Stress-induced flowering: the third category of flowering response

Epigenomic and transcriptomic persistence of heat stress memory in strawberry (Fragaria vesca)

BACKGROUND

In plants, epigenetic stress memory has so far been found to be largely transient. Here, we wanted to assess the heritability of heat stress-induced epigenetic and transcriptomic changes following woodland strawberry (Fragaria vesca) reproduction. Strawberry is an ideal model to study epigenetic inheritance because it presents two modes of reproduction: sexual (self-pollinated plants) and asexual (clonally propagated plants named daughter plants). Taking advantage of this model, we investigated whether heat stress-induced DNA methylation changes can be transmitted via asexual reproduction.

RESULTS

Our genome-wide study provides evidence for stress memory acquisition and maintenance in F. vesca. We found that specific DNA methylation marks or epimutations are stably transmitted over at least three asexual generations. Some of the epimutations were associated with transcriptional changes after heat stress.

CONCLUSION

Our findings show that the strawberry methylome and transcriptome respond with a high level of flexibility to heat stress. Notably, independent plants acquired the same epimutations and those were inherited by their asexual progenies. Overall, the asexual progenies can retain some information in the genome of past stresses encountered by their progenitors. This molecular memory, also documented at the transcriptional level, might be involved in functional plasticity and stress adaptation. Finally, these findings may contribute to novel breeding approaches for climate-ready plants.

A protocol for increased throughput phenotyping of plant resistance to the pollen beetle

BACKGROUND

Improving crop resistance to insect herbivores is a major research objective in breeding programs. Although genomic technologies have increased the speed at which large populations can be genotyped, breeding programs still suffer from phenotyping constraints. The pollen beetle (Brassicogethes aeneus) is a major pest of oilseed rape for which no resistant cultivar is available to date, but previous studies have highlighted the potential of white mustard as a source of resistance and introgression of this resistance appears to be a promising strategy. Here we present a phenotyping protocol allowing mid-throughput (i.e., increased throughput compared to current methods) acquisition of resistance data, which could then be used for genetic mapping of QTLs.

RESULTS

Contrasted white mustard genotypes were selected from an initial field screening and then evaluated for their resistance under controlled conditions using a standard phenotyping method on entire plants. We then upgraded this protocol for mid-throughput phenotyping, by testing two alternative methods. We found that phenotyping on detached buds did not provide the same resistance contrasts as observed with the standard protocol, in contrast to the phenotyping protocol with miniaturized plants. This protocol was then tested on a large panel composed of hundreds of plants. A significant variation in resistance among genotypes was observed, which validates the large-scale application of this new phenotyping protocol.

CONCLUSION

The combination of this mid-throughput phenotyping protocol and white mustard as a source of resistance against the pollen beetle offers a promising avenue for breeding programs aiming to improve oilseed rape resistance. © 2022 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Functional characterization of sugarcane ScFTIP1 reveals its role in Arabidopsis flowering

The timing of floral transition is essential for reproductive success in flowering plants. In sugarcane, flowering time affects the production of sugar and biomass. Although the function of the crucial floral pathway integrators, FLOWERING LOCUS T (FT), in sugarcane, has been uncovered, the proteins responsible for FT export and the underlying mechanism remain unexplored. In this study, we identified a member of the multiple C2 domain and transmembrane region proteins (MCTPs) family in sugarcane, FT-interacting protein 1 (ScFTIP1), which was localized to the endoplasmic reticulum. Ectopic expression of ScFTIP1 in the Arabidopsis mutant ftip1-1 rescued the late-flowering phenotype. ScFTIP1 interacted with AtFT in vitro and in vivo assays. Additionally, ScFTIP1 interacted with ScFT1 and the floral inducer ScFT3. Furthermore, we found that the NAC member, ScNAC23, could directly bind to the ScFTIP1 promoter and negatively regulate its transcription. Overall, our findings revealed the function of ScFTIP1 and proposed a potential mechanism underlying flowering regulation in sugarcane.

Flowering time: From physiology, through genetics to mechanism

Plant species have evolved different requirements for environmental/endogenous cues to induce flowering. Originally, these varying requirements were thought to reflect the action of different molecular mechanisms. Thinking changed when genetic and molecular analysis in Arabidopsis thaliana revealed that a network of environmental and endogenous signaling input pathways converge to regulate a common set of "floral pathway integrators." Variation in the predominance of the different input pathways within a network can generate the diversity of requirements observed in different species. Many genes identified by flowering time mutants were found to encode general developmental and gene regulators, with their targets having a specific flowering function. Studies of natural variation in flowering were more successful at identifying genes acting as nodes in the network central to adaptation and domestication. Attention has now turned to mechanistic dissection of flowering time gene function and how that has changed during adaptation. This will inform breeding strategies for climate-proof crops and help define which genes act as critical flowering nodes in many other species.

The roles of non-coding RNAs in male reproductive development and abiotic stress responses during this unique process in flowering plants

Successful male reproductive development is the guarantee for sexual reproduction of flowering plants. Male reproductive development is a complicated and multi-stage process that integrates physiological processes and adaptation and tolerance to a myriad of environmental stresses. This well-coordinated process is governed by genetic and epigenetic machineries. Non-coding RNAs (ncRNAs) play pleiotropic roles in the plant growth and development. The identification, characterization and functional analysis of ncRNAs and their target genes have opened a new avenue for comprehensively revealing the regulatory network of male reproductive development and its response to environmental stresses in plants. This review briefly addresses the types, origin, biogenesis and mechanisms of ncRNAs in plants, highlights important updates on the roles of ncRNAs in regulating male reproductive development and emphasizes the contribution of ncRNAs, especially miRNAs and lncRNAs, in responses to abiotic stresses during this unique process in flowering plants.

Tropical cyclone winds and precipitation stimulate cone production in the masting species longleaf pine (Pinus palustris)

Many trees exhibit masting - where reproduction is temporally variable and synchronous over large areas. Several dominant masting species occur in tropical cyclone (TC)-prone regions, but it is unknown whether TCs correlate with mast seeding. We analyzed long-term data (1958-2022) to test the hypothesis that TCs influence cone production in longleaf pine (Pinus palustris). We integrate field observations, weather data, satellite imagery, and hurricane models to test whether TCs influence cone production via: increased precipitation; canopy density reduction; and/or mechanical stress from wind. Cone production was 31% higher 1 yr after hurricanes and 71% higher after 2 yr, before returning to baseline levels. Cyclone-associated precipitation was correlated with increased cone production in wet years and cone production increased after low-intensity winds (≤ 25 m s-1 ) but not with high-intensity winds (> 25 m s-1 ). Tropical cyclones may stimulate cone production via precipitation addition, but high-intensity winds may offset any gains. Our study is the first to support the direct influence of TCs on reproduction, suggesting a previously unknown environmental correlate of masting, which may occur in hurricane-prone forests world-wide.

Designing salt stress-resilient crops: Current progress and future challenges

Excess soil salinity affects large regions of land and is a major hindrance to crop production worldwide. Therefore, understanding the molecular mechanisms of plant salt tolerance has scientific importance and practical significance. In recent decades, studies have characterized hundreds of genes associated with plant responses to salt stress in different plant species. These studies have substantially advanced our molecular and genetic understanding of salt tolerance in plants and have introduced an era of molecular design breeding of salt-tolerant crops. This review summarizes our current knowledge of plant salt tolerance, emphasizing advances in elucidating the molecular mechanisms of osmotic stress tolerance, salt-ion transport and compartmentalization, oxidative stress tolerance, alkaline stress tolerance, and the trade-off between growth and salt tolerance. We also examine recent advances in understanding natural variation in the salt tolerance of crops and discuss possible strategies and challenges for designing salt stress-resilient crops. We focus on the model plant Arabidopsis (Arabidopsis thaliana) and the four most-studied crops: rice (Oryza sativa), wheat (Triticum aestivum), maize (Zea mays), and soybean (Glycine max).

