SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 Research Articles

Aintegumenta And Redundant Aintegumenta-Like6 Are Required For Bract Outgrowth In Arabidopsis.

Plants consist of fundamental units of growth called phytomers (leaf or bract, axillary bud, node, and internode), which are repeated and modified throughout shoot development to give plants plasticity for survival and adaptation. One phytomer modification is the suppression or outgrowth of bracts, the leaves subtending the flowers. The floral meristem identity regulator LEAFY (LFY) and the organ boundary genes BLADE-ON-PETIOLE1 (BOP1) and BOP2, have been shown to suppress bract development in Arabidopsis, as mutations in these genes result in bract outgrowth. However, much less is known about the mechanisms that promote bract outgrowth in Arabidopsis mutants such as these. Further understanding of this mechanism may provide a potential tool for modifying leaf development. Here, we showed that the MADS-box genes SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), FRUITFUL (FUL), and AGAMOUS-LIKE24 (AGL24) play more important roles than BOP1/2 and LFY in bract suppression, and that AINTEGUMENTA (ANT) and the partially redundant AINTEGUMENTA-LIKE6 (AIL6) are necessary for bract outgrowth in these mutant backgrounds. We also showed that misexpression of AIL6 alone is sufficient for bract outgrowth. Our data reveal a mechanism for bract suppression and outgrowth and provide insight into phytomer plasticity.

Candidate gene analysis distinguishes regulatory mechanisms for phenological transitions in Indian and Snowball cauliflower

ABSTRACT The present study analysed expression of 13 candidate genes in relation to different developmental transitions (vegetative–curding–flowering) in Indian and snowball cauliflwer using quantitative real-time PCR (qRT-PCR). Expression levels of FRUITFULL-c (BoFUL-c), FLOWERING LOCUS T (BoFT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), and LEAFY(BoFLY) increased from seedling to full curd stages in all varieties. VERNALIZATION2 (BoVRN2) and APETALA2 (BoAP2) genes showed a contrasting trend in Pusa Meghna (Indian type) and Pusa Snowball Kt-25 (Snowball type). High expression of BoVRN3, BoVIN2, and BoAP2 in Pusa Snowball Kt-25 fitted well with its vernalisation requirement. The increasing expression of BoFT, SOC1, and BoVIN3 while decreasing trend in BoLFY, REPRODUCTIVE MERISTEM (BoREM1), CAULIFLOWER (BoCAL), and BoFUL-d during seedling–curd initiation–full curd stages in Pusa Shukti (mid-late) matches with Pusa Snowball Kt-25, highlighting their genetic closeness. Hierarchical clustering of these 13 candidate genes grouped all the genes into two major clusters: one had the CAULIFLOWER CURD EXPRESSION 1 (CCE1), BoLFY, BoREM1, BoFUL-c, BoFUL-d, LEAFY Homologous (BoFH), and BoCAL genes while the rest of the genes constituted a second cluster. A significant interaction effect was observed in four candidate varieties and two growing situations (i.e. normal and lower temperature range) for curding-related phenological traits. The information will be helpful in understanding the curding behaviour.

Gibberellin signaling modulates flowering via the DELLA-BRAHMA-NF-YC module in Arabidopsis.

Gibberellin (GA) plays a key role in floral induction by activating the expression of floral integrator genes in plants, but the epigenetic regulatory mechanisms underlying this process remain unclear. Here, we show that BRAHMA (BRM), a core subunit of the chromatin-remodeling SWItch/sucrose nonfermentable (SWI/SNF) complex that functions in various biological processes by regulating gene expression, is involved in GA-signaling-mediated flowering via the formation of the DELLA-BRM-NF-YC module in Arabidopsis (Arabidopsis thaliana). DELLA, BRM, and NF-YC transcription factors interact with one another, and DELLA proteins promote the physical interaction between BRM and NF-YC proteins. This impairs the binding of NF-YCs to SOC1, a major floral integrator gene, to inhibit flowering. On the other hand, DELLA proteins also facilitate the binding of BRM to SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1). The GA-induced degradation of DELLA proteins disturbs the DELLA-BRM-NF-YC module, prevents BRM from inhibiting NF-YCs, and decreases the DNA-binding ability of BRM, which promote the deposition of H3K4me3 on SOC1 chromatin, leading to early flowering. Collectively, our findings show that BRM is a key epigenetic partner of DELLA proteins during the floral transition. Moreover, they provide molecular insights into how GA signaling coordinates an epigenetic factor with a transcription factor to regulate the expression of a flowering gene and flowering in plants.

