TaVRT-2, a member of the StMADS-11 clade of flowering repressors, is regulated by vernalization and photoperiod in wheat

MWCNTs Alleviated saline-alkali stress by optimizing photosynthesis and sucrose metabolism in rice seedling

Saline and alkali stress affects the growth and development, survival rate, and final yield of rice, while new nano materials can have a positive effect on rice growth. In order to investing the effects of carboxymethyl multi walled carbon nanotubes (MWCNTs) on the growth and development of rice seedlings under salt alkali stress, rice seedlings were cultured using rice variety "Songjing 3" using nutrient solution water culture method. The effects of MWCNTs on water absorption capacity, leaf photosynthesis, and sucrose metabolism of rice seedlings under 50 mmol/L saline-alkali stress (1NaCl: 9Na2SO4: 9NaHCO3: 1Na2CO3) conditions were investigated. The results showed that MWCNTs can improve the water use ability of roots and leaves, especially the water absorption ability of roots, which provides a guarantee for the improvement of rice biomass and the enhancement of leaf photosynthetic capacity under adverse conditions. After treatment with MWCNTs, the photosynthetic rate (Pn), stomatal conductance (gs), and transpiration rate (Tr) of leaves increased significantly, and the photochemical quenching value (qP), photochemical quantum efficiency value (Fv/Fm), and electron transfer rate value (ETR) of chlorophyll fluorescence parameters increased significantly, which is beneficial to the improvement of the PSII photosynthetic system. MWCNTs treatment promoted the increase of photosynthetic pigment content in leaves under salt and alkali stress, improved the ratio of Chla and Chlb parameters, increased the activities of key photosynthetic enzymes (RUBPCase and PEPCase) in leaves, increased the value of total lutein cycle pool (VAZ), and significantly enhanced the deepoxidation effect of lutein cycle (DEPS), which can effectively alleviate the stomatal and non stomatal constraints on leaf photosynthesis caused by salt and alkali stress. MWCNTs treatment significantly enhanced the activities of sucrose phosphate synthase (SPS) and sucrose synthase (SS) under salt and alkali stress, and decreased the activities of soluble acid invertase (SAInv) and alkaline/neutral invertase (A/N-Inv), indicating that MWCNTs promoted sucrose synthesis while inhibiting sucrose decomposition, thereby promoting sucrose accumulation in rice leaves. This study can provide theoretical and experimental basis for the application of MWCNTs to the production of rice under salt and alkali stress, and can find a new way for rice production in saline and alkaline lands.

Diversity of gene expression responses to light quality in barley

Light quality influence on barley development is poorly understood. We exposed three barley genotypes with either sensitive or insensitive response to two light sources producing different light spectra, fluorescent bulbs, and metal halide lamps, keeping constant light intensity, duration, and temperature. Through RNA-seq, we identified the main genes and pathways involved in the genotypic responses. A first analysis identified genotypic differences in gene expression of development-related genes, including photoreceptors and flowering time genes. Genes from the vernalization pathway of light quality-sensitive genotypes were affected by fluorescent light. In particular, vernalization-related repressors reacted differently: HvVRN2 did not experience relevant changes, whereas HvOS2 expression increased under fluorescent light. To identify the genes primarily related to light quality responses, and avoid the confounding effect of plant developmental stage, genes influenced by development were masked in a second analysis. Quantitative expression levels of PPD-H1, which influenced HvVRN1 and HvFT1, explained genotypic differences in development. Upstream mechanisms (light signaling and circadian clock) were also altered, but no specific genes linking photoreceptors and the photoperiod pathway were identified. The variety of light-quality sensitivities reveals the presence of possible mechanisms of adaptation of winter and facultative barley to latitudinal variation in light quality, which deserves further research.

Molecular Cytological Analysis and Specific Marker Development in Wheat-Psathyrostachys huashanica Keng 3Ns Additional Line with Elongated Glume

Psathyrostachys huashanica Keng (2n = 2x = 14, NsNs) is an excellent gene resource for wheat breeding, which is characterized by early maturity, low plant height, and disease resistance. The wheat-P. huashanica derivatives were created by the elite genes of P. huashanica and permeate into common wheat through hybridization. Among them, a long-glume material 20JH1155 was identified, with larger grains and longer spike than its parents. In the present study, the methods of cytological observation, GISH, and sequential FISH analysis showed that 20JH1155 contained 21 pairs of wheat chromosomes and a pair of P. huashanica. There were some differences in 5A and 7B chromosomes between 20JH1155 and parental wheat 7182. Molecular marker, FISH, and sequence cloning indicated 20JH1155 alien chromosomes were 3Ns of P. huashanica. In addition, differentially expressed genes during immature spikelet development of 20JH1155 and 7182 and predicted transcription factors were obtained by transcriptome sequencing. Moreover, a total of 7 makers derived from Ph#3Ns were developed from transcriptome data. Taken together, the wheat-P. huashanica derived line 20JH1155 provides a new horizon on distant hybridization of wheat and accelerates the utilization of genes of P. huashanica.

Identification of QTL underlying the main stem related traits in a doubled haploid barley population

Lodging reduces grain yield in cereal crops. The height, diameter and strength of stem are crucial for lodging resistance, grain yield, and photosynthate transport in barley. Understanding the genetic basis of stem benefits barley breeding. Here, we evaluated 13 stem related traits after 28 days of heading in a barley DH population in two consecutive years. Significant phenotypic correlations between lodging index (LI) and other stem traits were observed. Three mapping methods using the experimental data and the BLUP data, detected 27 stable and major QTLs, and 22 QTL clustered regions. Many QTLs were consistent with previously reported traits for grain filling rate, internodes, panicle and lodging resistance. Further, candidate genes were predicted for stable and major QTLs and were associated with plant development and adverse stress in the transition from vegetative stage to reproductive stage. This study provided potential genetic basis and new information for exploring barley stem morphology, and laid a foundation for map-based cloning and further fine mapping of these QTLs.

Genetic Dissection of Three Major Quantitative Trait Loci for Spike Compactness and Length in Bread Wheat (Triticum aestivum L.)

Spike compactness (SC) and length (SL) are the components of spike morphology and are strongly related to grain yield in wheat (Triticum aestivum L.). To investigate quantitative trait loci (QTL) associated with SC and SL, a recombinant inbred lines (RIL) population derived from the cross of Bailangmai (BLM, a Tibet landrace) and Chuanyu 20 (CY20, an improved variety) was employed in six environments. Three genomic regions responsible for SC and SL traits were identified on chromosomes 2A and 2D using bulked segregant exome sequencing (BSE-Seq). By constructing genetic maps, six major QTL were repeatedly detected in more than four environments and the best linear unbiased estimation (BLUE) datasets, explaining 7.00-28.56% of the phenotypic variation and the logarithm of the odd (LOD) score varying from 2.50 to 13.22. They were co-located on three loci, designed as QSc/Sl.cib-2AS, QSc/Sl.cib-2AL, and QSc/Sl.cib-2D, respectively. Based on the flanking markers, their interactions and effects on the corresponding trait and other agronomic traits were also analyzed. Comparison analysis showed that QSc/Sl.cib-2AS and QSc/Sl.cib-2AL were possibly two novel loci for SC and SL. QSc/Sl.cib-2AS and QSc/Sl.cib-2D showed pleiotropic effects on plant height and grain morphology, while QSc/Sl.cib-2AL showed effects on spikelet number per spike (SNS) and grain width (GW). Based on the gene annotation, orthologous search, and spatiotemporal expression patterns of genes, TraesCS2A03G0410600 and TraesCS2A03G0422300 for QSc/Sl.cib-2AS, and TraesCS2D03G1129300 and TraesCS2D03G1131500 for QSc/Sl.cib-2D were considered as potential candidate genes, respectively. These results will be useful for fine mapping and developing new varieties with high yield in the future.

