Chinese jujube (Ziziphus jujuba Mill) is an economically important fruit species native to China with high nutritious and medicinal value. Genotyping-by-sequencing (GBS) was used to detect and genotype single nucleotide polymorphisms (SNPs) in a core collection of 150 Chinese jujube accessions and further to characterize their genetic diversity, population structure, and linkage disequilibrium (LD). A total of 4,680 high-quality SNPs were identified, of which 38 sets of tri-allelic SNPs were detected. The average polymorphism information content (PIC) values based on bi-allelic SNPs and tri-allelic SNPs were 0.27 and 0.38, respectively. STRUCTURE and principal coordinate analyses based on SNPs revealed that the 150 accessions could be clustered into two groups. However, neighbor-joining trees indicated the accessions should be grouped into three major clusters. Our data confirm that the resolving power for genetic diversity was similar for the SSRs and SNPs. In contrast, regarding population structure, the resolving power was higher for SSRs than for SNPs. The linkage disequilibrium (LD) pattern in Chinese jujube was investigated for the first time. We observed a relatively rapid LD decay with a short range (approximately 10 kb) for all pseudo-chromosomes and for individual pseudo-chromosomes. Our findings provide important information for future genome-wide association analyses and marker-assisted selective breeding of Chinese jujube.

Transcription factors play vital roles in the developmental processes of plants. The SQUAMOSA promoter binding protein (SBP) genes encode a family of plant-specific transcription factors and plays many crucial roles in plant development. In this study, 16 SBP-box gene family members were identified in Ziziphus jujuba Mill. Dongzao (Dongzao), which were distributed over 8 chromosomes. They were classified into seven groups according to their phylogenetic relationships with other SBP-box gene families. Within each group, genes shared similar exon-intron structures and motif locations. The number of exons varied among the groups. We identified 12 homologous gene pairs between Dongzao and Arabidopsis. Expression profiling revealed that ZjSBP02 and ZjSBP14 expressed highly in mature fruits, ZjSBP01 expressed higher in mature leaves than other tissues and the expression level of ZjSBP12 was much higher in the flowers. The transcriptome analysis indicated that ZjSBPs had different expression patterns in various tissues. This study represents the first systematic analysis of the SBP-box gene family in Z. jujuba. The data presented here provides a foundation for understanding the crucial roles of ZjSBP genes in plant growth and development.

Background: Crown gall (CG) (Agrobacterium tumefaciens) and the root lesion nematodes (RLNs) (Pratylenchus vulnus) are major challenges faced by the California walnut industry, reducing productivity and increasing the cost of establishing and maintaining orchards. Current nematode control strategies include nematicides, crop rotation, and tolerant cultivars, but these methods have limits. Developing genetic resistance through novel approaches like RNA interference (RNAi) can address these problems. RNAi-mediated silencing of CG disease in walnut (Juglans regiaL.) has been achieved previously. We sought to place both CG and nematode resistance into a single walnut rootstock genotype using co-transformation to stack the resistance genes.A.tumefaciens, carrying self-complimentary iaaM and ipt transgenes, andAgrobacterium rhizogenes, carrying a self-complimentary Pv010 gene fromP.vulnus, were used as co-transformation vectors. RolABC genes were introduced by the resident T-DNA in theA.rhizogenesRi-plasmid used as a vector for plant transformation. Pv010 and Pv194 (transgenic control) genes were also transferred separately usingA.tumefaciens. To test for resistance, transformed walnut roots were challenged withP.vulnusand microshoots were challenged with a virulent strain ofA.tumefaciens.Results: Combining the two bacterial strains at a 1:1 rather than 1:3 ratio increased the co-transformation efficiency. Although complete immunity to nematode infection was not observed, transgenic lines yielded up to 79% fewer nematodes per root followingin vitroco-culture than untransformed controls. Transgenic line 33-3-1 exhibited complete crown gall control and 32% fewer nematodes. The transgenic plants had thicker, longer roots than untransformed controls possibly due to insertion of rolABC genes. When the Pv010 gene was present in roots with or without rolABC genes there was partial or complete control of RLNs. Transformation using only one vector showed 100% control in some lines.Conclusions: CG and nematode resistance gene stacking controlled CG and RLNs simultaneously in walnuts. Silencing genes encoding iaaM, ipt, and Pv010 decrease CG formation and RLNs populations in walnut. Beneficial plant genotype and phenotype changes are caused by co-transformation usingA.tumefaciensandA.rhizogenesstrains. Viable resistance against root lesion nematodes in walnut plants may be accomplished in the future using this gene stacking technology.

