The CONSTANS gene of Arabidopsis promotes flowering and encodes a protein showing similarities to zinc finger transcription factors

The Cm14-3-3μ protein and CCT transcription factor CmNRRa delay flowering in chrysanthemum

Floral transition from vegetative to reproductive growth is pivotal in the plant life cycle. NUTRITION RESPONSE AND ROOT GROWTH (OsNRRa) as a CONSTANS, CONSTANS-LIKE, TOC1 (CCT) domain protein delays flowering in rice and an orthologous gene CmNRRa inhibits flowering in chrysanthemum; however, the mechanism remains unknown. In this study, using yeast two-hybrid screening, we identified the 14-3-3 family member Cm14-3-3µ as a CmNRRa-interacting protein. Biochemical assays using a combination of bimolecular fluorescence complementation (BiFC), pull-down, and Co-immunoprecipitation (Co-IP) were performed to confirm the physical interaction between CmNRRa and Cm14-3-3µ in chrysanthemum. In addition, expression analysis showed that CmNRRa, but not Cm14-3-3µ, responded to the diurnal rhythm, whereas both genes were highly expressed in the leaves. Moreover, the function in flowering time regulation of Cm14-3-3µ is similar to that of CmNRRa. Furthermore, CmNRRa repressed chrysanthemum FLOWERING LOCUS T-like 3 (CmFTL3) and APETALA 1 (AP1)/FRUITFULL (FUL)-like gene (CmAFL1), but induced TERMINAL FLOWER1 (CmTFL1) directly by binding to their promoters. Cm14-3-3µ enhanced the ability of CmNRRa to regulate the expression of these genes. These findings suggest that there is a synergistic relationship between CmNRRa and Cm14-3-3µ in flowering repression in chrysanthemum.

BBX7 interacts with BBX8 to accelerate flowering in chrysanthemum

The quantitative control of FLOWERING LOCUS T (FT) activation is important for the floral transition in flowering plants. However, the flowering regulation mechanisms in the day-neutral, summer-flowering chrysanthemum plant remain unclear. In this study, the chrysanthemum BBX7 homolog CmBBX7 was isolated and its flowering function was identified. The expression of CmBBX7 showed a diurnal rhythm and CmBBX7 exhibited higher expression levels than CmBBX8. Overexpression of CmBBX7 in transgenic chrysanthemum accelerated flowering, whereas lines transfected with a chimeric repressor (pSRDX-CmBBX7) exhibited delayed flowering. Yeast single hybridization, luciferase, electrophoretic mobility shift, and chromatin immunoprecipitation assays showed that CmBBX7 directly targets CmFTL1. In addition, we found that CmBBX7 and CmBBX8 interact to positively regulate the expression of CmFTL1 through binding to its promoter. Collectively, these results highlight CmBBX7 as a key cooperator in the BBX8-FT module to control chrysanthemum flowering.

Fine mapping and causal gene identification of a novel QTL for early flowering by QTL-seq, Target-seq and RNA-seq in spring oilseed rape

A novel quantitative trait locus for early flowering in spring oilseed rape, BnaC08cqDTF, was mapped to an 86-kb region on chromosome C08, and its causal gene, CRY2, was uncovered. Days to flowering is a very important agronomic and adaptive trait of Brassica napus oilseed rape (AACC, 2n = 38). We previously identified BnaC08cqDTF as a novel candidate quantitative trait locus (QTL) for early flowering in spring oilseed rape. Here, we present fine mapping of the locus and a study of its causal gene. Initial mapping was performed by QTL sequencing of DNA pools of BC₃F₂ plants with extreme flowering times derived from crosses between the spring-type cv. No. 4512 (early flowering) and cv. No. 5246 (late flowering), along with fine mapping by target sequencing of the BC₃F₂ and BC₄F₂ populations. Fine mapping narrowed down BnaC08cqDTF to an 86-kb region on chromosome C08. The region harbored fifteen genes. After comparative analyses of the DNA sequences for mutation between A and C syntenic regions and detected by RNA-seq and qRT-PCR between the two parents, we found that BnaC08G0010400ZS harbors an A/G nonsynonymous mutation in exon 3. This single nucleotide polymorphism (SNP) haplotype was also correlated with early flowering in a 256 accession panel. BnaC08G0010400ZS is a homolog of the AT1G04400 gene (CRY2) in Arabidopsis. The analyses of transgenic Arabidopsis verified that BnaC08G0010400ZS is responsible for early flowering. Our results contribute to a better understanding of the genetic control mechanism of early flowering in spring Brassica napus and will promote the breeding for early mature varieties.

Structural variations and environmental specificities of flowering time-related genes in Brassica napus

We found that the flowering time order of accessions in a genetic population considerably varied across environments, and homolog copies of essential flowering time genes played different roles in different locations. Flowering time plays a critical role in determining the life cycle length, yield, and quality of a crop. However, the allelic polymorphism of flowering time-related genes (FTRGs) in Brassica napus, an important oil crop, remains unclear. Here, we provide high-resolution graphics of FTRGs in B. napus on a pangenome-wide scale based on single nucleotide polymorphism (SNP) and structural variation (SV) analyses. A total of 1337 FTRGs in B. napus were identified by aligning their coding sequences with Arabidopsis orthologs. Overall, 46.07% of FTRGs were core genes and 53.93% were variable genes. Moreover, 1.94%, 0.74%, and 4.49% FTRGs had significant presence-frequency differences (PFDs) between the spring and semi-winter, spring and winter, and winter and semi-winter ecotypes, respectively. SNPs and SVs across 1626 accessions of 39 FTRGs underlying numerous published qualitative trait loci were analyzed. Additionally, to identify FTRGs specific to an eco-condition, genome-wide association studies (GWASs) based on SNP, presence/absence variation (PAV), and SV were performed after growing and observing the flowering time order (FTO) of plants in a collection of 292 accessions at three locations in two successive years. It was discovered that the FTO of plants in a genetic population changed a lot across various environments, and homolog copies of some key FTRGs played different roles in different locations. This study revealed the molecular basis of the genotype-by-environment (G × E) effect on flowering and recommended a pool of candidate genes specific to locations for breeding selection.

CO interacts with JAZ repressors and bHLH subgroup IIId factors to negatively regulate jasmonate signaling in Arabidopsis seedlings

CONSTANS (CO) is a master flowering-time regulator that integrates photoperiodic and circadian signals in Arabidopsis thaliana. CO is expressed in multiple tissues, including young leaves and seedling roots, but little is known about the roles and underlying mechanisms of CO in mediating physiological responses other than flowering. Here, we show that CO expression is responsive to jasmonate. CO negatively modulated jasmonate-imposed root-growth inhibition and anthocyanin accumulation. Seedlings from co mutants were more sensitive to jasmonate, whereas overexpression of CO resulted in plants with reduced sensitivity to jasmonate. Moreover, CO mediated the diurnal gating of several jasmonate-responsive genes under long-day conditions. We demonstrate that CO interacts with JASMONATE ZIM-DOMAIN (JAZ) repressors of jasmonate signaling. Genetic analyses indicated that CO functions in a CORONATINE INSENSITIVE1 (COI1)-dependent manner to modulate jasmonate responses. Furthermore, CO physically associated with the basic helix-loop-helix (bHLH) subgroup IIId transcription factors bHLH3 and bHLH17. CO acted cooperatively with bHLH17 in suppressing jasmonate signaling, but JAZ proteins interfered with their transcriptional functions and physical interaction. Collectively, our results reveal the crucial regulatory effects of CO on mediating jasmonate responses and explain the mechanism by which CO works together with JAZ and bHLH subgroup IIId factors to fine-tune jasmonate signaling.

Parallel mechanisms detect different photoperiods to independently control seasonal flowering and growth in plants

For nearly 100 years, we have known that both growth and flowering in plants are seasonally regulated by the length of the day (photoperiod). Intense research focus and powerful genetic tools have propelled studies of photoperiodic flowering, but far less is known about photoperiodic growth, in part because tools were lacking. Here, using a new genetic tool that visually reports on photoperiodic growth, we identified a seasonal growth regulation pathway, from photoperiod detection to gene expression. Surprisingly, this pathway functions in long days but is distinct from the canonical long day photoperiod flowering mechanism. This is possible because the two mechanisms detect the photoperiod in different ways: flowering relies on measuring photoperiod by directly detecting duration of light intensity while the identified growth pathway relies on measuring photosynthetic period indirectly by detecting the duration of photosynthetic metabolite production. In turn, the two pathways then control expression of genes required for flowering or growth independently. Finally, our tools allow us to show that these two types of photoperiods, and their measurement systems, are dissociable. Our results constitute a new view of seasonal timekeeping in plants by showing that two parallel mechanisms measure different photoperiods to control plant growth and flowering, allowing these processes to be coordinated independently across seasons.

