Heading Date Research Articles

Interactions among the Phenological Events of Winter Wheat in the North China Plain-Based on Field Data and Improved MODIS Estimation

Identification of complete drivers for phenology changes is crucial for developing prediction models of plant phenology. In addition to climatic factors, the interaction among phenological events has recently been reported as an important driver for the phenology changes of forests, savannas, and grasslands. However, open questions remain as to whether the phenological interaction exists in agricultural ecosystems, among which winter wheat plays a vital role in feeding human beings. In this study, we investigated the interaction among the phenological events of winter wheat in the North China Plain (NCP) using both field and satellite data. Considering the large discrepancies between the existing satellite estimation and field measurements of winter wheat phenology, we first improved the MODIS-based estimation of green-up date (GUD), heading date (HD), and maturity date (MD) through a re-calibrated relative threshold method (RTM) in the NCP. The GUD, HD, and MD were accurately estimated with the mean absolute errors (MAE) and root mean squared errors (RMSE) lower than 7.5 days, compared with the RMSEs ranging from 12.0 to 36.1 days in previous studies. Then, the relationships among the GUD, HD, and MD were analyzed using the field data collected at agricultural meteorological stations. The GUD (HD) showed a significantly positive correlation with the HD (MD). Quantitatively, a one-day earlier GUD (HD) would result in an earlier HD (MD) of 0.57 days (0.60 days). Furthermore, we applied the partial correlation analysis to the improved MODIS estimation of GUD, HD, and MD to investigate their interactions by considering the simultaneous influences from climatic factors. The results showed that the HD (MD) with 85.2% (94.5%) of all winter wheat pixels presented a significantly positive correlation with the GUD (HD). Meanwhile, the GUD (HD) with 84.2% (33.3%) of the entire winter wheat area presented a significantly negative correlation with pre-season temperature. These results suggest that both the climatic factors and phenological interactions should be included in the future development of winter wheat phenology models to improve the prediction accuracies.

Studies on the Temperature Response and Critical Day-length Affecting the Heading Date of Major Cultivating Rice Varieties in Recent Korean Paddy Field

Studies on the Temperature Response and Critical Day-length Affecting the Heading Date of Major Cultivating Rice Varieties in Recent Korean Paddy Field

Evidence for rice Heading date 16 contribution to yield increase under low-nutrient conditions

ABSTRACT Breeding new rice cultivars that are tolerant to low-nutrient condition is a solution to saving the usage of commercial fertilizer. We isolated Hitomebore EMS mutant, 520-6. Seedling growth of 520-6 is tolerant to low-nutrient supply, especially to low phosphorus (low P) supply and genetic mapping revealed the existence of nonsynonymous substitution within Os03g0793500 9th exon in 520-6. Os03g0793500 is reported as Heading date 16 (Hd16)/Early flowering1 (EL1), which is related with the rice flowering pathway. Hd16/EL1 encodes a casein kinase-I protein, and phosphorylates the floral repressor Ghd7 and the rice DELLA protein Slender rice 1 (SLR1). 520-6 carries the same nonfunctional Hd16 allele to that of Koshihikari, and the parental cultivar, Hitomebore, carries the functional Hd16 allele, as with Nipponbare. mRNA accumulation of GA-biosynthesis-related gene, OsGA2ox3 was enhanced in 520-6 compared with Hitomebore, indicating that Hd16 takes a part in feedback regulation of the GA biosynthetic gene. 520-6 and near-isogenic line (NIL) with nonfunctional Hd16 allele showed heavy straw weight and panicle weight in paddy fields with low nitrogen input and no fertilizer application in Kashimadai at Miyagi prefecture and Hikone at Shiga prefecture, respectively. In addition, plants with nonfunctional Hd16 allele showed late flowering phenotype in all tested fields. These results imply that disruption of Hd16 contributes to the improvement of rice growth by positively regulating GA signaling and late flowering, which resulted in increased rice yield under low-nutrient conditions.

Control of flowering in rice through synthetic microProteins.

Photoperiod-dependent flowering in rice is regulated by HEADING DATE 1 (Hd1), which acts as both an activator and repressor of flowering in a daylength-dependent manner. To investigate the use of microProteins as a tool to modify rice sensitivity to the photoperiod, we designed a synthetic Hd1 microProtein (Hd1miP) capable of interacting with Hd1 protein, and overexpressed it in rice. Transgenic OX-Hd1miP plants flowered significantly earlier than wild type plants when grown in non-inductive long day conditions. Our results show the potential of microProteins to serve as powerful tools for modulating crop traits and unraveling protein function.