Co-regulatory effects of hormone and mRNA-miRNA module on flower bud formation of Camellia oleifera.

Few flower buds in a high-yield year are the main factors restricting the yield of Camellia oleifera in the next year. However, there are no relevant reports on the regulation mechanism of flower bud formation. In this study, hormones, mRNAs, and miRNAs were tested during flower bud formation in MY3 ("Min Yu 3," with stable yield in different years) and QY2 ("Qian Yu 2," with less flower bud formation in a high-yield year) cultivars. The results showed that except for IAA, the hormone contents of GA3, ABA, tZ, JA, and SA in the buds were higher than those in the fruit, and the contents of all hormones in the buds were higher than those in the adjacent tissues. This excluded the effect of hormones produced from the fruit on flower bud formation. The difference in hormones showed that 21-30 April was the critical period for flower bud formation in C. oleifera; the JA content in MY3 was higher than that in QY2, but a lower concentration of GA3 contributed to the formation of the C. oleifera flower bud. JA and GA3 might have different effects on flower bud formation. Comprehensive analysis of the RNA-seq data showed that differentially expressed genes were notably enriched in hormone signal transduction and the circadian system. Flower bud formation in MY3 was induced through the plant hormone receptor TIR1 (transport inhibitor response 1) of the IAA signaling pathway, the miR535-GID1c module of the GA signaling pathway, and the miR395-JAZ module of the JA signaling pathway. In addition, the expression of core clock components GI (GIGANTEA) and CO (CONSTANS) in MY3 increased 2.3-fold and 1.8-fold over that in QY2, respectively, indicating that the circadian system also played a role in promoting flower bud formation in MY3. Finally, the hormone signaling pathway and circadian system transmitted flowering signals to the floral meristem characteristic genes LFY (LEAFY) and AP1 (APETALA 1) via FT (FLOWERING LOCUS T) and SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CO 1) to regulate flower bud formation. These data will provide the basis for understanding the mechanism of flower bud alternate formation and formulating high yield regulation measures for C. oleifera.

COP1 Mediates Dark-Induced Stomatal Closure by Suppressing FT, TSF and SOC1 Expression to Promote NO Accumulation in Arabidopsis Guard Cells

RING-finger-type ubiquitin E3 ligase Constitutively Photomorphogenic 1 (COP1) and floral integrators such as FLOWERING LOCUS T (FT), TWIN SISTER OF FT (TSF) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) have been identified as regulators of stomatal movement. However, little is known about their roles and relationship in dark-induced stomatal closure. Here, we demonstrated that COP1 is required for dark-induced stomatal closure using cop1 mutant. The cop1 mutant closed stomata in response to exogenous nitric oxide (NO) but not hydrogen peroxide (H2O2), and H2O2 but not NO accumulated in cop1 in darkness, further indicating that COP1 acts downstream of H2O2 and upstream of NO in dark-induced stomatal closure. Expression of FT, TSF and SOC1 in wild-type (WT) plants decreased significantly with dark duration time, but this process was blocked in cop1. Furthermore, ft, tsf, and soc1 mutants accumulated NO and closed stomata faster than WT plants in response to darkness. Altogether, our results indicate that COP1 transduces H2O2 signaling, promotes NO accumulation in guard cells by suppressing FT, TSF and SOC1 expression, and consequently leads to stomatal closure in darkness. These findings add new insights into the mechanisms of dark-induced stomatal closure.

Arabidopsis flowering integrator SOC1 transcriptionally regulates autophagy in response to long-term carbon starvation.

