Heading Date Research Articles

The WD40 domain-containing protein Ehd5 positively regulates flowering in rice (Oryza sativa).

Heading date (flowering time), which greatly influences regional and seasonal adaptability in rice (Oryza sativa), is regulated by many genes in different photoperiod pathways. Here, we characterized a heading date gene, Early heading date 5 (Ehd5), using a modified bulked segregant analysis method. The ehd5 mutant showed late flowering under both short-day and long-day conditions, as well as reduced yield, compared to the wild type. Ehd5, which encodes a WD40 domain-containing protein, is induced by light and follows a circadian rhythm expression pattern. Transcriptome analysis revealed that Ehd5 acts upstream of the flowering genes Early heading date 1 (Ehd1), RICE FLOWERING LOCUS T 1 (RFT1), and Heading date 3a (Hd3a). Functional analysis showed that Ehd5 directly interacts with Rice outermost cell-specific gene 4 (Roc4) and Grain number, plant height, and heading date 8 (Ghd8), which might affect the formation of Ghd7-Ghd8 complexes, resulting in increased expression of Ehd1, Hd3a and RFT1. Taken together, these results demonstrate that Ehd5 functions as a positive regulator of rice flowering and provide insight into the molecular mechanisms underlying heading date.

Improving rice eating and cooking quality by enhancing endogenous expression of a nitrogen-dependent floral regulator.

Improving rice eating and cooking quality (ECQ) is one of the primary tasks in rice production to meet the rising demands of consumers. However, improving grain ECQ without compromising yield faces a great challenge under varied nitrogen (N) supplies. Here, we report the approach to upgrade rice ECQ by native promoter-controlled high expression of a key N-dependent floral and circadian clock regulator Nhd1. The amplification of endogenous Nhd1 abundance alters rice heading date but does not affect the entire length of growth duration, N use efficiency and grain yield under both low and sufficient N conditions. Enhanced expression of Nhd1 reduces amylose content, pasting temperature and protein content while increasing gel consistence in grains. Metabolome and transcriptome analyses revealed that increased expression of Nhd1 mainly regulates the metabolism of carbohydrates and amino acids in the grain filling stage. Moreover, expression level of Nhd1 shows a positive relationship with grain ECQ in some local main cultivars. Thus, intensifying endogenous abundance of Nhd1 is a promising strategy to upgrade grain ECQ in rice production.

LHD3 Encoding a J-Domain Protein Controls Heading Date in Rice

Heading date is one of the most important agronomic traits of rice, which critically affects rice ecogeographical adaptation, yield and quality. In this study, a late heading date 3 (lhd3) mutant was screened from the 60Co-γ irradiation mutant library. The lhd3 delayed heading date in rice under both short day and long day conditions. Map-based cloning combined with Mutmap strategy was adopted to isolate the causal LHD3 gene. The LHD3 gene encodes a DNA_J domain protein, which was ubiquitously expressed in various plant organs, and dominant expressed in stems and leaves. Subcellular localization analysis showed that LHD3 was localized to nucleus, indicating that LHD3 may interact with other elements to regulate the expression of flowering genes. The transcriptions of the heading activators Ehd1, Hd3a and RFT1 significantly decreased in the lhd3 mutant, suggesting that LHD3 may control the heading date through the Ehd1-Hd3a/RFT1 photoperiodic flowering pathway. The variation and haplotype analyses of the genomic region of LHD3 showed that there were 7 haplotypes in the LHD3 region from 4 702 accessions. The haplotypes of LHD3 can be divided into two classes: class a and class b, and the heading dates of these two classes were significantly different. Further study showed that two single nucleotide polymorphisms (SNPs), SNP10 (G2100C) in Hap II and SNP3 (C861T) in Hap VII, may be the functional sites causing early and late heading in accessions. Nucleotide diversity analysis showed LHD3 had been selected in the indica population, rather than in the japonica population. Therefore, the present study sheds light on the regulation of LHD3 on heading date in rice and suggests that LHD3 is a novel promising new target for rice molecular design and breeding improvement.

