Background: Compared with otherPopulusspecies,Populus euphraticaOliv. exhibits better tolerance to abiotic stress, especially those involving extreme temperatures. However, little is known about gene regulation and signaling pathways involved in low temperature stress responses in this species. Recent development of Illumina/Solexa-based deep-sequencing technologies has accelerated the study of global transcription profiling under specific conditions. To understand the gene network controlling low temperature perception inP. euphratica, we performed transcriptome sequencing using Solexa sequence analysis to generate a leaf transcriptome at a depth of 10 gigabases for each sample.Results: Using the Trinity method, 52,081,238 high-quality trimmed reads were assembled into a non-redundant set and 108,502 unigenes with an average length of 1,047 bp were generated. After performing functional annotations by aligning all-unigenes with public protein databases, 85,584 unigenes were annotated. Differentially expressed genes were investigated using the FPKM method by applying the Benjamini and Hochberg corrections. Overall, 2,858 transcripts were identified as differentially expressed unigenes in at least two samples and 131 were assigned as unigenes expressed differently in all three samples. In 4°C-treated sample and -4°C-treated sample, 1,661 and 866 differently expressed unigenes were detected at an estimated absolute log₂-fold change of > 1, respectively. Among them, the respective number of up-regulated unigenes in C4 and F4 sample was 1,113 and 630, while the respective number of down-regulated ungenes is 548 and 236. To increase our understanding of these differentially expressed genes, we performed gene ontology enrichment and metabolic pathway enrichment analyses. A large number of early cold (below or above freezing temperature)-responsive genes were identified, suggesting that a multitude of transcriptional cascades function in cold perception. Analyses of multiple cold-responsive genes, transcription factors, and some key transduction components involved in ABA and calcium signaling revealed their potential function in low temperature responses inP. euphratica.Conclusions: Our results provide a global transcriptome picture ofP. euphraticaunder low temperature stress. The potential cold stress related transcripts identified in this study provide valuable information for further understanding the molecular mechanisms of low temperature perception inP. euphratica.

Plants are continuously affected by unfavorable external stimuli, which influences their productivity and growth. Differences in gene composition and expression patterns lead homologous polyploid plants to exhibit different physiological phenomena, among which enhanced environmental adaptability is a powerful phenotype conferred by polyploidization. The mechanisms underlying the differences in stress tolerance between diploids and autotetraploids at the molecular level remain unclear. In this research, a full-length transcription profile obtained via the single-molecule real-time (SMRT) sequencing of high-quality single RNA molecules for use as background was combined with next-generation transcriptome and proteome technologies to probe the variation in the molecular mechanisms of autotetraploids. Tetraploids exhibited an increase in ABA content of 78.4% under natural conditions and a superior stress-resistance phenotype under severe drought stress compared with diploids. The substantial differences in the transcriptome profiles observed between diploids and autotetraploids under normal growth conditions were mainly related to ABA biosynthesis and signal transduction pathways, and 9-cis-epoxycarotenoid dioxygenase 1 (NCED1) and NCED2, which encode key synthetic enzymes, were significantly upregulated. The increased expression of the ABRE-binding factor 5-like (ABF5-like) gene was a pivotal factor in promoting the activation of the ABA signaling pathway and downstream target genes. In addition, ABA strongly induced the expression of osmotic proteins to increase the stress tolerance of the plants at the translational level. We consider the intrinsic mechanisms by which ABA affects drought resistance in tetraploids and diploids to understand the physiological and molecular mechanisms that enhance abiotic stress tolerance in polyploid plants.