Overexpression of two CONSTANS-like 2 (MiCOL2) genes from mango delays flowering and enhances tolerance to abiotic stress in transgenic Arabidopsis

The CO/COL gene family plays an important role in regulating photoperiod-dependent flowering time in plants. In this study, two COL2 gene homologs, MiCOL2A and MiCOL2B, were isolated from 'SiJiMi' mango, and their expression patterns and functions were characterized. The MiCOL2A and MiCOL2B genes both belonged to the group Ⅰ of CO/COL gene family. MiCOL2A and MiCOL2B exhibited distinct circadian rhythms and were highly expressed in leaves during the flowering induction period. Subcellular localization analysis revealed that MiCOL2A and MiCOL2B are localized in the nucleus. The overexpression of MiCOL2A and MiCOL2B significantly delayed flowering time in Arabidopsis under both long-day (LD) and short-day (SD) conditions. The MiCOL2A and MiCOL2B overexpression Arabidopsis plants exhibited more tolerance to slat and drought stress after abiotic stress treatments, with greater ROS scavenging capacity and protective enzyme activity, less cell damage and death and higher expression of stress response genes than wild type plants. Bimolecular fluorescence complementation (BiFC) analysis showed that MiCOL2A and MiCOL2B interacted with several stress-related proteins, including zinc finger protein 4 (MiZFP4), MYB30-INTERACTING E3 LIGASE 1 (MiMIEL1) and RING zinc finger protein 34 (MiRZFP34). The results indicate that MiCOL2A and MiCOL2B are not only involved in flowering time but also play a positive role in abiotic stress responses in plants.

Epistatic interactions among multiple copies of FLC genes with naturally occurring insertions correlate with flowering time variation in radish

Brassicaceae crops, which underwent whole-genome triplication during their evolution, have multiple copies of flowering-related genes. Interactions among multiple gene copies may be involved in flowering time regulation; however, this mechanism is poorly understood. In this study, we performed comprehensive, high-throughput RNA sequencing analysis to identify candidate genes involved in the extremely late-bolting (LB) trait in radish. Then, we examined the regulatory roles and interactions of radish FLOWERING LOCUS C (RsFLC) paralogs, the main flowering repressor candidates. Seven flowering integrator genes, five vernalization genes, nine photoperiodic/circadian clock genes and eight genes from other flowering pathways were differentially expressed in the early-bolting (EB) cultivar 'Aokubinagafuto' and LB radish cultivar 'Tokinashi' under different vernalization conditions. In the LB cultivar, RsFLC1 and RsFLC2 expression levels were maintained after 40 days of cold exposure. Bolting time was significantly correlated with the expression rates of RsFLC1 and RsFLC2. Using the EB × LB F2 population, we performed association analyses of genotypes with or without 1910- and 1627-bp insertions in the first introns of RsFLC1 and RsFLC2, respectively. The insertion alleles prevented the repression of their respective FLC genes under cold conditions. Interestingly, genotypes homozygous for RsFLC2 insertion alleles maintained high RsFLC1 and RsFLC3 expression levels under cold conditions, and two-way analysis of variance revealed that RsFLC1 and RsFLC3 expression was influenced by the RsFLC2 genotype. Our results indicate that insertions in the first introns of RsFLC1 and RsFLC2 contribute to the late-flowering trait in radish via different mechanisms. The RsFLC2 insertion allele conferred a strong delay in bolting by inhibiting the repression of all three RsFLC genes, suggesting that radish flowering time is determined by epistatic interactions among multiple FLC gene copies.

BIN2 phosphorylates the Thr280 of CO to restrict its function in promoting Arabidopsis flowering

CONSTANS (CO) is a central regulator of floral initiation in response to photoperiod. In this study, we show that the GSK3 kinase BIN2 physically interacts with CO and the gain-of-function mutant bin2-1 displays late flowering phenotype through down-regulation of FT transcription. Genetic analyses show that BIN2 genetically acts upstream of CO in regulating flowering time. Further, we illustrate that BIN2 phosphorylates the Thr280 residue of CO. Importantly, the BIN2 phosphorylation of Thr280 residue restricts the function of CO in promoting flowering through affecting its DNA-binding activity. Moreover, we reveal that the N-terminal part of CO harboring the B-Box domain mediates the interaction of both CO-CO and BIN2-CO. We find that BIN2 inhibits the formation of CO dimer/oligomer. Taken together, this study reveals that BIN2 regulates flowering time through phosphorylating the Thr280 of CO and inhibiting the CO-CO interaction in Arabidopsis.

Transcriptome profiling at the transition to the reproductive stage uncovers stage and tissue-specific genes in wheat

BACKGROUND

The transition from vegetative to floral phase is the result of complex crosstalk of exogenous and endogenous floral integrators. This critical physiological event is the response to environmental interaction, which causes biochemical cascades of reactions at different internal tissues, organs, and releases signals that make the plant moves from vegetative status to a reproductive phase. This network controlling flowering time is not deciphered largely in bread wheat. In this study, a comparative transcriptome analysis at a transition time in combination with genetic mapping was used to identify responsible genes in a stage and tissue-specific manner. For this reason, two winter cultivars that have been bred in Germany showing contrasting and stable heading time in different environments were selected for the analysis.

RESULTS

In total, 670 and 1075 differentially expressed genes in the shoot apical meristem and leaf tissue, respectively, could be identified in 23 QTL intervals for the heading date. In the transition apex, Histone methylation H3-K36 and regulation of circadian rhythm are both controlled by the same homoeolog genes mapped in QTL TaHd112, TaHd124, and TaHd137. TaAGL14 gene that identifies the floral meristem was mapped in TaHd054 in the double ridge. In the same stage, the homoeolog located on chromosome 7D of FLOWERING TIME LOCUS T mapped on chr 7B, which evolved an antagonist function and acts as a flowering repressor was uncovered. The wheat orthologue of transcription factor ASYMMETRIC LEAVES 1 (AS1) was identified in the late reproductive stage and was mapped in TaHd102, which is strongly associated with heading date. Deletion of eight nucleotides in the AS1 promoter could be identified in the binding site of the SUPPRESSOR OF CONSTANS OVEREXPRESSION 1 (SOC1) gene in the late flowering cultivar. Both proteins AS1 and SOC1 are inducing flowering time in response to gibberellin biosynthesis.

CONCLUSION

The global transcriptomic at the transition phase uncovered stage and tissue-specific genes mapped in QTL of heading date in winter wheat. In response to Gibberellin signaling, wheat orthologous transcription factor AS1 is expressed in the late reproductive phase of the floral transition. The locus harboring this gene is the strongest QTL associated with the heading date trait in the German cultivars. Consequently, we conclude that this is another indication of the Gibberellin biosynthesis as the mechanism behind the heading variation in wheat.