Grain yield and adaptation of spring wheat to Norwegian growing conditions is driven by allele frequency changes at key adaptive loci discovered by genome-wide association mapping

Key messageAdaptation to the Norwegian environment is associated with polymorphisms in the Vrn-A1 locus. Historical selection for grain yield in Nordic wheat is associated with TaGS5-3A and TaCol-5 loci.Grain yields in Norwegian spring wheat increased by 18 kg ha−1 per year between 1972 and 2019 due to introduction of new varieties. These gains were associated with increments in the number of grains per spike and extended length of the vegetative period. However, little is known about the genetic background of this progress. To fill this gap, we conducted genome-wide association study on a panel consisting of both adapted (historical and current varieties and lines in the Nordics) and important not adapted accessions used as parents in the Norwegian wheat breeding program. The study concerned grain yield, plant height, and heading and maturity dates, and detected 12 associated loci, later validated using independent sets of recent breeding lines. Adaptation to the Norwegian cropping conditions was found to be associated with the Vrn-A1 locus, and a previously undescribed locus on chromosome 1B associated with heading date. Two loci associated with grain yield, corresponding to the TaGS5-3A and TaCol-5 loci, indicated historical selection pressure for high grain yield. A locus on chromosome 2A explained the tallness of the oldest accessions. We investigated the origins of the beneficial alleles associated with the wheat breeding progress in the Norwegian material, tracing them back to crosses with Swedish, German, or CIMMYT lines. This study contributes to the understanding of wheat adaptation to the Norwegian growing conditions, sheds light on the genetic basis of historical wheat improvement and aids future breeding efforts by discovering loci associated with important agronomic traits in wheat.

UAV time-series imagery with novel machine learning to estimate heading dates of rice accessions for breeding

Timely monitoring of rice heading dates is essential for estimating growth status and grain yield in rice breeding. This study aims to develop a machine learning method to classify growth stages and estimate the days from sowing to initial heading (IHD) and days from sowing to full heading (FHD) of rice accessions from unmanned aerial vehicle (UAV)-based imagery. A two-year field experiment was conducted on different rice accessions, including doubled-haploid (DH) lines, early maturing F1 hybrids, and cultivars at two different locations (i.e., EXP 1 and EXP 2). A neural network, namely Res2Net50, was first used to classify the rice growth stages based on UAV RGB images. The partial least squares regression (PLSR) model was then developed to predict IHD and FHD by using canopy reflectance extracted from multispectral images. The results showed that the Res2Net50 model successfully identified five growth stages with overall accuracies of 86% and 83% in EXP 1 and EXP 2, respectively. PLSR models developed with image data after the Res2Net50 classification achieved good performances on predicting IHD and FHD with the coefficient of determination (R2) of 0.60–0.78, root mean square error (RMSE) ranging from 3.9 days to 5.1 days, and relative root mean square error (rRMSE) varied between 4% to 6%. Model validation with ten cultivars further demonstrated the capability of proposed method for IHD and FHD predictions and achieved the rRMSE of 3%-4%, which was comparable with that obtained by field inspection. Furthermore, the feasibility of the proposed method in monitoring of the rice heading dynamics was validated by EXP 2 using the model transfer. The proposed approach enables quantification of heading dates of diverse rice accessions in breeding and could be used as a high-throughput screening technique for accelerating rice breeding.

A single amino acid change led to structural and functional differentiation of PvHd1 to control flowering in switchgrass.

Switchgrass, a forage and bioenergy crop, occurs as two main ecotypes with different but overlapping ranges of adaptation. The two ecotypes differ in a range of characteristics, including flowering time. Flowering time determines the duration of vegetative development and therefore biomass accumulation, a key trait in bioenergy crops. No causal variants for flowering time differences between switchgrass ecotypes have, as yet, been identified. In this study, we mapped a robust flowering time quantitative trait locus (QTL) on chromosome 4K in a biparental F2 population and characterized the flowering-associated transcription factor gene PvHd1, an ortholog of CONSTANS in Arabidopsis and Heading date 1 in rice, as the underlying causal gene. Protein modeling predicted that a serine to glycine substitution at position 35 (p.S35G) in B-Box domain 1 greatly altered the global structure of the PvHd1 protein. The predicted variation in protein compactness was supported in vitro by a 4 °C shift in denaturation temperature. Overexpressing the PvHd1-p.35S allele in a late-flowering CONSTANS-null Arabidopsis mutant rescued earlier flowering, whereas PvHd1-p.35G had a reduced ability to promote flowering, demonstrating that the structural variation led to functional divergence. Our findings provide us with a tool to manipulate the timing of floral transition in switchgrass cultivars and, potentially, expand their cultivation range.