Plant nucleoside N-ribohydrolases: riboside binding and role in nitrogen storage mobilization

Cells save their energy during nitrogen starvation by selective autophagy of ribosomes and degradation of RNA to ribonucleotides and nucleosides. Nucleosides are hydrolyzed by nucleoside N-ribohydrolases (nucleosidases, NRHs). Subclass I of NRHs preferentially hydrolyzes the purine ribosides while subclass II is more active towards uridine and xanthosine. Here, we performed a crystallographic and kinetic study to shed light on nucleoside preferences among plant NRHs followed by in vivo metabolomic and phenotyping analyses to reveal the consequences of enhanced nucleoside breakdown. We report the crystal structure of Zea mays NRH2b (subclass II) and NRH3 (subclass I) in complexes with the substrate analog forodesine. Purine and pyrimidine catabolism are inseparable because nucleobase binding in the active site of ZmNRH is mediated via a water network and is thus unspecific. Dexamethasone-inducible ZmNRH overexpressor lines of Arabidopsis thaliana, as well as double nrh knockout lines of moss Physcomitrium patents, reveal a fine control of adenosine in contrast to other ribosides. ZmNRH overexpressor lines display an accelerated early vegetative phase including faster root and rosette growth upon nitrogen starvation or osmotic stress. Moreover, the lines enter the bolting and flowering phase much earlier. We observe changes in the pathways related to nitrogen-containing compounds such as β-alanine and several polyamines, which allow plants to reprogram their metabolism to escape stress. Taken together, crop plant breeding targeting enhanced NRH-mediated nitrogen recycling could therefore be a strategy to enhance plant growth tolerance and productivity under adverse growth conditions.

Yield reduction caused by elevated temperatures and high nitrogen fertilization is mitigated by SP6A overexpression in potato (Solanum tuberosum L.)

Potatoes (Solanum tuberosum L.) are a fundamental staple for millions of people worldwide. They provide essential amino acids, vitamins, and starch - a vital component of the human diet, providing energy and serving as a source of fiber. Unfortunately, global warming is posing a severe threat to this crop, leading to significant yield losses, and thereby endangering global food security. Industrial agriculture traditionally relies on excessive nitrogen (N) fertilization to boost yields. However, it remains uncertain whether this is effective in combating heat-related yield losses of potato. Therefore, our study aimed to investigate the combinatory effects of heat stress and N fertilization on potato tuber formation. We demonstrate that N levels and heat significantly impact tuber development. The combination of high N and heat delays tuberization, while N deficiency initiates early tuberization, likely through starvation-induced signals, independent of SELF-PRUNING 6A (SP6A), a critical regulator of tuberization. We also found that high N levels in combination with heat reduce tuber yield rather than improve it. However, our study revealed that SP6A overexpression can promote tuberization under these inhibiting conditions. By utilizing the excess of N for accumulating tuber biomass, SP6A overexpressing plants exhibit a shift in biomass distribution towards the tubers. This results in an increased yield compared to wild-type plants. Our results highlight the role of SP6A overexpression as a viable strategy for ensuring stable potato yields in the face of global warming. As such, our findings provide insights into the complex factors impacting potato crop productivity.

Exploring the impact of light intensity under speed breeding conditions on the development and growth of lentil and chickpea

The use of high-performant varieties could help to improve the production of food legumes and thus meet the demand of the growing world population. However, long periods needed to develop new varieties through traditional breeding are a major obstacle. Thus, new techniques allowing faster genetic advance are needed. Speed breeding using longer periods of light exposure on plants, appears to be a good solution for accelerating plant life cycles and generation turnover. However, applying extended photoperiod causes plant stress and mortality due to lack of information on the adequate intensity to be used in speed breeding protocol. This study examines the impact of light intensity under speed breeding conditions on the development and growth of lentils and chickpeas, with a keen interest in enhancing genetic gain in these key food legumes. Four distinct levels of light intensity (T1: Green-house: 2000 µmol/m2/s; T2: 148-167 µmol/m2/s; T3: 111-129 µmol/m2/s; T4: 74-93 µmol/m2/s) under a photoperiod of 18 h of light and 6 h of darkness were tested in a growth chamber. Significant variation depending on light intensity was observed for plant height, total biomass, number of secondary stems, pods number, number of seeds per plant, growth rate, green canopy cover, time to flowering, time of pod set, time to maturity, vegetative stage length, reproduction stage length and seed filling stage length. Light intensity significantly influenced flowering/maturity and plant's stress compared to normal conditions in green-house where flowering/maturity were around 67/97 days for lentil and 79/111 days for chickpea. Therefore, lentils in treatment 2 flowered and reached maturity in 30/45 days respectively, with high stress, while chickpeas in the same treatment did not flower. In contrast, treatment 4 showed interesting results, promoting optimal growth with low stress, and flowering/maturity in 27/46 days and 28/54 days, respectively for lentils and chickpeas. These results underline the crucial importance of light management in speed breeding to accelerate vegetative growth and phenology while allowing healthy growth conditions for plants to produce enough seeds for generation turnover.

Accumulation of Phosphorylated SnRK2 Substrate 1 Promotes Drought Escape in Arabidopsis

Plants adopt optimal tolerance strategies depending on the intensity and duration of stress. Retaining water is a priority under short-term drought conditions, whereas maintaining growth and reproduction processes takes precedence over survival under conditions of prolonged drought. However, the mechanism underlying changes in the stress response depending on the degree of drought is unclear. Here, we report that SNF1-related protein kinase 2 (SnRK2) substrate 1 (SNS1) is involved in this growth regulation under conditions of drought stress. SNS1 is phosphorylated and stabilized by SnRK2 protein kinases reflecting drought conditions. It contributes to the maintenance of growth and promotion of flowering as drought escape by repressing stress-responsive genes and inducing FLOWERING LOCUS T (FT) expression, respectively. SNS1 interacts with the histone methylation reader proteins MORF-related gene 1 (MRG1) and MRG2, and the SNS1-MRG1/2 module cooperatively regulates abscisic acid response. Taken together, these observations suggest that the phosphorylation and accumulation of SNS1 in plants reflect the intensity and duration of stress and can serve as a molecular scale for maintaining growth and adopting optimal drought tolerance strategies under stress conditions.

Extensive post-transcriptional regulation revealed by integrative transcriptome and proteome analyses in salicylic acid-induced flowering in duckweed (Lemna gibba)

Duckweed is an aquatic model plant with tremendous potential in industrial and agricultural applications. Duckweed rarely flowers which significantly hinders the resource collection and heterosis utilization. Salicylic acid (SA) can significantly induce duckweed to flower; however, the underlying regulatory mechanisms remain largely unknown. In this work, transcriptome and proteome were conducted in parallel to examine the expression change of genes and proteins in Lemna gibba under SA treatment. A high-quality reference transcriptome was generated using Iso-Seq strategy, yielding 42,281 full-length transcripts. A total of 422, 423, and 417 differentially expressed genes (DEGs), as well as 213, 51, and 92 differentially expressed proteins (DEPs), were identified at flower induction, flower initiation, and flowering stages by ssRNA-seq and iTRAQ methods. Most DEGs and DEPs were only regulated at either the transcriptomic or proteomic level. Additionally, DEPs exhibited low expression correlations with the corresponding mRNAs, suggesting that post-transcriptional regulation plays a pivotal role in SA-induced flowering in L. gibba. Specifically, the genes related to photosynthesis, stress, and hormone metabolism were mainly regulated at the mRNA level, those associated with mitochondrial electron transport / ATP synthesis, nucleotide synthesis, and secondary metabolism were regulated at the protein level, while those related to redox metabolism were regulated at the mRNA and/or protein levels. The post-transcriptional regulation of genes relevant to hormone synthesis, transcription factors, and flowering was also extensively analyzed and discussed. This is the first study of integrative transcriptomic and proteomic analyses in duckweed, providing novel insights of post-transcriptional regulation in SA-induced flowering of L. gibba.

