Accelerated Flowering Time Research Articles

Differential responses of two fenugreek (Trigonella foenum-graecum L.) landraces pretreated with melatonin to prolonged drought stress and subsequent recovery

BackgroundDrought impairs growth, disturbs photosynthesis, and induces senescence in plants, which results in crop productivity reduction and ultimately jeopardizes human food security. The objective of this study was to determine major parameters associated with drought tolerance and recovery ability of fenugreek (Trigonella foenum-graecum L.), by examining differential biochemical and phenological responses and underlying enzyme activities as well as melatonin roles during drought stress and re-watering for two contrasting landraces. Moreover, the relative expression of three key genes involved in the biosynthesis pathway of diosgenin, including SQS, CAS, and BG, was investigated.ResultsDepending on the conditions, drought stress enhanced the activity of antioxidant enzymes and the osmoregulating compounds, non-enzymatic antioxidants, hydrogen peroxide content, and lipid peroxidation levels in most cases. Severe drought stress accelerated flowering time in Shushtar landrace (SHR) but had no significant effects on Varamin (VR). Pretreatment with melatonin delayed flowering time in SHR and caused high drought resistance in this landrace. Furthermore, melatonin significantly enhanced drought adaptability in VR by improving plant recovery ability.DiscussionBased on our results plants’ responses to drought stress and melatonin pretreatment were completely landrace-specific. Drought stress caused an increase in the relative expression of CAS gene and ultimately the accumulation of steroidal saponins in SHR. Melatonin compensated for the decrease in biomass production due to drought stress and finally increased steroidal saponins performance in SHR. Our study showed that melatonin can improve drought stress and recovery in fenugreek, but different factors such as genotype, melatonin concentration, and plant age should be considered.

Response of off-season strawberries (Fragaria sp.) production under the effects of paclobutrazol and drought stress

Strawberry (Fragaria sp.) is a fruit crop harvested seasonally with the peak season from August to November while the off-season harvest is January to June with limited harvest. The purpose of this study was to find the concentration of paclobutrazol and the level of drought stress for off-season strawberry production. This research conducted on April to July 2023. The experiment used a factorial Randomized Block Design consisting of 2 factors and 3 replications with 16 treatment combinations. The first factor was paclobutrazol consisting of four levels, namely P0 = control, P1 = 10,000 ppm, P2 = 20,000 ppm and P3 = 30,000 ppm and the second factor was the level of drought stress consisting of four levels i.e. C0 = 100% field capacity, C1 = 80% field capacity, C2 = 60% field capacity and C3 = 40% field capacity. The results showed that paclobutrazol accelerated flowering time, increased fruit set, leaf relative water content, root length, chlorophyll content, but decreased the number of fruits formed, harvested fruits, fruit diameter, harvested fruit weight, weight per fruit, root oven dry weight, percentage of fallen fruits and total soluble solids. Drought stress level increased leaf relative water content, root length, root oven dry weight, percentage of fallen fruit, percentage of fruit set, but decreased number of flowers formed, fruits harvested, weight of fruits harvested, weight per fruit, fruit diameter, total soluble solids, chlorophyll content and delayed flowering time.

FvWRKY50 is an important gene that regulates both vegetative growth and reproductive growth in strawberry.

The WRKY transcription factors play important roles in plant growth and resistance, but only a few members have been identified in strawberry. Here we identified a WRKY transcription factor, FvWRKY50, in diploid strawberry which played essential roles in strawberry vegetative growth, and reproductive growth. Knocking out FvWRKY50 by genome editing accelerated flowering time and leaf senescence but delayed anthocyanin accumulation in fruit. Further analysis showed that FvWRKY50 acted as a transcriptional repressor to negatively regulate the expression of flowering- and leaf senescence-related genes, including FvFT2, FvCO, FvFT3, and FvSAUR36. Notably, FvWRKY50 directly upregulated the expression of FvCHI and FvDFR by binding their promoter under normal conditions, but at low temperature FvWRKY50 was phosphorylated by FvMAPK3 and then induced protein degradation by ubiquitination, delaying anthocyanin accumulation. In addition, the homozygous mutant of FvWRKY50 was smaller while the biallelic mutant showed normal size. These new findings provide important clues for us to further reveal the regulatory mechanisms of strawberry growth and fruit ripening.