Genome-wide identification and expression analysis disclose the pivotal PHOSPHATIDYLETHANOLAMINE BINDING PROTEIN members that may be utilized for yield improvement of Chenopodium quinoa

Quinoa (Chenopodium quinoa) is a prospective orphan crop that needs yield improvement. Previous studies indicate PHOSPHATIDYLETHANOLAMINE BINDING PROTEIN (PEBP) family genes are highly associated with the key agronomic traits of crops. Characterizing the pivotal PEBP genes will speed up the domestication and yield improvement of quinoa. Previous investigations on PEBP genes of Chenopodium species indicated that, the PEBP genes, despite in the same subclade, may have experienced functional diversification. Especially, the allotetraploidy (AABB) and numerous segmental duplications and chromosomal rearrangements in quinoa make it more difficult to understand the functions of PEBP genes. More recently, 6 quinoa FT subfamily genes were predicted to be related to flowering of quinoa. However, investigation on the whole PEBP family members is still lacking. In this study, we obtained 23 PEBP genes, including 5 MFT, 11 FTL and 7 TFL genes. We found 7 orthologous gene pairs, from sub-genome A and sub-genome B, respectively, showing collinearities with sugar beet. Evolution analysis on PEBP genes of two quinoa sub-genomes, sugar beet and relatives of diploid ancestors indicated that, the reasons for gene duplication events varied and 4 tandem duplications are the major reason for PEBP family expansion. Tissue-specific expression analysis suggested that expression patterns are mostly differing between orthologous gene pairs. Analysis on gene expressions at 6 stages suggested the possible positive roles of CqFTL1/CqFTL2, CqFTL5, CqFTL8, CqFTL6/CqFTL9 and CqTFL6/CqTFL7, and negative roles of CqTFL1/CqTFL2/CqTFL3, CqTFL4/CqTFL5 in inflorescence branching. Expression analysis in ABA-treated seed, in combination with the cis-acting element distribution analysis, indicated that CqMFT2, CqMFT3 and CqMFT4 may regulate seed germination via ABA signaling. Observations on responses to night break and photoperiod changes highlighted the roles of CqFTL5 and CqFTL8 under short day, and CqFTL6 under long day for quinoa flowering. Further, co-expression network analysis indicated that 64 transcription factors may act upstream of CqFTL5 and CqFTL8 to regulate flowering. Together, this study will help us identify the pivotal PEBP genes that may be utilized for quinoa breeding in future.

Transcriptome analysis of critical genes related to flowering in Mikania micrantha at different altitudes provides insights for a potential control

BACKGROUND

Mikania micrantha is a vine with strong invasion ability, and its strong sexual reproduction ability is not only the main factor of harm, but also a serious obstacle to control. M. micrantha spreads mainly through seed production. Therefore, inhibiting the flowering and seed production of M. micrantha is an effective strategy to prevent from continuing to spread.

RESULT

The flowering number of M. micrantha is different at different altitudes. A total of 67.01 Gb of clean data were obtained from nine cDNA libraries, and more than 83.47% of the clean reads were mapped to the reference genome. In total, 5878 and 7686 significantly differentially expressed genes (DEGs) were found in E2 vs. E9 and E13 vs. E9, respectively. Based on the background annotation and gene expression, some candidate genes related to the flowering pathway were initially screened, and their expression levels in the three different altitudes in flower bud differentiation showed the same trend. That is, at an altitude of 1300 m, the flower integration gene and flower meristem gene were downregulated (such as SOC1 and AP1), and the flowering inhibition gene was upregulated (such as FRI and SVP). Additionally, the results showed that there were many DEGs involved in the hormone signal transduction pathway in the flower bud differentiation of M. micrantha at different altitudes.

CONCLUSIONS

Our results provide abundant sequence resources for clarifying the underlying mechanisms of flower bud differentiation and mining the key factors inhibiting the flowering and seed production of M. micrantha to provide technical support for the discovery of an efficient control method.

Wild emmer wheat, the progenitor of modern bread wheat, exhibits great diversity in the VERNALIZATION1 gene

Wild emmer wheat is an excellent reservoir of genetic variability that can be utilized to improve cultivated wheat to address the challenges of the expanding world population and climate change. Bearing this in mind, we have collected a panel of 263 wild emmer wheat (WEW) genotypes across the Fertile Crescent. The genotypes were grown in different locations and phenotyped for heading date. Genome-wide association mapping (GWAS) was carried out, and 16 SNPs were associated with the heading date. As the flowering time is controlled by photoperiod and vernalization, we sequenced the VRN1 gene, the most important of the vernalization response genes, to discover new alleles. Unlike most earlier attempts, which characterized known VRN1 alleles according to a partial promoter or intron sequences, we obtained full-length sequences of VRN-A1 and VRN-B1 genes in a panel of 95 wild emmer wheat from the Fertile Crescent and uncovered a significant sequence variation. Phylogenetic analysis of VRN-A1 and VRN-B1 haplotypes revealed their evolutionary relationships and geographic distribution in the Fertile Crescent region. The newly described alleles represent an attractive resource for durum and bread wheat improvement programs.

PEBP Signaling Network in Tubers and Tuberous Root Crops

Tubers and tuberous root crops are essential carbohydrate sources and staple foods for humans, second only to cereals. The developmental phase transition, including floral initiation and underground storage organ formation, is controlled by complex signaling processes involving the integration of environmental and endogenous cues. FLOWERING LOCUS T (FT) and TERMINAL FLOWER 1/CENTRORADIALIS (TFL1/CEN), members of the phosphatidylethanolamine-binding protein (PEBP) gene family, play a central role in this developmental phase transition process. FT and FT-like proteins have a function to promote developmental phase transition, while TFL1/CEN act oppositely. The balance between FT and TFL1/CEN is critical to ensure a successful plant life cycle. Here, we present a summarized review of the role and signaling network of PEBP in floral initiation and underground storage organ formation, specifically in tubers and tuberous root crops. Lastly, we point out several questions that need to be answered in order to have a more complete understanding of the PEBP signaling network, which is crucial for the agronomical improvement of tubers and tuberous crops.

Genome-wide identification of BBX gene family and their expression patterns under salt stress in soybean

BACKGROUND

BBX genes are key players in the regulation of various developmental processes and stress responses, which have been identified and functionally characterized in many plant species. However, our understanding of BBX family was greatly limited in soybean.

RESULTS

In this study, 59 BBX genes were identified and characterized in soybean, which can be phylogenetically classified into 5 groups. GmBBXs showed diverse gene structures and motif compositions among the groups and similar within each group. Noticeably, synteny analysis suggested that segmental duplication contributed to the expansion of GmBBX family. Moreover, our RNA-Seq data indicated that 59 GmBBXs showed different transcript profiling under salt stress, and qRT-PCR analysis confirmed their expression patterns. Among them, 22 GmBBXs were transcriptionally altered with more than two-fold changes by salt stress, supporting that GmBBXs play important roles in soybean tolerance to salt stress. Additionally, Computational assay suggested that GmBBXs might potentially interact with GmGI3, GmTOE1b, GmCOP1, GmCHI and GmCRY, while eight types of transcription factors showed potentials to bind the promoter regions of GmBBX genes.

CONCLUSIONS

Fifty-nine BBX genes were identified and characterized in soybean, and their expression patterns under salt stress and computational assays suggested their functional roles in response to salt stress. These findings will contribute to future research in regard to functions and regulatory mechanisms of soybean BBX genes in response to salt stress.

Limited conservation in cross-species comparison of GLK transcription factor binding suggested wide-spread cistrome divergence

Non-coding cis-regulatory variants in animal genomes are an important driving force in the evolution of transcription regulation and phenotype diversity. However, cistrome dynamics in plants remain largely underexplored. Here, we compare the binding of GOLDEN2-LIKE (GLK) transcription factors in tomato, tobacco, Arabidopsis, maize and rice. Although the function of GLKs is conserved, most of their binding sites are species-specific. Conserved binding sites are often found near photosynthetic genes dependent on GLK for expression, but sites near non-differentially expressed genes in the glk mutant are nevertheless under purifying selection. The binding sites' regulatory potential can be predicted by machine learning model using quantitative genome features and TF co-binding information. Our study show that genome cis-variation caused wide-spread TF binding divergence, and most of the TF binding sites are genetically redundant. This poses a major challenge for interpreting the effect of individual sites and highlights the importance of quantitatively measuring TF occupancy.

Genome-wide identification and expression pattern analysis of quinoa BBX family

BBX is a transcription factor encoding zinc finger protein that plays a key role in plant growth and development as well as in responding to abiotic stresses. However, in quinoa, which is known as a "super grain" and has extremely high nutritional value, this gene family has not yet been thoroughly studied. In this study, in order to fully understand the family function of the BBX in quinoa, a total of 31 BBX members were identified by bioinformatics methods. These BBX members were mainly acidic proteins, and most of their secondary structures were random coil s, 31 CqBBX members were unevenly distributed on 17 chromosomes, and the analysis of replication events found that quinoa BBX genes produced a total of 14 pairs of gene replication. The BBX genes were divided into five subfamilies according to phylogenetics, and its gene structure and conserved motif were basically consistent with the classification of its phylogenetic tree. In addition, a total of 43 light response elements, hormone response elements, tissue-specific expression response elements, and abiotic stress response elements were found in the promoter region, involving stress elements such as drought and low temperature. Finally, the expression patterns of CqBBX genes in different tissues and abiotic stresses were studied by combining transcriptome data and qRT-PCR , and all 13 genes responded to drought, salt, and low-temperature stress to varying degrees. This study is the first comprehensive study of the BBX family of quinoa, and its results provide important clues for further analysis of the function of the abiotic stress response.