Estimating wheat grain yield by assimilating phenology and LAI with the WheatGrow model based on theoretical uncertainty of remotely sensed observation

Assimilating remotely sensed observation into crop model solves the model parameterization in regional scale by considering the uncertainty of observation and simulation. However, a fixed value of observation uncertainty could not describe the spatio-temporal heterogeneity of observation error. This study developed a method to estimate wheat yield in China by assimilating remotely sensed observation into WheatGrow model. A dynamic background value of WheatGrow and a theoretical uncertainty of remotely sensed observation were proposed, and a strategy assimilating phenology and LAI hierarchically was applied at county and plot scales. At the county scale, phenology was estimated using the time sequence of PlanetScope images, sowing date was estimated using one-class support vector classification, heading and maturity date were estimated using function-fitting method. The revisiting cycle of PlanetScope was used to determine the theoretical uncertainty of remotely sensed observed sowing date (RS-sowing date), while the uncertainty in RS-heading and RS-maturity dates were calculated using field measurements. LAI was estimated using Sentinel-2 images. The theoretical uncertainty of remotely sensed observed LAI (RS-LAI) was developed using a synthetic dataset. At the plot scale, RS-heading date and RS-LAI were estimated using the same method as for the county scale based on images obtained with a RedEdge-MX camera carried by drone. The results indicated that the theoretical uncertainty sufficiently estimated the trend of LAI error with canopy density. The assimilation strategies based on theoretical uncertainty relieved the error propagation caused by poor parameterization of model background value and the RS observation error in dense canopy, outperforming the results based on constant uncertainty. After hierarchical assimilation based on theoretical uncertainty, the root mean square errors of phenology, LAI and yield were 4.3 d, 0.75, and 825 kg/ha at the county scale, and 4.1 d, 0.57 and 969 kg/ha at the plot scale. These results showed that the hierarchical assimilation based on theoretical uncertainty could improve the accuracy of yield estimation.

Introducing MdTFL1 Promotes Heading Date and Produces Semi-Draft Phenotype in Rice.

Flowering time (in rice, termed the heading date), plant height, and grain number are crucial agronomic traits for rice productivity. The heading date is controlled via environmental factors (day length and temperature) and genetic factors (floral genes). TERMINAL FLOWER 1 (TFL1) encodes a protein that controls meristem identity and participates in regulating flowering. In this study, a transgenic approach was used to promote the heading date in rice. We isolated and cloned apple MdTFL1 for early flowering in rice. Transgenic rice plants with antisense MdTFL1 showed an early heading date compared with wild-type plants. A gene expression analysis suggested that introducing MdTFL1 upregulated multiple endogenous floral meristem identity genes, including the (early) heading date gene family FLOWERING LOCUS T and MADS-box transcription factors, thereby shortening vegetable development. Antisense MdTFL1 also produced a wide range of phenotypic changes, including a change in overall plant organelles that affected an array of traits, especially grain productivity. The transgenic rice exhibited a semi-draft phenotype, increased leaf inclination angle, restricted flag leaf length, reduced spikelet fertility, and fewer grains per panicle. MdTFL1 plays a central role in regulating flowering and in various physiological aspects. These findings emphasize the role of TFL1 in regulating flowering in shortened breeding and expanding its function to produce plants with semi-draft phenotypes.

Rice florigens control a common set of genes at the shoot apical meristem including the F-BOX BROADER TILLER ANGLE 1 that regulates tiller angle and spikelet development.