Integrating Smart Greenhouse Cover, Reduced Nitrogen Dose and Biostimulant Application as a Strategy for Sustainable Cultivation of Cherry Tomato

Fruit yield and quality of greenhouse tomatoes are strongly influenced by light conditions and nitrogen (N) availability, however, the interaction between these factors is still unclear. We evaluated the effects on cherry tomatoes of two tunnel plastic covers with different optical properties and three N doses, also in combination with a biostimulant treatment. We compared a diffuse light film (Film1) and a conventional clear film (Film2), and three N levels, corresponding to 50% (N50), 75% (N75) and 100% (N100) of the optimal dose, with and without a microbial plus a protein hydrolysed biostimulant, compared to a non-treated control. The three experimental treatments significantly interacted on several yield and quality parameters. In control plants (untreated with biostimulants), the early yield was higher at reduced N doses compared to N100, with greater increments under the diffusive Film1 compared to the clear Film2 (+57.7% and +37.0% vs. +31.7% and +16.0%, in N50 and N75 respectively). Film1 boosted the total fruit production at all the N rates and with or without biostimulants, compared to Film2, with stronger effects under sub-optimal N (+29.4% in N50, +21.2% in N75, and +7.8% in N100, in plants untreated with biostimulant). Total yield decreased with decreasing N levels, while it always increased with the application of biostimulants, which counterbalanced the detrimental effects of N shortage. Quality traits were mainly affected by the cover film and the biostimulant treatment. The diffusive film increased the content of carotenoids, lycopene and total phenols compared to the clear one, and the biostimulants increased texture, soluble solids, phenols and ascorbic acid compared to the untreated control. It is worth noting that in plants fertilized at 75% of the reference N dose, the biostimulants determined higher yield than the N100 untreated control, under both the covers (+48% in Film1 and +20% in Film2). In conclusion, the diffusive film improved the fruit yield and quality of greenhouse tomatoes in the spring-summer period, presumably avoiding plant stress due to high-intensity direct light. Reduced N rates limited the plant productivity, however, the biostimulant application was effective in compensating for the detrimental effects of sub-optimal supply of N synthetic fertilizers.

Transcriptional survey of abiotic stress response in maize (Zea mays) in the level of gene co-expression network and differential gene correlation analysis

Abstract. Maize may be exposed to several abiotic stresses in the field. Therefore, identifying the tolerance mechanisms of natural field stress is mandatory. Gene expression data of maize upon abiotic stress were collected, and 560 differentially expressed genes (DEGs) were identified through meta-analysis. The most significant gene ontology terms in up-regulated genes were 'response to abiotic stress' and 'chitinase activity'. 'Phosphorelay signal transduction system' was the most significant enriched biological process in down-regulated DEGs. The co-expression analysis unveiled seven modules of DEGs, with a notable positive correlation between the modules and abiotic stress. Furthermore, the statistical significance was strikingly high for the turquoise, green and yellow modules. The turquoise group played a central role in orchestrating crucial adaptations in metabolic and stress response pathways in maize when exposed to abiotic stress. Within three up-regulated modules, Zm.7361.1.A1_at, Zm.10386.1.A1_a_at and Zm.10151.1.A1_at emerged as hub genes. These genes might introduce novel candidates implicated in stress tolerance mechanisms, warranting further comprehensive investigation and research. In parallel, the R package glmnet was applied to fit a logistic LASSO regression model on the DEGs profile to select candidate genes associated with abiotic responses in maize. The identified hub genes and LASSO regression genes were validated on an independent microarray dataset. Additionally, Differential Gene Correlation Analysis (DGCA) was performed on LASSO and hub genes to investigate the gene-gene regulatory relationship. The P value of DGCA of 16 pairwise gene comparisons was lower than 0.01, indicating a gene-gene significant change in correlation between control and abiotic stress. Integrated weighted gene correlation network analysis and logistic LASSO analysis revealed Zm.11185.1.S1_at, Zm.2331.1.S1_x_at and Zm.17003.1.S1_at. Notably, these 3 genes were identified in the 16 gene-pair comparisons. This finding highlights the notable significance of these genes in the abiotic stress response. Additional research into maize stress tolerance may focus on these three genes.

Are Arabidopsis thaliana plants able to recover from exposure to gamma radiation? A molecular perspective

Most plant research focuses on the responses immediately after exposure to ionizing irradiation (IR). However, it is as important to investigate how plants recover after exposure since this has a profound effect on future plant growth and development and hence on the long-term consequences of exposure to stress. This study aimed to investigate the IR-induced responses after exposure and during recovery by exposing 1-week old A. thaliana seedlings to gamma dose rates ranging from 27 to 103.7 mGy/h for 2 weeks and allowing them to recover for 4 days. A high-throughput RNAsequencing analysis was carried out. An enrichment of GO terms related to the metabolism of hormones was observed both after irradiation and during recovery at all dose rates. While plants exposed to the lowest dose rate activate defence responses after irradiation, they recover from the IR by resuming normal growth during the recovery period. Plants exposed to the intermediate dose rate invest in signalling and defence after irradiation. During recovery, in the plants exposed to the highest dose rate, fundamental metabolic processes such as photosynthesis and RNA modification were still affected. This might lead to detrimental effects in the long-term or in the next generations of those irradiated plants.

An ecological transcriptome approach to capture the molecular and physiological mechanisms of mass flowering in Shorea curtisii

Climatic factors have commonly been attributed as the trigger of general flowering, a unique community-level mass flowering phenomenon involving most dipterocarp species that forms the foundation of Southeast Asian tropical rainforests. This intriguing flowering event is often succeeded by mast fruiting, which provides a temporary yet substantial burst of food resources for animals, particularly frugivores. However, the physiological mechanism that triggers general flowering, particularly in dipterocarp species, is not well understood largely due to its irregular and unpredictable occurrences in the tall and dense forests. To shed light on this mechanism, we employed ecological transcriptomic analyses on an RNA-seq dataset of a general flowering species, Shorea curtisii (Dipterocarpaceae), sequenced from leaves and buds collected at multiple vegetative and flowering phenological stages. We assembled 64,219 unigenes from the transcriptome of which 1,730 and 3,559 were differentially expressed in the leaf and the bud, respectively. Differentially expressed unigene clusters were found to be enriched with homologs of Arabidopsis thaliana genes associated with response to biotic and abiotic stresses, nutrient level, and hormonal treatments. When combined with rainfall data, our transcriptome data reveals that the trees were responding to a brief period of drought prior to the elevated expression of key floral promoters and followed by differential expression of unigenes that indicates physiological changes associated with the transition from vegetative to reproductive stages. Our study is timely for a representative general flowering dipterocarp species that occurs in forests that are under the constant threat of deforestation and climate change as it pinpoints important climate sensitive and flowering-related homologs and offers a glimpse into the cascade of gene expression before and after the onset of floral initiation.

Involvement of CONSTANS-like Proteins in Plant Flowering and Abiotic Stress Response

The process of flowering in plants is a pivotal stage in their life cycle, and the CONSTANS-like (COL) protein family, known for its photoperiod sensing ability, plays a crucial role in regulating plant flowering. Over the past two decades, homologous genes of COL have been identified in various plant species, leading to significant advancements in comprehending their involvement in the flowering pathway and response to abiotic stress. This article presents novel research progress on the structural aspects of COL proteins and their regulatory patterns within transcription complexes. Additionally, we reviewed recent information about their participation in flowering and abiotic stress response, aiming to provide a more comprehensive understanding of the functions of COL proteins.

An overview of floral regulatory genes in annual and perennial plants

The floral initiation in angiosperms is a complex process influenced by endogenous and exogenous signals. With this approach, we aim to provide a comprehensive review to integrate this complex floral regulatory process and summarize the regulatory genes and their functions in annuals and perennials. Seven primary paths leading to flowering have been discovered in Arabidopsis under several growth condition that include; photoperiod, ambient temperature, vernalization, gibberellins, autonomous, aging and carbohydrates. These pathways involve a series of interlinked signaling pathways that respond to both internal and external signals, such as light, temperature, hormones, and developmental cues, to coordinate the expression of genes that are involved in flower development. Among them, the photoperiodic pathway was the most important and conserved as some of the fundamental loci and mechanisms are shared even by closely related plant species. The activation of floral regulatory genes such as FLC, FT, LFY, and SOC1 that determine floral meristem identity and the transition to the flowering stage result from the merging of these pathways. Recent studies confirmed that alternative splicing, antisense RNA and epigenetic modification play crucial roles by regulating the expression of genes related to blooming. In this review, we documented recent progress in the floral transition time in annuals and perennials, with emphasis on the specific regulatory mechanisms along with the application of various molecular approaches including overexpression studies, RNA interference and Virus-induced flowering. Furthermore, the similarities and differences between annual and perennial flowering will aid significant contributions to the field by elucidating the mechanisms of perennial plant development and floral initiation regulation.