Autophagy is a highly conserved, self-digestion process that is essential for plant adaptations to various environmental stresses. Although the core components of autophagy in plants have been well established, the molecular basis for its transcriptional regulation remains to be fully characterized. In this study, we demonstrate that SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), a MADS-box family transcription factor that determines flowering transition in Arabidopsis, functions as a transcriptional repressor of autophagy. EMSAs, ChIP-qPCR assays, and dual-luciferase receptor assays showed that SOC1 can bind to the promoters of ATG4b, ATG7, and ATG18c via the conserved CArG box. qRT-PCR analysis showed that the three ATG genes ATG4b, ATG7, and ATG18c were up-regulated in the soc1-2 mutant. In line with this, the mutant also displayed enhanced autophagy activity, as revealed by increased autophagosome formation and elevated autophagic flux compared with the wild type. More importantly, SOC1 negatively affected the tolerance of plants to long-term carbon starvation, and this process requires a functional autophagy pathway. Finally, we found that SOC1 was repressed upon carbon starvation at both the transcriptional and protein levels. Overall, our study not only uncovers an important transcriptional mechanism that contributes to the regulation of plant autophagy in response to nutrient starvation, but also highlights novel cellular functions of the flowering integrator SOC1.

Effects of Water-deficit Stress and Gibberellic Acid on Floral Gene Expression and Floral Determinacy in ‘Washington’ Navel Orange

Effects of water-deficit stress and foliar-applied gibberellic acid (GA3) on ‘Washington’ navel orange (Citrus sinensis) floral gene expression and inflorescence number were quantified. Trees subjected to 8 weeks of water-deficit stress [average stem water potential (SWP) −2.86 MPa] followed by 3 weeks of re-irrigation (SWP recovered to > −1.00 MPa) produced more inflorescences in week 11 than trees well-irrigated (SWP > −1.00 MPa) for the full 11 weeks (P < 0.001). After 8 weeks of water-deficit stress, bud expression of flowering locus t (FT), suppressor of overexpression of constans1 (SOC1), leafy (LFY), apetala1 (AP1), apetala2 (AP2), sepallata1 (SEP1), pistillata (PI), and agamous (AG) increased during the re-irrigation period (weeks 9 and 10), but only AP1, AP2, SEP1, PI, and AG expression increased to levels significantly greater than that of well-irrigated trees. Foliar-applied GA3 (50 mg·L−1) in weeks 2 through 8 of the water-deficit stress treatment did not reduce bud FT, SOC1, or LFY expression, but prevented the upregulation AP1, AP2, SEP1, PI, and AG expression that occurred during re-irrigation in water-deficit stressed trees not treated with GA3. Applications of GA3 to water-deficit stressed trees reduced inflorescence number 95% compared with stressed trees without GA3. Thus, GA3 inhibited citrus (Citrus sp.) floral development in response to water-deficit stress through downregulating AP1 and AP2 expression, which likely led to the failed activation of the downstream floral organ identity genes. The results reported herein suggest that bud determinacy and subsequent floral development in response to water-deficit stress in ‘Washington’ navel orange are controlled by AP1 and AP2 transcript levels, which regulate downstream floral organ identity gene activity and the effect of GA3 on citrus flower formation. The water-deficit stress floral-induction pathway provides an alternative to low-temperature induction that increases the potential for successful flowering in citrus trees grown in areas experiencing warmer, drier winters due to global climate change.