Impacts of Radio-Frequency Electromagnetic Field (RF-EMF) on Lettuce (Lactuca sativa)—Evidence for RF-EMF Interference with Plant Stress Responses

The increased use of wireless technology causes a significant exposure increase for all living organisms to radio frequency electromagnetic fields (RF-EMF). This comprises bacteria, animals, and also plants. Unfortunately, our understanding of how RF-EMF influences plants and plant physiology remains inadequate. In this study, we examined the effects of RF-EMF radiation on lettuce plants (Lactuca sativa) in both indoor and outdoor environments using the frequency ranges of 1890-1900 MHz (DECT) at 2.4 GHz and 5 GHz (Wi-Fi). Under greenhouse conditions, RF-EMF exposure had only a minor impact on fast chlorophyll fluorescence kinetics and no effect on plant flowering time. In contrast, lettuce plants exposed to RF-EMF in the field showed a significant and systemic decrease in photosynthetic efficiency and accelerated flowering time compared to the control groups. Gene expression analysis revealed significant down-regulation of two stress-related genes in RF-EMF-exposed plants: violaxanthin de-epoxidase (VDE) and zeaxanthin epoxidase (ZEP). RF-EMF-exposed plants had lower Photosystem II's maximal photochemical quantum yield (FV/FM) and non-photochemical quenching (NPQ) than control plants under light stress conditions. In summary, our results imply that RF-EMF might interfere with plant stress responses and reduced plant stress tolerance.

Need for speed: a breakthrough speed breeding protocol for hemp

Need for speed: a breakthrough speed breeding protocol for hemp

Morphological and physiologic response of black rice M5 gamma ray irradiation to drought stress

Drought stress is one of the factors that affect plant growth, both in terms of morphology and physiology. Bantul M4 local black rice produces crops that have high proline content and low production. This study aims to examine the response to morphology, physiology and selection of M5 black rice irradiated by gamma rays which are tolerant to drought stress. This research was conducted in the Taman Keceh screen house, Wonogiri Regency at an altitude of 141 masl from June to September 2021. This study used a non-replicated experimental design with drought stress treatment using 50% and 100% water gravimetry. Observation of morphological characters by measuring plant height, number of productive tillers, and flowering age. Observation of physiological characters by measuring stomatal conductance, and transpiration. The results showed that the morphological response decreased plant height, increased the number of productive tillers, and accelerated flowering time. Physiological response to narrow stomatal conductance, transpiration.

GATA25, a novel regulator, accelerates the flowering time of Arabidopsis thaliana

Intrinsic and exogenous signals in conjunction precisely regulate the initiation of flowering. Both signals influence flowering time, which is an integral part of plant reproduction. The signals converge through different pathways, and their coordinated action leads to the onset of flowering. Genetic pathways related to the regulation of flowering time are well-known from research into the molecular genetics of Arabidopsis thaliana. Specifically, crucial components of the photoperiodic pathway and floral integrators play a critically significant role in flowering. In this study, we found that GATA25 is a novel transcription factor that accelerates flowering time under long days. GATA25 encodes C-X2-C-X20-C-X2-C conserved cysteine residues of the zinc-finger domain and CCT domain which process photoperiodic flowering and regulate circadian rhythms. Flowering was accelerated by overexpression of GATA25 throughout the Arabidopsis thaliana. In contrast, GATA25 fused to SRDX (SUPERMAN repressive domain X)-motif plants showed delayed flowering. We also demonstrated that GATA25 induced the expression of floral integrator genes and photoperiodic pathway-related genes. Together, these results suggest that GATA25 might act to accelerate flowering time.