Rice flowering is triggered by transcriptional reprogramming at the shoot apical meristem (SAM) mediated by florigenic proteins produced in leaves in response to changes in photoperiod. Florigens are more rapidly expressed under short days (SDs) compared to long days (LDs) and include the HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T1 (RFT1) phosphatidylethanolamine binding proteins. Hd3a and RFT1 are largely redundant at converting the SAM into an inflorescence, but whether they activate the same target genes and convey all photoperiodic information that modifies gene expression at the SAM is currently unclear. We uncoupled the contribution of Hd3a and RFT1 to transcriptome reprogramming at the SAM by RNA sequencing of dexamethasone-inducible over-expressors of single florigens and wild-type plants exposed to photoperiodic induction. Fifteen highly differentially expressed genes common to Hd3a, RFT1, and SDs were retrieved, 10 of which still uncharacterized. Detailed functional studies on some candidates revealed a role for LOC_Os04g13150 in determining tiller angle and spikelet development and the gene was renamed BROADER TILLER ANGLE 1 (BRT1). We identified a core set of genes controlled by florigen-mediated photoperiodic induction and defined the function of a novel florigen target controlling tiller angle and spikelet development.

Detection of QTL for High-Temperature Tolerance in Rice Using a High-Density Bin Map

Rice is sensitive to high-temperature stress during almost all stages of growth and development. High-temperature stress has become one of the main factors restricting high yield and superior quality of rice. In this study, recombinant inbred lines (RILs) derived from an indica rice cross between two restorer lines were planted in two years. One sowing date was applied in 2019, and four sowing dates were set in 2020 according to the period of local high temperatures in recent years. Two traits closely related to high-temperature tolerance, heading date (HD), and spikelet fertility (SF) were measured. In each trial, the HD showed a bimodal distribution, whereas SF had a continuous and left-skewed distribution. QTL analysis was performed using a high-density bin map. For HD, a total of six QTL were detected. All of them correspond in position to the cloned genes, among which qHD8 in the DTH8/Ghd8 region showed the largest genetic effect. For SF, a total of eight QTL were detected. Five of them, qSF1, qSF2, qSF3.1, qSF3.2, and qSF8, showed high-temperature tolerance and had an important potential in rice breeding.

Adaptation to high latitudes through a novel allele of Hd3a strongly promoting heading date in rice.

A novel Hd3a allele strongly promoting rice heading date was identified, and it functions through florigen activation complex (FAC) and was selected during the spread of rice cultivation to high-latitude areas. Heading date is a critical agronomic trait for rice that determines the utilization of light and temperature conditions and thereby affects grain yield. Rice is a short day (SD) plant, and its photoperiodic information is processed by complex pathways and integrated by florigens to control flowering. In this study, we identified a novel allele for the florigen gene Heading date 3a (Hd3a), characterized by a C435G substitution in its coding region, by a genome-wide association study (GWAS) approach in a panel of 199 high-latitude japonica rice varieties. The C435G substitution induces plants to flower 10days earlier in high-latitude area (long day condition). Then, we mutated C435 to G in Hd3a by prime editing and found the point mutation plants flowered 12days earlier. Further molecular experiments showed the novel Hd3a protein can interact with GF14b protein and increase the expression of OsMADS14, the output gene of florigen activation complex (FAC). Molecular signatures of selection indicated that the novel Hd3a allele was selected during the process of rice cultivation expansion into high-latitude areas. Collectively, these results provide new insights into heading date regulation in high-latitude areas and advance improvements to rice adaptability to enhance crop yield.

Fine mapping and genetic analysis identified a C2H2-type zinc finger as a candidate gene for heading date regulation in wheat.