Expression of coffee florigen CaFT1 reveals a sustained floral induction window associated with asynchronous flowering in tropical perennials

The behavior of florigen(s) and environment-influenced regulatory pathways that control floral initiation in tropical perennials species with complex phenological cycles is poorly understood. Understanding the mechanisms underlying this process is important for food production in the face of climate change, thus, we used Coffea sp. L. (Rubiaceae) as a model to explore this issue. Homologs of FLOWERING LOCUS T (CaFT1) and environment-related regulators CONSTANS (CaCO), PHYTOCHROME INTERACTING FACTOR 4 (CaPIF4) and FLOWERING LOCUS C (CaFLC) were retrieved from coffee genomes and identified through phylogenetic analysis. Overexpression of CaFT1 in Arabidopsis caused early-flowering phenotype and yeast two hybrid studies indicated CaFT1 binding to bZIP floral regulator FD, which suggests that CaFT1 is a coffee florigen. Expression of CaFT1 and other floral regulators, together with carbohydrate analysis, were evaluated over one year using three contrasting genotypes, two C. arabica cultivars and C. canephora. All genotypes showed active and variable CaFT1 transcription from February until October, indicating the potential window for floral induction that reached a maximum in the cold period of June. CaCO expression, as expected, varied over a 24-hour day period and monthly with day length, whereas expression of temperature-responsive homologs, CaFLC and CaPIF4, did not correlate with temperature changes nor CaFT1 expression, suggesting alternative FT regulatory pathways in coffee. Based on our results, we suggest a continuum of floral induction that allows different starting points for floral activation, which explains developmental asynchronicity and prolonged anthesis events in tropical perennial species.

Evolutionary Conservation and Transcriptome Analyses Attribute Perenniality and Flowering to Day-Length Responsive Genes in Bulbous Barley (Hordeum bulbosum)

Rapid population growth and dramatic climatic turnovers are challenging global crop production. These challenges are spurring plant breeders to enhance adaptation and sustainability of major crops. One intriguing approach is to turn annual systems into perennial ones, yet long-term classical breeding efforts to induce perenniality have achieved limited success. Here, we report the results of our investigation of the genetic basis of bulb formation in the nonmodel organism Hordeum bulbosum, a perennial species closely related to barley. To identify candidate genes that regulate bulb formation in H. bulbosum, we applied two complementary approaches. First, we explored the evolutionary conservation of expressed genes among annual Poaceae species. Next, we assembled a reference transcriptome for H. bulbosum and conducted a differential expression (DE) analysis before and after stimulating bulb initiation. Low conservation was identified in genes related to perenniality in H. bulbosum compared with other species, including bulb development and sugar accumulation genes. We also inspected these genes using a DE analysis, which enabled identification of additional genes responsible for bulb initiation and flowering regulation. We propose a molecular model for the regulation of bulb formation involving storage organ development and starch biosynthesis genes. The high conservation observed along a major part of the pathway between H. bulbosum and barley suggests a potential for the application of biotechnological techniques to accelerate breeding toward perenniality in barley.

CRISPR/Cas9-Mediated Targeted Mutagenesis of BnaCOL9 Advances the Flowering Time of Brassica napus L

Rapeseed (Brassica napus L.) is one of the most important oil crops in the world. The planting area and output of rapeseed are affected by the flowering time, which is a critical agronomic feature. COL9 controls growth and development in many different plant species as a member of the zinc finger transcription factor family. However, BnaCOL9 in rapeseed has not been documented. The aim of this study was to apply CRISPR/Cas9 technology to create an early-flowering germplasm resource to provide useful material for improving the early-maturing breeding of rapeseed. We identified four COL9 homologs in rapeseed that were distributed on chromosomes A05, C05, A03, and C03. We successfully created quadruple BnaCOL9 mutations in rapeseed using the CRISPR/Cas9 platform. The quadruple mutants of BnaCOL9 flowered earlier than the wild-type. On the other hand, the flowering time of the BnaCOL9 overexpression lines was delayed. An analysis of the expression patterns revealed that these genes were substantially expressed in the leaves and flowers. A subcellular localization experiment demonstrated that BnaCOL9 was in the nucleus. Furthermore, we discovered that two key flowering-related genes, BnaCO and BnaFT, were highly elevated in the BnaCOL9 mutants, but dramatically downregulated in the BnaCOL9 overexpression lines. Our findings demonstrate that BnaCOL9 is a significant flowering inhibitor in rapeseed and may be employed as a crucial gene for early-maturing breeding.

AcBBX5, a B-box transcription factor from pineapple, regulates flowering time and floral organ development in plants

Flowering is an important factor to ensure the success of plant reproduction, and reasonable flowering time is crucial to the crop yield. BBX transcription factors can regulate several growth and development processes. However, there is little research on whether BBX is involved in flower formation and floral organ development of pineapple. In this study, AcBBX5, a BBX family gene with two conserved B-box domains, was identified from pineapple. Subcellular localization analysis showed that AcBBX5 was located in the nucleus. Transactivation analysis indicated that AcBBX5 had no significant toxic effects on the yeast system and presented transcriptional activation activity in yeast. Overexpression of AcBBX5 delayed flowering time and enlarged flower morphology in Arabidopsis. Meanwhile, the expression levels of AtFT, AtSOC1, AtFUL and AtSEP3 were decreased, and the transcription levels of AtFLC and AtSVP were increased in AcBBX5-overexpressing Arabidopsis, which might lead to delayed flowering of transgenic plants. Furthermore, transcriptome data and QRT-PCR results showed that AcBBX5 was expressed in all floral organs, with the high expression levels in stamens, ovaries and petals. Yeast one-hybrid and dual luciferase assay results showed that AcBBX5 bound to AcFT promoter and inhibited AcFT gene expression. In conclusion, AcBBX5 was involved in flower bud differentiation and floral organ development, which provides an important reference for studying the functions of BBX and the molecular regulation of flower.

Bifunctional regulators of photoperiodic flowering in short day plant rice

Photoperiod is acknowledged as a crucial environmental factor for plant flowering. According to different responses to photoperiod, plants were divided into short-day plants (SDPs), long-day plants (LDPs), and day-neutral plants (DNPs). The day length measurement system of SDPs is different from LDPs. Many SDPs, such as rice, have a critical threshold for day length (CDL) and can even detect changes of 15 minutes for flowering decisions. Over the last 20 years, molecular mechanisms of flowering time in SDP rice and LDP Arabidopsis have gradually clarified, which offers a chance to elucidate the differences in day length measurement between the two types of plants. In Arabidopsis, CO is a pivotal hub in integrating numerous internal and external signals for inducing photoperiodic flowering. By contrast, Hd1 in rice, the homolog of CO, promotes and prevents flowering under SD and LD, respectively. Subsequently, numerous dual function regulators, such as phytochromes, Ghd7, DHT8, OsPRR37, OsGI, OsLHY, and OsELF3, were gradually identified. This review assesses the relationship among these regulators and a proposed regulatory framework for the reversible mechanism, which will deepen our understanding of the CDL regulation mechanism and the negative response to photoperiod between SDPs and LDPs.

Genome-wide identification of the mango CONSTANS (CO) family and functional analysis of two MiCOL9 genes in transgenic Arabidopsis

CONSTANS/CONSTANS-like (CO/COL) transcription factors play a vital role in the photoperiodic flowering pathway. However, the biological functions of COL genes in mango are unclear. In this study, we identified 31 COL genes from the 'Jin Huang' mango genome and divided them into three groups according to the specific gene structure and protein domain characteristics. These 31 MiCOL genes were heterogeneously distributed on 14 chromosomes. Expression pattern analysis showed that most MiCOL genes were mainly expressed in leaves and stems and during the floral induction period, followed by the floral differentiation period. The expression of COL genes was induced by drought and salt stress, but the expression patterns of different genes were different, which may suggest that MiCOL genes are involved in the abiotic stress response of mango. Under salt and drought conditions, two MiCOL9 genes can improve the resistance of Arabidopsis by improving the scavenging ability of ROS and proline accumulation and reducing the MDA content. Additionally, overexpression of MiCOL9 genes significantly inhibited flowering in transgenic Arabidopsis. This work provides an important foundation for understanding the biological roles of mango COL genes in plant growth, development and stress responses.

