Project description:Populus simonii is an important tree in the genus Populus, widely distributed in the Northern Hemisphere and having a long cultivation history. Although this species has ecologically and economically important values, its genome sequence is currently not available, hindering the development of new varieties with wider adaptive and commercial traits. Here, we report a chromosome-level genome assembly of P. simonii using PacBio long-read sequencing data aided by Illumina paired-end reads and related genetic linkage maps. The assembly is 441.38 Mb in length and contain 686 contigs with a contig N50 of 1.94 Mb. With the linkage maps, 336 contigs were successfully anchored into 19 pseudochromosomes, accounting for 90.2% of the assembled genome size. Genomic integrity assessment showed that 1,347 (97.9%) of the 1,375 genes conserved among all embryophytes can be found in the P. simonii assembly. Genomic repeat analysis revealed that 41.47% of the P. simonii genome is composed of repetitive elements, of which 40.17% contained interspersed repeats. A total of 45,459 genes were predicted from the P. simonii genome sequence and 39,833 (87.6%) of the genes were annotated with one or more related functions. Phylogenetic analysis indicated that P. simonii and Populus trichocarpa should be placed in different sections, contrary to the previous classification according to morphology. The genome assembly not only provides an important genetic resource for the comparative and functional genomics of different Populus species, but also furnishes one of the closest reference sequences for identifying genomic variants in an F1 hybrid population derived by crossing P. simonii with other Populus species.
Project description:BackgroundNAC (NAM, ATAF1–2, and CUC2) family is one of the largest plant-specific transcription factor families known to play significant roles in plant development processes and stress responses.ResultsIn the study, a total of 112 NACs were identified to be differentially expressed in the comparisons of leaves and stems, leaves and roots, roots and stems of Populus simonii×P. nigra among 289 members by RNA-Seq. And 148, 144 and 134 NACs were detected to be salt-responsive in the roots, stems and leaves under 150?mM NaCl stress, respectively. Among them, a total of 53 salt-responsive NACs were shared across the three tissues. Under salt stress, 41/37 NACs were identified to be up/down-regulated in the leaves of Populus simonii × P.nigra among 170 non-redundant NACs by RT-qPCR, which was similar with RNA-Seq results. The expression pattern analysis of 6 NACs including four randomly up-regulated genes (NAC86, NAC105, NAC139 and NAC163) and two down-regulated genes (NAC15 and NAC149) indicated a few NACs showed specific temporal and spatial expression patterns in the three tissues of Populus simonii×P.nigra. Based on transcriptome screening and phylogenic analysis of differentially expressed NACs in different tissues under salt stress, 18 potential NACs associated with wood formation and 20 involved in stress responses were identified in Populus simonii×P.nigra.ConclusionsThe study further gains an understanding of the connection of tissue specificity and gene function in poplar, and lays the foundation of functional analysis of poplar NACs in stress responses.
Project description:A dwarf mutant (dwf1) was obtained among 15 transgenic lines, when TaLEA (Tamarix androssowii late embryogenesis abundant gene) was introduced into Populus simonii × Populus nigra by Agrobacterium tumefaciens-mediated transformation. Under the same growth conditions, dwf1 height was significantly reduced compared with the wild type and the other transgenic lines. Because only one transgenic line (dwf1) displayed the dwarf phenotype, we considered that T-DNA insertion sites may play a role in the mutant formation. The mechanisms underlying this effect were investigated using TAIL-PCR (thermal asymmetric interlaced PCR) and microarrays methods. According to the TAIL-PCR results, two flanking sequences located on chromosome IV and VIII respectively, were cloned. The results indicated the integration of two independent T-DNA copies. We searched for the potential genes near to the T-DNA insertions. The nearest gene was a putative poplar AP2 transcription factor (GI: 224073210). Expression analysis showed that AP2 was up-regulated in dwf1 compared with the wild type and the other transgenic lines. According to the microarrays results, a total of 537 genes involved in hydrolase, kinase and transcription factor activities, as well as protein and nucleotide binding, showed significant alterations in gene expression. These genes were expressed in more than 60 metabolic pathways, including starch, sucrose, galactose and glycerolipid metabolism and phenylpropanoids and flavonoid biosyntheses. Our transcriptome and T-DNA insertion sites analyses might provide some useful insights into the dwarf mutant formation.