Bin-based genome-wide association analyses improve power and resolution in QTL mapping and identify favorable alleles from multiple parents in a four-way MAGIC rice population.

A whole genome bin map was developed for a MAGIC population. Association studies for heading date at bin level exhibited powerful QTL mapping and identified favorable alleles. The presumed advantages of multiparent advanced generation intercross (MAGIC) population in quantitative trait locus (QTL) mapping were not fully utilized in the previous studies in which genome-wide association studies (GWAS) were conducted at only single nucleotide polymorphism level. In this study, we genotyped a rice four-way MAGIC population of 247 F7 lines and their parents by sequencing. A total of 5934 bins with an average length of 65kb were constructed and covered 97% of the genome. The MAGIC population showed low population structure and balanced parental contributions. A bin-based GWAS for heading date identified 4 QTLs in three environments. Three major QTLs were mapped exactly to the bins where the major heading date genes DTH3, Ghd7.1 and Ghd8 were located. Multiple comparisons showed that different parental alleles had varied genetic effects. Like DTH3, the alleles of the Guichao 2/YJSM, IR34 and Cypress had larger, intermediate and no effects, respectively. Based on comparative sequencing of 8 known heading date genes undetected in this MAGIC population, only Ghd7 exhibited diverse function among parents. The failure in Ghd7 mapping was well explained by its interaction with Hd1 because Ghd7 had no effects on heading date when combined with the nonfunctional hd1 carried by all four parents. Overall, bin-based GWAS have more mapping power and higher resolution with a MAGIC population and provide favorable alleles to breeders. The use of more diversified parents is encouraged to develop a MAGIC population for detecting more QTLs for important agronomical traits.

Genome-wide association analysis of panicle exsertion and uppermost internode in rice (Oryza sativa L.)

BackgroundRice (Oryza sativa L.) yield is seriously influenced by panicle exsertion (PE) and the uppermost internode (UI) through panicle enclosure or energy transport during grain-filling stages. We evaluated the traits of PE and UI of 205 rice accessions in two independent environments and performed genome-wide association (GWAS) to explore the key genes controlling PE and UI, which could be used to improve panicle enclosure in rice breeding.ResultsIn this study, extensive genetic variation was found in both PE and UI among the 205 rice accessions, and 10.7% of accessions had panicle enclosure (PE/UI ≤ 0). Correlation analysis revealed that PE was significantly positively correlated with 1000-grain weight (1000-GW) but negatively correlated with heading date (HD), and UI was significantly positively correlated with HD but no significantly correlated with 1000-GW. A total of 22 and 24 quantitative trait loci (QTLs) were identified for PE and UI using GWAS, respectively. Eight loci for PE and nine loci for UI were simultaneously detected both in 2015 and in 2016, seven loci had adjacent physical positions between PE and UI, and ten loci for PE and seven loci for UI were located in previously reported QTLs. Further, we identified the CYP734A4 gene, encoding a cytochrome P450 monooxygenase, and the OsLIS-L1 gene, encoding a lissencephaly type-1-like protein, as causal genes for qPE14 and qUI14, and for qPE19, respectively. PE and UI were both significantly shorter in these two genes’ mutants than in WT. Allelic Hap.1/2/4 of CYP734A4 and Hap.1/2/4 of OsLIS-L1 increased PE, UI, PE/UI, and 1000-GW, but Hap.3 of CYP734A4 and Hap.3 of OsLIS-L1 reduced them. In addition, six candidate genes were also detected for four key novel loci, qPE16, qPE21, qUI1, and qUI18, that seemed to be related to PE and UI.ConclusionsOur results provide new information on the genetic architecture of PE and UI in rice, confirming that the CYP734A4 and OsLIS-L1 genes participate in PE and UI regulation, which could improve our understanding of the regulatory mechanism of PE and UI for rice breeding in the future.