A minor-effect QTL, Qhd.2AS, that affects heading date in wheat was mapped to a genomic interval of 1.70-Mb on 2AS, and gene analysis indicated that the C2H2-type zinc finger protein gene TraesCS2A02G181200 is the best candidate for Qhd.2AS. Heading date (HD) is a complex quantitative trait that determines the regional adaptability of cereal crops, and identifying the underlying genetic elements with minor effects on HD is important for improving wheat production in diverse environments. In this study, a minor QTL for HD that we named Qhd.2AS was detected on the short arm of chromosome 2A by Bulked Segregant Analysis and validated in a recombinant inbred population. Using a segregating population of 4894 individuals, Qhd.2AS was further delimited to an interval of 0.41cM, corresponding to a genomic region spanning 1.70Mb (from 138.87 to 140.57Mb) that contains 16 high-confidence genes based on IWGSC RefSeq v1.0. Analyses of sequence variations and gene transcription indicated that TraesCS2A02G181200, which encodes a C2H2-type zinc finger protein, is the best candidate gene for Qhd.2AS that influences HD. Screening a TILLING mutant library identified two mutants with premature stop codons in TraesCS2A02G181200, both of which exhibited a delay in HD of 2-4days. Additionally, variations in its putative regulatory sites were widely present in natural accession, and we also identified the allele which was positively selected during wheat breeding. Epistatic analyses indicated that Qhd.2AS-mediated HD variation is independent of VRN-B1 and environmental factors. Phenotypic investigation of homozygous recombinant inbred lines (RILs) and F2:3 families showed that Qhd.2AS has no negative effect on yield-related traits. These results provide important cues for refining HD and therefore improving yield in wheat breeding programs and will deepen our understanding of the genetic regulation of HD in cereal plants.

Integrating biophysical crop growth models and whole genome prediction for their mutual benefit: a case study in wheat phenology.

Running crop growth models (CGM) coupled with whole genome prediction (WGP) as a CGM-WGP model introduces environmental information to WGP and genomic relatedness information to the genotype-specific parameters modelled through CGMs. Previous studies have primarily used CGM-WGP to infer prediction accuracy without exploring its potential to enhance CGM and WGP. Here, we implemented a heading and maturity date wheat phenology model within a CGM-WGP framework and compared it with CGM and WGP. The CGM-WGP resulted in more heritable genotype-specific parameters with more biologically realistic correlation structures between genotype-specific parameters and phenology traits compared with CGM-modelled genotype-specific parameters that reflected the correlation of measured phenotypes. Another advantage of CGM-WGP is the ability to infer accurate prediction with much smaller and less diverse reference data compared with that required for CGM. A genome-wide association analysis linked the genotype-specific parameters from the CGM-WGP model to nine significant phenology loci including Vrn-A1 and the three PPD1 genes, which were not detected for CGM-modelled genotype-specific parameters. Selection on genotype-specific parameters could be simpler than on observed phenotypes. For example, thermal time traits are theoretically more independent candidates, compared with the highly correlated heading and maturity dates, which could be used to achieve an environment-specific optimal flowering period. CGM-WGP combines the advantages of CGM and WGP to predict more accurate phenotypes for new genotypes under alternative or future environmental conditions.

Effect of Transplanting Date on Agronomic and Grain Quality Traits Using Early-Maturing Rice Varieties

This study aimed to investigate how transplanting date affects the agronomic and grain quality traits of two early-maturing rice varieties. The experiment was conducted in the rice research field of Chungnam Agricultural Research and Extension Services in South Korea and rice materials were transplanted at intervals of approximately 15 days from 16 April to 16 July in 2019 and 2020. Results showed that agronomic and grain quality traits varied according to the transplanting date and earlier transplanting resulted in a longer period of days from transplanting to heading (DTH). The spikelet number m−2 was highly correlated with the milled rice yield (r = 0.963 ** for Jinbuol, r = 0.909 ** for Yeoreumi) and it significantly decreased as the transplanting date was delayed, which was leading to lower yield. The mean temperature during the grain filling stage had a negative correlation with head rice rate (r2 = 0.825 ** for Jinbuol, r2 = 0.803 ** for Yeoreumi) and the number of days from transplanting to heading showed negative correlation with protein content (r2 = 0.777 ** for Jinbuol, r2 = 0.833 ** for Yeoreumi). Therefore, increasing the number of days from transplanting to heading date can lead to higher milled rice yield and lower protein content and avoiding heading dates on 17 July can improve the appearance traits. As a result, it is suggested that early transplanting is advantageous to increase the milled rice yield and grain quality of early-maturing rice.

Genome-edited HEADING DATE 3a knockout enhances leaf production in Perilla frutescens.