Drought, which directly affected the yield of crops and trees, is a natural disaster with a profound impact on the economy. Improved water-use efficiency (WUE) and drought tolerance are currently known to be the relatively effective strategies to alleviate drought stress. OPEN STOMATA1 (OST1), the core of ABA signal, can further provide WUE by regulating the stomata closure and photosynthesis. Methyl jasmonate (MeJA) and abscisic acid (ABA) crosstalk is supposed to be involved in response to drought stress. However, detailed molecular mechanism is seriously insufficient. Here, Populus euphratica, which is naturally growing in arid and semiarid regions, was selected as the material to perform yeast mating using PeOST1 as a bait. We report that a nucleus-localized factor PeJAZ2 participated in MeJA signaling interacts with PeOST1. Overexpression of PeJAZ2 in poplar remarkably increased water deficit tolerance and WUE both in severe- and mild- drought stresses by regulating ABA signaling rather than ABA synthesis. Furthermore, PeJAZ2 overexpressing lines were shown to promote the ABA-induced stomatal closure and the hydrogen peroxide (H₂O₂) production. Collectively, these convincing evidences establish a mechanism that PeJAZ2 act as a positive regulator in response to drought stress via ABA-induced stomatal closure caused by H₂O₂ production, and provide a new sight for interpreting the cross-talk of ABA and JA signaling in regulating WUE and drought stress, to provide a basis for the drought tolerance mechanism of P. euphratica.

A PP2C homolog gene was cloned from the drought-treated cDNA library of Populus euphratica. Multiple sequence alignment analysis suggested that the gene is a potential ortholog of HAB1. The expression of this HAB1 ortholog (PeHAB1) was markedly induced by drought and moderately induced by ABA. To characterize its function in ABA signaling, we generated transgenic Arabidopsis thaliana plants overexpressing this gene. Transgenic lines exhibited reduced responses to exogenous ABA and reduced tolerance to drought compared to wide-type lines. Yeast two-hybrid analyses indicated that PeHAB1 could interact with the ABA receptor PYL4 in an ABA-independent manner. Taken together; these results indicated that PeHAB1 is a new negative regulator of ABA responses in poplar.

Lycium ruthenicum of Solanaceae was widely used as healthy vegetables and natural medicine foods for containing numerous functional components in leaves, roots and fruits. In the present study, tetraploid plants of L. ruthenicum were obtained efficiently by treating their leaves with colchicine in vitro. The highest induction frequency of the tetraploids was 31.4%, which was obtained by preculturing the leaves for 10 days and then treating them with 100 mg/L of colchicine concentration for 48 h. The ploidy levels of the regenerated plants were determined by flow cytometry and chromosome counting methods. Cytological, morphological, and histological characterization validated the results of flow cytometry, revealing the differences between the two kinds of ploidy plants in their tissue culture stage and field production stages. Morphological indexes also provide a simple and intuitionistic method for distinguishing tetraploid from diploid plants. As the chromosome number increased, the stomatal size and number of the chloroplasts in the stomata also increased, but the stomatal density decreased. The results indicate that the chromosome number is correlated with the stomatal index. The generated tetraploid is a potentially useful cultivated variety and will be beneficial for producing triploid progeny in the future.

Lycium chinense, a type of medicinal and edible plant, is rich in bioactive compounds beneficial to human health. In order to meet the market requirements for the yield and quality of L. chinense, polyploid induction is usually an effective way to increase plant biomass and improve the content of bioactive components. This study established the most effective tetraploid induction protocol by assessing various preculture durations, colchicine concentrations, and exposure times. The peak tetraploid induction efficacy, 18.2%, was achieved with a 12-day preculture and 24-h exposure to 50 mg L^–1 colchicine. Compared to diploids, tetraploids exhibited potentially advantageous characteristics such as larger leaves, more robust stems, and faster growth rates. Physiologically, tetraploids demonstrated increased stomatal size and chloroplast count in stomata but reduced stomatal density. Nutrient analysis revealed a substantial increase in polysaccharides, calcium, iron, and zinc in tetraploid leaves. In addition, seventeen carotenoids were identified in the leaves of L. chinense. Compared to the diploid, lutein, β-carotene, neoxanthin, violaxanthin, and (E/Z)-phytoene exhibited higher levels in tetraploid strains T39 and T1, with T39 demonstrating a greater accumulation than T1. The findings suggest that the generated tetraploids harbor potential for further exploitation and lay the foundation for the selection and breeding of novel genetic resources of Lycium.