Isolation and Functional Characterization of Two SHORT VEGETATIVE PHASE Homologous Genes from Mango

The SHORT VEGETATIVE PHASE (SVP) gene is a transcription factor that integrates flowering signals and plays an important role in the regulation of flowering time in many plants. In this study, two full-length cDNA sequences of SVP homologous genes—MiSVP1 and MiSVP2—were obtained from ‘SiJiMi’ mango. Sequence analysis showed that the MiSVPs had typical MADS-box domains and were highly conserved between each other. The analysis of expression patterns showed that the MiSVPs were expressed during flower development and highly expressed in vegetative tissues, with low expression in flowers/buds. The MiSVPs could responded to low temperature, NaCl, and PEG treatment. Subcellular localization revealed that MiSVP1 and MiSVP2 were localized in the nucleus. Transformation of Arabidopsis revealed that overexpression of MiSVP1 delayed flowering time, overexpression of MiSVP2 accelerated flowering time, and neither MiSVP1 nor MiSVP2 had an effect on the number of rosette leaves. Overexpression of MiSVP1 increased the expression of AtFLC and decreased the expression of AtFT and AtSOC1, and overexpression of MiSVP2 increased the expression levels of AtSOC1 and AtFT and decreased the expression levels of AtFLC. Point-to-point and bimolecular fluorescence complementation (BiFC) assays showed that MiSVP1 and MiSVP2 could interact with SEP1-1, SOC1D, and AP1-2. These results suggest that MiSVP1 and MiSVP2 may play a significant roles in the flowering process of mango.

Utilizing MIKC-type MADS-box protein SOC1 for yield potential enhancement in maize

Key messageOverexpression of Zea mays SOC gene promotes flowering, reduces plant height, and leads to no reduction in grain production per plant, suggesting enhanced yield potential, at least, through increasing planting density.MIKC-type MADS-box gene SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) is an integrator conserved in the plant flowering pathway. In this study, the maize SOC1 (ZmSOC1) gene was cloned and overexpressed in transgenic maize Hi-II genotype. The T0 plants were backcrossed with nontransgenic inbred B73 to produce first generation backcross (BC1) seeds. Phenotyping of both transgenic and null segregant (NT) BC1 plants was conducted in three independent experiments. The BC1 transgenic plants showed new attributes such as increased vegetative growth, accelerated flowering time, reduced overall plant height, and increased grain weight. Second generation backcross (BC2) plants were evaluated in the field using two planting densities. Compared to BC2 NT plants, BC2 transgenic plants, were 12–18% shorter, flowered 5 days earlier, and showed no reduction in grain production per plant and an increase in fat, starch, and simple sugars in the grain. Transcriptome comparison in young leaves of 56-day-old BC1 plants revealed that the overexpressed ZmSOC1 resulted in 107 differentially expressed genes. The upregulated transcription factor DNA BINDING WITH ONE FINGER 5.4 (DOF5.4) was among the genes responsible for the reduced plant height. Modulating expression of SOC1 opens a new and effective approach to promote flowering and reduce plant height, which may have potential to enhance crop yield and improve grain quality.

Stepwise increases in FT1 expression regulate seasonal progression of flowering in wheat (Triticum aestivum).