ORANGE negatively regulates flowering time in Arabidopsisthaliana

Floral transition is an important process in plant development, which is regulated by at least four flowering pathways: the photoperiod, vernalization, autonomous, and gibberellin (GA)-dependent pathways. The DnaJ-like zinc finger domain-containing protein ORANGE (OR) was originally cloned from the cauliflower or mutant, which has distinct phenotypes of the carotenoid-accumulating curd, the elongated petioles, and the delayed-flowering time. OR has been demonstrated to interact with phytoene synthase for carotenoid biosynthesis in plastids and with eukaryotic release factor 1-2 (eRF1-2) in the nucleus for the first two phenotypes, respectively. In this study, we showed that overexpression of OR in Arabidopsis thaliana resulted in a delayed-flowering phenotype resembling the cauliflower or mutant. Our results indicated that OR negatively regulates the expression of the flowering integrator genes FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1). Both GA3 and vernalization treatments could not rescue the delayed-flowering phenotype of the OR-overexpressing seedlings, suggesting the repression of floral transition by OR does not depend on SOC1-mediated vernalization or GA-dependent pathways. Moreover, our analysis revealed that transcripts of OR and FT fluctuated in opposite directions diurnally, and the overexpression of OR repressed the accumulation of CONSTANS (CO), FT, and SOC1 transcripts in a 16 h/8 h light/dark long-day cycle. Our results indicated the possibility that OR represses flowering through the CO-FT-SOC1-mediated photoperiodic flowering pathway.

Differentially Expressed Genes Related to Flowering Transition between Once- and Continuous-Flowering Roses.

Roses are the most important cut flower crops and widely used woody ornamental plants in gardens throughout the world, and they are model plants for studying the continuous-flowering trait of woody plants. To analyze the molecular regulation mechanism of continuous flowering, comparative transcriptome data of once- and continuous-flowering roses in our previous study were used to conduct weighted gene co-expression network analysis (WGCNA) to obtain the candidate genes related to flowering transitions. The expression patterns of candidate genes at different developmental stages between Rosa chinensis “Old Blush” (continuous-flowering cultivar) and R. “Huan Die” (once-flowering cultivar) were investigated, and the relationship of the key gene with the endogenous hormone was analyzed. The results showed that the expression trends of VIN3-LIKE 1 (VIL1), FRIGIDA- LIKE 3 (FRI3), APETALA 2- LIKE (AP2-like) and CONSTANS-LIKE 2 (CO-like 2) genes were significantly different between “Old Blush” and “Huan Die”, and the expression trends of SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) and CO-like 2 were consistent in the flowering transition of “Old Blush” under different environments. The changes in cytokinin and gibberellic acid (GA3) content were different in the two rose cultivars. The overall change trend of the abscisic acid and GA3 in the flowering transition of “Old Blush” under different environments was consistent. The promoter sequence of CO-like 2 contained a P-box element associated with gibberellin response, as well as binding sites for transcription factors. In a word, we found CO-like 2 associated with continuous flowering and some factors that may synergistically regulate continuous flowering. The results provided a reference for elucidating the molecular regulatory mechanisms of continuous-flowering traits in roses.

A mutation in the pPLA-IIα gene encoding PATATIN-RELATED PHOSPHOLIPASE a causes late flowering in Arabidopsis

Arabidopsis PATATIN-RELATED PHOSPHOLIPASE 2A (pPLA-IIα) participates in the responses to various growth conditions. The factors affecting pPLA-IIα gene expression and pPLA-IIα protein activity for gycerolipids have been studied thoroughly, but the role of pPLA-IIα during the reproductive phase remains unclear. The effect of pPLA-IIα on flowering time was therefore investigated. ppla-iiα mutants flowered later than wild-type plants under long day conditions. Expression of the floral stimulators FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) was downregulated in ppla-iiα mutants compared with their expression in wild-type plants, but expression of the floral repressor FLOWERING LOCUS C (FLC) was upregulated. In addition, expression levels of COLDAIR, a long intronic noncoding RNA, decreased in ppla-iiα mutants. Taken together, these data indicate that pPLA-IIα acts as a positive regulator of flowering time through repression of FLC expression.

GmFULc Is Induced by Short Days in Soybean and May Accelerate Flowering in Transgenic Arabidopsis thaliana.

