BackgroundHistone methylation and acetylation regulate biological processes in plants through various histone modifications (HMs) gene families. However, knowledge of HMs genes is limited in horticultural deciduous trees, including apple (Malus domestica).ResultsHere, a comprehensive study of identifying and investigating HMs genes was performed using the recently published apple genome. In total, 198 MdHMs were identified, including 71 histone methyltransferases, 44 histone demethylases, 57 histone acetylases, and 26 histone deacetylases. Detailed analysis of the MdHMs, including chromosomes locations, gene structures, protein motif and protein-protein interactions were performed, and their orthologous genes were also predicted against nine plant species. Meanwhile, a syntenic analysis revealed that tandem, segmental, and whole genome duplications were involved in the evolution and expansion of the MdHMs gene family. Most MdHMs underwent purifying selection. The expression profiles of 198 MdHMs were investigated in response to 6-BA treatment and different flowering varieties (easy-flowering ‘Yanfu No.6’ and difficult-flowering ‘Nagafu No.2’) using transcriptome sequencing data, and most MdHMs were involved in flower induction processes. Subsequent quantitative real-time PCR was then performed to confirm the expression levels of candidate MdHMs under different flowering-related circumstances.ConclusionMdHMs were involved in, and responsive to, flower induction in apple. This study established an MdHMs platform that provided valuable information and presented enriched biological theories on flower induction in apple. The data could also be used to study the evolutionary history and functional prospects of MdHMs genes, as well as other trees.Electronic supplementary materialThe online version of this article (10.1186/s12870-018-1388-0) contains supplementary material, which is available to authorized users.

Guaranteeing successful flowering is very important in economic plant species, especially apple (Malus domestica Borkh.), which is difficult to induce to flower. However, the gene expression and networks involved in flowering have not been totally characterized. Here, we employed mRNA and microRNA (miRNA) sequencing to understand the different responses to gibberellin- and its inhibitor paclobutrazol- (PAC) mediated flower induction. Significant opposite cytological and morphological changes were observed in treated terminal buds, which led to a reduced flowering rate under gibberellin and an increased flowering rate under PAC. We also found that the differentially expressed mRNAs, miRNAs and miRNA target genes participated in different biological networks including hormones, photosynthesis, redox state and other metabolic processes, which provided important clues to understand the complex networks involved in apple flower induction. Additionally, we subsequently focused on one important candidate, MdSPL3, which is one of 31 apple SPL gene family members and whose transcription was inhibited by gibberellin but promoted by PAC. Functional investigation showed that MdSPL3 was located in the nucleus, and ectopic MdSPL3 activated floral meristem identity genes, promoted the formation of floral primordia and led to an earlier flowering phenotype in Arabidopsis. Our research identified critical mRNA and miRNA responsive to gibberellin or PAC, and provided a candidate framework for flower induction. This carefully orchestrated regulatory cross-talk highlighted potential targets for developing regulatory techniques and genetic improvement of flower induction in apple.

In this paper, a novel change detection technique is proposed based on multiscale superpixel segmentation and stacked denoising autoencoders (SDAE). This approach is designed to achieve superpixelbased change detection, in which the basic analysis unit is between pixel-based and object-based ones. Given two original images, the difference image (DI) is obtained by conventional DI generation methods. Then, we propose a multiscale superpixel segmentation which is guided by the changing degrees estimated from the DI. Different from traditional multiscale superpixel, the proposed multiscale superpixel segmentation is employed in a single map. In the proposed method, SDAE is used to learn the difference representation between bi-temporal superpixels. Bi-temporal superpixels are stacked and fed into SDAE for its pretraining, and then SDAE is fine-tuned according to pseudo labels generated by traditional unsupervised methods. After fine-tuned with back propagation, the SDAE can be used to classify all superpixel pairs into changed or unchanged ones. The experimental results on real remote sensing datasets have demonstrated the effectiveness of the proposed approach.

Adventitious root (AR) formation, which is controlled by endogenous and environmental factors, is indispensable for vegetative asexual propagation. However, comprehensive proteomic data on AR formation are still lacking. The aim of this work was to study indole-3-butyric acid (IBA)-induced AR formation in the dwarf apple rootstock ‘T337’. In this study, the effect of IBA on AR formation was analysed. Subsequent to treatment with IBA, both the rooting rate and root length of ‘T337’ increased significantly. An assessment of hormone levels in basal stem cuttings suggested that auxin, abscisic acid, and brassinolide were higher in basal stem cuttings that received the exogenous IBA application; while zeatin riboside, gibberellins, and jasmonic acid were lower than non-treated basal stem cuttings. To explore the underlying molecular mechanism, an isobaric tags for relative and absolute quantification (iTRAQ)-based proteomic technique was employed to identify the expression profiles of proteins at a key period of adventitious root induction (three days after IBA treatment). In total, 3355 differentially expressed proteins (DEPs) were identified. Many DEPs were closely related to carbohydrate metabolism and energy production, protein homeostasis, reactive oxygen and nitric oxide signaling, and cell wall remodeling biological processes; as well as the phytohormone signaling, which was the most critical process in response to IBA treatment. Further, RT-qPCR analysis was used to evaluate the expression level of nine genes that are involved in phytohormone signaling and their transcriptional levels were mostly in accordance with the protein patterns. Finally, a putative work model was proposed. Our study establishes a foundation for further research and sheds light on IBA-mediated AR formation in apple as well as other fruit rootstock cuttings.

Alternate bearing (AB) trees, including Malus prunifolia, are characterized by alternating cycles of heavy (ON tree) and low (OFF tree) fruit loads. The mechanisms regulating the AB phenomenon have not been fully characterized. We completed an iTRAQ-based investigation of M. prunifolia to identify the proteome and metabolic differences between the leaves of ON and OFF trees. We identified 667 differentially expressed proteins, and they influenced multiple biochemical pathways, including photosynthesis, carbohydrate metabolism, glycolysis, protein processing, redox activities, and secondary metabolism. Bioinformatics analyses indicated photosynthesis was the most significant biological process affecting the AB. We observed that 47 photosynthetic proteins affecting photosystem I and II reaction centers, cytochrome b6/f complex, electron transport, and light-harvesting chlorophyll were less abundant in ON tree leaves than in OFF tree leaves. Additionally, physiological analyses validated the potential metabolic activities. Nitrogen and phosphorus contents were significantly higher in ON tree leaves, while potassium levels were lower. Starch content, ZR, GA levels, and flower control gene expression levels (i.e., MdFT1, MdLFY, MdAP1, and MdSPL9) were lower in ON tree leaves than in OFF tree leaves, suggesting they affected the AB phenotype. Our findings help further investigate on the photosynthesis as well as other processes in AB. Those identified DEPs and important biological processes can be useful theoretical basis and provide new insights into the molecular mechanisms regulating AB in perennial woody plants.