Beyond NPK: Mineral Nutrient-Mediated Modulation in Orchestrating Flowering Time

Flowering time in plants is a complex process regulated by environmental conditions such as photoperiod and temperature, as well as nutrient conditions. While the impact of major nutrients like nitrogen, phosphorus, and potassium on flowering time has been well recognized, the significance of micronutrient imbalances and their deficiencies should not be neglected because they affect the floral transition from the vegetative stage to the reproductive stage. The secondary major nutrients such as calcium, magnesium, and sulfur participate in various aspects of flowering. Micronutrients such as boron, zinc, iron, and copper play crucial roles in enzymatic reactions and hormone biosynthesis, affecting flower development and reproduction as well. The current review comprehensively explores the interplay between microelements and flowering time, and summarizes the underlying mechanism in plants. Consequently, a better understanding of the interplay between microelements and flowering time will provide clues to reveal the roles of microelements in regulating flowering time and to improve crop reproduction in plant industries.

SALT OVERLY SENSITIVE2 stabilizes phytochrome-interacting factors PIF4 and PIF5 to promote Arabidopsis shade avoidance

Sun-loving plants trigger the shade avoidance syndrome (SAS) to compete against their neighbors for sunlight. Phytochromes are plant red (R) and far-red (FR) light photoreceptors that play a major role in perceiving the shading signals and triggering SAS. Shade induces a reduction in the level of active phytochrome B (phyB), thus increasing the abundance of PHYTOCHROME-INTERACTING FACTORS (PIFs), a group of growth-promoting transcription factors. However, whether other factors are involved in modulating PIF activity in the shade remains largely obscure. Here, we show that SALT OVERLY SENSITIVE2 (SOS2), a protein kinase essential for salt tolerance, positively regulates SAS in Arabidopsis thaliana. SOS2 directly phosphorylates PIF4 and PIF5 at a serine residue close to their conserved motif for binding to active phyB. This phosphorylation thus decreases their interaction with phyB and posttranslationally promotes PIF4 and PIF5 protein accumulation. Notably, the role of SOS2 in regulating PIF4 and PIF5 protein abundance and SAS is more prominent under salt stress. Moreover, phyA and phyB physically interact with SOS2 and promote SOS2 kinase activity in the light. Collectively, our study uncovers an unexpected role of salt-activated SOS2 in promoting SAS by modulating the phyB-PIF module, providing insight into the coordinated response of plants to salt stress and shade.

Pathogenic and Saprophytic Growth Rates of Fusarium oxysporum f. sp. vasinfectum Interact to Affect Variation in Inoculum Density and Interannual Infection Risk

Fusarium wilt of cotton caused by the soilborne fungal pathogen Fusarium oxysporum f. sp. vasinfectum race 4 (FOV4) is a contemporary epidemic affecting cotton production in Far West Texas. The spatial distribution of soilborne FOV4 can be heterogeneous at small scales, and the factors that lead to this heterogeneity require investigation. Hypothetical causes include dissemination of spores through soils and variable saprophytic growth of the fungus. In the field, FOV4 DNA was quantified from soil during and after the cotton-growing season, and though the average amounts of DNA were not different between these time points, the variances of DNA across space were significantly different. Variability was higher when pathogenic growth of the fungus was expected owing to the presence of live cotton plants and lower when saprophytic growth was expected after cropping. In sterile-environment growth chamber experiments, the abundance of organic matter influenced the fungal vegetative growth rate and maximum amount as measured through quantitative PCR and the timing of the fungus' increasing its rate of spore production as measured through dilution plating. To investigate movement of spores in soils, spore mobility in experimental columns was quantified. Soil composition and organic matter abundance affected spore mobility, indicating that the timing of spore production relative to the availability of growth resources will affect the spatial spread of FOV4 and suggesting that soil properties affect the retention of conidia. The spatial spread of FOV4 through soil varies temporally and is affected by the shift between pathogenic and saprophytic growth modes of the fungus.

Perturbation of protein homeostasis brings plastids at the crossroad between repair and dismantling

The chloroplast proteome is a dynamic mosaic of plastid- and nuclear-encoded proteins. Plastid protein homeostasis is maintained through the balance between de novo synthesis and proteolysis. Intracellular communication pathways, including the plastid-to-nucleus signalling and the protein homeostasis machinery, made of stromal chaperones and proteases, shape chloroplast proteome based on developmental and physiological needs. However, the maintenance of fully functional chloroplasts is costly and under specific stress conditions the degradation of damaged chloroplasts is essential to the maintenance of a healthy population of photosynthesising organelles while promoting nutrient redistribution to sink tissues. In this work, we have addressed this complex regulatory chloroplast-quality-control pathway by modulating the expression of two nuclear genes encoding plastid ribosomal proteins PRPS1 and PRPL4. By transcriptomics, proteomics and transmission electron microscopy analyses, we show that the increased expression of PRPS1 gene leads to chloroplast degradation and early flowering, as an escape strategy from stress. On the contrary, the overaccumulation of PRPL4 protein is kept under control by increasing the amount of plastid chaperones and components of the unfolded protein response (cpUPR) regulatory mechanism. This study advances our understanding of molecular mechanisms underlying chloroplast retrograde communication and provides new insight into cellular responses to impaired plastid protein homeostasis.

Salicylic Acid Treatment and Its Effect on Seed Yield and Seed Molecular Composition of Pisum sativum under Abiotic Stress

The reproductive stage of plant development has the most critical impact on yield. Flowering is highly sensitive to abiotic stress, and increasing temperatures and drought harm crop yields. Salicylic acid is a phytohormone that regulates flowering and promotes stress resilience in plants. However, the exact molecular mechanisms and the level of protection are far from understood and seem to be species-specific. Here, the effect of salicylic acid was tested in a field experiment with Pisum sativum exposed to heat stress. Salicylic acid was administered at two different stages of flowering, and its effect on the yield and composition of the harvested seeds was followed. Plants treated with salicylic acid produced larger seed pods, and a significant increase in dry weight was found for the plants with a delayed application of salicylic acid. The analyses of the seed proteome, lipidome, and metabolome did not show any negative impact of salicylic treatment on seed composition. Identified processes that could be responsible for the observed improvement in seed yields included an increase in polyamine biosynthesis, accumulation of storage lipids and lysophosphatidylcholines, a higher abundance of components of chromatin regulation, calmodulin-like protein, and threonine synthase, and indicated a decrease in sensitivity to abscisic acid signaling.

Flowering under enhanced ionising radiation conditions and its regulation through epigenetic mechanisms

As sessile organisms, plants have to deal with unfavourable conditions by acclimating or adapting in order to survive. Regulation of flower induction is one such mechanism to ensure reproduction and species survival. Flowering is a tightly regulated process under the control of a network of genes, which can be affected by environmental cues and stress. The effects of ionising radiation (IR) on flowering, however, have been poorly studied. Understanding the effects of ionising radiation on flowering, including the timing, gene pathways, and epigenetics involved, is crucial in the continuing effort of environmental radiation protection. The review shows that plants alter their flowering pattern in response to IR, with various flowering related genes (eg. FLOWERING LOCUS C (FLC), FLOWERING LOCUS T (FT), CONSTANS (CO), GIGANTEA (GI), APETALA1 (AP1), LEAFY (LFY)) and epigenetic processes (DNA methylation, and miRNA expression eg. miRNA169, miR156, miR172) being affected. Thereby, showing a hypothetical IR-induced flowering mechanism. Further research on the interaction between IR and flowering in plants is, however, needed to elucidate the mechanisms behind the stress-induced flowering response.