Interactions between SQUAMOSA and SHORT VEGETATIVE PHASE MADS-box proteins regulate meristem transitions during wheat spike development

Inflorescence architecture is an important determinant of crop productivity. The number of spikelets produced by the wheat inflorescence meristem (IM) before its transition to a terminal spikelet (TS) influences the maximum number of grains per spike. Wheat MADS-box genes VERNALIZATION 1 (VRN1) and FRUITFULL 2 (FUL2) (in the SQUAMOSA-clade) are essential to promote the transition from IM to TS and for spikelet development. Here we show that SQUAMOSA genes contribute to spikelet identity by repressing MADS-box genes VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT2), SHORT VEGETATIVE PHASE 1 (SVP1), and SVP3 in the SVP clade. Constitutive expression of VRT2 resulted in leafy glumes and lemmas, reversion of spikelets to spikes, and downregulation of MADS-box genes involved in floret development, whereas the vrt2 mutant reduced vegetative characteristics in spikelets of squamosa mutants. Interestingly, the vrt2 svp1 mutant showed similar phenotypes to squamosa mutants regarding heading time, plant height, and spikelets per spike, but it exhibited unusual axillary inflorescences in the elongating stem. We propose that SQUAMOSA-SVP interactions are important to promote heading, formation of the TS, and stem elongation during the early reproductive phase, and that downregulation of SVP genes is then necessary for normal spikelet and floral development. Manipulating SVP and SQUAMOSA genes can contribute to engineering spike architectures with improved productivity.

Evolution and expression of the MADS-box flowering transition genes AGAMOUS-like 24/SHORT VEGETATIVE PHASE with emphasis in selected Neotropical orchids

In angiosperms the reproductive transition results in the transformation of a vegetative apical meristem (SAM) into an inflorescence meristem (IM), capable of forming floral meristems (FM). Two key players in the flowering transition are AGAMOUS-like 24 (AGL24) and SHORT VEGETATIVE PHASE (SVP). They are eudicot MADS-box paralogs performing opposite roles, as AGL24 positively regulates flowering while SVP represses the reproductive transition in Arabidopsis. We confirm that the Arabidopsis functional reference cannot be readily extrapolated to all eudicots as there are additional duplications of AGL24 in early divergent eudicots and core eudicots with significant sequence variation. In addition, we found that in monocots, two additional independent duplication events have resulted in at least three clades of AGL24/SVP homologs, some only found in Orchidaceae. Protein sequence analyses and comparative evolutionary rates point to higher rates of relaxed negative selection in the Core Eudicot AGL24 B and the Orch SVP-like B clades, in eudicots and monocots respectively. On the other hand, expression data points to plesiomorphic pleiotropic roles of AGL24/SVP genes likely similar to SVP core eudicot genes, and the acquisition of new roles as flowering positive regulators in Core Eudicot AGL24 A genes. Our research presents evidence on the diversification and recruitment of AGL24/SVP homologs in flowering transition in orchids. Although, broad expression of most copies does not allow to determine if they act as flowering repressors or promoters, the restricted expression of some homologs in the SAM suggests putative roles in maintaining the vegetative phase. If so studying in detail the function of AGL24/SVP homologs in orchids is critical to identify putative flowering repressors in a lineage where other canonical repressors remain elusive.

Yield-Related QTL Clusters and the Potential Candidate Genes in Two Wheat DH Populations

In the present study, four large-scale field trials using two doubled haploid wheat populations were conducted in different environments for two years. Grain protein content (GPC) and 21 other yield-related traits were investigated. A total of 227 QTL were mapped on 18 chromosomes, which formed 35 QTL clusters. The potential candidate genes underlying the QTL clusters were suggested. Furthermore, adding to the significant correlations between yield and its related traits, correlation variations were clearly shown within the QTL clusters. The QTL clusters with consistently positive correlations were suggested to be directly utilized in wheat breeding, including 1B.2, 2A.2, 2B (4.9–16.5 Mb), 2B.3, 3B (68.9–214.5 Mb), 4A.2, 4B.2, 4D, 5A.1, 5A.2, 5B.1, and 5D. The QTL clusters with negative alignments between traits may also have potential value for yield or GPC improvement in specific environments, including 1A.1, 2B.1, 1B.3, 5A.3, 5B.2 (612.1–613.6 Mb), 7A.1, 7A.2, 7B.1, and 7B.2. One GPC QTL (5B.2: 671.3–672.9 Mb) contributed by cultivar Spitfire was positively associated with nitrogen use efficiency or grain protein yield and is highly recommended for breeding use. Another GPC QTL without negatively pleiotropic effects on 2A (50.0–56.3 Mb), 2D, 4D, and 6B is suggested for quality wheat breeding.

Ectopic expression of VRT-A2 underlies the origin of Triticum polonicum and Triticum petropavlovskyi with long outer glumes and grains

Polish wheat (Triticum polonicum) is a unique tetraploid wheat species characterized by an elongated outer glume. The genetic control of the long-glume trait by a single semi-dominant locus, P1 (from Polish wheat), was established more than 100 years ago, but the underlying causal gene and molecular nature remain elusive. Here, we report the isolation of VRT-A2, encoding an SVP-clade MADS-box transcription factor, as the P1 candidate gene. Genetic evidence suggests that in T. polonicum, a naturally occurring sequence rearrangement in the intron-1 region of VRT-A2 leads to ectopic expression of VRT-A2 in floral organs where the long-glume phenotype appears. Interestingly, we found that the intron-1 region is a key ON/OFF molecular switch for VRT-A2 expression, not only because it recruits transcriptional repressors, but also because it confers intron-mediated transcriptional enhancement. Genotypic analyses using wheat accessions indicated that the P1 locus is likely derived from a single natural mutation in tetraploid wheat, which was subsequently inherited by hexaploid T. petropavlovskyi. Taken together, our findings highlight the promoter-proximal intron variation as a molecular basis for phenotypic differentiation, and thus species formation in Triticum plants.

Ectopic expression of Triticum polonicum VRT-A2 underlies elongated glumes and grains in hexaploid wheat in a dosage-dependent manner

Flower development is an important determinant of grain yield in crops. In wheat (Triticum spp.), natural variation for the size of spikelet and floral organs is particularly evident in Triticum turgidum ssp. polonicum (also termed Triticum polonicum), a tetraploid subspecies of wheat with long glumes, lemmas, and grains. Using map-based cloning, we identified VEGETATIVE TO REPRODUCTIVE TRANSITION 2 (VRT2), which encodes a MADS-box transcription factor belonging to the SHORT VEGETATIVE PHASE family, as the gene underlying the T. polonicum long-glume (P1) locus. The causal P1 mutation is a sequence rearrangement in intron-1 that results in ectopic expression of the T. polonicum VRT-A2 allele. Based on allelic variation studies, we propose that the intron-1 mutation in VRT-A2 is the unique T. polonicum subspecies-defining polymorphism, which was later introduced into hexaploid wheat via natural hybridizations. Near-isogenic lines differing for the P1 locus revealed a gradient effect of P1 across spikelets and within florets. Transgenic lines of hexaploid wheat carrying the T. polonicum VRT-A2 allele show that expression levels of VRT-A2 are highly correlated with spike, glume, grain, and floral organ length. These results highlight how changes in expression profiles, through variation in cis-regulation, can affect agronomic traits in a dosage-dependent manner in polyploid crops.

TaVrt2, an SVP-like gene, cooperates with TaVrn1 to regulate vernalization-induced flowering in wheat

TaVrn1, encoding a MADS-box transcription factor (TF), is the central regulator of wheat vernalization-induced flowering. Considering that the MADS-box TF usually works by forming hetero- or homodimers, we conducted yeast-two-hybrid screening and identified an SVP-like MADS-box protein TaVrt2 interacting with TaVrn1. However, the specific function of TaVrt2 and the biological implication of its interaction with TaVrn1 remained unknown. We validated the function of TaVrt2 and TaVrn1 by wheat transgenic experiments and their interaction through multiple protein-binding assays. Population genetic analysis also was used to display their interplay. Transcriptomic sequencing and chromatin immunoprecipitation assays were performed to identify their common targets. TaVrt2 and TaVrn1 are flowering promoters in the vernalization pathway and interact physically in vitro, in planta and in wheat cells. Additionally, TaVrt2 and TaVrn1 were significantly induced in leaves by vernalization, suggesting their spatio-temporal interaction during vernalization. Genetic analysis indicated that TaVrt2 and TaVrn1 had significant epistatic effects on flowering time. Furthermore, native TaVrn1 was up-regulated significantly in TaVrn1-OE (overexpression) and TaVrt2-OE lines. Moreover, TaVrt2 could bind with TaVrn1 promoter directly. A TaVrt2-mediated positive feedback loop of TaVrn1 during vernalization was proposed, providing additional understanding on the regulatory mechanism underlying vernalization-induced flowering.