Background: Polyploid plants often exhibit enhanced stress tolerance. The underlying physiological and molecular bases of such mechanisms remain elusive. Here, we characterized the drought tolerance of autotetraploid sour jujube at phenotypic, physiological and molecular levels. Results: The study findings showed that the autotetraploid sour jujube exhibited a superior drought tolerance and enhanced regrowth potential after dehydration in comparison with the diploid counterpart. Under drought stress, more differentially expressed genes (DEGs) were detected in autotetraploid sour jujube and the physiological responses gradually triggered important functions. Through GO enrichment analysis, many DEGs between the diploid and autotetraploid sour jujube after drought-stress exposure were annotated to the oxidation–reduction process, photosystem, DNA binding transcription factor activity and oxidoreductase activity. Six reactive oxygen species scavenging-related genes were specifically differentially expressed and the larger positive fold-changes of the DEGs involved in glutathione metabolism were detected in autotetraploid. Consistently, the lower O²⁻ level and malonaldehyde (MDA) content and higher antioxidant enzymes activity were detected in the autotetraploid under drought-stress conditions. In addition, DEGs in the autotetraploid after stress exposure were significantly enriched in anthocyanin biosynthesis, DNA replication, photosynthesis and plant hormone, including auxin, abscisic acid and gibberellin signal-transduction pathways. Under osmotic stress conditions, genes associated with the synthesis and transport of osmotic regulators including anthocyanin biosynthesis genes were differentially expressed, and the soluble sugar, soluble protein and proline contents were significantly higher in the autotetraploid. The higher chlorophyll content and DEGs enriched in photosynthesis suggest that the photosynthetic system in the autotetraploid was enhanced compared with diploid during drought stress. Moreover, several genes encoding transcription factors (TFs) including GRAS, Bhlh, MYB, WRKY and NAC were induced specifically or to higher levels in the autotetraploid under drought-stress conditions, and hub genes, LOC107403632, LOC107422279, LOC107434947, LOC107412673 and LOC107432609, related to 18 up-regulated transcription factors in the autotetraploid compared with the diploid were identified. Conclusion: Taken together, multiple responses contribute to the enhanced drought tolerance of autotetraploid sour jujube. This study could provide an important basis for elucidating the mechanism of tolerance variation after the polyploidization of trees.

Acer miaotaiense (P. C. Tsoong) is a rare and highly endangered plant in China. Because of the lack of genomic information and the limited number of available molecular markers, there are insufficient tools to determine the genetic diversity of this species. Here, 93,305 unigenes were obtained by multiple assembled contigs with a transcriptome sequencing program. Furthermore, 12,819 expressed sequence tag-derived simple sequence repeat (EST-SSR) markers were generated, 300 were randomly selected and synthesized, 19 primer pairs were identified as highly polymorphic (average number of alleles (N_a) = 8, expected heterozygosity (H_e) = 0.635, polymorphism information content (PIC) = 0.604) and were further used for population genetic analysis. All 261 samples were grouped into two genetic clusters by UPGMA, a principal component analyses and a STRUCTURE analyses. A moderate level of genetic differentiation (genetic differentiation index (F_st) = 0.059–0.116, gene flow = 1.904–3.993) among the populations and the major genetic variance (81.01%) within populations were revealed by the AMOVA. Based on the results, scientific conservation strategies should be established using in situ and ex situ conservation strategies. The study provides useful genetic information for the protection of precious wild resources and for further research on the origin and evolution of this endangered plant and its related species.