Environmental cues regulate the transition of many plants from vegetative to flowering development. Day length, or photoperiod, is one cue that synchronizes flowering by changing seasons. Consequently, the molecular mechanism of flowering control is prominent in Arabidopsis and rice, where essential genes like FLOWERING LOCUS T (FT) homolog, HEADING DATE 3a (Hd3a), have been connected to flowering regulation. Perilla is a nutrient-rich leaf vegetable, and the flowering mechanism remains largely elusive. We identified flowering-related genes under short-day conditions using RNA sequencing to develop an enhanced leaf production trait using the flowering mechanism in the perilla. Initially, an Hd3a-like gene was cloned from the perilla and defined as PfHd3a. Furthermore, PfHd3a is highly rhythmically expressed in mature leaves under short-day and long-day conditions. Ectopic expression of PfHd3a in Atft-1 mutant plants has been shown to complement Arabidopsis FT function, resulting in early flowering. In addition, our genetic approaches revealed that overexpression of PfHd3a in perilla caused early flowering. In contrast, the CRISPR/Cas9 generated PfHd3a-mutant perilla showed significantly late flowering, resulting in approximately 50% leaf production enhancement compared to the control. Our results suggest that PfHd3a plays a vital role in regulating flowering in the perilla and is a potential target for molecular breeding in the perilla.

Two florigens and a florigen-like protein form a triple regulatory module at the shoot apical meristem to promote reproductive transitions in rice.

Many plant species monitor and respond to changes in day length (photoperiod) for aligning reproduction with a favourable season. Day length is measured in leaves and, when appropriate, leads to the production of floral stimuli called florigens that are transmitted to the shoot apical meristem to initiate inflorescence development1. Rice possesses two florigens encoded by HEADING DATE 3a (Hd3a) and RICE FLOWERING LOCUS T 1 (RFT1)2. Here we show that the arrival of Hd3a and RFT1 at the shoot apical meristem activates FLOWERING LOCUS T-LIKE 1 (FT-L1), encoding a florigen-like protein that shows features partially differentiating it from typical florigens. FT-L1 potentiates the effects of Hd3a and RFT1 during the conversion of the vegetative meristem into an inflorescence meristem and organizes panicle branching by imposing increasing determinacy to distal meristems. A module comprising Hd3a, RFT1 and FT-L1 thus enables the initiation and balanced progression of panicle development towards determinacy.

The CCT transcriptional activator Ghd2 constantly delays the heading date by upregulating CO3 in rice

CONSTANS, CO-like, and TOC1 (CCT) family genes play important roles in regulating heading date, which exerts a large impact on the regional and seasonal adaptation of rice. Previous studies have shown that Grain number, plant height, and heading date2 (Ghd2) exhibits a negative response to drought stress by directly upregulating Rubisco activase and exerting a negative effect on heading date. However, the target gene of Ghd2 regulating heading date is still unknown. In this study, CO3 is identified by analyzing Ghd2 ChIP-seq data. Ghd2 activates CO3 expression by binding to the CO3 promoter through its CCT domain. EMSA experiments show that the motif CCACTA in the CO3 promoter was recognized by Ghd2. A comparison of the heading dates among plants with CO3 knocked out or overexpressed and double-mutants with Ghd2 overexpressed and CO3 knocked out shows that CO3 negatively and constantly regulates flowering by repressing the transcription of Ehd1, Hd3a, and RFT1. In addition, the target genes of CO3 are explored via a comprehensive analysis of DAP-seq and RNA-seq data. Taken together, these results suggest that Ghd2 directly binds to the downstream gene CO3, and the Ghd2–CO3 module constantly delays heading date via the Ehd1-mediated pathway.