Transcription factor OsNF-YB9 regulates reproductive growth and development in rice

OsNF-YB9 controls heading by affecting expression of regulators of flowering. It affects the development of the reproductive meristem by interacting with MADS1 and controlling expression of hormone-related genes. Nuclear Factor-Y (NF-Y) family of transcription factors takes part in many aspects of growth and development in eukaryotes. They have been classified into three subunit classes, namely, NF-YA, NF-YB and NF-YC. In plants, this transcription factor family is much diverged and takes part in several developmental processes and stress. We investigated NF-Y subunit genes of rice (Oryza sativa) and found OsNF-YB9 as the closest homologue of LEAFY COTYLEDON1. OsNF-YB9 delayed the heading date when ectopically expressed in rice. Expression of several heading date regulating genes such as Hd1, Ehd1, Hd3a and RFT1 were altered. OsNF-YB9 overexpression also resulted in morphological defects in the reproductive organs and led to pseudovivipary. OsNF-YB9 interacted with MADS1, a key regulator of floral development. This NF-Y subunit acted upstream to several transcription factors as well as signalling proteins involved in brassinosteroid and gibberellic acid metabolism and cell cycle. OsNF-YB9 and OsNF-YC12 interacted in planta and the latter also delayed heading in rice upon overexpression suggesting its involvement in a similar pathway. Our data provide new insights into the rice heading date pathway integrating these OsNF-Y subunit members to the network. These features can be exploited to improve vegetative growth and yield of rice plants in future.

‘Bodrami’, Mid-Maturing Brown Rice Cultivar with High Grain Quality and Soft Texture Suitable for Cooking

‘Bodrami’ is a brown rice cultivar suitable for cooking, developed by crossing ‘Hwaseong’ and ‘Congsengla’ cultivars at Rural Development Administration, Korea, in 2003. Cooked brown rice of ‘Bodrami’ naturally has a soft texture, and after 24 hours of warm treatment, it maintained its soft texture and it was evaluated that the taste and texture of cooked brown rice were better than that of another rice cultivar. ‘Bodrami’ is a mid-maturing rice cultivar. The average heading date in ordinary planting was August 11th in Suwon, Korea, which also exhibits strong to blast leaf and rice stripe virus, and brown rice yield of ‘Bodrami’ had a yield of 5.56 MT/ha in ordinary planting. The advantages of eating brown rice are high intake of GABA (which is excellent for controlling blood), γ-oryzanol (which is good for Antioxidation), rice embryos (rich in fiber), and rice bran (rich in minerals). Another advantage of ‘Bodrami’ is that, compared to glutinous rice varieties (which is a higher glycemic index), it has a lower glycemic index and a smooth texture. The consumption of white rice has been decreasing recently, while interest in brown rice has been increasing as a consequence of these advantages. ‘Bodrami’ was developed in response to recent changes in consumption preferences. (Registration No. 5644)

Identification and mapping of a photoperiod response gene (QPpd.zafu-4A) on wild emmer wheat (Triticum turgidum L.) chromosome 4AL

Heading date (HD) is an important agronomic trait, influencing directly or indirectly yield and quality traits. Previous experiments showed that the chromosome arm substitution line (CASL) 4AL of wild emmer in the background of Chinese Spring (CS) was about 18–22 days later in HD than CS. In this study, CASL4AL flowered roughly 20 days earlier than CS grown under long day (LD) with short day (SD) vernalization, but failed to flower when planted under controlled SD conditions. The above results suggest CASL4AL carries an extremely sensitive photoperiod response gene. CASL4AL showed a major difference from CS in restricted young spike development, remaining at the double-ridge stage and floret-primordium differentiation stage much longer than CS under SD. To map this gene, the F2 population from cross between CS and CASL4AL were explored in two consecutive years. In 2016, a HD related QTL flanked by M576 and wmc468 with a LOD score (8.5) was detected. In 2017, this QTL was repeatedly detected with a higher LOD score (10.03), and therefore named as QPpd.zafu-4A. A total of 27 genes were annotated and possible candidate was discussed. This work lays a foundation for map-based cloning of QPpd.zafu-4A and elucidating its molecular mechanism in affecting HD.

