Invertase plays a crucial role in carbohydrate partitioning and plant development as it catalyses the irreversible hydrolysis of sucrose into glucose and fructose. The invertase family in plants is composed of two sub-families: acid invertases, which are targeted to the cell wall and vacuole; and neutral/alkaline invertases, which function in the cytosol. In this study, 5 cell wall invertase genes (PtCWINV1-5), 3 vacuolar invertase genes (PtVINV1-3) and 16 neutral/alkaline invertase genes (PtNINV1-16) were identified in the Populus genome and found to be distributed on 14 chromosomes. A comprehensive analysis of poplar invertase genes was performed, including structures, chromosome location, phylogeny, evolutionary pattern and expression profiles. Phylogenetic analysis indicated that the two sub-families were both divided into two clades. Segmental duplication is contributed to neutral/alkaline sub-family expansion. Furthermore, the Populus invertase genes displayed differential expression in roots, stems, leaves, leaf buds and in response to salt/cold stress and pathogen infection. In addition, the analysis of enzyme activity and sugar content revealed that invertase genes play key roles in the sucrose metabolism of various tissues and organs in poplar. This work lays the foundation for future functional analysis of the invertase genes in Populus and other woody perennials.

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To obtain a comprehensive overview of the dynamic transcriptome during male floral bud development in Populus tomentosa, high-throughput RNA-seq was conducted during eight flowering-related stages. Among the 109,212 de novo assembled unigenes, 6,959 were differentially expressed during the eight stages. The overrepresented classed of genes identified by Gene Ontology (GO) enrichment included ‘response to environmental stimuli’ and ‘plant-type spore development’. One-third of the differentially expressed genes were transcription factors (TFs). Several genes and gene families were analyzed in depth, including MADS-box TFs, Squamosa promoter binding protein-like family, receptor-like kinases, FLOWERING LOCUS T/TERMINAL-FLOWER-LIKE 1 family, key genes involved in anther and tapetum development, as well as LEAFY, WUSCHEL and CONSTANS. The results provided new insights into the roles of these and other well known gene families during the annual flowering cycle. To explore the mechanisms regulating poplar flowering, a weighted gene co-expression network was constructed using 98 floral-related genes involved in flower meristem identity and flower development. Many modules of co-expressed genes and hub genes were identified, such as APETALA1 and HUA1. This work provides many new insights on the annual flowering cycle in a perennial plant, and a major new resource for plant biology and biotechnology.

Populus has a wide ecogeographical range spanning the Northern Hemisphere, and interspecific hybrids are common. Populus tomentosa Carr. is widely distributed and cultivated in the eastern region of Asia, where it plays multiple important roles in forestry, agriculture, conservation, and urban horticulture. Reference genomes are available for several Populus species, however, our goals were to produce a very high quality de novo chromosome-level genome assembly in P. tomentosa genome that could serve as a reference for evolutionary and ecological studies of hybrid speciation throughout the genus. Here, combining long-read sequencing and Hi-C scaffolding, we present a high-quality, haplotype-resolved genome assembly. The genome size was 740.2 Mb, with a contig N50 size of 5.47 Mb and a scaffold N50 size of 46.68 Mb, consisting of 38 chromosomes, as expected with the known diploid chromosome number (2n = 2x = 38). A total of 59,124 protein-coding genes were identified. Phylogenomic analyses revealed that P. tomentosa is comprised of two distinct subgenomes, which we deomonstrate is likely to have resulted from hybridization between Populus adenopoda as the female parent and Populus alba var. pyramidalis as the male parent, with an origin of approximately 3.93 Ma.

Abscisic acid (ABA) plays a fundamental role in plant response and adaptation to abiotic stresses, such as drought, high salinity and low temperature. Populus hopeiensis exhibits exceptional tolerance to water-deficit environments and is therefore an excellent choice for studying drought tolerance in trees. This study provides a global view of transcriptome dynamics in P. hopeiensis in response to exogenous ABA using Illumina RNA-sequencing. Endogenous ABA content increased and reached a peak at 8 h after ABA treatment and then significantly decreased at latter time points. Differential expression analysis and Gene ontology enrichment revealed that the number of transcripts exhibited significant increase during the first 8 hours after ABA treatment, which then significantly decreased at 12 and 24 h. Transcription factors (TFs) analysis showed that six different patterns were observed based on the expression of the six TFs families (AP2/ERF, NAC, MYB, MYB-related, bZIP and WRKY) and the majority of differentially expressed TFs increased rapidly after ABA treatment. This study provides a robust resource for investigating the functions of genes induced by ABA and will help to develop a better understanding of the molecular regulatory mechanism in response to drought in poplar.