COR/LEA Proteins as Indicators of Frost Tolerance in Triticeae: A Comparison of Controlled versus Field Conditions

Low temperatures in the autumn induce enhanced expression/relative accumulation of several cold-inducible transcripts/proteins with protective functions from Late-embryogenesis-abundant (LEA) superfamily including dehydrins. Several studies dealing with plants grown under controlled conditions revealed a correlation (significant quantitative relationship) between dehydrin transcript/protein relative accumulation and plant frost tolerance. However, to apply these results in breeding, field experiments are necessary. The aim of the review is to provide a summary of the studies dealing with the relationships between plant acquired frost tolerance and COR/LEA transcripts/proteins relative accumulation in cereals grown in controlled and field conditions. The impacts of cold acclimation and vernalisation processes on the ability of winter-type Triticeae to accumulate COR/LEA proteins are discussed. The factors determining dehydrin relative accumulation under controlled cold acclimation treatments versus field trials during winter seasons are discussed. In conclusion, it can be stated that dehydrins could be used as suitable indicators of winter survival in field-grown winter cereals but only in plant prior to the fulfilment of vernalisation requirement.

O-linked N-acetylglucosamine transferase is involved in fine regulation of flowering time in winter wheat

Vernalization genes underlying dramatic differences in flowering time between spring wheat and winter wheat have been studied extensively, but little is known about genes that regulate subtler differences in flowering time among winter wheat cultivars, which account for approximately 75% of wheat grown worldwide. Here, we identify a gene encoding an O-linked N-acetylglucosamine (O-GlcNAc) transferase (OGT) that differentiates heading date between winter wheat cultivars Duster and Billings. We clone this TaOGT1 gene from a quantitative trait locus (QTL) for heading date in a mapping population derived from these two bread wheat cultivars and analyzed in various environments. Transgenic complementation analysis shows that constitutive overexpression of TaOGT1b from Billings accelerates the heading of transgenic Duster plants. TaOGT1 is able to transfer an O-GlcNAc group to wheat protein TaGRP2. Our findings establish important roles for TaOGT1 in winter wheat in adaptation to global warming in the future climate scenarios.

De Novo Genome Assembly of the Japanese Wheat Cultivar Norin 61 Highlights Functional Variation in Flowering Time and Fusarium-Resistant Genes in East Asian Genotypes

Bread wheat is a major crop that has long been the focus of basic and breeding research. Assembly of its genome has been difficult because of its large size and allohexaploid nature (AABBDD genome). Following the first reported assembly of the genome of the experimental strain Chinese Spring (CS), the 10+ Wheat Genomes Project was launched to produce multiple assemblies of worldwide modern cultivars. The only Asian cultivar in the project is Norin 61, a representative Japanese cultivar adapted to grow across a broad latitudinal range, mostly characterized by a wet climate and a short growing season. Here, we characterize the key aspects of its chromosome-scale genome assembly spanning 15 Gb with a raw scaffold N50 of 22 Mb. Analysis of the repetitive elements identified chromosomal regions unique to Norin 61 that encompass a tandem array of the pathogenesis-related 13 family. We report novel copy-number variations in the B homeolog of the florigen gene FT1/VRN3, pseudogenization of its D homeolog and the association of its A homeologous alleles with the spring/winter growth habit. Furthermore, the Norin 61 genome carries typical East Asian functional variants different from CS, ranging from a single nucleotide to multi-Mb scale. Examples of such variation are the Fhb1 locus, which confers Fusarium head-blight resistance, Ppd-D1a, which confers early flowering, Glu-D1f for Asian noodle quality and Rht-D1b, which introduced semi-dwarfism during the green revolution. The adoption of Norin 61 as a reference assembly for functional and evolutionary studies will enable comprehensive characterization of the underexploited Asian bread wheat diversity.

Integrated transcriptome and proteome analysis provides insight into chilling-induced dormancy breaking in Chimonanthus praecox

Chilling has a critical role in the growth and development of perennial plants. The chilling requirement (CR) for dormancy breaking largely depends on the species. However, global warming is expected to negatively affect chilling accumulation and dormancy release in a wide range of perennial plants. Here, we used Chimonanthus praecox as a model to investigate the CR for dormancy breaking under natural and artificial conditions. We determined the minimum CR (570 chill units, CU) needed for chilling-induced dormancy breaking and analyzed the transcriptomes and proteomes of flowering and non-flowering flower buds (FBs, anther and ovary differentiation completed) with different CRs. The concentrations of ABA and GA3 in the FBs were also determined using HPLC. The results indicate that chilling induced an upregulation of ABA levels and significant downregulation of SHORT VEGETATIVE PHASE (SVP) and FLOWERING LOCUS T (FT) homologs at the transcript level in FBs when the accumulated CR reached 570 CU (IB570) compared to FBs in November (FB.Nov, CK) and nF16 (non-flowering FBs after treatment at 16 °C for -300 CU), which suggested that dormancy breaking of FBs could be regulated by the ABA-mediated SVP-FT module. Overexpression in Arabidopsis was used to confirm the function of candidate genes, and early flowering was induced in 35S::CpFT1 transgenic lines. Our data provide insight into the minimum CR (570 CU) needed for chilling-induced dormancy breaking and its underlying regulatory mechanism in C. praecox, which provides a new tool for the artificial regulation of flowering time and a rich gene resource for controlling chilling-induced blooming.

Phenology and related traits for wheat adaptation

Wheat is a major food crop, with around 765 million tonnes produced globally. The largest wheat producers include the European Union, China, India, Russia, United States, Canada, Pakistan, Australia, Ukraine and Argentina. Cultivation of wheat across such diverse global environments with variation in climate, biotic and abiotic stresses, requires cultivars adapted to a range of growing conditions. One intrinsic way that wheat achieves adaptation is through variation in phenology (seasonal timing of the lifecycle) and related traits (e.g., those affecting plant architecture). It is important to understand the genes that underlie this variation, and how they interact with each other, other traits and the growing environment. This review summarises the current understanding of phenology and developmental traits that adapt wheat to different environments. Examples are provided to illustrate how different combinations of alleles can facilitate breeding of wheat varieties with optimal crop performance for different growing regions or farming systems.

A flowering inhibitor of the temperature-dependent pathway in Crocus sativus L

Saffron is the world highest-priced spice because its production requires intensive hand labour. Reduce saffron production costs require containerised plant production under controlled conditions and expand the flowering period. Controlling the flowering process and identify the factors involved in saffron flowering is crucial to introduce technical improvements. The research carried out so far in saffron has allowed an extensive knowledge of the influence of temperature on the flower induction, but the molecular mechanisms controlling flowering induction processes are largely unknown. The present study is the first conducted to isolate and characterize a regulator gene of saffron floral induction the Short Vegetative Phase (SVP) gene, which represses the floral initiation genes in the temperature response pathway, which involved in saffron flower induction. The results obtained from both phylogenetic analysis and T-coffee alignment confirms that the isolated sequence belongs to the SVP gene clades of MADS-box gene family. Gene expression analysis in different developmental stages revealed the highest expression of SVP transcript (CsSVP) during the dormancy and the vegetative stages, but decrease when flower development initiated and it was the least in late September when flower primordia are developed. Furthermore, its expression increased in the apical bud when corms are storage at 9-10 ºC, thus inhibiting flower induction. Additionally, comparison of the CsSVP transcript in apical buds from big and small corms, differing in their flowering capacity, indicates that the CsSVP transcript is present only in vegetative buds. Taken together, these results suggested inhibitory role of the SVP gene.

Genome-wide analysis of MIKC-type MADS-box genes in wheat: pervasive duplications, functional conservation and putative neofunctionalization

Wheat (Triticum aestivum) is one of the most important crops worldwide. Given a growing global population coupled with increasingly challenging cultivation conditions, facilitating wheat breeding by fine-tuning important traits is of great importance. MADS-box genes are prime candidates for this, as they are involved in virtually all aspects of plant development. Here, we present a detailed overview of phylogeny and expression of 201 wheat MIKC-type MADS-box genes. Homoeolog retention is significantly above the average genome-wide retention rate for wheat genes, indicating that many MIKC-type homoeologs are functionally important and not redundant. Gene expression is generally in agreement with the expected subfamily-specific expression pattern, indicating broad conservation of function of MIKC-type genes during wheat evolution. We also found extensive expansion of some MIKC-type subfamilies, especially those potentially involved in adaptation to different environmental conditions like flowering time genes. Duplications are especially prominent in distal telomeric regions. A number of MIKC-type genes show novel expression patterns and respond, for example, to biotic stress, pointing towards neofunctionalization. We speculate that conserved, duplicated and neofunctionalized MIKC-type genes may have played an important role in the adaptation of wheat to a diversity of conditions, hence contributing to the importance of wheat as a global staple food.