Automatic estimation of heading date of paddy rice using deep learning

BackgroundAccurate estimation of heading date of paddy rice greatly helps the breeders to understand the adaptability of different crop varieties in a given location. The heading date also plays a vital role in determining grain yield for research experiments. Visual examination of the crop is laborious and time consuming. Therefore, quick and precise estimation of heading date of paddy rice is highly essential.ResultsIn this work, we propose a simple pipeline to detect regions containing flowering panicles from ground level RGB images of paddy rice. Given a fixed region size for an image, the number of regions containing flowering panicles is directly proportional to the number of flowering panicles present. Consequently, we use the flowering panicle region counts to estimate the heading date of the crop. The method is based on image classification using Convolutional Neural Networks. We evaluated the performance of our algorithm on five time series image sequences of three different varieties of rice crops. When compared to the previous work on this dataset, the accuracy and general versatility of the method has been improved and heading date has been estimated with a mean absolute error of less than 1 day.ConclusionAn efficient heading date estimation method has been described for rice crops using time series RGB images of crop under natural field conditions. This study demonstrated that our method can reliably be used as a replacement of manual observation to detect the heading date of rice crops.

Characterization of phytochrome C functions in the control of de-etiolation and agronomic traits in rice

Although phytochrome A (phyA) and phyB have been functionally characterized, functions of phyC in rice growth and development have remained elusive because of the functional dependency of phyC on the phyB protein. In this study, we introduced PHYB(C364A), in which the chromophore attachment site cysteine 364 was converted to alanine, into the phyAphyB double mutant (aabb) and the phyAphyBphyC triple mutant (aabbcc) to produce PHYB(C364A)/aabb lines and PHYB(C364A)/aabbcc lines, respectively. PHYB(C364A)/aabbcc lines were insensitive to red light (R) and far-red light (FR), suggesting that PHYB(C364A) protein was biologically inactive. Functions of phyC were characterized using the PHYB(C364A)/aabb lines, without the functional interference of phyA or phyB. Phytochrome C responded to R and FR to trigger de-etiolation in the very-low-fluence response and low-fluence response in the PHYB(C364A)/aabb lines. Compared with the aabb mutant, seedlings of PHYB(C364A)/aabb lines showed higher chlorophyll content and reduced leaf angle. The PHYB(C364A)/aabb lines also showed a delayed heading date under long-day conditions. Phytochrome C-regulated agronomic traits were measured at the mature stage. The PHYB(C364A)/aabb lines showed significantly increased plant height, panicle length, grain number per main panicle, seed-setting rate, grain size, and grain weight, compared with those of the aabb mutant. Taken together, the present findings confirm that phyC perceives R and FR, and plays an important role in photomorphogenesis and yield determination in rice.

Hd1 function conversion in regulating heading is dependent on gene combinations of Ghd7, Ghd8, and Ghd7.1 under long-day conditions in rice

Ghd7, Ghd8, Ghd7.1, and Hd1 are all pleiotropic genes regulating heading date, plant height, and yield in rice. Early studies showed that Hd1 promoted heading under short-day conditions (SD) and delayed heading under long-day conditions (LD). Recent studies found that Hd1 also promoted heading in some genetic backgrounds under LD. In this study, we developed a series of near-isogenic lines for Ghd7, Ghd8, Ghd7.1, and Hd1 in the Zhenshan 97 (ZS97) and Minghui 63 (MH63) backgrounds and recorded their heading dates. In the ZS97 background, Ghd7 alone triggered the conversion of Hd1 function from promoting to suppressing heading under LD. Ghd8 alone and Ghd7.1 alone did not promote but enhanced Ghd7-mediated Hd1 function conversion. In the MH63 background, Ghd7 alone and Ghd7.1 alone did not convert Hd1 function under LD, but they jointly promoted Hd1 function conversion. Conversion of Hd1 function occurred only under LD but not SD. Transcript analysis showed that downregulation or upregulation of Ehd1 and Hd3a by Hd1 in the lines under LD was determined by genetic background. In summary, multiple gene combinations of Ghd7, Ghd7.1, and Ghd8 and unknown genes caused conversion of Hd1 function. Moreover, the different gene combinations had a big difference in photoperiod sensitivities. These findings lay a solid foundation for further unveiling the molecular mechanism of Hd1 function conversion and provide guidance for heading date improvement in rice.

Using Heading date 1 preponderant alleles from indica cultivars to breed high-yield, high-quality japonica rice varieties for cultivation in south China.