Flowering is regulated by genes that respond to changing daylengths and temperature, which have been well studied using controlled conditions; however, the molecular processes underpinning flowering in nature remain poorly understood. Here, we investigate the genetic pathways that coordinate flowering and inflorescence development of wheat (Triticum aestivum) as daylengths extend naturally in the field, using lines that contain variant alleles for the key photoperiod gene, Photoperiod-1 (Ppd-1). We found flowering involves a stepwise increase in the expression of FLOWERING LOCUS T1 (FT1), which initiates under day-neutral conditions of early spring. The incremental rise in FT1 expression is overridden in plants that contain a photoperiod-insensitive allele of Ppd-1, which hastens the completion of spikelet development and accelerates flowering time. The accelerated inflorescence development of photoperiod-insensitive lines is promoted by advanced seasonal expression of floral meristem identity genes. The completion of spikelet formation is promoted by FLOWERING LOCUS T2, which regulates spikelet number and is activated by Ppd-1. In wheat, flowering under natural photoperiods is regulated by stepwise increases in the expression of FT1, which responds dynamically to extending daylengths to promote early inflorescence development. This research provides a strong foundation to improve yield potential by fine-tuning the photoperiod-dependent control of inflorescence development.

Knockouts of a late flowering gene via CRISPR-Cas9 confer early maturity in rice at multiple field locations.

OsGhd7 gene was discovered by screening our rice activation tagging population. CRISPR-Cas9 created knockouts of OsGhd7 conferred early flowering and early maturity in rice varieties across multiple geographical locations in China. Our research shows that OsGhd7 is a good target for breeding early maturity rice varieties, and an excellent example of the advantages of applying the CRISPR-Cas9 technology for trait improvement. Flowering time (heading date) is an important trait for crop cultivation and yield. In this study, we discovered a late flowering gene OsGhd7 by screening our rice activation tagging population, and demonstrated that overexpression of OsGhd7 delayed flowering time in rice, and the delay in flowering time depended on the transgene expression level. OsGhd7 is a functional allele of the Ghd7 gene family; knockouts of OsGhd7 generated by CRISPR-Cas9 significantly accelerated flowering time and the earliness of the flowering time depended on field location. The homozygous OsGhd7 knockout lines showed approximately 8, 10, and 20days earlier flowering than controls at three different locations in China (Changsha City, Sanya City, and Beijing City, respectively) that varied from 18.25° N to 39.90° N. Furthermore, knockouts of OsGhd7 also showed an early flowering phenotype in different rice varieties, indicating OsGhd7 can be used as a common target gene for using the CRISPR technology to modulate rice flowering time. The importance of OsGhd7 and CRISPR technology for breeding early maturity rice varieties are discussed.

Regulatory function of EARLI1-LIKE HYBRID PROLINE-RICH PROTEIN 1 in the floral transition of Arabidopsis thaliana

The plasma membrane- and endoplasmic reticulum-localized proteins encoded by the EARLI1 (EARLY ARABIDOPSIS ALUMINUM INDUCED 1) subfamily of genes contain a signal peptide, a proline-rich domain and an eight-cysteine motif. We previously showed that knockdown of EARLI1 subfamily genes in the late-flowering background of Col-FRI-Sf2 accelerates flowering time, suggesting that EARLI1 genes participate in maintenance of vegetative growth and prevention of premature reproductive growth. We show here that ELHyPRP1 (EARLI1-LIKE HYBRID PROLINE-RICH PROTEIN 1, AT4G12490), a member of this subfamily, is induced by environmental factors such as cold and long-day photoperiod. Detailed analyses with RNA interference and overexpressing lines demonstrated that modulation of ELHyPRP1 can affect the expression of photoperiod, vernalization, gibberellin, age, and autonomous flowering pathway genes. When ELHyPRP1 and other EARLI1 subfamily genes were silenced by RNA interference, most genes participating in the promotion of flowering were activated, while suppressors of the floral transition were repressed. Downregulation of ELHyPRP1 leads to increased expression of the flowering time genes FT and SOC1, and enhanced circadian expression patterns of genes associated with the promotion of the floral transition. Together with the silencing of ELHyPRP1, the flowering repressor FLC and the GA signalling repressor RGA were inhibited. ELHyPRP1 transgenic tobacco plants displayed late-flowering phenotypes and their flowering time was remarkably delayed in comparison to the wild-type Qinyan 95 tobacco plants grown under long-day photoperiod. These results indicate that ELHyPRP1 may be involved in balancing biomass accumulation and seed proliferation.