Focusing the GWAS Lens on days to flower using latent variable phenotypes derived from global multienvironment trials

Adaptation constraints within crop species have resulted in limited genetic diversity in some breeding programs and areas where new crops have been introduced, for example, for lentil (Lens culinaris Medik.) in North America. An improved understanding of the underlying genetics involved in phenology-related traits is valuable knowledge to aid breeders in overcoming limitations associated with unadapted germplasm and expanding their genetic diversity by introducing new, exotic material. We used a large, 18 site-year, multienvironment dataset phenotyped for phenology-related traits across nine locations and over 3 yr along with accompanying latent variable phenotypes derived from a photothermal model and principal component analysis (PCA) of days from sowing to flower (DTF) data for a lentil diversity panel (324 accessions), which has also been genotyped with an exome capture array. Genome-wide association studies (GWAS) on DTF across multiple environments helped confirm associations with known flowering-time genes and identify new quantitative trait loci (QTL), which may contain previously unknown flowering time genes. Additionally, the use of latent variable phenotypes, which can incorporate environmental data such as temperature and photoperiod as both GWAS traits and as covariates, strengthened associations, revealed additional hidden associations, and alluded to potential roles of the associated QTL. Our approach can be replicated with other crop species, and the results from our GWAS serve as a resource for further exploration into the complex nature of phenology-related traits across the major growing environments for cultivated lentil.

A bZIP transcription factor (CiFD) regulates drought- and low-temperature-induced flowering by alternative splicing in citrus

Drought and low temperature are two key environmental factors that induce adult citrus flowering. However, the underlying regulation mechanism is poorly understood. The bZIP transcription factor FD is a key component of the florigen activation complex (FAC) which is composed of FLOWERING LOCUS T (FT), FD, and 14-3-3 proteins. In this study, isolation and characterization of CiFD in citrus found that there was alternative splicing (AS) of CiFD, forming two different proteins (CiFDα and CiFDβ). Further investigation found that their expression patterns were similar in different tissues of citrus, but the subcellular localization and transcriptional activity were different. Overexpression of the CiFD DNA sequence (CiFD-DNA), CiFDα, or CiFDβ in tobacco and citrus showed early flowering, and CiFD-DNA transgenic plants were the earliest, followed by CiFDβ and CiFDα. Interestingly, CiFDα and CiFDβ were induced by low temperature and drought, respectively. Further analysis showed that CiFDα can form a FAC complex with CiFT, Ci14-3-3, and then bind to the citrus APETALA1 (CiAP1) promoter and promote its expression. However, CiFDβ can directly bind to the CiAP1 promoter independently of CiFT and Ci14-3-3. These results showed that CiFDβ can form a more direct and simplified pathway that is independent of the FAC complex to regulate drought-induced flowering through AS. In addition, a bHLH transcription factor (CibHLH96) binds to CiFD promoter and promotes the expression of CiFD under drought condition. Transgenic analysis found that CibHLH96 can promote flowering in transgenic tobacco. These results suggest that CiFD is involved in drought- and low-temperature-induced citrus flowering through different regulatory patterns.

Early flowering changes robusta coffee yield responses to climate stress and management

A shift towards earlier flowering is a widely noted consequence of climate change for the world's plants. However, whether early flowering changes the way in which plants respond to climate stress, and in turn plant yield, remains largely unexplored. Using 10 years of flowering time and yield observations (Total N = 5580) from 558 robusta coffee (Coffea canephora) farms across Vietnam we used structural equation modelling (SEM) to examine the drivers of flowering day anomalies and the consequent effects of this on coffee climate stress sensitivity and management responses (i.e. irrigation and fertilization). SEM allowed us to model the cascading and interacting effects of differences in flowering time, growing season length and climate stress. Warm nights were the main driver of early flowering (i.e. flowering day anomalies <0), which in turn corresponded to longer growing seasons. Early flowering was linked to greater sensitivity of yield to temperature during flowering (i.e. early in the season). In contrast, when late flowering occurred yield was most sensitive to temperature and rainfall later in the growing season, after flowering and fruit development. The positive effects of tree age and fertilizer on yield, apparent under late flowering conditions, were absent when flowering occurred early. Late flowering models predicted yields under early flowering conditions poorly (a 50 % reduction in cross-validated R² of 0.54 to 0.27). Likewise, models based on early flowering were unable to predict yields well under late flowering conditions (a 75 % reduction in cross-validated R², from 0.58 to 0.14). Our results show that early flowering changes the sensitivity of coffee production to climate stress and management and in turn our ability to predict yield. Our results indicate that changes in plant phenology need to be taken into account in order to more accurately assess climate risk and management impacts on plant performance and crop yield.

S-acylated and nucleus-localized SALT OVERLY SENSITIVE3/CALCINEURIN B-LIKE4 stabilizes GIGANTEA to regulate Arabidopsis flowering time under salt stress

The precise timing of flowering in adverse environments is critical for plants to secure reproductive success. We report a mechanism in Arabidopsis (Arabidopsis thaliana) controlling the time of flowering by which the S-acylation-dependent nuclear import of the protein SALT OVERLY SENSITIVE3/CALCINEURIN B-LIKE4 (SOS3/CBL4), a Ca2+-signaling intermediary in the plant response to salinity, results in the selective stabilization of the flowering time regulator GIGANTEA inside the nucleus under salt stress, while degradation of GIGANTEA in the cytosol releases the protein kinase SOS2 to achieve salt tolerance. S-acylation of SOS3 was critical for its nuclear localization and the promotion of flowering, but partly dispensable for salt tolerance. SOS3 interacted with the photoperiodic flowering components GIGANTEA and FLAVIN-BINDING, KELCH REPEAT, F-BOX1 and participated in the transcriptional complex that regulates CONSTANS to sustain the transcription of CO and FLOWERING LOCUS T under salinity. Thus, the SOS3 protein acts as a Ca2+- and S-acylation-dependent versatile regulator that fine-tunes flowering time in a saline environment through the shared spatial separation and selective stabilization of GIGANTEA, thereby connecting two signaling networks to co-regulate the stress response and the time of flowering.

A de novo gene originating from the mitochondria controls floral transition in Arabidopsis thaliana

De novo genes created in the plant mitochondrial genome have frequently been transferred into the nuclear genome via intergenomic gene transfer events. Therefore, plant mitochondria might be a source of de novo genes in the nuclear genome. However, the functions of de novo genes originating from mitochondria and the evolutionary fate remain unclear. Here, we revealed that an Arabidopsis thaliana specific small coding gene derived from the mitochondrial genome regulates floral transition. We previously identified 49 candidate de novo genes that induce abnormal morphological changes on overexpression. We focused on a candidate gene derived from the mitochondrial genome (sORF2146) that encodes 66 amino acids. Comparative genomic analyses indicated that the mitochondrial sORF2146 emerged in the Brassica lineage as a de novo gene. The nuclear sORF2146 emerged following an intergenomic gene transfer event in the A. thaliana after the divergence between Arabidopsis and Capsella. Although the nuclear and mitochondrial sORF2146 sequences are the same in A. thaliana, only the nuclear sORF2146 is transcribed. The nuclear sORF2146 product is localized in mitochondria, which may be associated with the pseudogenization of the mitochondrial sORF2146. To functionally characterize the nuclear sORF2146, we performed a transcriptomic analysis of transgenic plants overexpressing the nuclear sORF2146. Flowering transition-related genes were highly regulated in the transgenic plants. Subsequent phenotypic analyses demonstrated that the overexpression and knockdown of sORF2146 in transgenic plants resulted in delayed and early flowering, respectively. These findings suggest that a lineage-specific de novo gene derived from mitochondria has an important regulatory effect on floral transition.

Comparative transcriptome analysis on drought stress-induced floral formation of Curcuma kwangsiensis

The rhizomes and tubers of Curcuma kwangsiensis have extensive medicinal value in China. However, the inflorescences of C. kwangsiensis are rarely known in horticulture, because of its low field flowering rate. In order to improve the flowering rate of C. kwangsiensis, we conducted drought stress treatment on the rhizome of C. kwangsiensis. The flowering rate of rhizome was the highest after 4d of drought stress treatment, and the buds on the rhizome could be obviously swell on the 4th day of rehydration culture. In order to identify the genes regulating the flowering time of Curcuma kwangsiensis, comparative transcriptome analysis was performed on the buds on rhizomes before drought stress treatment, 4 d after drought stress treatment and 4 d after rehydration culture. During this process, a total of 20 DEGs controlling flowering time and 23 DEGs involved in ABA synthesis and signal transduction were identified, which might regulate the flowering of C. kwangsiensis under drought stress. Some floral integration factors, such as SOC1 and FTIP, were up-regulated under drought stress for 4 d, indicating that C. kwangsiensis had flowering trend under drought stress. The results of the present study will provide theoretical support for the application of Curcuma kwangsiensis in gardening.

