PdRabG3f interfered with gibberellin-mediated internode elongation and xylem developing in poplar.

As a member of the small GTPases family, Rab GTPases play a key role in specifying transport pathways in the intracellular membrane trafficking system and are involved in plant growth and development. By quantitative trait locus (QTL) mapping, PdRabG3f was identified as a candidate gene associated with shoot height in a hybrid offspring of Populus deltoides 'Danhong' × Populus simonii 'Tongliao1'. PdRabG3f localized to the nucleus, endoplasmic reticulum and tonoplast and was primarily expressed in the xylem and cambium. Overexpression of PdRabG3f in Populus alba × Populus glandulosa (84 K poplar) had inhibitory effects on vertical and radical growth. In the transgenic lines, there were evident changes in the levels of 15 gibberellin (GA) derivatives, and the application of exogenous GA3 partially restored the phenotypes mediated by GAs deficiency. The interaction between PdRabG3f and RIC4, which was the GA-responsive factor, provided additional explanation for PdRabG3f's inhibitory effect on poplar growth. RNA-seq analysis revealed differentially expressed genes (DEGs) associated with cell wall, xylem, and gibberellin response. PdRabG3f interfering endogenous GAs levels in poplar might involve the participation of MYBs and ultimately affected internode elongation and xylem development. This study provides a potential mechanism for gibberellin-mediated regulation of plant growth through Rab GTPases.

PeCLH2 Gene Positively Regulate Salt Tolerance in Transgenic Populus alba × Populus glandulosa.

Salt is an important environmental stress factor, which seriously affects the growth, development and distribution of plants. Chlorophyllase plays an important role in stress response. Nevertheless, little is known about the physiological and molecular mechanism of chlorophyll (Chlase, CLH) genes in plants. We cloned PeCLH2 from Populus euphratica and found that PeCLH2 was differentially expressed in different tissues, especially in the leaves of P. euphratica. To further study the role of PeCLH2 in salt tolerance, PeCLH2 overexpression and RNA interference transgenic lines were established in Populus alba × Populus glandulosa and used for salt stress treatment and physiologic indexes studies. Overexpressing lines significantly improved tolerance to salt treatment and reduced reactive oxygen species production. RNA interference lines showed the opposite. Transcriptome analysis was performed on leaves of control and transgenic lines under normal growth conditions and salt stress to predict genes regulated during salt stress. This provides a basis for elucidating the molecular regulation mechanism of PeCLH2 in response to salt stress and improving the tolerance of poplar under salt stress.

Transcriptome Analysis of Populus euphratica under Salt Treatment and PeERF1 Gene Enhances Salt Tolerance in Transgenic Populus alba × Populus glandulosa.

Populus euphratica is mainly distributed in desert environments with dry and hot climate in summer and cold in winter. Compared with other poplars, P. euphratica is more resistant to salt stress. It is critical to investigate the transcriptome and molecular basis of salt tolerance in order to uncover stress-related genes. In this study, salt-tolerant treatment of P. euphratica resulted in an increase in osmo-regulatory substances and recovery of antioxidant enzymes. To improve the mining efficiency of candidate genes, the analysis combining both the transcriptome WGCNA and the former GWAS results was selected, and a range of key regulatory factors with salt resistance were found. The PeERF1 gene was highly connected in the turquoise modules with significant differences in salt stress traits, and the expression levels were significantly different in each treatment. For further functional verification of PeERF1, we obtained stable overexpression and dominant suppression transgenic lines by transforming into Populus alba × Populusglandulosa. The growth and physiological characteristics of the PeERF1 overexpressed plants were better than that of the wild type under salt stress. Transcriptome analysis of leaves of transgenic lines and WT revealed that highly enriched GO terms in DEGs were associated with stress responses, including abiotic stimuli responses, chemical responses, and oxidative stress responses. The result is helpful for in-depth analysis of the salt tolerance mechanism of poplar. This work provides important genes for poplar breeding with salt tolerance.

Genome-Wide Analysis of the AAAP Gene Family in Populus and Functional Analysis of PsAAAP21 in Root Growth and Amino Acid Transport.

The adventitious root (AR) is the basis for successful propagation by plant cuttings and tissue culture and is essential for maintaining the positive traits of a variety. Members of the amino acid/auxin permease (AAAP) gene family play indispensable roles in various plant metabolisms and have few studies on root growth and amino acid transport. In this study, with a systematic bioinformatics analysis of the Populus AAAP family, 83 PtrAAAPs were identified from Populus trichocarpa and grouped into 8 subfamilies. Subsequently, chromosomal distribution, genetic structure, cis-elements analysis, and expression pattern analysis of the AAAP family were performed and the potential gene AAAP21 regulating root development was screened by combining the results of RNA-Seq and QTL mapping. PsAAAP21 was proven as promoting root development by enhancing AR formation. Differentially expressed genes (DEGs) from RNA-seq results of overexpressing lines were enriched to multiple amino acid-related pathways, and the amino acid treatment to transgenic lines indicated that PsAAAP21 regulated amino acid transport, including tyrosine, methionine, and arginine. Analysis of the AAAP gene family provided a theoretical basis for uncovering the functions of AAAP genes. The identification of PsAAAP21 on root promotion and amino acid transport in Populus will help with breeding new woody plant species with strong rooting ability.

Genome-Wide Identification of Long Non-Coding RNAs and Their Potential Functions in Poplar Growth and Phenylalanine Biosynthesis.

Poplar is an important bioenergy tree species. lncRNAs play important roles in various biological regulatory processes, and their expression pattern is more tissue-specific than mRNAs. In this study, P. deltoides "Danhong" (Pd) and P. simonii "Tongliao1" (Ps) with different growth rates and wood quality were used as experimental materials, and the transcriptomes of their shoot apical meristem, xylem, and phloem were sequenced. Furthermore, high-throughput RNA sequencing analysis revealed that the expression patterns of genes and lncRNAs are different between the two genotypes. 6,355 lncRNAs were identified. Based on target prediction, lncRNAs and target genes were involved in ADP binding, oxidoreductase activity, phenylpropanoid biosynthesis, and cyanoamino acid metabolism. The DElncRNAs in two poplars were co-expressed with transcription factors and structural genes of lignin and flavonoid pathways. In addition, we found the potential target lncRNAs of miRNA. This result provides basic evidence for a better understanding of the regulatory role of lncRNAs in regulating phenylalanine molecular pathways and wood formation.

Leaf Size Development Differences and Comparative Trancriptome Analyses of Two Poplar Genotypes.

The plant leaf, the main organ of photosynthesis, is an important regulator of growth. To explore the difference between leaf size of Populusdeltoides 'Danhong' (Pd) and Populus simonii 'Tongliao1' (Ps), we investigated the leaf length, leaf width, leaf thickness, leaf area, leaf mass per area (LMA), and cell size of leaves from two genotypes and profiled the transcriptome-wide gene expression patterns through RNA sequencing. Our results show that the leaf area of Pd was significantly larger than that of Ps, but the epidermal cell area was significantly smaller than that of Ps. The difference of leaf size was caused by cell numbers. Transcriptome analysis also revealed that genes related to chromosome replication and DNA repair were highly expressed in Pd, while genes such as the EXPANSIN (EXPA) family which promoted cell expansion were highly expressed in Ps. Further, we revealed that the growth-regulating factors (GRFs) played a key role in the difference of leaf size between two genotypes through regulation of cell proliferation. These data provide a valuable resource for understanding the leaf development of the Populus genus.