Summary Heading date 1 (Hd1) is an important gene for the regulation of flowering in rice, but its variation in major cultivated rice varieties, and the effect of this variation on yield and quality, remains unknown. In this study, we selected 123 major rice varieties cultivated in China from 1936 to 2009 to analyse the relationship between the Hd1 alleles and yield‐related traits. Among these varieties, 19 haplotypes were detected in Hd1, including two major haplotypes (H8 and H13) in the japonica group and three major haplotypes (H14, H15 and H16) in the indica group. Analysis of allele frequencies showed that the secondary branch number was the major aimed for Chinese indica breeding. In the five major haplotypes, SNP316(C‐T) was the only difference between the two major japonica haplotypes, and SNP495(C‐G) and SNP614(G‐A) are the major SNPs in the three indica haplotypes. Association analysis showed that H16 is the most preponderant allele in modern cultivated Chinese indica varieties. Backcrossing this allele into the japonica variety Chunjiang06 improved yield without decreasing grain quality. Therefore, our analysis offers a new strategy for utilizing these preponderant alleles to improve yield and quality of japonica varieties for cultivation in the southern areas of China.

Advancing crop modelling capabilities through cultivar-specific parameters sets for the Italian rice germplasm

Rice is one of the excellences of Italian agriculture, so that modern research techniques are mobilised to support farmers and local stakeholders in the main harvested areas in Northern Italy. Crop modelling is among the most prominent tools, as proved by the model-based services developed for yield forecasting and blast disease risk alert. Here we propose a methodology to obtain cultivar-specific parameters sets to improve the current crop modelling capabilities, using field observations collected on the main Italian rice cultivars. The definition of cultivar-specific parameters sets was based on the calibration of the crop model WOFOST_GT using long-term (2004–2015) experimental data collected in two sites (167 field trials). Our results proved a satisfactory accuracy in reproducing field observations of heading (average RRMSE = 5.9% ± 1.3%) and maturity date (22.6% ± 4.7%), canopy height (10% ± 1.4%), and yield (11.1% ± 4.1%) across cultivars and years. The analysis of the cultivar-specific parameters sets allowed highlighting the inter-relationships between model parameters, which revealed similarities with standard classifications of grain shape, phenological development and stem length. Our study is meant to deepen our modelling knowledge of the Italian rice varietal landscape, thus fostering future applications at different spatial and temporal resolutions.

Unraveling the genetic complexity underlying sorghum response to water availability.

Understanding the adaptation mechanisms of sorghum to drought and the underlying genetic architecture may help to improve its production in a wide range of environments. By crossing a high yielding parent (HYP) and a drought tolerant parent (DTP), we obtained 140 recombinant inbred lines (RILs), which were genotyped with 120 DArT and SSR markers covering 14 linkage groups (LGs). A subset of 100 RILs was evaluated three times in control and drought treatments to genetically dissect their response to water availability. Plants with early heading date (HD) in the drought treatment maintained yield (YLD) level by reducing seed number SN and increasing hundred seed weight (HSW). In contrast, early HD in the control treatment increased SN, HSW and YLD. In total, 133 significant QTL associated with the measured traits were detected in ten hotspot regions. Antagonistic, pleiotropic effects of a QTL cluster mapped on LG-6 may explain the observed trade-offs between SN and HSW: Alleles from DTP reduced SN and the alleles from HYP increased HSW under drought stress, but not in the control treatment. Our results illustrate the importance of considering genetic and environmental factors in QTL mapping to better understand plant responses to drought and to improve breeding programs.

Study of Variability and Genetic Diversity of 50% Heading Date and Seed Yield in Blackgram (Vigna mungo L.)

The present investigation involves study of variability and genetic diversity of few developmental characters such as date of maximum flower per plant (DMF), number of seeds per plant (NSPP) and seed weight per plant (SWPP) in blackgram (Vigna mungo L.). These three quantitative characters were studied in 24 lines and three years under different environmental conditions. The model proposed by Perkins and Jinks was followed in this study. In the analysis, greater portion of total phenotypic variation (s2p) appeared to be due to the environmental variations (s2e). The highest heritability (h2 b) (0.8181) was found for SWPP, while the highest genetic advance (G.A.=172.5508), high genetic advance of percentage (G.A.%=332.5627) and high genetic co-efficient of variability (G.C.V.=161.4381) were estimated in NSPP. The present investigation deals with the analysis of phenotypic, genotypic and environmental co-efficient of variability, range, mean with standard error, heritability (in broad sense), genetic advance and genetic advance of percentage. Genetic co-efficient of variability was very much pronounced and varied from treatment to treatment, year to year and lines to lines for all the characters, which indicates that the characters were quantitative in nature and under polygenic control. Therefore, further research would be undertaken for improving the characters of this pulse.
 South Asian J. Agric., 7(1&2): 1-5

