Litchi is an evergreen woody tree widely cultivated in subtropical and tropical regions. Defective flowering is a major challenge for litchi production in time of climate change and global warming. Previous studies have shown that high temperature conditions encourage the growth of rudimentary leaves in panicles and suppress litchi flowering, while reactive oxygen species (ROS) generated by methyl viologen dichloride hydrate (MV) promote flowering and abortion of rudimentary leaves. To understand the molecular function of the ROS-induced abortion of rudimentary leaves in litchi, we sequenced and de novo assembled the litchi transcriptome. Our assembly encompassed 82,036 unigenes with a mean size of 710 bp, and over 58% (47,596) of unigenes showed significant similarities to known sequences in GenBank non-redundant (nr) protein database. 5,865 unigenes were found to be differentially expressed between ROS-treated and un-treated rudimentary leaves, and genes encoding signaling components of plant hormones such as ABA and ethylene were significantly enriched. Our transcriptome data represents the comprehensive collection of expressed sequence tags (ESTs) of litchi leaves, which is a vital resource for future studies on the genomics of litchi and other closely related species. The identified differentially expressed genes also provided potential candidates for functional analysis of genes involved in litchi flowering underlying the control of rudimentary leaves in the panicles.

Litchi is an important woody fruit tree. Floral initiation in litchi is triggered by low temperatures. However, defective flowering is a major challenge for litchi production in times of climate change and global warming. Previous studies have shown that the reactive oxygen species (ROS) generated by methyl viologen dichloride hydrate (MV) promotes flowering. In this study, potted trees were transferred to growth chambers for low-temperature (LT), medium-temperature (MT), and high-temperature (HT) treatments. Trees at MT were subjected to ROS treatment to promote flowering, and those at LT were induced to flower. RNA-sequencing was applied to obtain a global transcriptome of the apical meristem and reveal potential gene networks controlling the transformation from vegetative meristems (VM) into inflorescence meristems (IM). We assembled 73,117 unigenes with a mean size of 790 bp and 11741 unigenes were identified as both chilling and ROS responsive genes (CRRGs), of which 48 were identified as flowering-related CRRGs, 59 were plant hormone signal transduction CRRGs, and 146 were plant hormone biosynthesis-related CRRGs. Genes co-expression network analysis indicated inner relationships, suggesting that ROS and chilling promotes the VM to IM transition through a regulatory gene network of transcription factors, hormones, and flowering regulators.

Litchi is an important subtropical fruit tree that requires an appropriately low temperature to trigger floral initiation. Our previous studies have shown that reactive oxygen species (ROS) are involved in litchi flowering. To identify oxidative stress-induced flowering related genes in leaves, ‘Nuomici’ potted trees were grown at medium low-temperature conditions (18/13 °C for day/night, medium-temperature). The trees were treated with the ROS generator methyl viologen dichloride hydrate (MV) as the MV-generated ROS treatment (MM, medium-temperature plus MV) and water as the control treatment (M, medium-temperature plus water). Sixteen RNA-sequencing libraries were constructed, and each library generated more than 5,000,000 clean reads. A total of 517 differentially expressed genes (DEGs) were obtained. Among those DEGs, plant hormone biosynthesis and signal transduction genes, ROS-specific transcription factors, such as AP2/ERF and WRKY genes, stress response genes, and flowering-related genes FLOWERING LOCUS T1 (FT1) and FLOWERING LOCUS T2 (FT2) were significantly enriched. Then, as a confirmatory experiment, the potted trees were uniformly sprayed with MV, N,N’-dimethylthiourea (DMTU, ROS scavenger) plus MV, and water at medium-temperature. The results showed that the MV-generated ROS promoted flowering and changed related gene expression, but these effects were repressed by DMTU treatment. The results of our studies indicate that ROS could promote flowering and partly bypass chilling for litchi flowering.