Low-temperature-induced changes in the transcriptome reveal a major role of CgSVP genes in regulating flowering of Cymbidium goeringii

BACKGROUND

Cymbidium goeringii is one of the most horticulturally important and popular ornamental plants in the orchid family (Orchidaceae). It blooms in winter during January-March and a period of low temperature is necessary for its normal flowering, otherwise there is flower bud abortion, which seriously affects the economic benefits. However, the molecular mechanism underlying winter-blooming behavior in C. goeringii is unclear.

RESULTS

In this research, we firstly study the flowering physiology of C. goeringii by cytobiology observations and physiological experiments. Using comparative transcriptome analysis, we identified 582 differentially expressed unigenes responding to cold treatment that were involved in metabolic process, flowering time, hormone signaling, stress response, and cell cycle, implying their potential roles in regulating winter-blooming of C. goeringii. Twelve MADS-box genes among them were investigated by full-length cDNA sequence analysis and expression validation, which indicated that three genes within the SHORT VEGETATIVE PHASE (SVP) sub-group had the most significant repressed expression after cold treatment. Further analysis revealed that the SVP genes showed population variation in expression that correlated with cold-regulated flowering and responded to low temperature earlier than the flowering pathway integrators CgAP1, CgSOC1, and CgLFY, suggesting a potential role of CgSVP genes in the early stage of low-temperature-induced blooming of C. goeringii. Moreover, a yeast two-hybrid experiment confirmed that CgSVP proteins interacted with CgAP1 and CgSOC1, suggesting that they may synergistically control the process of C. goeringii flowering in winter.

CONCLUSIONS

This study represents the first exploration of flowering physiology of C. goeringii and provides gene expression information that could facilitate our understanding of molecular regulation of orchid plant winter-flowering, which could provide new insights and practical guidance for improving their flowering regulation and molecular breeding.

Gene regulatory network and abundant genetic variation play critical roles in heading stage of polyploidy wheat

BACKGROUND

The extensive adaptability of polyploidy wheat is attributed to its complex genome, and accurately controlling heading stage is a prime target in wheat breeding process. Wheat heading stage is an essential growth and development processes since it starts at a crucial point in the transition from vegetative phase to reproductive phase.

MAIN BODY

Heading stage is mainly decided by vernalization, photoperiod, hormone (like gibberellic acid, GA), and earliness per se (Eps). As a polyploidy species, common wheat possesses the abundant genetic variation, such as allelic variation, copy number variation etc., which have a strong effect on regulation of wheat growth and development. Therefore, understanding genetic manipulation of heading stage is pivotal for controlling the heading stage in wheat. In this review, we summarized the recent advances in the genetic regulatory mechanisms and abundant variation in genetic diversity controlling heading stage in wheat, as well as the interaction mechanism of different signals and the contribution of different genetic variation. We first summarized the genes involved in vernalization, photoperoid and other signals cross-talk with each other to control wheat heading stage, then the abundant genetic variation related to signal components associated with wheat heading stage was also elaborated in detail.

CONCLUSION

Our knowledge of the regulatory network of wheat heading can be used to adjust the duration of the growth phase for the purpose of acclimatizing to different geographical environments.

Global analysis of H3K4me3/H3K27me3 in Brachypodium distachyon reveals VRN3 as critical epigenetic regulation point in vernalization and provides insights into epigenetic memory

Vernalization, the requirement of plants for long-term exposure to low environmental temperature for flowering, is an epigenetic phenomenon. Histone modification regulation has been revealed in vernalization, but is limited to key genes. Now, we know that VRN1 is epigenetically critical for monocots. Genome-wide analysis is still unavailable, however. We performed chromatin immunoprecipitation-sequencing for H3K4me3/H3K27me3 in Brachypodium distachyon to obtain a global view of histone modifications in vernalization on a genome-wide scale and for different pathways/genes. Our data showed that H3K4me3 and H3K27me3 play distinct roles in vernalization. Unlike H3K4me3, H3K27me3 exhibited regional regulation, showed main regulation targets in vernalization and contributed to epigenetic memory. For genes in four flowering regulation pathways, only FT2 (functional ortholog of VRN3 in B. distachyon) and VRN1 showed coordinated changes in H3K4me3/H3K27me3. The epigenetic response at VRN3 was weaker under short-day than under long-day conditions. VRN3 was revealed as an epigenetic regulation point integrating vernalization and day length signals. We globally identified genes maintaining vernalization-induced epigenetic changes. Most of these genes showed dose-dependent vernalization responses, revealing a quantitative 'recording system' for vernalization. Our studies shed light on the epigenetic role of VRN3 and H3K4me3/H3K27me3 in vernalization and reveal genes underlying epigenetic memory, laying the foundation for further study.

A transcriptome screen for positive selection in domesticated breadfruit and its wild relatives (Artocarpus spp.)

PREMISE OF THE STUDY

Underutilized crops, such as breadfruit (Artocarpus altilis, Moraceae) have the potential to improve global food security. Humans have artificially selected many cultivars of breadfruit since its domestication began approximately 3500 years ago. The goal of this research was to identify transcriptomic signals of positive selection and to develop genomic resources that may facilitate the development of improved breadfruit cultivars in the future.

METHODS

A reference transcriptome of breadfruit was assembled de novo and annotated. Twenty-four transcriptomes of breadfruit and its wild relatives were generated and analyzed to reveal signals of positive selection that may have resulted from local adaptation or natural selection. Emphasis was placed on MADS-box genes, which are important because they often regulate fruiting timing and structures, and on carotenoid biosynthesis genes, which can impact the nutritional quality of the fruit.

KEY RESULTS

Over 1000 genes showed signals of positive selection, and these genes were enriched for localization to plastids. Nucleotide sites and individuals under positive selection were discovered in MADS-box genes and carotenoid biosynthesis genes, with several sites located in cofactor or DNA-binding domains. A McDonald-Kreitman test comparing wild to cultivated samples revealed selection in one of the carotenoid biosynthesis genes, abscisic acid 8'-hydroxylase 3.

CONCLUSIONS

This research highlights some of the many genes that may have been intentionally or unintentionally selected for during the human-mediated dispersal of breadfruit and stresses the importance of conserving a varied germplasm collection. It has revealed candidate genes for further study and produced new genomic resources for breadfruit.

Transcriptomic Insights into Phenological Development and Cold Tolerance of Wheat Grown in the Field

Cold acclimation and winter survival in cereal species is determined by complicated environmentally regulated gene expression. However, studies investigating these complex cold responses are mostly conducted in controlled environments that only consider the responses to single environmental variables. In this study, we have comprehensively profiled global transcriptional responses in crowns of field-grown spring and winter wheat (Triticum aestivum) genotypes and their near-isogenic lines with the VRN-A1 alleles swapped. This in-depth analysis revealed multiple signaling, interactive pathways that influence cold tolerance and phenological development to optimize plant growth and development in preparation for a wide range of over-winter stresses. Investigation of genetic differences at the VRN-A1 locus revealed that a vernalization requirement maintained a higher level of cold response pathways while VRN-A1 genetically promoted floral development. Our results also demonstrated the influence of genetic background on the expression of cold and flowering pathways. The link between delayed shoot apex development and the induction of cold tolerance was reflected by the gradual up-regulation of abscisic acid-dependent and C-REPEAT-BINDING FACTOR pathways. This was accompanied by the down-regulation of key genes involved in meristem development as the autumn progressed. The chromosome location of differentially expressed genes between the winter and spring wheat genetic backgrounds showed a striking pattern of biased gene expression on chromosomes 6A and 6D, indicating a transcriptional regulation at the genome level. This finding adds to the complexity of the genetic cascades and gene interactions that determine the evolutionary patterns of both phenological development and cold tolerance traits in wheat.