Field and saccharification performances of poplars severely downregulated in CAD1

Lignin is one of the main factors causing lignocellulosic biomass recalcitrance to enzymatic hydrolysis. Glasshouse-grown poplars severely downregulated for CINNAMYL ALCOHOL DEHYDROGENASE 1 (CAD1), the enzyme catalysing the last step in the monolignol-specific branch of lignin biosynthesis, have increased saccharification yields and normal growth. Here, we assess the performance of these hpCAD poplars in the field under short rotation coppice culture for two consecutive rotations of 1 yr and 3 yr. While 1-yr-old hpCAD wood had 10% less lignin, 3-yr-old hpCAD wood had wild-type lignin levels. Because of their altered cell wall composition, including elevated levels of cinnamaldehydes, both 1-yr-old and 3-yr-old hpCAD wood showed enhanced saccharification yields upon harsh alkaline pretreatments (up to +85% and +77%, respectively). In contrast with previous field trials with poplars less severely downregulated for CINNAMYL ALCOHOL DEHYDROGENASE (CAD), the hpCAD poplars displayed leaning phenotypes, early bud set, early flowering and yield penalties. Moreover, hpCAD wood had enlarged vessels, decreased wood density and reduced relative and free water contents. Our data show that the phenotypes of CAD-deficient poplars are strongly dependent on the environment and underpin the importance of field trials in translating basic research towards applications.

Drought and low temperature-induced NF-YA1 activates FT expression to promote citrus flowering

Flower induction in adult citrus is mainly regulated by drought and low temperatures. However, the mechanism of FLOWERING LOCUS T regulation of citrus flowering (CiFT) under two flower-inductive stimuli remains largely unclear. In this study, a citrus transcription factor, nuclear factor YA (CiNF-YA1), was found to specifically bind to the CiFT promoter by forming a complex with CiNF-YB2 and CiNF-YC2 to activate CiFT expression. CiNF-YA1 was induced in juvenile citrus by low temperature and drought treatments. Overexpression of CiNF-YA1 increased drought susceptibility in transgenic citrus, whereas suppression of CiNF-YA1 enhanced drought tolerance in silenced citrus plants. Furthermore, a GOLDEN₂ ^- LIKE protein (CiFE) that interacts with CiFT protein was also isolated. Further experimental evidence showed that CiFE binds to the citrus LEAFY (CiLFY) promoter and activates its expression. In addition, the expressions of CiNF-YA1 and CiFE showed a seasonal increase during the floral induction period and were induced by artificial drought and low-temperature treatments at which floral induction occurred. These results indicate that CiNF-YA1 may activate CiFT expression in response to drought and low temperatures by binding to the CiFT promoter. CiFT then forms a complex with CiFE to activate CiLFY, thereby promoting the flowering of adult citrus.

Facing energy limitations - approaches to increase basil (Ocimum basilicum L.) growth and quality by different increasing light intensities emitted by a broadband LED light spectrum (400-780 nm)

Based on the current trend towards broad-bandwidth LED light spectra for basil productions in multi-tiered controlled-environment horticulture, a recently developed white broad-bandwidth LED light spectrum (400-780 nm) including far-red wavelengths with elevated red and blue light fractions was employed to cultivate basil. Four Ocimum basilicum L. cultivars (cv. Anise, cv. Cinnamon, cv. Dark Opal and cv. Thai Magic) were exposed to two different rising light intensity conditions (I_Low and I_High). In dependence of the individual cultivar-specific plant height increase over time, basil cultivars were exposed to light intensities increasing from ~ 100 to ~ 200 µmol m^-2 s^-1 under I_Low, and from 200 to 400 µmol m^-2 s^-1 under I_High (due to the exponential light intensity increases with decreasing proximity to the LED light fixtures). Within the first experiment, basils' morphological developments, biomass yields and time to marketability under both light conditions were investigated and the energy consumptions were determined to calculate the basils' light use efficiencies. In detail, cultivar-dependent differences in plant height, leaf and branch pair developments over time are described. In comparison to the I_Low light conditions, I_High resulted in accelerated developments and greater yields of all basil cultivars and expedited their marketability by 3-5 days. However, exposure to light intensities above ~ 300 µmol m^-2 s^-1 induced light avoidance responses in the green-leafed basil cultivars cv. Anise, cv. Cinnamon and cv. Thai Magic. In contrast, I_Low resulted in consumer-preferred visual qualities and greater biomass efficiencies of the green-leafed basil cultivars and are discussed as a result of their ability to adapt well to low light conditions. Contrarily to the green-leafed cultivars, purple-leafed cv. Dark Opal developed insufficiently under I_Low, but remained light-tolerant under I_High, which is related to its high anthocyanin contents. In a second experiment, cultivars' volatile organic compound (VOC) contents and compositions over time were investigated. While VOC contents per gram of leaf dry matter gradually decreased in purple-leafed cv. Dark Opal between seedling stage to marketability, their contents gradually increased in the green cultivars. Regardless of the light treatment applied, cultivar-specific VOC compositions changed tremendously in a developmental stage-dependent manner.

Effects of drought on grassland phenology depend on functional types

Shifts in flowering phenology are important indicators of climate change. However, the role of precipitation in driving phenology is far less understood compared with other environmental cues, such as temperature. We use a precipitation reduction gradient to test the direction and magnitude of effects on reproductive phenology and reproduction across 11 plant species in a temperate grassland, a moisture-limited ecosystem. Our experiment was conducted in a single, relatively wet year. We examine the effects of precipitation for species, functional types, and the community. Our results provide evidence that reduced precipitation shifts phenology, alters flower and fruit production, and that the magnitude and direction of the responses depend on functional type and species. For example, early-blooming species shift toward earlier flowering, whereas later-blooming species shift toward later flowering. Because of opposing species-level shifts, there is no overall shift in community-level phenology. This study provides experimental evidence that changes in rainfall can drive phenological shifts. Our results additionally highlight the importance of understanding how plant functional types govern responses to changing climate conditions, which is relevant for forecasting phenology and community-level changes. Specifically, the implications of divergent phenological shifts between early- and late-flowering species include resource scarcity for pollinators and seed dispersers and new temporal windows for invasion.

The Disease Progression and Molecular Defense Response in Chenopodium Quinoa Infected with Peronospora Variabilis, the Causal Agent of Quinoa Downy Mildew

Downy mildew disease, caused by the biotrophic oomycete Peronospora variabilis, is the largest threat to the cultivation of quinoa (Chenopodium quinoa Willd.) in the Andean highlands, and occurs worldwide. However, so far, no molecular study of the quinoa-Peronospora interaction has been reported. Here, we developed tools to study downy mildew disease in quinoa at the gene expression level. P. variabilis was isolated and maintained, allowing the study of downy mildew disease progression in two quinoa cultivars under controlled conditions. Quinoa gene expression changes induced by P. variabilis were analyzed by qRT-PCR, for quinoa homologues of A. thaliana pathogen-associated genes. Overall, we observed a slower disease progression and higher tolerance in the quinoa cultivar Kurmi than in the cultivar Maniqueña Real. The quinoa orthologs of putative defense genes such as the catalase CqCAT2 and the endochitinase CqEP3 showed no changes in gene expression. In contrast, quinoa orthologs of other defense response genes such as the transcription factor CqWRKY33 and the chaperone CqHSP90 were significantly induced in plants infected with P. variabilis. These genes could be used as defense response markers to select quinoa cultivars that are more tolerant to P. variabilis infection.

Role of metabolites in flower development and discovery of compounds controlling flowering time

Flowering is one of the most important physiological processes of plants that ensures continuity of genetic flow from one generation to the next and also maintains food security. Therefore, impact of various climate-related abiotic stresses on flowering have been assessed to evaluate the long-term impact of global climate change. In contrast to the enormous volume of research that has been conducted at the genetic, transcriptional, post-transcriptional, and protein level, much less attention has been paid to understand the role of various metabolites in flower induction and floral organ development during normal growth or in stressed environmental condition. This review article aims at summarizing information on various primary (e.g., carbohydrates, lipids, fatty acid derivatives, protein and amino acids) and secondary metabolites (e.g., polyamines, phenolics, neuro-indoles, phenylpropanoid, flavonoids and terpenes) that have so far been identified either during flower induction or in individual floral organs implying their possible role in organ development. Specialized metabolites responsible for flower colour, scent and shape to support plant-pollinator interaction have been extensively reviewed by many research groups and hence are not considered in this article. Many of the metabolites discussed here may be used as metabolomarkers to identify tolerant crop genotypes. Several agrochemicals have been successfully used to release endodormancy in temperate trees. Along the same line, a strategy that combines metabolite profiling, screening of small-molecule libraries, and structural alteration of selected compounds has been proposed in order to identify novel lead compounds that can regulate flowering time when applied exogenously.

