The NAC (NAM, ATAF and CUC) gene family plays a crucial role in the transcriptional regulation of various biological processes and has been identified and characterized in multiple plant species. However, genome-wide identification of this gene family has not been implemented in Juglans mandshurica, and specific functions of these genes in the development of fruits remain unknown. In this study, we performed genome-wide identification and functional analysis of the NAC gene family during fruit development and identified a total of 114 JmNAC genes in the J. mandshurica genome. Chromosomal location analysis revealed that JmNAC genes were unevenly distributed in 16 chromosomes; the highest numbers were found in chromosomes 2 and 4. Furthermore, according to the homologues of JmNAC genes in Arabidopsis thaliana, a phylogenetic tree was constructed, and the results demonstrated 114 JmNAC genes, which were divided into eight subgroups. Four JmNAC gene pairs were identified as the result of tandem duplicates. Tissue-specific analysis of JmNAC genes during different developmental stages revealed that 39 and 25 JmNAC genes exhibited upregulation during the mature stage in walnut exocarp and embryos, indicating that they may serve key functions in fruit development. Furthermore, 12 upregulated JmNAC genes were common in fruit ripening stage in walnut exocarp and embryos, which demonstrated that these genes were positively correlated with fruit development in J. mandshurica. This study provides new insights into the regulatory functions of JmNAC genes during fruit development in J. mandshurica, thereby improving the understanding of characteristics and evolution of the JmNAC gene family.

Background: Black cottonwood (Populus deltoides) is one of the keystone forest tree species, and has become the main breeding parents in poplar hybrid breeding. However, the genetic diversity and population structure of the introduced resources are not fully understood.Results: In the present study, five loci containing null alleles were excluded and 15 pairs of SSR (simple sequence repeat) primers were used to analyze the genetic diversity and population structure of 384 individuals from six provenances (Missouri, Iowa, Washington, Louisiana, and Tennessee (USA), and Quebec in Canada) ofP. deltoides. Ultimately, 108 alleles (N_a) were detected; the expected heterozygosity (H_e) per locus ranged from 0.070 to 0.905, and the average polymorphic information content (PIC) was 0.535. The provenance ‘Was’ had a relatively low genetic diversity, while ‘Que’, ‘Lou’, and ‘Ten’ provenances had high genetic diversity, with Shannon’s information index (I) above 1.0. The mean coefficient of genetic differentiation (F_st) and gene flow (N_m) were 0.129 and 1.931, respectively. Analysis of molecular variance (AMOVA) showed that 84.88% of the genetic variation originated from individuals. Based on principal coordinate analysis (PCoA) and STRUCTURE cluster analysis, individuals distributed in the Mississippi River Basin were roughly classified as one group, while those distributed in the St. Lawrence River Basin and Columbia River Basin were classified as another group. The cluster analysis based on the population level showed that provenance ‘Iow’ had a small gene flow and high degree of genetic differentiation compared with the other provenances, and was classified into one group. There was a significant relationship between genetic distance and geographical distance.Conclusions: P. deltoidesresources have high genetic diversity and there is a moderate level of genetic differentiation among provenances. Geographical isolation and natural conditions may be the main factors causing genetic differences among individuals. Individuals reflecting population genetic information can be selected to build a core germplasm bank. Meanwhile, the results could provide theoretical support for the scientific management and efficient utilization ofP. deltoidesgenetic resources, and promote the development of molecular marker-assisted breeding of poplar.