Flowering is an important developmental process from vegetative to reproductive growth in plant; thus, it is necessary to analyze the genes involved in the regulation of flowering time. The MADS-box transcription factor family exists widely in plants and plays an important role in the regulation of flowering time. However, the molecular mechanism of GmFULc involved in the regulation of plant flowering is not very clear. In this study, GmFULc protein had a typical MADS domain and it was a member of MADS-box transcription factor family. The expression analysis revealed that GmFULc was induced by short days (SD) and regulated by the circadian clock. Compared to wild type (WT), overexpression of GmFULc in transgenic Arabidopsis caused significantly earlier flowering time, while ful mutants flowered later, and overexpression of GmFULc rescued the late-flowering phenotype of ful mutants. ChIP-seq of GmFULc binding sites identified potential direct targets, including TOPLESS (TPL), and it inhibited the transcriptional activity of TPL. In addition, the transcription levels of FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) and LEAFY (LFY) in the downstream of TPL were increased in GmFULc- overexpression Arabidopsis, suggesting that the early flowering phenotype was associated with up-regulation of these genes. Our results suggested that GmFULc inhibited the transcriptional activity of TPL and induced expression of FT, SOC1 and LFY to promote flowering.

Identification and Characterization of MIKCc-Type MADS-Box Genes in the Flower Organs of Adonis amurensis.

Adonis amurensis is a perennial herbaceous flower that blooms in early spring in northeast China, where the night temperature can drop to −15 °C. To understand flowering time regulation and floral organogenesis of A. amurensis, the MIKCc-type MADS (Mcm1/Agamous/ Deficiens/Srf)-box genes were identified and characterized from the transcriptomes of the flower organs. In this study, 43 non-redundant MADS-box genes (38 MIKCc, 3 MIKC*, and 2 Mα) were identified. Phylogenetic and conserved motif analysis divided the 38 MIKCc-type genes into three major classes: ABCDE model (including AP1/FUL, AP3/PI, AG, STK, and SEPs/AGL6), suppressor of overexpression of constans1 (SOC1), and short vegetative phase (SVP). qPCR analysis showed that the ABCDE model genes were highly expressed mainly in flowers and differentially expressed in the different tissues of flower organs, suggesting that they may be involved in the flower organ identity of A. amurensis. Subcellular localization revealed that 17 full-length MADSs were mainly localized in the nucleus: in Arabidopsis, the heterologous expression of three full-length SOC1-type genes caused early flowering and altered the expression of endogenous flowering time genes. Our analyses provide an overall insight into MIKCc genes in A. amurensis and their potential roles in floral organogenesis and flowering time regulation.

The SOC1-like gene BoMADS50 is associated with the flowering of Bambusa oldhamii

Bamboo is known for its edible shoots and beautiful texture and has considerable economic and ornamental value. Unique among traditional flowering plants, many bamboo plants undergo extensive synchronized flowering followed by large-scale death, seriously affecting the productivity and application of bamboo forests. To date, the molecular mechanism of bamboo flowering characteristics has remained unknown. In this study, a SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1)-like gene, BoMADS50, was identified from Bambusa oldhamii. BoMADS50 was highly expressed in mature leaves and the floral primordium formation period during B. oldhamii flowering and overexpression of BoMADS50 caused early flowering in transgenic rice. Moreover, BoMADS50 could interact with APETALA1/FRUITFULL (AP1/FUL)-like proteins (BoMADS14-1/2, BoMADS15-1/2) in vivo, and the expression of BoMADS50 was significantly promoted by BoMADS14-1, further indicating a synergistic effect between BoMADS50 and BoAP1/FUL-like proteins in regulating B. oldhamii flowering. We also identified four additional transcripts of BoMADS50 (BoMADS50-1/2/3/4) with different nucleotide variations. Although the protein-CDS were polymorphic, they had flowering activation functions similar to those of BoMADS50. Yeast one-hybrid and transient expression assays subsequently showed that both BoMADS50 and BoMADS50-1 bind to the promoter fragment of itself and the SHORT VEGETATIVE PHASE (SVP)-like gene BoSVP, but only BoMADS50-1 can positively induce their transcription. Therefore, nucleotide variations likely endow BoMADS50-1 with strong regulatory activity. Thus, BoMADS50 and BoMADS50-1/2/3/4 are probably important positive flowering regulators in B. oldhamii. Moreover, the functional conservatism and specificity of BoMADS50 and BoMADS50-1 might be related to the synchronized and sporadic flowering characteristics of B. oldhamii.