Genetic basis of the very short life cycle of 'Apogee' wheat

Background

‘Apogee’ has a very short life cycle among wheat cultivars (flowering 25 days after planting under a long day and without vernalization), and it is a unique genetic material that can be used to accelerate cycling breeding lines. However, little is known about the genetic basis of the super-short life of Apogee wheat.

Results

In this study, Apogee was crossed with a strong winter wheat cultivar ‘Overland’, and 858 F₂ plants were generated and tested in a greenhouse under constant warm temperature and long days. Apogee wheat was found to have the early alleles for four flowering time genes, which were ranked in the order of vrn-A1 > VRN-B1 > vrn-D3 > PPD-D1 according to their effect intensity. All these Apogee alleles for early flowering showed complete or partial dominance effects in the F₂ population. Surprisingly, Apogee was found to have the same alleles at vrn-A1a and vrn-D3a for early flowering as observed in winter wheat cultivar ‘Jagger.’ It was also found that the vrn-A1a gene was epistatic to VRN-B1 and vrn-D3. The dominant vrn-D3a alone was not sufficient to cause the transition from vegetative to reproductive development in winter plants without vernalization but was able to accelerate flowering in those plants that carry the vrn-A1a or Vrn-B1 alleles. The genetic effects of the vernalization and photoperiod genes were validated in Apogee x Overland F₃ populations.

Conclusion

VRN-A1, VRN-B1, VRN-D3, and PPD-D1 are the major genes that enabled Apogee to produce the very short life cycle. This study greatly advanced the molecular understanding of the multiple flowering genes under different genetic backgrounds and provided useful molecular tools that can be used to accelerate winter wheat breeding schemes.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4239-8) contains supplementary material, which is available to authorized users.

Prevalent Exon-Intron Structural Changes in the APETALA1/FRUITFULL, SEPALLATA, AGAMOUS-LIKE6, and FLOWERING LOCUS C MADS-Box Gene Subfamilies Provide New Insights into Their Evolution

AP1/FUL, SEP, AGL6, and FLC subfamily genes play important roles in flower development. The phylogenetic relationships among them, however, have been controversial, which impedes our understanding of the origin and functional divergence of these genes. One possible reason for the controversy may be the problems caused by changes in the exon-intron structure of genes, which, according to recent studies, may generate non-homologous sites and hamper the homology-based sequence alignment. In this study, we first performed exon-by-exon alignments of these and three outgroup subfamilies (SOC1, AG, and STK). Phylogenetic trees reconstructed based on these matrices show improved resolution and better congruence with species phylogeny. In the context of these phylogenies, we traced evolutionary changes of exon-intron structures in each subfamily. We found that structural changes have occurred frequently following gene duplication and speciation events. Notably, exons 7 and 8 (if present) suffered more structural changes than others. With the knowledge of exon-intron structural changes, we generated more reasonable alignments containing all the focal subfamilies. The resulting trees showed that the SEP subfamily is sister to the monophyletic group formed by AP1/FUL and FLC subfamily genes and that the AGL6 subfamily forms a sister group to the three abovementioned subfamilies. Based on this topology, we inferred the evolutionary history of exon-intron structural changes among different subfamilies. Particularly, we found that the eighth exon originated before the divergence of AP1/FUL, FLC, SEP, and AGL6 subfamilies and degenerated in the ancestral FLC-like gene. These results provide new insights into the origin and evolution of the AP1/FUL, FLC, SEP, and AGL6 subfamilies.

The Relationships between Development and Low Temperature Tolerance in Barley Near Isogenic Lines Differing for Flowering Behavior

Flowering time, vernalization requirement, photoperiod sensitivity and low temperature tolerance are key traits in the Triticeae. We characterized a set of isogenic genetic stocks-representing single and pairwise substitutions of spring alleles at the VRN-H1, VRN-H2 and VRN-H3 loci in a winter barley background-at the structural, functional and phenotypic levels. High density mapping with reference to the barley genome sequence confirmed that in all cases target VRN alleles were present in the near isogenic lines (NILs) and allowed estimates of introgression size (at the genetic and physical levels) and gene content. Expression data corroborated the structural and phenotypic results. The latter confirmed that substitution of a spring allele at any of the VRN loci is sufficient to eliminate vernalization requirement. There was no significant change in low temperature tolerance with substitution of a spring allele at VRN-H2, but there were significant losses in cold tolerance with substitutions at VRN-H1 and VRN-H3. Reductions in cold tolerance are ascribed to an accelerated transition from the vegetative to reproductive state. The set of NILs will be a rich resource for understanding the genetics of vernalization, low temperature tolerance and other traits encoded/regulated by genes within the introgressed intervals.

Vernalization, gibberellic acid and photo period are important signals of yield formation in timothy (Phleum pratense)

Timothy (Phleum pratense) is a widely grown perennial forage grass in the Nordic region. The canopy consists of three tiller types, of which the stem forming vegetative elongating (ELONG) tiller and generative (GEN) tillers contribute the most to dry matter yield. In this study, the regulation of tiller formation by vernalization, day length (DL) [12 h, short day length (SD); 16 h, long day length (LD)] and gibberellic acid (GA) was investigated in two timothy cultivars. Vernalization resulted in a shift of ELONG to GEN tillers. No vernalization was required for the development of ELONG tillers but SD strictly arrested stem elongation. Vernalization is an important regulator of tiller development but it seemed to be upstream regulated by DL. LD was essential for floral transition and could not be substituted by GA and/or vernalization treatments. Genotypic variation was found in the development of GEN tillers. The ability to produce GEN tillers was associated with significant upregulation of PpVRN3. PpVRN1 expression peaked at the time of vegetative/generative transition, and PpVRN3 after the transfer to LD, suggesting them to have similar functions with cereal vernalization genes. PpVRN1 alone was not sufficient to activate flowering, and upregulation of PpVRN3 possibly together with PpPpd1 was required. Although vernalization downregulated PpMADS10, this gene did not act as a clear flowering repressor. Our results show that flowering signals alter the tiller composition, so they have important effects on yield formation of timothy.

Comparative analysis of the cold acclimation and freezing tolerance capacities of seven diploid Brachypodium distachyon accessions

BACKGROUND AND AIMS

Cold is a major constraint for cereal cultivation under temperate climates. Winter-hardy plants interpret seasonal changes and can acquire the ability to resist sub-zero temperatures. This cold acclimation process is associated with physiological, biochemical and molecular alterations in cereals. Brachypodium distachyon is considered a powerful model system to study the response of temperate cereals to adverse environmental conditions. To date, little is known about the cold acclimation and freezing tolerance capacities of Brachypodium. The main objective of this study was to evaluate the cold hardiness of seven diploid Brachypodium accessions.

METHODS

An integrated approach, involving monitoring of phenological indicators along with expression profiling of the major vernalization regulator VRN1 orthologue, was followed. In parallel, soluble sugars and proline contents were determined along with expression profiles of two COR genes in plants exposed to low temperatures. Finally, whole-plant freezing tests were performed to evaluate the freezing tolerance capacity of Brachypodium.

KEY RESULTS

Cold treatment accelerated the transition from the vegetative to the reproductive phase in all diploid Brachypodium accessions tested. In addition, low temperature exposure triggered the gradual accumulation of BradiVRN1 transcripts in all accessions tested. These accessions exhibited a clear cold acclimation response by progressively accumulating proline, sugars and COR gene transcripts. However, whole-plant freezing tests revealed that these seven diploid accessions only have a limited capacity to develop freezing tolerance when compared with winter varieties of temperate cereals such as wheat and barley. Furthermore, little difference in terms of survival was observed among the accessions tested despite their previous classification as either spring or winter genotypes.

CONCLUSIONS

This study is the first to characterize the freezing tolerance capacities of B. distachyon and provides strong evidence that some diploid accessions such as Bd21 have a facultative growth habit.