Litchi (Litchi chinensis), a prominent fruit tree in the Sapindaceae, initiates flowering in response to low autumn and winter temperatures. This study investigates the epigenetic regulation of this process, focusing on the marks histone H3 lysine 27 trimethylation (H3K27me3) and its deposition genes during the chilling-induced floral induction and initiation stages. Our genomic analysis delineated the H3K27me3 deposition landscape across the pre-floral induction (PFId), floral induction (FId), and floral initiation (FIn) stages. We identified 5,635 differentially H3K27me3-modified genes (DHGs) in buds and 4,801 DHGs in leaves. Integration of the RNA-seq and ChIP-seq datasets identified 1,001 differentially regulated genes (DRGs) in buds and 675 DRGs in leaves, offering insights into the genes potentially targeted by H3K27me3. To probe the functional role of H3K27me3, we employed GSK343, a histone H3 lysine methyltransferase inhibitor. Treatment with GSK343 during the chilling-induced flowering process led to reduced H3K27me3 deposition at the TREHALOSE-6-PHOSPHATE SYNTHASE 1 (LcTPS1) and FRIGIDA (LcFRI) loci, resulting in increased gene expression. This manipulation delayed flowering and reduced flowering rates, confirming the pivotal role of H3K27me3 in chilling-induced flowering in litchi. Gene co-expression network analysis identified SHORT VEGETATIVE PHASE 10 (LcSVP10) as a crucial regulator in litchi flowering. Overexpression of LcSVP10 in Arabidopsis thaliana delayed flowering, indicating a conserved function in flowering time control. Our results elucidate the molecular and epigenetic mechanisms that govern floral induction in litchi and highlight the potential of epigenetic modifications to regulate flowering time in horticultural plants.

Litchi is an important Sapindaceae fruit tree. Flowering in litchi is triggered by low temperatures in autumn and winter. It can be divided into early-, medium-, and late-flowering phenotypes according to the time for floral induction. Early-flowering varieties need low chilling accumulation level for floral induction, whereas the late-flowering varieties require high chilling accumulation level. In the present study, RNA-Seq of 87 accessions was performed and transcriptome-based genome-wide association studies (GWAS) was used to identify candidate genes involved in chilling accumulation underlying the time for floral induction. A total of 98,155 high-quality single-nucleotide polymorphism (SNP) sites were obtained. A total of 1,411 significantly associated SNPs and 1,115 associated genes (AGs) were identified, of which 31 were flowering-related, 23 were hormone synthesis-related, and 27 were hormone signal transduction-related. Association analysis between the gene expression of the AGs and the flowering phenotypic data was carried out, and differentially expressed genes (DEGs) in a temperature-controlled experiment were obtained. As a result, 15 flowering-related candidate AGs (CAGs), 13 hormone synthesis-related CAGs, and 11 hormone signal transduction-related CAGs were further screened. The expression levels of the CAGs in the early-flowering accessions were different from those in the late-flowering ones, and also between the flowering trees and non-flowering trees. In a gradient chilling treatment, flowering rates of the trees and the CAGs expression were affected by the treatment. Our present work for the first time provided candidate genes for genetic regulation of flowering in litchi using transcriptome-based GWAS.

Passion fruit (Passiflora edulis), a commercially vital tropical crop, faces flowering instability due to photoperiod-sensitive flowering patterns, particularly under the cloudy, rainy climates of subtropical regions. To mitigate floral suppression during unfavorable light conditions, this study implemented a dual-modality strategy combining 16 h daily supplementary lighting (460 nm blue + 630 nm red spectrum) and foliar application of a high-phosphorus-containing nutrient, the Plant-Prod (nitrogen–phosphorus–potassium = 10:52:10) grown in field ‘Qinmi No. 9’. The treatment significantly stimulated lateral branch formation, internode elongation, flower retention, stage IV flower bud development, and enhanced photosynthetic efficiency. Physiological analyses revealed that the treatment increased the net photosynthetic rate (Pn), reduced the intercellular carbon dioxide concentration (Ci), and enhanced stomatal conductance (Gs), indicating the improvement of carbon assimilation. Controlled seedling trials further confirmed these effects, with treated groups exhibiting accelerated lateral branching and stress resilience. This integrated approach, combining optimized supplemental lighting and precision phosphorus fertilization, offers a practical and scalable strategy to stabilize passion fruit yields in climate-variable regions, with immediate potential for commercial orchards and greenhouse production.