Introduction: The above-ground parts of terrestrial plants are collectively known as the phyllosphere. The surface of the leaf blade is a unique and extensive habitat for microbial communities. Phyllosphere bacteria are the second most closely associated microbial group with plants after fungi and viruses, and are the most abundant, occupying a dominant position in the phyllosphere microbial community. Host species are a major factor influencing the community diversity and structure of phyllosphere microorganisms.Methods: In this study, six Populus spp. were selected for study under the same site conditions and their phyllosphere bacterial community DNA fragments were paired-end sequenced using 16S ribosomal RNA (rRNA) gene amplicon sequencing. Based on the distribution of the amplicon sequence variants (ASVs), we assessed the alpha-diversity level of each sample and further measured the differences in species abundance composition among the samples, and predicted the metabolic function of the community based on the gene sequencing results.Results: The results revealed that different Populus spp. under the same stand conditions resulted in different phyllosphere bacterial communities. The bacterial community structure was mainly affected by the carbon and soluble sugar content of the leaves, and the leaf nitrogen, phosphorus and carbon/nitrogen were the main factors affecting the relative abundance of phyllosphere bacteria.Discussion: Previous studies have shown that a large proportion of the variation in the composition of phyllosphere microbial communities was explained by the hosts themselves. In contrast, leaf-borne nutrients were an available resource for bacteria living on the leaf surface, thus influencing the community structure of phyllosphere bacteria. These were similar to the conclusions obtained in this study. This study provides theoretical support for the study of the composition and structure of phyllosphere bacterial communities in woody plants and the factors influencing them.

Plants with heterosis/hybrid vigor perform better than their parents in many traits. However, the biological mechanisms underlying heterosis remain unclear. To investigate the significance of DNA methylation to heterosis, a comprehensive analysis of whole-genome DNA methylome profiles of Populus deltoides cl.'55/65' and '10/17' parental lines and their intraspecific F1 hybrids lines was performed using methylated DNA immunoprecipitation (MeDIP) and high-throughput sequencing. Here, a total of 486.27 million reads were mapped to the reference genome of Populus trichocarpa, with an average unique mapping rate of 57.8%. The parents with similar genetic background had distinct DNA methylation levels. F1 hybrids with hybrid vigor possessed non-additive DNA methylation level (their levels were higher than mid-parent values). The DNA methylation levels in promoter and repetitive sequences and transposable element of better-parent F1 hybrids and parents and lower-parent F1 hybrids were different. Compared with the maternal parent, better-parent F1 hybrids had fewer hypermethylated genes and more hypomethylated ones. Compared with the paternal parent and lower-parent L1, better-parent F1 hybrids had more hypermethylated genes and fewer hypomethylated ones. The differentially methylated genes between better-parent F1 hybrids, the parents and lower-parent F1 hybrids were enriched in the categories metabolic processes, response to stress, binding, and catalytic activity, development, and involved in hormone biosynthesis, signaling pathway. The methylation patterns of the parents both partially and dynamically passed onto their hybrids, and F1 hybrids has a non-additive mathylation level. A multidimensional process is involved in the formation of heterosis.

Decomposition of forest litter is an essential process for returning nutrients to the soil, which is crucial for preserving soil fertility and fostering the regular biological cycle and nutrient balance of the forest ecosystem. About 70% of the land-based forest litter is made up primarily of leaf litter. However, research on the complex effects and key determinants of leaf litter decomposition is still lacking. In this study, we examined the characteristics of nutrient release and microbial diversity structure during the decomposition of three types of litter in arid and semi-arid regions using 16S rRNA and ITS sequencing technology as well as nutrient content determination. It was revealed that the nutrient content and rate of decomposition of mixed litters were significantly different from those of single species. Following litter mixing, the richness and diversity of the microbial community on leaves significantly increased. It was determined that there was a significant correlation between bacterial diversity and content (Total N, Total P, N/P, and C/P). This study provided a theoretical framework for investigating the decomposition mechanism of mixed litters by revealing the microbial mechanism of mixed decomposition of litters from the microbial community and nutrient levels.

Melatonin is an antioxidant that is widely distributed in plants and animals. It is a conservative molecule. In early studies, scientists often used isolation and identification techniques to observe whether the endogenous melatonin cycle in plants was related to the external photoperiod, plant growth, and development cycles, including seed germination, plant rooting, and floral induction. With the development of isolation and identification technology, there is ample evidence that plants possess a variety of melatonin-synthesis pathways. The comprehensive application of molecular biology, genomics, and computational biology has also led to a comprehensive understanding of the physiological functions of plant melatonin. In this paper, we not only highlight the candidate genes from Arabidopsis thaliana and Oryza sativa that might be contributing to increasing plant endogenous melatonin but also elucidate and characterize the role of melatonin in plant growth and development in response to biotic and abiotic stresses.