TamiR1123 originated from a family of miniature inverted-repeat transposable elements (MITE) including one inserted in the Vrn-A1a promoter in wheat

More than half of spring wheat cultivars have a dominant Vrn-A1a allele that has an insertion of a miniature inverted-repeat transposable element (MITE) in its promoter. In this study, we found that the MITE present in the Vrn-A1a gene (MITE_VRN) is a nearly perfect palindrome and it can form highly stable hairpin loops when expressed as RNA. MITE_VRN also possessed sequences of a microRNA in Triticum aestivum (TamiR1123). The P(32) labeled TamiR1123 probe detected two RNA molecules on a small RNA gel blot, one expected for MITE_VRN, and the other expected for TamiR1123. These results demonstrated that MITE_VRN was expressed as RNAs and TamiR1123 was originated from the MITE_VRN family. The isogenic line TDD carrying the dominant Vrn-A1a allele with MITE_VRN showed higher TamiR1123 and Vrn-A1a transcript levels than the isogenic line TDE carrying the recessive vrn-A1a allele without MITE_VRN. TamiR1123 were greatly up-regulated by plant age but slightly down-regulated by low temperature and short days. These findings have pointed to alternative regulatory mechanisms for plant development governed by Vrn-A1a in spring wheat.

Insights into the maize pan-genome and pan-transcriptome

Genomes at the species level are dynamic, with genes present in every individual (core) and genes in a subset of individuals (dispensable) that collectively constitute the pan-genome. Using transcriptome sequencing of seedling RNA from 503 maize (Zea mays) inbred lines to characterize the maize pan-genome, we identified 8681 representative transcript assemblies (RTAs) with 16.4% expressed in all lines and 82.7% expressed in subsets of the lines. Interestingly, with linkage disequilibrium mapping, 76.7% of the RTAs with at least one single nucleotide polymorphism (SNP) could be mapped to a single genetic position, distributed primarily throughout the nonpericentromeric portion of the genome. Stepwise iterative clustering of RTAs suggests, within the context of the genotypes used in this study, that the maize genome is restricted and further sampling of seedling RNA within this germplasm base will result in minimal discovery. Genome-wide association studies based on SNPs and transcript abundance in the pan-genome revealed loci associated with the timing of the juvenile-to-adult vegetative and vegetative-to-reproductive developmental transitions, two traits important for fitness and adaptation. This study revealed the dynamic nature of the maize pan-genome and demonstrated that a substantial portion of variation may lie outside the single reference genome for a species.

Vernalization requirement duration in winter wheat is controlled by TaVRN-A1 at the protein level

Winter wheat requires a period of low temperatures to accelerate flowering (vernalization). This requirement could make winter wheat more vulnerable to elevated global temperature via insufficient vernalization. All known vernalization genes are cloned according to qualitative variation in vernalization requirement between spring and winter wheat, but the genes controlling quantitative variation for more or less vernalization requirement among winter wheat cultivars remain unknown. We report here that the gene for the vernalization requirement duration in winter wheat was cloned using a BC(1)F(2:3) population that segregated in a 3:1 ratio of early-flowering plants and late-flowering plants after vernalization for 3 weeks. The positional cloning of the gene for vernalization requirement duration demonstrated that this trait is controlled by TaVRN-A1 at the protein level. The Ala(180) in vrn-A1a, encoded by the dominant allele for 3-week vernalization, was mutated to Val(180) in vrn-A1b, encoded by the recessive allele for 6-week vernalization. Further studies with in vitro protein pull-down assays and immunoprecipitation analyses indicated that the mutated Val(180) in vrn-A1b protein decreased the ability to bind with TaHOX1 (the first homeobox protein in Triticum aestivum). The direct binding of TaVRN-A1 and TaHOX1 proteins was confirmed in the nucleus of living plant cells by bimolecular fluorescence complementation (BiFC) analyses. The TaHOX1 gene was found to be upregulated by low temperatures, and to have a significant genetic effect on heading date, suggesting that TaHOX1 functions in the flowering pathway in winter wheat.

Adaptation to seasonality and the winter freeze

Flowering plants initially diversified during the Mesozoic era at least 140 million years ago in regions of the world where temperate seasonal environments were not encountered. Since then several cooling events resulted in the contraction of warm and wet environments and the establishment of novel temperate zones in both hemispheres. In response, less than half of modern angiosperm families have members that evolved specific adaptations to cold seasonal climates, including cold acclimation, freezing tolerance, endodormancy, and vernalization responsiveness. Despite compelling evidence for multiple independent origins, the level of genetic constraint on the evolution of adaptations to seasonal cold is not well understood. However, the recent increase in molecular genetic studies examining the response of model and crop species to seasonal cold offers new insight into the evolutionary lability of these traits. This insight has major implications for our understanding of complex trait evolution, and the potential role of local adaptation in response to past and future climate change. In this review, we discuss the biochemical, morphological, and developmental basis of adaptations to seasonal cold, and synthesize recent literature on the genetic basis of these traits in a phylogenomic context. We find evidence for multiple genetic links between distinct physiological responses to cold, possibly reinforcing the coordinated expression of these traits. Furthermore, repeated recruitment of the same or similar ancestral pathways suggests that land plants might be somewhat pre-adapted to dealing with temperature stress, perhaps making inducible cold traits relatively easy to evolve.

Low temperatures induce rapid changes in chromatin state and transcript levels of the cereal VERNALIZATION1 gene

Transcriptional activation of the VERNALIZATION1 gene mediates the acceleration of flowering by prolonged cold (vernalization) in temperate cereals. This study examined the earliest stages of the transcriptional response of VRN1 to low temperatures. Time-course analyses, using a sensitive quantitative PCR assay, showed that in sprouting barley seedlings VRN1 transcripts begin to accumulate within 24 hours of the onset of cold. The kinetics of the initial transcriptional response of VRN1 to cold was similar to the cold-induced genes DEHYDRIN5 (DHN5) and COLD REGULATED 14B (COR14B), but occurred at lower levels compared to cold acclimation genes or the response to longer cold treatments. Temperatures between 15 and -2 °C induced expression of VRN1 within 24 hours, with a maximal response observed between 2 and -2 °C. Transcriptional induction was also observed in undifferentiated callus cells. There were significant increases in histone acetylation levels at the VRN1 locus in response to 24-hour cold treatment. Sodium butyrate, a histone deacetylation inhibitor, triggered an increase in histone acetylation at VRN1 chromatin and elevated VRN1 transcript levels. The transcriptional response of VRN1 to short-term cold treatment was examined in near-isogenic lines that have different VRN1 genotypes, showing that an allele of the barley VRN1 gene with an insertion in the first intron and high basal expression levels has a reduced transcriptional response to short term cold treatment. This study suggests that low-temperature induction of VRN1 is a cellular response to cold triggered by the same mechanisms that mediate low-temperature induction of cold acclimation genes.

HVP10 encoding V-PPase is a prime candidate for the barley HvNax3 sodium exclusion gene: evidence from fine mapping and expression analysis

In cereals, a common salinity tolerance mechanism is to limit accumulation of Na(+) in the shoot. In a cross between the barley variety Barque-73 (Hordeum vulgare ssp. vulgare) and the accession CPI-71284 of wild barley (H. vulgare ssp. spontaneum), the HvNax3 locus on chromosome 7H was found to determine a ~10-25 % difference in leaf Na(+) accumulation in seedlings grown in saline hydroponics, with the beneficial exclusion trait originating from the wild parent. The Na(+) exclusion allele was also associated with a 13-21 % increase in shoot fresh weight. The HvNax3 locus was delimited to a 0.4 cM genetic interval, where it cosegregated with the HVP10 gene for vacuolar H(+)-pyrophosphatase (V-PPase). Sequencing revealed that the mapping parents encoded identical HVP10 proteins, but salinity-induced mRNA expression of HVP10 was higher in CPI-71284 than in Barque-73, in both roots and shoots. By contrast, the expression of several other genes predicted by comparative mapping to be located in the HvNax3 interval was similar in the two parent lines. Previous work demonstrated roles for V-PPase in ion transport and salinity tolerance. We therefore considered transcription levels of HVP10 to be a possible basis for variation in shoot Na(+) accumulation and biomass production controlled by the HvNax3 locus under saline conditions. Potential mechanisms linking HVP10 expression patterns to the observed phenotypes are discussed.

Construction of a high-quality yeast two-hybrid (Y2H) library and its application in identification of interacting proteins with key vernalization regulator TaVRN-A1 in wheat

BACKGROUND

Low temperature is required for the competence of winter wheat to flowering (vernalization), and several key components in the vernalization-mediated flowering pathway have been isolated. A Y2H library is a very useful platform to further unravel novel regulators in the flowering pathway. Thus, there is a necessity to construct a high-quality Y2H library using vernalized winter wheat plants.