Gene Mapping and Identification of a Missense Mutation in One Copy of VRN-A1 Affects Heading Date Variation in Wheat

Heading date (HD) is an important trait for wide adaptability and yield stability in wheat. The Vernalization 1 (VRN1) gene is a key regulatory factor controlling HD in wheat. The identification of allelic variations in VRN1 is crucial for wheat improvement as climate change becomes more of a threat to agriculture. In this study, we identified an EMS-induced late-heading wheat mutant je0155 and crossed it with wide-type (WT) Jing411 to construct an F2 population of 344 individuals. Through Bulk Segregant Analysis (BSA) of early and late-heading plants, we identified a Quantitative Trait Locus (QTL) for HD on chromosome 5A. Further genetic linkage analysis limited the QTL to a physical region of 0.8 Mb. Cloning and sequencing revealed three copies of VRN-A1 in the WT and mutant lines; one copy contained a missense mutation of C changed to T in exon 4 and another copy contained a mutation in intron 5. Genotype and phenotype analysis of the segregation population validated that the mutations in VRN-A1 contributed to the late HD phenotype in the mutant. Expression analysis of C- or T-type alleles in exon 4 of the WT and mutant lines indicated that this mutation led to lower expression of VRN-A1, which resulted in the late-heading of je0155. This study provides valuable information for the genetic regulation of HD and many important resources for HD refinement in wheat breeding programs.

How ambient temperature affects the heading date of foxtail millet (Setaria italica)

Foxtail millet (Setaria italica), a short-day plant, is one of the important crops for food security encountering climate change, particularly in regions where it is a staple food. Under the short-day condition in Taiwan, the heading dates (HDs) of foxtail millet accessions varied by genotypes and ambient temperature (AT). The allelic polymorphisms in flowering time (FT)-related genes were associated with HD variations. AT, in the range of 13°C-30°C that was based on field studies at three different latitudes in Taiwan and observations in the phytotron at four different AT regimes, was positively correlated with growth rate, and high AT promoted HD. To elucidate the molecular mechanism of foxtail millet HD, the expression of 14 key FT-related genes in four accessions at different ATs was assessed. We found that the expression levels of SiPRR95, SiPRR1, SiPRR59, SiGhd7-2, SiPHYB, and SiGhd7 were negatively correlated with AT, whereas the expression levels of SiEhd1, SiFT11, and SiCO4 were positively correlated with AT. Furthermore, the expression levels of SiGhd7-2, SiEhd1, SiFT, and SiFT11 were significantly associated with HD. A coexpression regulatory network was identified that shown genes involved in the circadian clock, light and temperature signaling, and regulation of flowering, but not those involved in photoperiod pathway, interacted and were influenced by AT. The results reveal how gene × temperature and gene × gene interactions affect the HD in foxtail millet and could serve as a foundation for breeding foxtail millet cultivars for shift production to increase yield in response to global warming.

QTL Mapping for Important Agronomic Traits Using a Wheat55K SNP Array-Based Genetic Map in Tetraploid Wheat

Wheat yield is highly correlated with plant height, heading date, spike characteristics, and kernel traits. In this study, we used the wheat55K single nucleotide polymorphism array to genotype a recombinant inbred line population of 165 lines constructed by crossing two tetraploid wheat materials, Icaro and Y4. A genetic linkage map with a total length of 6244.51 cM was constructed, covering 14 chromosomes of tetraploid wheat. QTLs for 12 important agronomic traits, including plant height (PH), heading date (HD), awn color (AC), spike-branching (SB), and related traits of spike and kernel, were mapped in multiple environments, while combined QTL-by-environment interactions and epistatic effects were analyzed for each trait. A total of 52 major or stable QTLs were identified, among which may be some novel loci controlling PH, SB, and kernel length-width ratio (LWR), etc., with LOD values ranging from 2.51 to 54.49, thereby explaining 2.40-66.27% of the phenotypic variation. Based on the 'China Spring' and durum wheat reference genome annotations, candidate genes were predicted for four stable QTLs, QPH.nwafu-2B.2 (165.67-166.99 cM), QAC.nwafu-3A.1 (419.89-420.52 cM), QAC.nwafu-4A.1 (424.31-447.4 cM), and QLWR.nwafu-7A.1 (166.66-175.46 cM). Thirty-one QTL clusters and 44 segregation distortion regions were also detected, and 38 and 18 major or stable QTLs were included in these clusters and segregation distortion regions, respectively. These results provide QTLs with breeding application potential in tetraploid wheat that broadens the genetic basis of important agronomic traits such as PH, HD, AC, SB, etc., and benefits wheat breeding.