Genome-Wide Identification and Characterization of the CCT Gene Family in Foxtail Millet (Setaria italica) Response to Diurnal Rhythm and Abiotic Stress

The CCT gene family plays important roles in diurnal rhythm and abiotic stress response, affecting crop growth and development, and thus yield. However, little information is available on the CCT family in foxtail millet (Setaria italica). In the present study, we identified 37 putative SiCCT genes from the foxtail millet genome. A phylogenetic tree was constructed from the predicted full-length SiCCT amino acid sequences, together with CCT proteins from rice and Arabidopsis as representatives of monocotyledonous and dicotyledonous plants, respectively. Based on the conserved structure and phylogenetic relationships, 13, 5, and 19 SiCCT proteins were classified in the COL, PRR, and CMF subfamilies, respectively. The gene structure and protein conserved motifs analysis exhibited highly similar compositions within the same subfamily. Whole-genome duplication analysis indicated that segmental duplication events played an important role in the expansion of the CCT gene family in foxtail millet. Analysis of transcriptome data showed that 16 SiCCT genes had significant diurnal rhythm oscillations. Under abiotic stress and exogenous hormonal treatment, the expression of many CMF subfamily genes was significantly changed. Especially after drought treatment, the expression of CMF subfamily genes except SiCCT32 was significantly up-regulated. This work provides valuable information for further study of the molecular mechanism of diurnal rhythm regulation, abiotic stress responses, and the identification of candidate genes for foxtail millet molecular breeding.

A Pleiotropic Flowering Time QTL Exhibits Gene-by-Environment Interaction for Fitness in a Perennial Grass

Appropriate flowering time is a crucial adaptation impacting fitness in natural plant populations. Although the genetic basis of flowering variation has been extensively studied, its mechanisms in nonmodel organisms and its adaptive value in the field are still poorly understood. Here, we report new insights into the genetic basis of flowering time and its effect on fitness in Panicum hallii, a native perennial grass. Genetic mapping in populations derived from inland and coastal ecotypes identified flowering time quantitative trait loci (QTL) and many exhibited extensive QTL-by-environment interactions. Patterns of segregation within recombinant hybrids provide strong support for directional selection driving ecotypic divergence in flowering time. A major QTL on chromosome 5 (q-FT5) was detected in all experiments. Fine-mapping and expression studies identified a gene with orthology to a rice FLOWERING LOCUS T-like 9 (PhFTL9) as the candidate underlying q-FT5. We used a reciprocal transplant experiment to test for local adaptation and the specific impact of q-FT5 on performance. We did not observe local adaptation in terms of fitness tradeoffs when contrasting ecotypes in home versus away habitats. However, we observed that the coastal allele of q-FT5 conferred a fitness advantage only in its local habitat but not at the inland site. Sequence analyses identified an excess of low-frequency polymorphisms at the PhFTL9 promoter in the inland lineage, suggesting a role for either selection or population expansion on promoter evolution. Together, our findings demonstrate the genetic basis of flowering variation in a perennial grass and provide evidence for conditional neutrality underlying flowering time divergence.

SlBBX28 positively regulates plant growth and flower number in an auxin-mediated manner in tomato

SlBBX28 is a positive regulator of auxin metabolism and signaling, affecting plant growth and flower number in tomato B-box domain-containing proteins (BBXs) comprise a family of transcription factors that regulate several processes, such as photomorphogenesis, flowering, and stress responses. For this reason, attention is being directed toward the functional characterization of these proteins, although knowledge in species other than Arabidopsis thaliana remains scarce. Particularly in the tomato, Solanum lycopersicum, only three out of 31 SlBBX proteins have been functionally characterized to date. To deepen the understanding of the role of these proteins in tomato plant development and yield, SlBBX28, a light-responsive gene, was constitutively silenced, resulting in plants with smaller leaves and fewer flowers per inflorescence. Moreover, SlBBX28 knockdown reduced hypocotyl elongation in darkness-grown tomato. Analyses of auxin content and responsiveness revealed that SlBBX28 promotes auxin-mediated responses. Altogether, the data revealed that SlBBX28 promotes auxin production and signaling, ultimately leading to proper hypocotyl elongation, leaf expansion, and inflorescence development, which are crucial traits determining tomato yield.

Transcriptome sequencing and DEG analysis in different developmental stages of floral buds induced by potassium chlorate in Dimocarpus longan

Potassium chlorate can promote off-season flowering in longan, but the molecular mechanisms are poorly understood. In this study, four-year-old 'Shixia' longan trees were injected in the trunk with potassium chlorate, and terminal buds were sampled and analyzed using transcriptomics and bioinformatics tools. To generate a reference longan transcriptome, we obtained 207,734 paired-end reads covering a total of 58,514,149 bp, which we assembled into 114,445 unigenes. Using this resource, we identified 3,265 differentially expressed genes (DEGs) that were regulated in longan terminal buds in response to potassium chlorate treatment for 2, 6 or 30 days, including 179 transcription factor genes. By reference to the Arabidopsis literature, we then defined 38 longan genes involved in flowering, from which we constructed the longan flowering pathway. According to RNA-seq data, at least 24 of these genes, which participate in multiple signaling pathways, are involved in potassium chlorate-stimulated floral induction, and the differential regulation in terminal buds of ten floral pathway genes (GI, CO, GID1, GA4, GA5, FLC, AP1, LFY, FT and SOC1) was confirmed by qRT-PCR. These data will contribute to an improved understanding of the functions of key genes involved in longan floral induction by potassium chlorate.

The tomato CONSTANS-LIKE protein SlCOL1 regulates fruit yield by repressing SFT gene expression

BACKGROUND

CONSTANS (CO) and CONSTANS-LIKE (COL) transcription factors have been known to regulate a series of cellular processes including the transition from the vegetative growth to flower development in plants. However, their role in regulating fruit yield in tomato is poorly understood.

RESULT

In this study, the tomato ortholog of Arabidopsis CONSTANS, SlCOL1, was shown to play key roles in the control of flower development and fruit yield. Suppression of SlCOL1 expression in tomato was found to lead to promotion of flower and fruit development, resulting in increased tomato fruit yield. On the contrary, overexpression of SlCOL1 disturbed flower and fruit development, and significantly reduced tomato fruit yield. Genetic and biochemical evidence indicated that SlCOL1 controls inflorescence development by directly binding to the promoter region of tomato inflorescence-associated gene SINGLE-FLOWER TRUSS (SFT) and negatively regulating its expression. Additionally, we found that SlCOL1 can also negatively regulate fruit size in tomato.

CONCLUSIONS

Tomato SlCOL1 binds to the promoter of the SFT gene, down-regulates its expression, and plays a key role in reducing the fruit size.

Characterization of walnut JrWOX11 and its overexpression provide insights into adventitious root formation and development and abiotic stress tolerance

The well-developed root system enables plant survival under various environmental stresses. WUSCHEL-RELATED HOMEOBOX GENE 11 (WOX11) plays a critical role in adventitious root formation and development in rice, Arabidopsis, and easy-to-root tree poplar. However, in difficult-to-root trees, the knowledge of WOX11 during adventitious root formation and development remains scarce. In this study, the JrWOX11 gene was isolated from a difficult-to-root tree walnut and heterologously expressed in the "84K" poplar. The results showed that JrWOX11 contained a similar structure and sequence to the homologous genes in rice, Arabidopsis, and poplar, but had different numbers and types of motifs and cis-elements. JrWOX11 lacked the motif GGAIQY compared to that in easy-to-root trees. In addition, JrWOX11 expression was induced by ABA, PEG, and NaCl treatments. Overexpression of JrWOX11 in poplar promoted root initiation and significantly increased adventitious root (ARs) number, lateral roots (LRs) number, and root hair (RH) length. Furthermore, the aboveground biomass was notably increased under NaCl and PEG treatments in transgenic plants. When NaCl and PEG were removed, the survival rate, aerial shoot development, and de novo root organogenesis were also markedly enhanced in transgenic shoot cuttings. The study provides valuable information on the differences between JrWOX11 and the homologous genes in rice, Arabidopsis, and poplar, and supports the critical role of JrWOX11 in the formation of AR and tolerance to salt and osmotic stresses.