Molecular Processes Underpinning Seasonal Regulation of Flowering in Bread Wheat ( <i>Triticum Aestivum L.</i>)

Plants integrate seasonal progression in daylength and temperature to determine the optimal time to flower and produce seed. In cereals, genes that regulate responses to changing daylengths and temperature have been well-studied using controlled conditions; however, the molecular processes underpinning flowering in nature are poorly understood. Here, we investigate the molecular pathways that coordinate flowering and inflorescence development in wheat as daylengths extend naturally in the field. We find that discrete photoperiods contribute to the initiation of flowering and control of yield-related traits as days becomes longer from winter into spring. This process involves step-wise increases in the expression of FLOWERING LOCUS T1 (FT1). Photoperiod-1 (Ppd-1) partially regulates the seasonal induction of FT1, which responds dynamically to changes in daylength to influence the rate of inflorescence development. The incremental rise in FT1 expression is overridden in plants that contain a photoperiod-insensitive allele of Ppd-1, which hastens the completion of spikelet development and accelerates flowering time. The completion of spikelet formation is promoted by FLOWERING LOCUS T2, which influences spikelet number and is activated by Ppd-1. This research advances our understanding of the seasonal regulation of flowering in wheat and provides a strong foundation to improve yield potential by fine-tuning the photoperiod-dependent control of inflorescence development.

Control of water-use efficiency by florigen.

A major issue in modern agriculture is water loss through stomata during photosynthetic carbon assimilation. In water-limited ecosystems, annual plants have strategies to synchronize their growth and reproduction to the availability of water. Some species or ecotypes of flowers are early to ensure that their life cycles are completed before the onset of late season terminal drought ("drought escape"). This accelerated flowering correlates with low water-use efficiency (WUE). The molecular players and physiological mechanisms involved in this coordination are not fully understood. We analyzed WUE using gravimetry, gas exchange, and carbon isotope discrimination in florigen deficient (sft mutant), wild-type (Micro-Tom), and florigen over-expressing (SFT-ox) tomato lines. Increased florigen expression led to accelerated flowering time and reduced WUE. The low WUE of SFT-ox was driven by higher stomatal conductance and thinner leaf blades. This florigen-driven effect on WUE appears be independent of abscisic acid (ABA). Our results open a new avenue to increase WUE in crops in an ABA-independent manner. Manipulation of florigen levels could allow us to produce crops with a life cycle synchronized to water availability.

Accelerated flowering time reduces lifetime water use without penalizing reproductive performance in Arabidopsis.

Natural selection driven by water availability has resulted in considerable variation for traits associated with drought tolerance and leaf‐level water‐use efficiency (WUE). In Arabidopsis, little is known about the variation of whole‐plant water use (PWU) and whole‐plant WUE (transpiration efficiency). To investigate the genetic basis of PWU, we developed a novel proxy trait by combining flowering time and rosette water use to estimate lifetime PWU. We validated its usefulness for large‐scale screening of mapping populations in a subset of ecotypes. This parameter subsequently facilitated the screening of water use and drought tolerance traits in a recombinant inbred line population derived from two Arabidopsis accessions with distinct water‐use strategies, namely, C24 (low PWU) and Col‐0 (high PWU). Subsequent quantitative trait loci mapping and validation through near‐isogenic lines identified two causal quantitative trait loci, which showed that a combination of weak and nonfunctional alleles of the FRIGIDA (FRI) and FLOWERING LOCUS C (FLC) genes substantially reduced plant water use due to their control of flowering time. Crucially, we observed that reducing flowering time and consequently water use did not penalize reproductive performance, as such water productivity (seed produced per unit of water transpired) improved. Natural polymorphisms of FRI and FLC have previously been elucidated as key determinants of natural variation in intrinsic WUE (δ13C). However, in the genetic backgrounds tested here, drought tolerance traits, stomatal conductance, δ13C. and rosette water use were independent of allelic variation at FRI and FLC, suggesting that flowering is critical in determining lifetime PWU but not always leaf‐level traits.