Project description:BackgroundTo optimize marker-assisted selection programs, knowledge of the genetic architecture of phenotypic traits is very important for breeders. Generally, most phenotypes, e.g. morphological and physiological traits, are quantitatively inherited, and thus detection of the genes underlying variation for these traits is difficult. Association mapping based on linkage disequilibrium has recently become a powerful approach to map genes or quantitative trait loci (QTL) in plants.ResultsIn this study, association analysis using 20 simple sequence repeat (SSR) markers was performed to detect the marker loci linked to 13 morphological traits and 10 physiological traits in a wild P. simonii population that consisted of 528 individuals sampled from 16 sites along the Yellow River in China. Based on a model controlling for both population structure (Q) and relative kinship (K), three SSR markers (GCPM_616-1 in 31.2 Mb on LG I, GCPM_4055-2 in 5.7 Mb on LG XV, and GCPM_3142 of unknown location) were identified for seven traits. GCPM_616-1 was associated with five morphological traits (R2 = 5.14-10.09%), whereas GCPM_3142 (15.03%) and GCPM_4055-2 (13.26%) were associated with one morphological trait and one physiological trait, respectively.ConclusionsThe results suggest that this wild population is suitable for association mapping and the identified markers will be suitable for marker-assisted selection breeding or detection of target genes or QTL in the near future.
Project description:Mitochondria, inherited maternally, are energy metabolism organelles that generate most of the chemical energy needed to power cellular various biochemical reactions. Deciphering mitochondrial genome (mitogenome) is important for elucidating vital activities of species. The complete chloroplast (cp) and nuclear genome sequences of Populus simonii (P. simonii) have been reported, but there has been little progress in its mitogenome. Here, we assemble the complete P. simonii mitogenome into three circular-mapping molecules (lengths 312.5, 283, and 186 kb) with the total length of 781.5 kb. All three molecules of the P. simonii mitogenome had protein-coding capability. Whole-genome alignment analyses of four Populus species revealed the fission of poplar mitogenome in P. simonii. Comparative repeat analyses of four Populus mitogenomes showed that there were no repeats longer than 350 bp in Populus mitogenomes, contributing to the stability of genome sizes and gene contents in the genus Populus. As the first reported multi-circular mitogenome in Populus, this study of P. simonii mitogenome are imperative for better elucidating their biological functions, replication and recombination mechanisms, and their unique evolutionary trajectories in Populus.
Project description:Hydrogen peroxide (H?O?) is one of the most abundant reactive oxygen species (ROS), which plays dual roles as a toxic byproduct of cell metabolism and a regulatory signal molecule in plant development and stress response. Populus simonii × Populus nigra is an important cultivated forest species with resistance to cold, drought, insect and disease, and also a key model plant for forest genetic engineering. In this study, H?O? response in P. simonii × P. nigra leaves was investigated using physiological and proteomics approaches. The seedlings of 50-day-old P. simonii × P. nigra under H?O? stress exhibited stressful phenotypes, such as increase of in vivo H?O? content, decrease of photosynthetic rate, elevated osmolytes, antioxidant accumulation, as well as increased activities of several ROS scavenging enzymes. Besides, 81 H?O?-responsive proteins were identified in the poplar leaves. The diverse abundant patterns of these proteins highlight the H?O?-responsive pathways in leaves, including 14-3-3 protein and nucleoside diphosphate kinase (NDPK)-mediated signaling, modulation of thylakoid membrane structure, enhancement of various ROS scavenging pathways, decrease of photosynthesis, dynamics of proteins conformation, and changes in carbohydrate and other metabolisms. This study provides valuable information for understanding H?O?-responsive mechanisms in leaves of P. simonii × P. nigra.