Identification of QTLs for wheat heading time across multiple-environments

KEY MESSAGE

The genetic response to changing climatic factors selects consistent across the tested environments and location-specific thermo-sensitive and photoperiod susceptible alleles in lower and higher altitudes, respectively, for starting flowering in winter wheat. Wheat breeders select heading date to match the most favorable conditions for their target environments and this is favored by the extensive genetic variation for this trait that has the potential to be further explored. In this study, we used a germplasm with broad geographic distribution and tested it in multi-location field trials across Germany over three years. The genotypic response to the variation in the climatic parameters depending on location and year uncovered the effect of photoperiod and spring temperatures in accelerating heading date in higher and lower latitudes, respectively. Spring temperature dominates other factors in inducing heading, whereas the higher amount of solar radiation delays it. A genome-wide scan of marker-trait associations with heading date detected two QTL: an adapted allele at locus TaHd102 on chromosome 5A that has a consistent effect on HD in German cultivars in multiple environments and a non-adapted allele at locus TaHd044 on chromosome 3A that accelerates flowering by 5.6 days. TaHd102 and TaHd044 explain 13.8% and 33% of the genetic variance, respectively. The interplay of the climatic variables led to the detection of environment specific association responding to temperature in lower latitudes and photoperiod in higher ones. Another locus TaHd098 on chromosome 5A showed epistatic interactions with 15 known regulators of flowering time when non-adapted cultivars from outside Germany were included in the analysis.

Rice and Arabidopsis BBX proteins: toward genetic engineering of abiotic stress resistant crops

Productivity of crop plants are enormously affected by biotic and abiotic stresses. The co-occurrence of several abiotic stresses may lead to death of crop plants. Hence, it is the responsibility of plant scientists to develop crop plants equipped with multistress tolerance pathways. A subgroup of zinc finger transcription factor family, known as B-box (BBX) proteins, play a key role in light and hormonal regulation pathways. In addition, BBX proteins act as key regulatory proteins in many abiotic stress regulatory pathways, including Ultraviolet-B (UV-B), salinity, drought, heat and cold, and heavy metal stresses. Most of the BBX proteins identified in Arabidopsis and rice respond to more than one abiotic stress. Considering the requirement of improving rice for multistress tolerance, this review discusses functionally characterized Arabidopsis and rice BBX proteins in the development of abiotic stress responses. Furthermore, it highlights the participation of BBX proteins in multistress regulation and crop improvement through genetic engineering.

Expression Patterns of Key Genes in the Photoperiod and Vernalization Flowering Pathways in Lilium longiflorum with Different Bulb Sizes

Lilium longiflorum is a wild Lilium, and its flowering transition requires a long period of cold exposure to meet the demand of vernalization. The responses of different sized bulbs to cold exposure and photoperiod are different, and the floral transition pathways of small and large bulbs are different. In this study, small and large bulbs were placed in cold storage for different weeks and then cultured at a constant ambient temperature of 25 °C under long day (LD) and short day (SD) conditions. Then, the flowering characteristics and expression patterns of key genes related to the vernalization and photoperiod pathways in different groups were calculated and analyzed. The results showed that the floral transition of Lilium longiflorum was influenced by both vernalization and photoperiod, that vernalization and LD conditions can significantly improve the flowering rate of Lilium longiflorum, and that the time from planting to visible flowering buds’ appearance was decreased. The flowering time and rate of large bulbs were greatly influenced by cold exposure, and the vernalization pathway acted more actively at the floral transition stage. The floral transition of small bulbs was affected more by the photoperiod pathway. Moreover, it was speculated that cold exposure may promote greater sensitivity of the small bulbs to LD conditions. In addition, the expression of LlVRN1, LlFKF1, LlGI, LlCO5, LlCO7, LlCO16, LlFT1, LlFT3 and LlSOC1 was high during the process of floral transition, and LlCO13, LlCO14 and LlCO15 were highly expressed in the vegetative stage. The expression of LlCO13 and LlCO14 was different under different lighting conditions, and the flowering induction function of LlCO9 and LlFT3 was related to vernalization. Moreover, LlFKF1, LlGI, LlCO5, LlCO16, LlSOC1 and LlFT2 were involved in the entire growth process of plants, while LlCO6, LlCO16 and LlFT1 are involved in the differentiation and formation of small bulblets of plants after the inflorescence stage, and this process is also closely related to LD conditions. This study has great significance for understanding the molecular mechanisms of the vernalization and photoperiod flowering pathways of Lilium longiflorum.

Altered Developmental and Metabolic Gene Expression in Basil Interspecific Hybrids

To understand the altered developmental changes and associated gene expression in inter-genomic combinations, a study was planned in two diverse yet closely related species of Ocimum, targeting their hybrid F1 and amphidiploids. The existing developmental variations between F1 and amphidiploids was analyzed through phenotypical and anatomical assessments. The absence of 8330 transcripts of F1 in amphidiploids and the exclusive presence of two transcripts related to WNK lysine-deficient protein kinase and geranylgeranyl transferase type-2 subunit beta 1-like proteins in amphidiploids provided a set of genes to compare the suppressed and activated functions between F1 and amphidiploids. The estimation of eugenol and methyleugenol, flavonoid, lignin and chlorophyll content was correlated with the average FPKM and differential gene expression values and further validated through qRT-PCR. Differentially expressed genes of stomatal patterning and development explained the higher density of stomata in F1 and the larger size of stomata in amphidiploids. Gene expression study of several transcription factors putatively involved in the growth and developmental processes of plants clearly amalgamates the transcriptome data linking the phenotypic differences in F1 and amphidiploids. This investigation describes the influence of interspecific hybridization on genes and transcription factors leading to developmental changes and alleviation of intergenomic instability in amphidiploids.

Genome-Wide Identification, Characterization, and Expression Profile Analysis of CONSTANS-like Genes in Woodland Strawberry (Fragaria vesca)

CONSTANS-like (CO-like) gene is one of the most important regulators in the flowering process of the plant, playing a core role in the photoperiodic flowering induction pathway. In this study, we identified 10 distinct CO-like genes (FveCOs) in woodland strawberry (Fragaria vesca). They were classified into three groups with specific gene structure characteristics or protein domains in each group. The effect of selection pressure on the FveCOs in the woodland strawberry was tested by Ka/Ks, and it was shown that the evolution rate of FveCOs was controlled by purification selection factors. Intraspecific synteny analysis of woodland strawberry FveCOs showed that at least one duplication event existed in the gene family members. Collinearity analysis of woodland strawberry genome with genomes of Arabidopsis, rice (Oryza sativa), and apple (Malus × domestica) showed that CO-like genes of F. vesca and Malus × domestica owned higher similarity for their similar genomes compared with those of other two species. The FveCOs showed different tissue-specific expression patterns. Moreover, real-time quantitative PCR results revealed that the expressions of the most FveCOs followed a 24-h rhythm oscillation under both long-day (LD) and short-day (SD) conditions. Further expression analysis showed that the individual expression changing profile of FveCO3 and FveCO5 was opposite to each other under both LD and SD conditions. Moreover, the expression of FveCO3 and FveCO5 was both negatively correlated with the flowering time variation of the woodland strawberry grown under LD and SD conditions, indicating their potential vital roles in the photoperiodic flowering regulation. Further protein interaction network analysis also showed that most of the candidate interaction proteins of FveCO3 and FveCO5 were predicted to be the flowering regulators. Finally, LUC assay indicated that both FveCO3 and FveCO5 could bind to the promoter of FveFT1, the key regulator of flowering regulation in the woodland strawberry, and thus activate its expression. Taken together, this study laid a foundation for understanding the exact roles of FveCOs in the reproductive development regulation of the woodland strawberry, especially in the photoperiodic flowering process.

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.