DELLA degradation by gibberellin promotes flowering via GAF1-TPR-dependent repression of floral repressors in Arabidopsis.

Flowering is the developmental transition from the vegetative to the reproductive phase. FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), and LEAFY (LFY) are floral integrators. These genes are repressed by several floral repressors including EARLY FLOWERING3 (ELF3), SHORT VEGETATIVE PHASE (SVP), TEMPRANILLO1 (TEM1), and TEM2. Although gibberellin (GA) promotes flowering by activating the floral integrator genes, the exact molecular mechanism remains unclear. DELLAs are negative regulators in GA signaling and act as coactivators of the transcription factor GAI ASSOCIATED FACTOR 1 (GAF1). GAs convert the GAF1 complex from a transcriptional activator to a repressor. Here, we show that GAF1 functions in the GA-dependent flowering pathway by regulating FT and SOC1 expression in Arabidopsis thaliana. We identified four flowering repressors, ELF3, SVP, TEM1, and TEM2, as GAF1-target genes. In response to GAs, GAF1 forms a transcriptional repressor complex and promotes the expression of FT and SOC1 through the repression of four flowering repressor genes, ELF3, SVP, TEM1, and TEM2.

GmIDD Is Induced by Short Days in Soybean and May Accelerate Flowering When Overexpressed in Arabidopsis via Inhibiting AGAMOUS-LIKE 18

Photoperiod is one of the main climatic factors that determine flowering time and yield. Some members of the INDETERMINATE DOMAIN (IDD) transcription factor family have been reported to be involved in regulation of flowering time in Arabidopsis, maize, and rice. In this study, the domain analysis showed that GmIDD had a typical ID domain and was a member of the soybean IDD transcription factor family. Quantitative real-time PCR analysis showed that GmIDD was induced by short day conditions in leaves and regulated by circadian clock. Under long day conditions, transgenic Arabidopsis overexpressing GmIDD flowered earlier than wild-type, and idd mutants flowered later, while the overexpression of GmIDD rescued the late-flowering phenotype of idd mutants. Chromatin immunoprecipitation sequencing assays of GmIDD binding sites in GmIDD-overexpression (GmIDD-ox) Arabidopsis further identified potential direct targets, including a transcription factor, AGAMOUS-like 18 (AGL18). GmIDD might inhibit the transcriptional activity of flower repressor AGL18 by binding to the TTTTGGTCC motif of AGL18 promoter. Furthermore, the results also showed that GmIDD overexpression increased the transcription levels of flowering time-related genes FLOWERING LOCUS T (FT), SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), LEAFY (LFY) and APETALA1 (AP1) in Arabidopsis. Taken together, GmIDD appeared to inhibit the transcriptional activity of AGL18 and induced the expression of FT gene to promote Arabidopsis flowering.

AGL19 directly interacts with floral signal integrator AGL24 in flowering time control of Brassica juncea

SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) and AGAMOUS-LIKE 24 (AGL24) are pivotal flowering signal integrators, which respectively, belong to TM3/SOC1 and STMADS11 clades of MIKC-type MADS-box family. AGAMOUS-LIKE 19 (AGL19), one member of TM3/SOC1 clade family, acts as an activator of flowering time. Previous studies have suggested that AGL19 together with AGL24 and SOC1 coordinately regulate flowering time. However, it remains unknown how AGL19 interacts with SOC1 and AGL24 in Brassica juncea. Here, an AGL19-like (BjuAGL19) was cloned from B. juncea, which was expressed in roots, stems, leaves, buds and flowers. Furthermore, both yeast one-hybrid and Dual-Glo Luciferase assays confirmed that BjuAGL19 protein could not target the promoters of BjuSOC1 and BjuAGL24. Interestingly, based on yeast two-hybrid and pull-down assays, BjuAGL19 protein directly interacted with BjuAGL24 protein, instead of BjuSOC1 protein. It is speculated that BjuAGL19 can bind to BjuAGL24 to form protein complex of BjuAGL19-BjuAGL24 and thus regulates flowering time in B. juncea. The results are very helpful for further elucidating the molecular mechanism of BjuAGL19 in flowering time control.