RESULT

We described the construction of a high-quality Y2H library using winter wheat plants with cold-treatment for different weeks to maximize pooling interacting proteins during vernalization. The resultant Y2H library contained ~2.5×10(6) independent clones, with a cell density of ~2.6×10(8) and an average insert size of ~ 1.5 kb. TaVRN-A1 was used as a "bait" to test the quality of the Y2H library. As a result, several cDNA clones encoding TaSOC1 and TaSVP1 that were known to have a direct binding with TaVRN-A1 were identified, demonstrating that the Y2H screen system constructed in this study was highly efficient. Additional proteins that were discovered but not characterized in previous studies could be novel partners of TaVRN-A1 in wheat.

CONCLUSION

We established a high-efficient Y2H screen system using the Matchmaker™ technology with several modifications in the critical steps. Ultimately, we provided a successful example to fast and economically create high-quality Y2H libraries for studies on protein interaction in hexaploid wheat.

Divergences of MPF2-like MADS-domain proteins have an association with the evolution of the inflated calyx syndrome within Solanaceae

The inflated calyx syndrome (ICS) is a post-floral novelty within Solanaceae. Previous work has shown that MPF2-like MADS-box genes have been recruited for the development and evolution of ICS through heterotopic expression from vegetative to floral organs. ICS seems to be a plesiomorphic trait in Physaleae, but it has been secondarily lost in some lineages during evolution. We hypothesized that molecular and functional divergences of MPF2-like proteins might play a role in the loss of ICS. In this study we analyzed the phylogeny, selection and various functions of MPF2-like proteins with respect to the evolution of ICS. Directional selection of MPF2-like orthologs toward evolution of ICS was detected. While auto-activation capacity between proteins varies in yeast, MPF2-like interaction with floral MADS-domain proteins is robustly detected, hence substantiating their integration into the floral developmental programs. Dimerization with A- (MPF3) and E-function (PFSEP1/3) proteins seems to be essential for ICS development within Solanaceae. Moreover, the occurrence of the enlarged sepals, reminiscent of ICS, and MPF2-like interactions with these specific partners were observed in transgenic Arabidopsis. The interaction spectrum relevant to ICS seems to be plesiomorphic, reinforcing the plesiomorphy of this trait. The inability of some MPF2-like to interact with either the A-function or any of the E-function partners characterized is correlated with the loss of ICS in the lineages that showed a MPF2-like expression in the calyx. Our findings suggest that, after recruitment of MPF2-like genes for floral development, diversification in their coding region due to directional selection leads to a modification of the MADS-domain protein interacting spectrum, which might serve as a constraint for the evolution of ICS within Solanaceae.

Cloning and characterization of SOC1 homologs in barley (Hordeum vulgare) and their expression during seed development and in response to vernalization

A number of genes are involved in the vernalization pathway, such as VRN1, VRN2 and VRN3/FT1, whose function has been studied in barley and wheat. However, the function of the flowering and vernalization integrator SUPPRESSOR OF OVEREXPRESSION OF CONSTANS 1 (SOC1) has not been well studied in Triticeae, and particularly in barley. Herein, we cloned and characterized two barley SOC1-like homologs, HvSOC1-like1 and HvSOC1-like2. Primary sequence analysis of the predicted HvSOC1-like1 and HvSOC1-like2 proteins showed that they are members of the type II MADS-box protein family. Phylogenetic analysis placed the predicted proteins with other SOC1 and SOC1-like proteins from different species neighboring those from other cereal plant species. Primary and secondary structures of the predicted proteins are conserved to each other and more distant to the recently identified barley ODDSOC1 proteins. Genomic organization of HvSOC1-like1 is very similar to the Arabidopsis and Brachypodium SOC1 genes and localized in highly syntenic chromosomal regions. Regulatory cis-acting elements detected in the HvSOC1-like1 promoter include the CArG-box, implicated in the regulation of SOC1 expression in Arabidopsis. Both HvSOC1-like1 and HvSOCI-like2 are expressed in vegetative and reproductive tissues and at different stages of seed development. Both are upregulated in a particular seed developmental stage suggesting their possible implication in seed development. Furthermore, HvSOC1-like1 was induced in two winter barley cultivars after vernalization treatment pointing to its probable involvement in the vernalization process. The study of the SOC1 genes reported here opens the way for a better understanding of both the vernalization process and seed development and germination in this important cereal crop.

CaJOINTLESS is a MADS-box gene involved in suppression of vegetative growth in all shoot meristems in pepper

In aiming to decipher the genetic control of shoot architecture in pepper (Capsicum spp.), the allelic late-flowering mutants E-252 and E-2537 were identified. These mutants exhibit multiple pleiotropic effects on the organization of the sympodial shoot. Genetic mapping and sequence analysis indicated that the mutants are disrupted at CaJOINTLESS, the orthologue of the MADS-box genes JOINTLESS and SVP in tomato and Arabidopsis, respectively. Late flowering of the primary and sympodial shoots of Cajointless indicates that the gene functions as a suppressor of vegetative growth in all shoot meristems. While CaJOINTLESS and JOINTLESS have partially conserved functions, the effect on flowering time and on sympodial development in pepper, as well as the epistasis over FASCICULATE, the homologue of the major determinant of sympodial development SELF-PRUNING, is stronger than in tomato. Furthermore, the solitary terminal flower of pepper is converted into a structure composed of flowers and leaves in the mutant lines. This conversion supports the hypothesis that the solitary flowers of pepper have a cryptic inflorescence identity that is suppressed by CaJOINTLESS. Formation of solitary flowers in wild-type pepper is suggested to result from precocious maturation of the inflorescence meristem.

Expression of vernalization responsive genes in wheat is associated with histone H3 trimethylation

The transition to flowering in winter wheat requires prolonged exposure to low temperature, a process called vernalization. This process is regulated by a genetic pathway that involves at least three genes, Triticum aestivum VERNALIZATION 1 (TaVRN1), Triticum aestivum VERNALIZATION 2 (TaVRN2) and Triticum aestivum FLOWERING LOCUS T-like 1 (TaFT1). These genes regulate flowering by integrating environmental and developmental cues. To determine whether the expression of these genes is associated with the chromatin methylation state during vernalization in wheat, the level of two markers of histone modifications, the activator histone H3 trimethylation of lysine 4 (H3K4me3) and the repressor histone H3 trimethylation of lysine 27 (H3K27me3) were measured at the promoter regions of these three genes. Bioinformatics analysis of these promoters demonstrates the presence of conserved cis-acting elements in the promoters of the three vernalization genes, TaVRN1, TaVRN2 and TaFT1. These elements are targeted by common transcription factors in the vernalization responsive cereals. These promoters also contain the functional "units" PRE/TRE targeted by Polycomb and Trithorax proteins that maintain repressed or active transcription states of developmentally regulated genes. These proteins are known to be associated with the regulation of H3K4me3 and H3K27me3. Expression studies indicate that TaVRN1 and TaFT1 are up-regulated by vernalization in winter wheat. This up-regulation is associated with increased level of the activator H3K4me3 with no change in the level of the repressor H3K27me3 at the promoter region. This study shows that the flowering transition induced by vernalization in winter wheat is associated with histone methylation at the promoter level of TaVRN1 and TaFT1 while the role of these markers is less evident in TaVRN2 repression. This may represent part of the cellular memory of vernalization in wheat.

Transcriptional Regulations on the Low-Temperature-Induced Floral Transition in an Orchidaceae Species, Dendrobium nobile: An Expressed Sequence Tags Analysis

Vernalization-induced flowering is a cold-relevant adaptation in many species, but little is known about the genetic basis behind in Orchidaceae species. Here, we reported a collection of 15017 expressed sequence tags (ESTs) from the vernalized axillary buds of an Orchidaceae species, Dendrobium nobile, which were assembled for 9616 unique gene clusters. Functional enrichment analysis showed that genes in relation to the responses to stresses, especially in the form of low temperatures, and those involving in protein biosynthesis and chromatin assembly were significantly overrepresented during 40 days of vernalization. Additionally, a total of 59 putative flowering-relevant genes were recognized, including those homologous to known key players in vernalization pathways in temperate cereals or Arabidopsis, such as cereal VRN1, FT/VRN3, and Arabidopsis AGL19. Results from this study suggest that the networks regulating vernalization-induced floral transition are conserved, but just in a part, in D. nobile, temperate cereals, and Arabidopsis.

