the structure and composition of TFs in tree plant and it will substantially contribute to the improving of this tree.

De Novo assembly of expressed transcripts and global transcriptomic analysis from seedlings of the paper mulberry (Broussonetia kazinoki x Broussonetia papyifera).

The paper mulberry is one of the multifunctional tree species in agroforestry systems and is also commonly utilized in traditional medicine in China and other Asian countries. However, little is known about its molecular genetics, which hinders research on and exploitation of this valuable resource. To discern the correlation between gene expression and the essential properties of the paper mulberry, we performed a transcriptomics analysis, assembling a total of 37,725 unigenes from 54,638,676 reads generated by RNA-seq. Among these, 22,692 unigenes showed greater than 60% similarity with genes from other species. The lengths of 13,566 annotated unigenes were longer than 1,000 bp. Functional clustering analysis with COG (Cluster of Orthologous Groups) revealed that 17,184 unigenes are primarily involved in transcription, translation, signal transduction, carbohydrate metabolism, secondary metabolism, and energy metabolism. GO (Gene Ontology) annotation suggests enrichment of genes encoding antioxidant activity, transporter activity, biosynthesis, metabolism and stress response, with a total of 30,659 unigenes falling in these categories. KEGG (Kyoto Encyclopedia of Genes and Genomes) metabolic pathway analysis showed that 7,199 unigenes are associated with 119 metabolic pathways. In addition to the basic metabolism, these genes are enriched for plant pathogen interaction, flavonoid metabolism and other secondary metabolic processes. Furthermore, differences in the transcriptomes of leaf, stem and root tissues were analyzed and 7,233 specifically expressed unigenes were identified. This global expression analysis provided novel insights about the molecular mechanisms of the biosynthesis of flavonoid, lignin and cellulose, as well as on the response to biotic and abiotic stresses including the remediation of contaminated soil by the paper mulberry.

Improved drought and salt tolerance of Arabidopsis thaliana by transgenic expression of a novel DREB gene from Leymus chinensis.

Dehydration-responsive element-binding (DREB) proteins are important transcription factors in plant stress responses and signal transduction. Based on high-throughput sequencing results, a new cDNA sequence encoding an LcDREB3a transcription factor from the drought-resistant forage grass, Leymus chinensis, was isolated by RACE PCR. Sequence similarity analysis indicates that the gene product is active in the ABA-responsive pathway, and real-time PCR-based expression analysis shows the transcript accumulates in response to a variety of stress treatments. These results indicate that LcDREB3a is involved in both ABA-dependent and -independent signal transduction in the stress-responsive process of L. chinensis. The identity of the gene product as a DREB transcription factor is supported by observations of its nuclear localization when transiently expressed as a GFP fusion in onion epidermal cells. Furthermore, LcDREB3a is able to activate reporter gene expression, and the protein is shown to specifically bind to the conserved DRE element in a yeast one-hybrid assay. The transgenic expression of LcDREB3a in Arabidopsis causes no growth retardation and induces the increased expression of stress tolerance genes compared to control, resulting in improved drought and salt stress tolerance. Thus, LcDREB3a, encoding a stress-inducible DREB transcription factor, could enhance the abiotic stress tolerance of plants.