Interactions between rising CO2 and temperature driveaccelerated flowering in model plants under changing conditions of the last century.

Past studies have shown that flowering times have accelerated over the last century. These responses are often attributed to rising temperature, although short-term field experiments with warming treatments have under-estimated accelerations in flowering time that have been observed in long-term field surveys. Thus, there appears to be a missing factor(s) for explaining accelerated flowering over the last century. Rising atmospheric CO2 concentration ([CO2]) is a possible candidate, and its contributions to affecting flowering time over historic periods are not well understood. This is likely because rising [CO2] is confounded with temperature in the field and preindustrial [CO2] studies are relatively rare. To address this, we tested the individual and interactive effects of rising [CO2] and temperature between preindustrial and modern periods on flowering time in the model system, Arabidopsis thaliana. We used a variety of genotypes originating from diverse locations, allowing us to test intraspecific responses to last-century climate change. We found that accelerated flowering time between the full-preindustrial and full-modern treatments was mainly driven by an interaction between rising [CO2] and temperature, rather than through the individual effects of either factor in isolation. Furthermore, accelerated flowering time was driven by enhanced plant growth rates and not through changes in plant size at flowering. Thus, the interaction between rising [CO2] and temperature may be key for explaining large accelerations in flowering times that have been observed over the last century and that could not be explained by rising temperature alone.

An early-flowering einkorn wheat mutant with deletions of PHYTOCLOCK 1/LUX ARRHYTHMO and VERNALIZATION 2 exhibits a high level of VERNALIZATION 1 expression induced by vernalization

Using heavy-ion beam mutagenesis of Triticum monococcum strain KU104-1, we identified a mutant that shows extra early-flowering; it was named extra early-flowering 3 (exe3). Here, we carried out expression analyses of clock-related genes, clock downstream genes and photoperiod pathway genes, and found that the clock component gene PHYTOCLOCK 1/LUX ARRHYTHMO (PCL1/LUX) was not expressed in exe3 mutant plants. A PCR analysis of DNA markers indicated that the exe3 mutant had a deletion of wheat PCL1/LUX (WPCL1), and that the WPCL1 deletion was correlated with the mutant phenotype in the segregation line. We confirmed that the original strain KU104-1 carried a mutation that produced a null allele of a flowering repressor gene VERNALIZATION 2 (VRN2). As a result, the exe3 mutant has both WPCL1 and VRN2 loss-of-function mutations. Analysis of plant development in a growth chamber showed that vernalization treatment accelerated flowering time in the exe3 mutant under short day (SD) as well as long day (LD) conditions, and the early-flowering phenotype was correlated with the earlier up-regulation of VRN1. The deletion of WPCL1 affects the SD-specific expression patterns of some clock-related genes, clock downstream genes and photoperiod pathway genes, suggesting that the exe3 mutant causes a disordered SD response. The present study indicates that VRN1 expression is associated with the biological clock and the VRN1 up-regulation is not influenced by the presence or absence of VRN2.

Phalaenopsis flowering locus VE regulates floral organ maturation.