Environment-mediated mutagenetic interference on genetic stabilization and circadian rhythm in plants

Many mortal organisms on this planet have developed the potential to merge all internal as well as external environmental cues to regulate various processes running inside organisms and in turn make them adaptive to the environment through the circadian clock. This moving rotator controls processes like activation of hormonal, metabolic, or defense pathways, initiation of flowering at an accurate period, and developmental processes in plants to ensure their stability in the environment. All these processes that are under the control of this rotating wheel can be changed either by external environmental factors or by an unpredictable phenomenon called mutation that can be generated by either physical mutagens, chemical mutagens, or by internal genetic interruption during metabolic processes, which alters normal functionality of organisms like innate immune responses, entrainment of the clock, biomass reduction, chlorophyll formation, and hormonal signaling, despite its fewer positive roles in plants like changing plant type, loss of vernalization treatment to make them survivable in different latitudes, and defense responses during stress. In addition, with mutation, overexpression of gene components sometimes supresses mutation effect and promote normal circadian genes abundance in the cell, while sometimes it affects circadian functionality by generating arrhythmicity and shows that not only mutation but overexpression also effects normal functional activities of plant. Therefore, this review mainly summarizes the role of each circadian clock genes in regulating rhythmicity, and shows that how circadian outputs are controlled by mutations as well as overexpression phenomenon.

Mutation of an Essential 60S Ribosome Assembly Factor MIDASIN 1 Induces Early Flowering in Arabidopsis

Ribosome biogenesis is tightly associated with plant growth and reproduction. Mutations in genes encoding ribosomal proteins (RPs) or ribosome biogenesis factors (RBFs) generally result in retarded growth and delayed flowering. However, the early-flowering phenotype resulting from the ribosome biogenesis defect is rarely reported. We previously identified that the AAA-ATPase MIDASIN 1 (MDN1) functions as a 60S RBF in Arabidopsis. Here, we found that its weak mutant mdn1-1 is early-flowering. Transcriptomic analysis showed that the expression of FLOWERING LOCUS C (FLC) is down-regulated, while that of some autonomous pathway genes and ABSCISIC ACID-INSENSITIVE 5 (ABI5) is up-regulated in mdn1-1. Phenotypic analysis revealed that the flowering time of mdn1-1 is severely delayed by increasing FLC expression, suggesting that the early flowering in mdn1-1 is likely associated with the downregulation of FLC. We also found that the photoperiod pathway downstream of CONSTANTS (CO) and FLOWERING LOCUS T (FT) might contribute to the early flowering in mdn1-1. Intriguingly, the abi5-4 allele completely blocks the early flowering in mdn1-1. Collectively, our results indicate that the ribosome biogenesis defect elicited by the mutation of MDN1 leads to early flowering by affecting multiple flowering regulation pathways.

Exploring the SiCCT Gene Family and Its Role in Heading Date in Foxtail Millet

CCT transcription factors are involved in the regulation of photoperiod and abiotic stress in Arabidopsis and rice. It is not clear that how CCT gene family expand and regulate heading date in foxtail millet. In this study, we conducted a systematic analysis of the CCT gene family in foxtail millet. Thirty-nine CCT genes were identified and divided into four subfamilies based on functional motifs. Analysis showed that dispersed duplication played a predominant role in the expansion of CCT genes during evolution. Nucleotide diversity analysis suggested that genes in CONSTANS (COL)-like, CCT MOTIF FAMILY (CMF)-like, and pseudoresponse response regulator (PRR)-like subfamilies were subjected to selection. Fifteen CCT genes were colocalized with previous heading date quantitative trait loci (QTL) and genome-wide association analysis (GWAS) signals. Transgenic plants were then employed to confirm that overexpression of the CCT gene SiPRR37 delayed the heading date and increased plant height. Our study first investigated the characterization and expansion of the CCT family in foxtail millet and demonstrated the role of SiPRR37. These results lay a significant foundation for further research on the function of CCT genes and provide a cue for the regulation of heading date.

Field transcriptome analysis reveals a molecular mechanism for cassava-flowering in a mountainous environment in Southeast Asia

The field survey in this article showed in 'KU50', a popular variety and late-branching type of cassava in Southeast Asia, that flowering rarely occurs in normal-field conditions in Southeast Asia but is strongly induced in the dry season in the mountainous region. Flowering time is correlated with the expression patterns of MeFT1 and homologs of Arabidopsis GI, PHYA, and NF-Ys. Cassava (Manihot esculenta Crantz) is a tropical crop that is propagated vegetatively rather than sexually by seed. Flowering rarely occurs in the erect-type variety grown in Southeast Asia, but it is known that cassava produces flowers every year in mountainous regions. Data pertaining to the effect of environmental factors on flowering time and gene expression in cassava, however, is limited. The aim of the present study was to determine the kinds of environmental conditions that regulate flowering time in cassava and the underlying molecular mechanisms. The flowering status of KU50, a popular variety in Southeast Asia and late-branching type of cassava, was monitored in six fields in Vietnam and Cambodia. At non-flowering and flowering field locations in North Vietnam, the two FLOWERING LOCUS T (FT)-like genes, MeFT1 and MeFT2, were characterized by qPCR, and the pattern of expression of flowering-related genes and genes responsive to environmental signals were analyzed by using RNA sequencing data from time-series samples. Results indicate that cassava flowering was induced in the dry season in the mountain region, and that flowering time was correlated with the expression of MeFT1, and homologs of Arabidopsis GI, PHYA, and NF-Ys. Based upon these data, we hypothesize that floral induction in cassava is triggered by some conditions present in the mountain regions during the dry season.

The regulatory role of CARBON STARVED ANTHER-mediated photoperiod-dependent male fertility in rice

Environmental signals, especially daylength, play important roles in determining fertility in photoperiod-sensitive genic male sterile (PGMS) lines that are critical to sustain production of high-yielding hybrid rice (Oryza sativa) varieties. However, the mechanisms by which PGMS lines perceive changes in photoperiod and transmit those signals to elicit downstream effects are not well understood. In this study, we compared the transcriptomes from the leaves and anthers of carbon starved anther (csa), a PGMS line, to wild-type (WT) tissues under different photoperiods. Components of circadian clock in the leaves, including Circadian Clock-Associated 1 and Pseudo-Response Regulator (PRR95), played vital roles in sensing the photoperiod signals. Photoperiod signals were weakly transduced to anthers, where gene expression was mainly controlled by the CSA allele. CSA played a critical role in regulating sugar metabolism and cell wall synthesis in anthers under short-day conditions, and transcription of key genes inducing csa-directed sterility was upregulated under long-day (LD) conditions though not to WT levels, revealing a mechanism to explain the partial restoration of fertility in rice under LD conditions. Eight direct targets of CSA regulation were identified, all of which were genes involved in sugar metabolism and transport (cell wall invertases, SWEETs, and monosaccharide transporters) expressed only in reproductive tissues. Several hub genes coordinating the effects of CSA regulation were identified as critical elements determining WT male fertility and further analysis of these and related genes will reveal insights into how CSA coordinates sugar metabolism, cell wall biosynthesis, and photoperiod sensing in rice anther development.

Exogenous melatonin improves the resistance to cucumber bacterial angular leaf spot caused by Pseudomonas syringae pv. Lachrymans

Pseudomonas syringae pv. Lachrymans (Psl) is a bacterial pathogen that causes cucumber bacterial angular leaf spot (BALS). It is known that melatonin (MT), as a pleiotropic signal molecule, can improve plant stress tolerance, but less information is available about the function of MT on plant resistance to bacteria disease. Here, we investigated the effect of MT on cucumber BALS. Our results show that MT inhibited the bacteria Psl growth significantly in vitro and attenuated cucumber BALS remarkably in vivo. The concentration of bacteria in leaves treated with 0.1 mM MT was approximately 10,000 times reduced at 5 days-post-inoculation (dpi), compared to the control without MT. Transcriptomic analysis showed that 225 differentially expressed genes (DEGs) were induced in leaves after just MT treatment for 3 h. The functions of these DEGs were mainly associated with hormone signal transduction, mitogen-activated protein kinase (MAPK) signaling pathway, and photosynthesis, suggesting that MT could regulate plant growth and induce plant immunity. Moreover, 665 DEGs were induced when leaves were treated with exogenous MT in combination with the bacteria inoculation for 12 h. The functions of these DEGs were much related to plant-pathogen interaction, hormone signal transduction, and amino acids biosynthesis pathways. Many MT-induced DEGs were involved in some distinct signal transduction pathways, such as calmodulin (CaM), polyamines (PAs), nitric oxide (NO), and salicylic acid (SA). The physiological analysis shows that exogenous MT spray reduced the stomatal aperture and enhanced the activities of antioxidant and defense enzymes, which were in consistent with the results of the transcriptome analysis. In addition, MT may function in regulating the metabolic balance between plant growth and defense. In conclusion, our results demonstrate that MT could alleviate the cucumber BALS via inhibiting propagation and invasion of Psl, activating plant signaling, enhancing antioxidative and defense systems, inducing stress-related genes expression, and regulating the plant growth-defense balance.