Methylation in DNA, histone, and RNA during flowering under stress condition: A review

Flowering is the most critical transition period in the whole lifecycle of plants, and it is a highly sensitive period to stress. New combinations of temperature, drought stress, carbon dioxide and other abiotic/biotic conditions resulting from contemporary climate change affect the flowering process. Plants have evolved several strategies to deal with environmental stresses, including epigenetic modifications. Numerous studies show that environmental stresses trigger methylation/demethylation during flowering to preserve/accelerate plant lifecycle. What's more, histone and DNA methylation can be induced to respond to stresses, resulting in changes of flowering gene expression and enhancing stress tolerance in plants. Furthermore, RNA methylation may influence stress-regulated flowering by regulating mRNA stability and antioxidant mechanism. Our review presents the involvement of methylation in stress-repressed and stress-induced flowering. The crosstalk between methylation and small RNAs, phytohormones and exogenous substances (such as salicylic acid, nitric oxide) during flowering under different stresses were discussed. The latest regulatory evidence of RNA methylation in stress-regulated flowering was collected for the first time. Meanwhile, the limited evidences of methylation in biotic stress-induced flowering were summarized. Thus, the review provides insights into understanding of methylation mechanism in stress-regulated flowering and makes use for the development of regulating plant flowering at epigenetic level in the future.

Comparison of anther transcriptomes in response to cold stress at the reproductive stage between susceptible and resistant Japonica rice varieties

BACKGROUND

Rice is one of the most important cereal crops in the world but is susceptible to cold stress (CS). In this study, we carried out parallel transcriptomic analysis at the reproductive stage on the anthers of two Japonica rice varieties with contrasting CS resistance: cold susceptible Longjing11 (LJ11) and cold resistant Longjing25 (LJ25).

RESULTS

According to the obtained results, a total of 16,762 differentially expressed genes (DEGs) were identified under CS, including 7,050 and 14,531 DEGs in LJ25 and LJ11, respectively. Examining gene ontology (GO) enrichment identified 35 up- and 39 down-regulated biological process BP GO terms were significantly enriched in the two varieties, with 'response to heat' and 'response to cold' being the most enriched. Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis identified 33 significantly enriched pathways. Only the carbon metabolism and amino acid biosynthesis pathways with down-regulated DEGs were enriched considerably in LJ11, while the plant hormone signal transduction pathway (containing 153 DEGs) was dramatically improved. Eight kinds of plant hormones were detected in the pathway, while auxin, abscisic acid (ABA), salicylic acid (SA), and ethylene (ETH) signaling pathways were found to be the top four pathways with the most DEGs. Furthermore, the protein-protein interaction (PPI) network analysis identified ten hub genes (co-expressed gene number ≥ 30), including six ABA-related genes. Various DEGs (such as OsDREB1A, OsICE1, OsMYB2, OsABF1, OsbZIP23, OsCATC, and so on) revealed distinct expression patterns among rice types when the DEGs between LJ11 and LJ25 were compared, indicating that they are likely responsible for CS resistance of rice in cold region.

CONCLUSION

Collectively, our findings provide comprehensive insights into complex molecular mechanisms of CS response and can aid in CS resistant molecular breeding of rice in cold regions.

Heterologous Expression and Characterization of Tea (Camellia sinensis) Polyamine Oxidase Homologs and Their Involvement in Stresses

Polyamine oxidase (PAO) is a key enzyme maintaining polyamine homeostasis, which affects plant physiological activities. Until now, the gene members and function of PAOs in tea (Camellia sinenesis) have not been fully identified. Here, through the expression in Escherichia coli and Nicotiana benthamiana, we identified six genes annotated as CsPAO in tea genome and transcriptome and determined their enzyme reaction modes and gene expression profiles in tea cultivar 'Yinghong 9'. We found that CsPAO1,2,3 could catalyze spermine, thermospermine, and norspermidine, and CsPAO2,3 could catalyze spermidine in the back-conversion mode, which indicated that the precursor of γ-aminobutyric acid might originate from the oxidation of putrescin but not spermidine. We further investigated the changes of CsPAO activity with temperature and pH and their stability. Kinetic parameters suggested that CsPAO2 was the major PAO modifying polyamine composition in tea, and it could be inactivated by β-hydroxyethylhydrazine and aminoguanidine. Putrescine content and CsPAO2 expression were high in tea flowers. CsPAO2 responded to wound, drought, and salt stress; CsPAO1 might be the main member responding to cold stress; anoxia induced CsPAO3. We conclude that in terms of phylogenetic tree, enzyme characteristics, and expression profile, CsPAO2 might be the dominant CsPAO in the polyamine degradation pathway.

LsARF3 mediates thermally induced bolting through promoting the expression of LsCO in lettuce (Lactuca sativa L.)

Lettuce (Lactuca sativa L.) is a leafy vegetable whose edible organs usually are leaf or stems, and thus high-temperature induced bolting followed by flower initiation is an undesirable trait in lettuce production. However, the molecular mechanism that controls lettuce bolting and flowering upon thermal treatments is largely unknown. Here, we identified a Lettuce auxin response factor 3 (LsARF3), the expression of which was enhanced by heat and auxin treatments. Interestingly, LsARF3 is preferentially expressed in stem apex, suggesting it might be associated with lettuce bolting. Transgenic lettuce overexpressing LsARF3 displayed early bolting and flowering, whereas knockout of LsARF3 dramatically delayed bolting and flowering in lettuce under normal or high temperature conditions. Furthermore, Exogenous application of IAA failed to rescue the late-bolting and -flowering phenotype of lsarf3 mutants. Several floral integrator genes including LsCO, LsFT, and LsLFY were co-expressed with LsARF3 in the overexpression and knockout lettuce plants. Yeast one-hybrid (Y1H) experiments suggested that LsARF3 could physically interact with the LsCO promoter, which was further confirmed by a dual luciferase assay in tobacco leaves. The results indicated that LsARF3 might directly modulate the expression of LsCO in lettuce. Therefore, these results demonstrate that LsARF3 could promote lettuce bolting in response to the high temperature by directly or indirectly activating the expression of floral genes such as LsCO, which provides new insights into lettuce bolting in the context of ARFs signaling and heat response.

Flowering time runs hot and cold

Evidence suggests that anthropogenically-mediated global warming results in accelerated flowering for many plant populations. However, the fact that some plants are late flowering or unaffected by warming, underscores the complex relationship between phase change, temperature, and phylogeny. In this review, we present an emerging picture of how plants sense temperature changes, and then discuss the independent recruitment of ancient flowering pathway genes for the evolution of ambient, low, and high temperature-regulated reproductive development. As well as revealing areas of research required for a better understanding of how past thermal climates have shaped global patterns of plasticity in plant phase change, we consider the implications for these phenological thermal responses in light of climate change.

Citrus FRIGIDA cooperates with its interaction partner dehydrin to regulate drought tolerance

Drought is a major environmental stress that severely affects plant growth and crop productivity. FRIGIDA (FRI) is a key regulator of flowering time and drought tolerance in model plants. However, little is known regarding its functions in woody plants, including citrus. Thus, we explored the functional role of the citrus FRI ortholog (CiFRI) under drought. Drought treatment induced CiFRI expression. CiFRI overexpression enhanced drought tolerance in transgenic Arabidopsis and citrus, while CiFRI suppression increased drought susceptibility in citrus. Moreover, transcriptomic profiling under drought conditions suggested that CiFRI overexpression altered the expression of numerous genes involved in the stress response, hormone biosynthesis, and signal transduction. Mechanistic studies revealed that citrus dehydrin likely protects CiFRI from stress-induced degradation, thereby enhancing plant drought tolerance. In addition, a citrus brassinazole-resistant (BZR) transcription factor family member (CiBZR1) directly binds to the CiFRI promoter to activate its expression under drought conditions. CiBZR1 also enhanced drought tolerance in transgenic Arabidopsis and citrus. These findings further our understanding of the molecular mechanisms underlying the CiFRI-mediated drought stress response in citrus.

