Background: Domain of unknown function (DUF) proteins represent a number of gene families that encode functionally uncharacterized proteins in eukaryotes. The DUF4228 gene family is one of these families in plants that has not been described previously. Results: In this study, we performed an extensive comparative analysis of DUF4228 proteins and determined their phylogeny in the plant lineage. A total of 489 high-confidence DUF4228 family members were identified from 14 land plant species, which sub-divided into three distinct phylogenetic groups: group I, group II and group III. A highly conserved DUF4228 domain and motif distribution existed in each group, implying their functional conservation. To reveal the possible biological functions of these DUF4228 genes, 25 ATDUF4228 sequences from Arabidopsis thaliana were selected for further analysis of characteristics such as their chromosomal position, gene duplications and gene structures. Ka/Ks analysis identified seven segmental duplication events, while no tandemly duplication gene pairs were found in A. thaliana. Some cis-elements responding to abiotic stress and phytohormones were identified in the upstream sequences of the ATDUF4228 genes. Expression profiling of the ATDUF4228 genes under abiotic stresses (mainly osmotic, salt and cold) and protein-protein interaction prediction suggested that some ATDUF4228 genes are may be involved in the pathways of plant resistance to abiotic stresses. Conclusion: These results expand our knowledge of the evolution of the DUF4228 gene family in plants and will contribute to the elucidation of the biological functions of DUF4228 genes in the future.

Salix psammophila (desert willow) is a shrub endemic to the Kubuqi Desert and the Mu Us Desert, China, that plays an important role in maintaining local ecosystems and can be used as a biomass feedstock for biofuels and bioenergy. However, the lack of information on phenotypic traits and molecular markers for this species limits the study of genetic diversity and population structure. In this study, nine phenotypic traits were analyzed to assess the morphological diversity and variation. The mean coefficient of variation of 17 populations ranged from 18.35% (branch angle (BA)) to 38.52% (leaf area (LA)). Unweighted pair-group method with arithmetic mean analysis of nine phenotypic traits of S. psammophila showed the same results, with the 17 populations clustering into five groups. We selected 491 genets of the 17 populations to analyze genetic diversity and population structure based on simple sequence repeat (SSR) markers. Analysis of molecular variance (AMOVA) revealed that most of the genetic variance (95%) was within populations, whereas only a small portion (5%) was among populations. Moreover, using the animal model with SSR-based relatedness estimated of S. psammophila, we found relatively moderate heritability values for phenotypic traits, suggesting that most of trait variation were caused by environmental or developmental variation. Principal coordinate and phylogenetic analyses based on SSR data revealed that populations P1, P2, P9, P16, and P17 were separated from the others. The results showed that the marginal populations located in the northeastern and southwestern had lower genetic diversity, which may be related to the direction of wind. These results provide a theoretical basis for germplasm management and genetic improvement of desert willow.

Juniperus sabina L., a shrub distributed in patches in arid and semi-arid areas of the northern hemisphere, plays an important role in preventing land desertification and maintaining ecosystems. However, few studies have reported genetic diversity and genetic structure of widely distributed populations of J. sabina in northwest China. Here, we evaluated the genetic diversity and genetic structure and predicted the isolation barriers among 11 populations based on 20 simple sequence repeats (SSRs). A total of 134 alleles were generated and the average number of alleles per locus was 6.70. The Shannon diversity index ranged from 0.659 to 0.951, with an average of 0.825. Population structure analysis revealed that the populations were assigned into two genetic groups. The analysis of molecular variance (AMOVA) indicated that 88% of genetic variation existed within populations. Moderate population differentiation was occurred with F_ST value of 0.090. Finally, we concluded that geographic isolation is the main factor affecting the genetic structure of J. sabina populations. The results of this study provide a foundation for the strategies for J. sabina genetic conservation and management.

Salix psammophila C. Wang & Chang Y. Yang is a desert plant species distributed in Northwest China. Here, we report the complete choroplast genome sequences in order to enrich its genetic resource. The total genome is 155,278 bp in length and contains a typical quadripartite structure, including a large single copy (LSC) region of 84,457 bp, a small single copy (SSC) region of 15,891 bp, and a pair of inverted repeats (IRs) of 27,465 bp. There were 130 genes in the genome, including 85 protein-coding genes, 37 tRNA genes and eight rRNA genes. The overall CG content in the plastome of S. psammophila is 36.72%. The phylogenetic tree based on 18 complete plastomes of Salicaceae support close relationships among S. psammophila, Salix taoensis, and Salix rehderiana.

Salix psammophila is an important tree species adapted to sand-fixing afforestation in arid areas, and its different plant type characteristics can have different ecological functions. To identify the genes affecting the plant type of S. psammophila, this study used RT-qPCR and RNA-seq technology to establish a method for screening the candidate genes of the S. psammophila plant type based on the correlation coefficient of the crown–height ratio. We then screened out the gene combination that can best control the expression of the S. psammophila plant type. The results show the following: (1) The expression levels of the FHY1 and TAC2 genes were positively correlated with the crown–height ratio, whereas those of the ATX1, RFK1, PYL1, ABF2, SPA2, TB1, ZFP4, and LAZY1b genes were negatively correlated with the crown–height ratio. (2) The ATX1 + FHY1 gene combination had the greatest influence on the plant type traits of S. psammophila, and the correlation between the gene combination and the crown–height ratio reached 0.74. (3) The double- gene combination screening method improved the screening efficiency and accuracy, as well as the sensitivity and specificity, indicating certain universality. This strategy can be used for the determination of other plants or other traits, providing a theoretical basis for the directional breeding of forest trees.