Genome-Wide Characterization Analysis of CCT Genes in Raphanus sativus and Their Potential Role in Flowering and Abiotic Stress Response

CCT genes play vital roles in flowering, plant growth, development, and response to abiotic stresses. Although they have been reported in many plants, the characterization and expression pattern of CCT genes is still limited in R. sativus. In this study, a total of 58 CCT genes were identified in R. sativus. Phylogenetic tree, gene structure, and conserved domains revealed that all CCT genes were classified into three groups: COL, CMF, and PRR. Genome-wide identification and evolutionary analysis showed that segmental duplication expanded the CCT gene families considerably, with the LF subgenome retaining more CCT genes. We observed strong purifying selection pressure for CCT genes. RsCCT genes showed tissue specificity, and some genes (such as RsCCT22, RsCCT36, RsCCT42 and RsCCT51) were highly expressed in flowers. Promoter cis-elements and RNA-seq data analysis showed that RsCCT genes could play roles in controlling flowering through the photoperiodic pathway and vernalization pathway. The expression profiles of RsCCT genes under Cd, Cr, Pb, and heat and salt stresses revealed that many RsCCT genes could respond to one or more abiotic stresses. Our findings could provide essential information for further studies on the function of RsCCT genes.

Identification of Stable and Multiple Environment Interaction QTLs and Candidate Genes for Fiber Productive Traits Under Irrigated and Water Stress Conditions Using Intraspecific RILs of Gossypium hirsutum var. MCU5 X TCH1218

Cotton productivity under water-stressed conditions is controlled by multiple quantitative trait loci (QTL). Enhancement of these productivity traits under water deficit stress is crucial for the genetic improvement of upland cotton, Gossypium hirsutum. In the present study, we constructed a genetic map with 504 single nucleotide polymorphisms (SNPs) covering a total span length of 4,416 cM with an average inter-marker distance of 8.76 cM. A total of 181 intra-specific recombinant inbred lines (RILs) were derived from a cross between G. hirsutum var. MCU5 and TCH1218 were used. Although 2,457 polymorphic SNPs were detected between the parents using the CottonSNP50K assay, only 504 SNPs were found to be useful for the construction of the genetic map. In the SNP genotyping, a large number of SNPs showed either >20% missing data, duplication, or segregation distortion. However, the mapped SNPs of this study showed collinearity with the physical map of the reference genome (G. hirsutum var.TM-1), indicating that there was no chromosomal rearrangement within the studied mapping population. RILs were evaluated under multi-environments and seasons for which the phenotypic data were acquired. A total of 53 QTL controlling plant height (PH), number of sympodial branches, boll number (BN), and boll weight (BW) were dissected by QTL analysis under irrigated and water stress conditions. Additionally, it was found that nine QTL hot spots not only co-localized for more than one investigated trait but were also stable with major QTL, i.e., with > 10% of phenotypic variation. One QTL hotspot on chromosome 22 flanked by AX-182254626-AX-182264770 with a span length of 89.4 cM co-localized with seven major and stable QTL linked to a number of sympodial branches both under irrigated and water stress conditions. In addition, putative candidate genes associated with water stress in the QTL hotspots were identified. Besides, few QTL from the hotspots were previously reported across various genetic architects in cotton validating the potential applications of these identified QTL for cotton breeding and improvement. Thus, the major and stable QTL identified in the present study would improve the cotton productivity under water-limited environments through marker-assisted selection.

TaCol-B5 modifies spike architecture and enhances grain yield in wheat

Spike architecture influences grain yield in wheat. We report the map-based cloning of a gene determining the number of spikelet nodes per spike in common wheat. The cloned gene is named TaCOL-B5 and encodes a CONSTANS-like protein that is orthologous to COL5 in plant species. Constitutive overexpression of the dominant TaCol-B5 allele but without the region encoding B-boxes in a common wheat cultivar increases the number of spikelet nodes per spike and produces more tillers and spikes, thereby enhancing grain yield in transgenic plants under field conditions. Allelic variation in TaCOL-B5 results in amino acid substitutions leading to differential protein phosphorylation by the protein kinase TaK4. The TaCol-B5 allele is present in emmer wheat but is rare in a global collection of modern wheat cultivars.

The quest for optimal plant architecture

Changes in plant architecture can improve cereal crop yield.

Transcriptomic Analysis of Early Flowering Signals in ‘Royal’ Flax

Canada is one of the world’s leading producers and exporters of flax seed, with most production occurring in the Prairie Provinces. However, reduced season length and risk of frost restricts production in the northern grain belt of the Canadian Prairies. To expand the growing region of flax and increase production in Canada, flax breeders need to develop earlier-flowering varieties capable of avoiding the risk of abiotic stress. A thorough understanding of flowering control of flax is essential for the efficient breeding of such lines. We identified 722 putative flax flowering genes that span all major flowering-time pathways. Frequently, we found multiple flax homologues for a single Arabidopsis flowering gene. We used RNA sequencing to quantify the expression of genes in the shoot apical meristem (SAM) at 10, 15, 19, and 29 days after planting (dap) using the ‘Royal’ cultivar. We observed the expression of 80% of putative flax flowering genes and the differential expression of only 30%; these included homologues of major flowering regulators, such as SOC1, FUL, and AP1. We also found enrichment of differentially expressed genes (DEGs) in transcription factor (TF) families involved in flowering. Finally, we identified the candidates’ novel flowering genes amongst the uncharacterized flax genes. Our transcriptomic dataset provides a useful resource for investigating the regulatory control of the transition to flowering in flax and for the breeding of northern-adapted varieties.

The Conserved and Specific Roles of the LUX ARRHYTHMO in Circadian Clock and Nodulation

LUX ARRHYTHMO (LUX) plays a key role in circadian rhythms and flowering. Here, we identified the MtLUX gene which is the putative ortholog of LUX in Medicago truncatula. The roles of MtLUX, in both the nodulation belowground and leaf movement aboveground, were investigated by characterizing a loss-of-function mtlux mutant. MtLUX was required for the control of flowering time under both long-day and short-day conditions. Further investigations showed that the early flowering in the mtlux mutant was correlated with the elevated expression level of the MtFTa1 gene but in a CO-like independent manner. MtLUX played a conserved role in the regulatory interactions with MtLHY, MtTOC1, and MtPRR genes, which is similar to those in other species. Meanwhile, the unexpected functions of MtLUX were revealed in nodule formation and nyctinastic leaf movement, probably through the indirect regulation in MtLHY. Its participation in nodulation is of interest in the context of functional conservation and the neo-functionalization of the products of LUX orthologs.

LUX ARRHYTHMO Interacts With ELF3a and ELF4a to Coordinate Vegetative Growth and Photoperiodic Flowering in Rice

The evening complex (EC) plays a critical role in photoperiod flowering in Arabidopsis. Nevertheless, the underlying functions of individual components and coordinate regulation mechanism of EC genes in rice flowering remain to be elucidated. Here, we characterized the critical role of LUX ARRHYTHMO (LUX) in photoperiod perception and coordinating vegetative growth and flowering in rice. Non-functional alleles of OsLUX extremely extended vegetative phase, leading to photoperiod-insensitive late flowering and great increase of grain yield. OsLUX displayed an obvious diurnal rhythm expression with the peak at dusk and promoted rice flowering via coordinating the expression of genes associated with the circadian clock and the output integrators of photoperiodic flowering. OsLUX combined with OsELF4a and OsELF3a or OsELF3b to form two ECs, of which the OsLUX-OsELF3a-OsELF4a was likely the dominant promoter for photoperiodic flowering. In addition, OsELF4a was also essential for promoting rice flowering. Unlike OsLUX, loss OsELF4a displayed a marginal influence under short-day (SD) condition, but markedly delayed flowering time under long-day (LD) condition. These results suggest that rice EC genes share the function of promoting flowering. This is agreement with the orthologs of SD plant, but opposite to the counterparts of LD species. Taken together, rice EC genes display similar but not identical function in photoperiodic flowering, probably through regulating gene expression cooperative and independent. These findings facilitate our understanding of photoperiodic flowering in plants, especially the SD crops.