BrABF3 promotes flowering through the direct activation of CONSTANS transcription in pak choi

Drought stress triggers the accumulation of the phytohormone abscisic acid (ABA), which in turn activates the expression of the floral integrator gene CONSTANS (CO), accelerating flowering. However, the molecular mechanism of ABA-induced CO activation remains elusive. Here, we conducted a yeast one-hybrid assay using the CO promoter from Brassica campestris (syn. Brassica rapa) ssp. chinensis (pak choi) to screen the ABA-induced pak choi library and identified the transcription activator ABF3 (BrABF3). BrABF3, the expression of which was induced by ABA in pak choi, directly bound to the CO promoter from both pak choi and Arabidopsis. The BrABF3 promoter is specifically active in the Arabidopsis leaf vascular tissue, where CO is mainly expressed. Impaired BrABF3 expression in pak choi decreased BrCO expression levels and delayed flowering, whereas ectopic expression of BrABF3 in Arabidopsis increased CO expression and induced earlier flowering under the long-day conditions. Electrophoretic mobility shift assay analysis showed that BrABF3 was enriched at the canonical ABA-responsive element-ABRE binding factor (ABRE-ABF) binding motifs of the BrCO promoter. The direct binding of BrABF3 to the ABRE elements of CO was further confirmed by chromatin immunoprecipitation quantitative PCR. In addition, the induction of BrCO transcription by BrABF3 could be repressed by BrCDF1 in the morning. Thus, our results suggest that ABA could accelerate the floral transition by directly activating BrCO transcription through BrABF3 in pak choi.

The high concentrations of abscisic, jasmonic, and salicylic acids produced under long days do not accelerate flowering in Chenopodium ficifolium 459

The survival and adaptation of angiosperms depends on the proper timing of flowering. The weedy species Chenopodium ficifolium serves as a useful diploid model for comparing the transition to flowering with the important tetraploid crop Chenopodium quinoa due to the close phylogenetic relationship. The detailed transcriptomic and hormonomic study of the floral induction was performed in the short-day accession C. ficifolium 459. The plants grew more rapidly under long days but flowered later than under short days. The high levels of abscisic, jasmonic, and salicylic acids at long days were accompanied by the elevated expression of the genes responding to oxidative stress. The increased concentrations of stress-related phytohormones neither inhibited the plant growth nor accelerated flowering in C. ficifolium 459 at long photoperiods. Enhanced content of cytokinins and the stimulation of cytokinin and gibberellic acid signaling pathways under short days may indicate the possible participation of these phytohormones in floral initiation. The accumulation of auxin metabolites suggests the presence of a dynamic regulatory network in C. ficifolium 459.

Sulfanilamide Regulates Flowering Time through Expression of the Circadian Clock Gene LUX

Flowering time is an agriculturally important trait that can be manipulated by various approaches such as breeding, growth control and genetic modifications. Despite its potential advantages, including fine-tuning the regulation of flowering time, few reports have explored the use of chemical compounds to manipulate flowering. Here, we report that sulfanilamide, an inhibitor of folate biosynthesis, delays flowering by repressing the expression of florigen FLOWERING LOCUS T (FT) in Arabidopsis thaliana. Transcriptome deep sequencing and quantitative polymerase chain reaction analyses showed that the expression of the circadian clock gene LUX ARRYTHMO/PHYTOCLOCK1 (LUX/PCL1) is altered by sulfanilamide treatment. Furthermore, in the lux nox mutant harboring loss of function in both LUX and its homolog BROTHER OF LUX ARRHYTHMO (BOA, also named NOX), the inhibitory effect of sulfanilamide treatment on FT expression was weak and the flowering time was similar to that of the wild type, suggesting that the circadian clock may contribute to the FT-mediated regulation of flowering by sulfanilamide. Sulfanilamide also delayed flowering time in arugula (Eruca sativa), suggesting that it is involved in the regulation of flowering across Brassicaceae. We propose that sulfanilamide is a novel modulator of flowering.

The tomato OST1-VOZ1 module regulates drought-mediated flowering

Flowering is a critical agricultural trait that substantially affects tomato fruit yield. Although drought stress influences flowering time, the molecular mechanism underlying drought-regulated flowering in tomato remains elusive. In this study, we demonstrated that loss of function of tomato OPEN STOMATA 1 (SlOST1), a protein kinase essential for abscisic acid (ABA) signaling and abiotic stress responses, lowers the tolerance of tomato plants to drought stress. slost1 mutants also exhibited a late flowering phenotype under both normal and drought stress conditions. We also established that SlOST1 directly interacts with and phosphorylates the NAC (NAM, ATAF and CUC)-type transcription factor VASCULAR PLANT ONE-ZINC FINGER 1 (SlVOZ1), at residue serine 67, thereby enhancing its stability and nuclear translocation in an ABA-dependent manner. Moreover, we uncovered several SlVOZ1 binding motifs from DNA affinity purification sequencing analyses and revealed that SlVOZ1 can directly bind to the promoter of the major flowering-integrator gene SINGLE FLOWER TRUSS to promote tomato flowering transition in response to drought. Collectively, our data uncover the essential role of the SlOST1-SlVOZ1 module in regulating flowering in response to drought stress in tomato and offer insights into a novel strategy to balance drought stress response and flowering.

Genetic Variation in Flowering Traits of Tasmanian Leptospermum scoparium and Association with Provenance Home Site Climatic Factors

Leptospermum scoparium is emerging as an economically important plant for the commercial production of mānuka honey and essential oils, both exhibiting unique antibacterial attributes. To support its domestication this is the first quantitative genetic study of variation for L. scoparium traits. It utilised plants from 200 open-pollinated families derived from 40 native populations, from across the species range in Tasmania, grown in a common garden field trial. The traits studied were survival, growth, and the flowering traits precocity, the timing of seasonal peak flowering, flowering duration, and flowering intensity. Significant genetic variation was evident at the population level for all traits studied and at the family level for three traits—growth, flowering precocity, and time to peak flowering. These three traits had moderate to high narrow-sense heritability estimates ranging from 0.27 to 0.69. For six of the traits studied, population differences were associated with climate attributes at the locations where seed was collected, suggesting adaptation to the local climate may have contributed to the observed population differentiation. Population level geographical trends suggest that genotypes to focus on for domestication originate from the eastern half of Tasmania for precociousness and the western half of Tasmania for earlier time to peak flowering and extended flowering duration.

Crosstalk Between Ethylene and Abscisic Acid During Changes in Soil Water Content Reveals a New Role for 1-Aminocyclopropane-1- Carboxylate in Coffee Anthesis Regulation

Coffee (Coffea arabica L.) presents an asynchronous flowering regulated by an endogenous and environmental stimulus, and anthesis occurs once plants are rehydrated after a period of water deficit. We evaluated the evolution of Abscisic Acid (ABA), ethylene, 1-aminocyclopropane-1-carboxylate (ACC) content, ACC oxidase (ACO) activity, and expression analysis of the Lysine Histidine Transporter 1 (LHT1) transporter, in the roots, leaves, and flower buds from three coffee genotypes (C. arabica L. cv Oeiras, Acauã, and Semperflorens) cultivated under field conditions with two experiments. In a third field experiment, the effect of the exogenous supply of ACC in coffee anthesis was evaluated. We found an increased ACC level, low ACO activity, decreased level of ethylene, and a decreased level of ABA in all tissues from the three coffee genotypes in the re-watering period just before anthesis, and a high expression of the LHT1 in flower buds and leaves. The ethylene content and ACO activity decreased from rainy to dry period whereas the ABA content increased. A higher number of opened and G6 stage flower buds were observed in the treatment with exogenous ACC. The results showed that the interaction of ABA-ACO-ethylene and intercellular ACC transport among the leaves, buds, and roots in coffee favors an increased level of ACC that is most likely, involved as a modulator in coffee anthesis. This study provides evidence that ACC can play an important role independently of ethylene in the anthesis process in a perennial crop.