Functional characterisation of HvCO1, the barley (Hordeum vulgare) flowering time ortholog of CONSTANS

Variation in photoperiod response is a major factor determining plant development and the agronomic performance of crops. The genetic control of photoperiodic flowering has been elucidated in the model plant Arabidopsis, and many of the identified genes are structurally conserved in the grasses. In this study, HvCO1, the closest barley ortholog of the key photoperiod response gene CONSTANS in Arabidopsis, was over-expressed in the spring barley Golden Promise. Over-expression of HvCO1 accelerated time to flowering in long- and short-day conditions and caused up-regulation of HvFT1 mRNA under long-day conditions. However, the transgenic plants retained a response to photoperiod, suggesting the presence of photoperiod response factors acting downstream of HvCO1 transcription. Analysis of a population segregating for HvCO1 over-expression and natural genetic variation at Ppd-H1 demonstrated that Ppd-H1 acts downstream of HvCO1 transcription on HvFT1 expression and flowering. Furthermore, variation at Ppd-H1 did not affect diurnal expression of HvCO1 or HvCO2. Over-expression of HvCO1 increased transcription of the spring allele of Vrn-H1 in long- and short-day conditions, while genetic variation at Ppd-H1 did not affect Vrn-H1 expression. Over-expression of HvCO1 and natural genetic variation at Ppd-H1 accelerated inflorescence development and stem elongation. Thus, HvCO1 probably induces flowering by activating HvFT1 whilst Ppd-H1 regulates HvFT1 independently of HvCO1 mRNA, and all three genes also appear to have a strong effect in promoting inflorescence development.

Agave tequilana MADS genes show novel expression patterns in meristems, developing bulbils and floral organs

Agave tequilana is a monocarpic perennial species that flowers after 5-8 years of vegetative growth signaling the end of the plant's life cycle. When fertilization is unsuccessful, vegetative bulbils are induced on the umbels of the inflorescence near the bracteoles from newly formed meristems. Although the regulation of inflorescence and flower development has been described in detail for monocarpic annuals and polycarpic species, little is known at the molecular level for these processes in monocarpic perennials, and few studies have been carried out on bulbils. Histological samples revealed the early induction of umbel meristems soon after the initiation of the vegetative to inflorescence transition in A. tequilana. To identify candidate genes involved in the regulation of floral induction, a search for MADS-box transcription factor ESTs was conducted using an A. tequilana transcriptome database. Seven different MIKC MADS genes classified into 6 different types were identified based on previously characterized A. thaliana and O. sativa MADS genes and sequences from non-grass monocotyledons. Quantitative real-time PCR analysis of the seven candidate MADS genes in vegetative, inflorescence, bulbil and floral tissues uncovered novel patterns of expression for some of the genes in comparison with orthologous genes characterized in other species. In situ hybridization studies using two different genes showed expression in specific tissues of vegetative meristems and floral buds. Distinct MADS gene regulatory patterns in A. tequilana may be related to the specific reproductive strategies employed by this species.

Timing is everything in plant development. The central role of floral repressors

Progress in understanding the molecular basis of flowering time control has revealed that floral repressors play a central role in modulating the floral transition and are essential to prevent the precocious onset of flowering. A number of cellular processes including chromatin remodeling, selective protein degradation, and transcriptional regulation mediated by transcription factors are involved in repressing the initiation of flowering. Floral repressors interact at different levels with floral inductive pathways and prevent the premature onset of flowering that could impact negatively on the reproductive success of plants. Despite recent advances, further studies will be needed to understand how the interactions between floral repressors and the regulatory networks involved in the control of flowering time have evolved in different species. Recent data suggest that a diversity of regulatory proteins act as central floral repressors in different plants, and even in those species where regulatory modules are conserved new elements that modulate the function of these pathways have been recruited to mediate specific adaptive responses. The development of genomic tools and predictive models that can integrate large datasets related to the flowering behavior of plant species will facilitate the characterization of the repressor mechanisms underlying flowering responses, a trait with implications in the yield of crop species. In a scenario of global climate change, an in depth understanding of these gene circuits will be essential for the development of crop varieties with improved yield.

Expression of dehydrins in wheat and barley under different temperatures

The review summarizes recent knowledge on the expression of cold-inducible dehydrins with a special attention to Wcs120 and Dhn5 genes in wheat and barley plants under different temperatures. When plants are exposed to cold, dehydrins start accumulating both in freezing-tolerant and freezing-susceptible plants; however, their accumulation correlates with plant acquired frost tolerance (FT). During a long-term cold acclimation (CA), dehydrin accumulation is significantly affected by Vrn1/Fr1 locus and the expression of the major vernalization gene VRN1, respectively. A different dynamics of dehydrin transcripts and proteins during CA is also observed. Transcripts reach their maximum within the first week of CA while proteins gradually accumulate until vernalization. Vernalization is associated with a significant decrease in dehydrin accumulation while the decrease of acquired FT is delayed. Studies carried out on plants grown at moderately cold temperatures (9-20 °C) have shown that both dehydrin transcripts and proteins can be detected even at these temperatures and that plants with different FT levels can be distinguished according to dehydrin accumulation without any exposure to severe cold. In conclusion, the potential use of these results in the breeding programmes aimed at the enhancement of wheat and barley FT is discussed.

Genetic basis of pearl millet adaptation along an environmental gradient investigated by a combination of genome scan and association mapping

Identifying the molecular bases of adaptation is a key issue in evolutionary biology. Genome scan is an efficient approach for identifying important molecular variation involved in adaptation. Association mapping also offers an opportunity to gain insight into genotype-phenotype relationships. Using these two approaches coupled with environmental data should help to come up with a refined picture of the evolutionary process underlying adaptation. In this study, we first conducted a selection scan analysis on a transcription factor gene family. We focused on the MADS-box gene family, a gene family which plays a crucial role in vegetative and flower development. Twenty-one pearl millet populations were sampled along an environmental gradient in West Africa. We identified one gene, i.e. PgMADS11, using Bayesian analysis to detect selection signatures. Polymorphism at this gene was also associated with flowering time variation in an association mapping framework. Finally, we found that PgMADS11 allele frequencies were closely associated with annual rainfall. Overall, we determined an efficient way to detect functional polymorphisms associated with climate variation in non-model plants by combining genome scan and association mapping. These results should help monitor the impact of recent climatic changes on plant adaptation.

Conserved and variable correlated mutations in the plant MADS protein network

BACKGROUND

Plant MADS domain proteins are involved in a variety of developmental processes for which their ability to form various interactions is a key requisite. However, not much is known about the structure of these proteins or their complexes, whereas such knowledge would be valuable for a better understanding of their function. Here, we analyze those proteins and the complexes they form using a correlated mutation approach in combination with available structural, bioinformatics and experimental data.

RESULTS

Correlated mutations are affected by several types of noise, which is difficult to disentangle from the real signal. In our analysis of the MADS domain proteins, we apply for the first time a correlated mutation analysis to a family of interacting proteins. This provides a unique way to investigate the amount of signal that is present in correlated mutations because it allows direct comparison of mutations in various family members and assessing their conservation. We show that correlated mutations in general are conserved within the various family members, and if not, the variability at the respective positions is less in the proteins in which the correlated mutation does not occur. Also, intermolecular correlated mutation signals for interacting pairs of proteins display clear overlap with other bioinformatics data, which is not the case for non-interacting protein pairs, an observation which validates the intermolecular correlated mutations. Having validated the correlated mutation results, we apply them to infer the structural organization of the MADS domain proteins.

CONCLUSION

Our analysis enables understanding of the structural organization of the MADS domain proteins, including support for predicted helices based on correlated mutation patterns, and evidence for a specific interaction site in those proteins.

Gene networks controlling the initiation of flower development

The onset of flower formation is a key regulatory event during the life cycle of angiosperm plants, which marks the beginning of the reproductive phase of development. It has been shown that floral initiation is under tight genetic control, and deciphering the underlying molecular mechanisms has been a main area of interest in plant biology for the past two decades. Here, we provide an overview of the developmental and genetic processes that occur during floral initiation. We further review recent studies that have led to the genome-wide identification of target genes of key floral regulators and discuss how they have contributed to an in-depth understanding of the gene regulatory networks controlling early flower development. We focus especially on a master regulator of floral initiation in Arabidopsis thaliana APETALA1 (AP1), but also outline what is known about the AP1 network in other plant species and the evolutionary implications.