An Integrative Analysis of Transcriptome, Proteome and Hormones Reveals Key Differentially Expressed Genes and Metabolic Pathways Involved in Flower Development in Loquat.

Flower development is a vital developmental process in the life cycle of woody perennials, especially fruit trees. Herein, we used transcriptomic, proteomic, and hormone analyses to investigate the key candidate genes/proteins in loquat (Eriobotrya japonica) at the stages of flower bud differentiation (FBD), floral bud elongation (FBE), and floral anthesis (FA). Comparative transcriptome analysis showed that differentially expressed genes (DEGs) were mainly enriched in metabolic pathways of hormone signal transduction and starch and sucrose metabolism. Importantly, the DEGs of hormone signal transduction were significantly involved in the signaling pathways of auxin, gibberellins (GAs), cytokinin, ethylene, abscisic acid (ABA), jasmonic acid, and salicylic acid. Meanwhile, key floral integrator genes FLOWERING LOCUS T (FT) and SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) and floral meristem identity genes SQUAMOSA PROMOTER BINDING LIKE (SPL), LEAFY (LFY), APETALA1 (AP1), and AP2 were significantly upregulated at the FBD stage. However, key floral organ identity genes AGAMOUS (AG), AP3, and PISTILLATA (PI) were significantly upregulated at the stages of FBE and FA. Furthermore, transcription factors (TFs) such as bHLH (basic helix-loop-helix), NAC (no apical meristem (NAM), Arabidopsis transcription activation factor (ATAF1/2) and cup-shaped cotyledon (CUC2)), MYB_related (myeloblastosis_related), ERF (ethylene response factor), and C2H2 (cysteine-2/histidine-2) were also significantly differentially expressed. Accordingly, comparative proteomic analysis of differentially accumulated proteins (DAPs) and combined enrichment of DEGs and DAPs showed that starch and sucrose metabolism was also significantly enriched. Concentrations of GA3 and zeatin were high before the FA stage, but ABA concentration remained high at the FA stage. Our results provide abundant sequence resources for clarifying the underlying mechanisms of the flower development in loquat.

Homeologs of Brassica SOC1, a central regulator of flowering time, are differentially regulated due to partitioning of evolutionarily conserved transcription factor binding sites in promoters

Evolution of Brassica genome post-polyploidization reveals asymmetrical genome fractionation and copy number variation. Herein, we describe the impact of promoter divergence among SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1) homeologs on expression and function in Brassica spp. SOC1, a regulated floral pathway integrator, is conserved as 3 redundant homeologs in diploid Brassicas. Even with high sequence identity within coding regions (92.8–100%), the spatio-temporal expression patterns of 9 SOC1 homologs in B. juncea and B. nigra indicates regulatory divergence. While LF and MF2 SOC1 homeologs are upregulated during floral transition, MF1 is barely expressed. Also, MF2 homeolog levels do not decline post-flowering, unlike LF. To investigate the underlying source of divergence, we analyzed the sequence and phylogeny of all reported (22) and isolated (21) upstream regions of Brassica SOC1. Full length upstream regions (4712–19189 bp) reveal 5 ubiquitously conserved ancestral Blocks, harboring binding sites of 18 TFs (TFBSs) characterized in Arabidopsis thaliana. The orthologs of these TFBSs are differentially conserved among Brassica SOC1 homeologs, imparting expression divergence. No crucial TFBSs are exclusively lost from LF_SOC1 promoter, while MF1_SOC1 has lost NF-Y binding site crucial for SOC1 activation by CONSTANS. MF2_SOC1 homeologs have lost important TFBSs (SEP3, AP1 and SMZ), responsible for SOC1 repression post-flowering. BjuAALF_SOC1 promoter (proximal 2 kb) shows ubiquitous reporter expression in B. juncea cv. Varuna transgenics, while BjuAAMF1_SOC1 promoter shows absence of reporter expression, validating the impact of TFBS divergence. Conservation of the original primary protein sequence is discovered in B. rapa homeologs (46) of 18 TFs. Co-regulation pattern of these TFs appeared similar for B. rapa LF and MF2 SOC1 homeologs; MF1 shows significant variation. Strong regulatory association is recorded for AP1, AP2, SEP3, FLC and CONSTANS/NF-Y, highlighting their importance in homeolog-specific SOC1 regulation. Correlation of B. juncea AP1, AP2 and FLC expression with SOC1 homeologs also complies with the TFBS differences. We thus conclude that redundant SOC1 loci contribute differentially to cumulative expression of SOC1 due to divergent selection of ancestral TFBSs.