Project description:DNA methylation and miRNAs provide crucial regulation of the transcriptional and post-transcriptional responses to abiotic stress. In this study, we used methylation-sensitive amplification polymorphisms to identify 1066 sites that were differentially methylated in response to temperature stress in Populus simonii. Among these loci, BLAST searches of miRBase identified seven miRNA genes. Expression analysis by quantitative real-time PCR suggested that the methylation pattern of these miRNA genes probably influences their expression. Annotation of these miRNA genes in the sequenced genome of Populus trichocarpa found three target genes (Potri.007G090400, Potri.014G042200, and Potri.010G176000) for the miRNAs produced from five genes (Ptc-MIR396e and g, Ptc-MIR156i and j, and Ptc-MIR390c) respectively. The products of these target genes function in lipid metabolism to deplete lipid peroxide. We also constructed a network based on the interactions between DNA methylation and miRNAs, miRNAs and target genes, and the products of target genes and the metabolic factors that they affect, including H2O2, malondialdehyde, catalase (CAT), and superoxide dismutase. Our results suggested that DNA methylation probably regulates the expression of miRNA genes, thus affecting expression of their target genes, likely through the gene-silencing function of miRNAs, to maintain cell survival under abiotic stress conditions.
Project description:Pollen tubes are an ideal model for the study of cell growth and morphogenesis because of their extreme elongation without cell division; however, the genetic basis of pollen germination and tube growth remains largely unknown. Using the Illumina/Solexa digital gene expression system, we identified 13,017 genes (representing 28.3% of the unigenes on the reference genes) at three stages, including mature pollen, hydrated pollen, and pollen tubes of Populus simonii × P. nigra. Comprehensive analysis of P. simonii × P. nigra pollen revealed dynamic changes in the transcriptome during pollen germination and pollen tube growth (PTG). Gene ontology analysis of differentially expressed genes showed that genes involved in functional categories such as catalytic activity, binding, transporter activity, and enzyme regulator activity were overrepresented during pollen germination and PTG. Some highly dynamic genes involved in pollen germination and PTG were detected by clustering analysis. Genes related to some key pathways such as the mitogen-activated protein kinase signaling pathway, regulation of the actin cytoskeleton, calcium signaling, and ubiquitin-mediated proteolysis were significantly changed during pollen germination and PTG. These data provide comprehensive molecular information toward further understanding molecular mechanisms underlying pollen germination and PTG.
Project description:In this project, we have investigated the proteome of the plasmodesmata (PD) enriched membrane fraction from poplar cell suspension cultures and quantitatively compared its protein composition with other membrane fractions. We build on the previously published literature on the PD proteome by using semiquantitative methods and, for the first time, demonstrate in vitro callose synthase activity from Populus PD proteins. To our knowledge, this study is the first proteomic investigation of the PD performed on a tree species.
Project description:176 ERF genes from Populus were identified by bioinformatics analysis, 13 of these in di-haploid Populus simonii × P. nigra were investigate by real-time RT-PCR, the results demonstrated that 13 ERF genes were highly responsive to salt stress, drought stress and ABA treatment, and all were expressed in root, stem, and leaf tissues, whereas their expression levels were markedly different in the various tissues. In roots, PthERF99, 110, 119, and 168 were primarily downregulated under drought and ABA treatment but were specifically upregulated under high salt condition. Interestingly, in poplar stems, all ERF genes showed the similar trends in expression in response to NaCl stress, drought stress, and ABA treatment, indicating that they may not play either specific or unique roles in stems in abiotic stress responses. In poplar leaves, PthERF168 was highly induced by ABA treatment, but was suppressed by high salinity and drought stresses, implying that PthERF168 participated in the ABA signaling pathway. The results of this study indicated that ERF genes could play essential but distinct roles in various plant tissues in response to different environment cues and hormonal treatment.