PaFVE is low ambient temperature-inducible and acts as a systemic regulator in the early stage of floral development in Phalaenopsis. Phalaenopsis aphrodite: subsp. formosana, a native orchid species of Taiwan, is an economically important ornamental crop that requires low ambient temperature for floral transition. Currently, limited genetic information about such orchid species hampers genetic manipulation for specific or improved floral traits, and the control of flowering time independent of temperature regulation. In this study, the sequence of the full-length of Phalaenopsis flowering locus VE (PaFVE) gene was determined. Spatial and temporal expression studies showed that mRNA transcripts of PaFVE were inducible by low ambient temperature, and high levels of expression occurred after spiking initiation and remained high throughout the early stage of floral development. Further investigation revealed that floral organ development was impeded in PaFVE-silenced P. aphrodite, but flowering time and floral organogenesis were not compromised. Analysis of the downstream flowering genes suggested that the delay in floral maturation is associated with a corresponding decrease in the expression of downstream flowering genes, PaSOC1, PaSOC1L and PaAGL24. The ectopic expression of PaFVE in Arabidopsis resulted in an accelerated flowering time, accompanied by an increase in the expression of AtSOC1, thus revealing the functional role of PaFVE as a floral regulator. Overall, our results demonstrate that PaFVE has evolutionarily diverged and conserved functions, and serves as a regulator of floral organ maturation in Phalaenopsis and a regulator of flowering time in Arabidopsis.

Hd18, Encoding Histone Acetylase Related to Arabidopsis FLOWERING LOCUS D, is Involved in the Control of Flowering Time in Rice

Flowering time is one of the most important agronomic traits in rice (Oryza sativa L.), because it defines harvest seasons and cultivation areas, and affects yields. We used a map-based strategy to clone Heading date 18 (Hd18). The difference in flowering time between the Japanese rice cultivars Koshihikari and Hayamasari was due to a single nucleotide polymorphism within the Hd18 gene, which encodes an amine oxidase domain-containing protein and is homologous to Arabidopsis FLOWERING LOCUS D (FLD). The Hayamasari Hd18 allele and knockdown of Hd18 gene expression delayed the flowering time of rice plants regardless of the day-length condition. Structural modeling of the Hd18 protein suggested that the non-synonymous substitution changed protein stability and function due to differences in interdomain hydrogen bond formation. Compared with those in Koshihikari, the expression levels of the flowering-time genes Early heading date 1 (Ehd1), Heading date 3a (Hd3a) and Rice flowering locus T1 (RFT1) were lower in a near-isogenic line with the Hayamasari Hd18 allele in a Koshihikari genetic background. We revealed that Hd18 acts as an accelerator in the rice flowering pathway under both short- and long-day conditions by elevating transcription levels of Ehd1 Gene expression analysis also suggested the involvement of MADS-box genes such as OsMADS50, OsMADS51 and OsMADS56 in the Hd18-associated regulation of Ehd1 These results suggest that, like FLD, its rice homolog accelerates flowering time but is involved in rice flowering pathways that differ from the autonomous pathways in Arabidopsis.

Density effects on late flowering mutants of Arabidopsis thaliana under continuous light.

In general, plant growth is inhibited under high-density conditions, while it is promoted under low-density conditions. This is known as the "density effect". Growing plants at high densities is often associated with an accelerated flowering time. Three major pathways [the long day (LD), gibberellic acid (GA), and autonomous/vernalization pathways] are known to play important roles in the control of flowering time. Circadian clock genes, namely, LHY, CCA1, GI, and ELF3, regulate the LD pathway. GAI and FCA control flowering via GA and autonomous pathways, respectively. The density effect on plant size is caused by specific factors such as the amount of nutrition obtained from the soil and touch frequency among plants. However, the molecular mechanism underlying the acceleration of flowering time due to density effects remains unclear. Here, we show the density effects on three Brassicaceae plants, namely, Brassica rapa var. nipposinica, Brassica napus, and Brassica chinensis f. honsaitai. They showed shorter stems and leaves when grown at high densities on soil under continuous light (LL). Shorter stems and leaves, as well as accelerated flowering times, were observed when a model plant, Arabidopsis thaliana, was grown under the same conditions. Unexpectedly, ethylene insensitive 2 (ein2) showed no differences in density effects in our experiments. The acceleration of flowering at higher densities was largely suppressed by gai, but not by gi, lhy;cca1, or fca. These results suggest that the promotion of flowering (as a density effect) is likely dependent on the GA pathway, but not the LD or autonomous pathways.