Nucleocytoplasmic OXIDATIVE STRESS 2 can relocate FLOWERING LOCUS T

Survival of a species depends on reproductive fitness and a plant's floral transition is controlled by developmental and environmental signals. In Arabidopsis, the floral integrators SOC1 (SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1) and FT (FLOWERING LOCUS T) sense various pathway signals to activate floral meristem identity genes. At high stress intensity, greater nuclear accumulation of the zinc-finger transcription factor OXS2 (OXIDATIVE STRESS 2) activates an early-flowering stress-escape response. Curiously, accumulation of OXS2 in the cytoplasm can delay flowering, prompting the hypothesis that in absence of stress, OXS2 helps to maintain vegetative growth. While the mechanism of stress-escape was identified as the OXS2-mediated transcription of SOC1, how cytoplasmic OXS2 delays flowering was unknown. Here, we report that OXS2 can interact indirectly with florigen FT and transcription factor FD (FLOWERING LOCUS D), the two proteins known to induce floral transition. By using 14-3-3Ω as a bridge linker, OXS2 can alter the subcellular distribution of FT. This lead to a speculation on how cytoplasmic OXS2 is able to prevent early flowering, by keeping FT from the nucleus.

Floral regulators FLC and SOC1 directly regulate expression of the B3-type transcription factor TARGET OF FLC AND SVP 1 at the Arabidopsis shoot apex via antagonistic chromatin modifications.

Integration of environmental and endogenous cues at plant shoot meristems determines the timing of flowering and reproductive development. The MADS box transcription factor FLOWERING LOCUS C (FLC) of Arabidopsis thaliana is an important repressor of floral transition, which blocks flowering until plants are exposed to winter cold. However, the target genes of FLC have not been thoroughly described, and our understanding of the mechanisms by which FLC represses transcription of these targets and how this repression is overcome during floral transition is still fragmentary. Here, we identify and characterize TARGET OF FLC AND SVP1 (TFS1), a novel target gene of FLC and its interacting protein SHORT VEGETATIVE PHASE (SVP). TFS1 encodes a B3-type transcription factor, and we show that tfs1 mutants are later flowering than wild-type, particularly under short days. FLC and SVP repress TFS1 transcription leading to deposition of trimethylation of Iysine 27 of histone 3 (H3K27me3) by the Polycomb Repressive Complex 2 at the TFS1 locus. During floral transition, after downregulation of FLC by cold, TFS1 transcription is promoted by SUPPRESSOR OF OVEREXPRESSION OF CONSTANS1 (SOC1), a MADS box protein encoded by another target of FLC/SVP. SOC1 opposes PRC function at TFS1 through recruitment of the histone demethylase RELATIVE OF EARLY FLOWERING 6 (REF6) and the SWI/SNF chromatin remodeler ATPase BRAHMA (BRM). This recruitment of BRM is also strictly required for SQUAMOSA PROMOTER BINDING PROTEIN-LIKE 9 (SPL9) binding at TFS1 to coordinate RNAPII recruitment through the Mediator complex. Thus, we show that antagonistic chromatin modifications mediated by different MADS box transcription factor complexes play a crucial role in defining the temporal and spatial patterns of transcription of genes within a network of interactions downstream of FLC/SVP during floral transition.