Estimation of planting date in paddy fields by time-series MODIS data for basin-scale rice production modeling

Projection of future changes in agricultural water demand and supply through numerical model simulations can be one of the reference materials used for long-term rural planning under climate change. With a distributed hydrological model incorporating an agricultural sub-model, time-series rice growth and its yield can be simulated in correspondence with time-series soil moisture simulated by a hydrological model. Whereas such an agro-hydrological model is useful for assessing the climate change impact on agriculture in that it can simulate the potential rice production and the water-related damages on it against the given rainfall and meteorological condition, one of the challenges in simulating a realistic situation by a model is how to give a planting date in the model in regions where it is not fixed to a certain calendar date and differs in different fields and in different years. In this study, we examined an algorithm to estimate planting date in paddy fields using satellite data. The data we used are the 16-day composite Enhanced Vegetation Index (EVI) product by the moderate resolution imaging spectroradiometer (MODIS), which provides global coverage with 250-m spatial resolution. The time series of the EVI values at each pixel was analyzed first to detect heading dates as the local maxima in each year. Considering the number of days for growing rice, the existence of the second and the third rice cropping was judged from the time intervals of the local maxima. The planting dates were then estimated from the determined heading dates and local minima of the EVI time-series EVI. The estimated planting dates were validated against national statistical data in Japan and also with field-surveyed data in Cambodia. They showed reasonable estimations in the areal statistics, but there remained gaps in the comparison at individual fields.

Wild barley shows a wider diversity in genes regulating heading date compared with cultivated barley

Heading date (HD) is an important agronomic trait that influences plant adaptability to varying environment and, ultimately, grain yield. In this study, two doubled haploid (DH) populations were used to identify new QTL for HD. One of the DH populations is originated from a cross between an Australian malting barley cv. Franklin and a wild barley accession TAM407227 and the other one is from the cross between a Syrian wild barley SYR01 and an Australian malting barley cv. Gairdner. Using three times of sowing (TOS) differing in daylength and temperature, we investigated quantitative trait loci (QTL) controlling HD from both populations. Fourteen QTL were identified for HD from different populations and sowing dates. The expression of HD related genes varied with the TOS, suggesting a significant QTL × environment interaction. By comparing the positions of previously mapped HD genes and those of QTL detected in this population, we found that eleven of the fourteen QTL identified in this study were located at similar positions to those reported genes for HD. Among the three new potential QTL, one was located at 73.5 cM on chromosome 2H, explaining 19.2% and 4.6% HD of DH lines in spring and summer growing, respectively. The wild barley parent TAM407227 contributed the early maturity allele. HORVU2Hr1G088460 within the interval of QTL could be the candidate gene. The second new QTL was identified on chromosome 3H from a summer sowing trial and the third one on chromosome 4H affected HD of DH lines only under spring sowing condition. These new QTL identified will provide alternative genetic resources for plant breeders developing barley varieties with improved HD adaptability to varying environments.

Dissection of Pleiotropic QTL Regions Controlling Wheat Spike Characteristics Under Different Nitrogen Treatments Using Traditional and Conditional QTL Mapping.

Optimal spike characteristics are critical in improving the sink capacity and yield potential of wheat even in harsh environments. However, the genetic basis of their response to nitrogen deficiency is still unclear. In this study, quantitative trait loci (QTL) for six spike-related traits, including heading date (HD), spike length (SL), spikelet number (SN), spike compactness (SC), fertile spikelet number (FSN), and sterile spikelet number (SSN), were detected under two different nitrogen (N) supplies, based on a high-density genetic linkage map constructed by PCR markers, DArTs, and Affymetrix Wheat 660 K SNP chips. A total of 157 traditional QTLand 54 conditional loci were detected by inclusive composite interval mapping, among which three completely low N-stress induced QTL for SN and FSN (qSn-1A.1, qFsn-1B, and qFsn-7D) were found to maintain the desired spikelet fertility and kernel numbers even under N deficiency through pyramiding elite alleles. Twenty-eight stable QTL showing significant differencet in QTL detection model were found and seven genomic regions (R2D, R4A, R4B, R5A, R7A, R7B, and R7D) clustered by these stable QTL were highlighted. Among them, the effect of R4B on controlling spike characteristics might be contributed from Rht-B1. R7A harboring three major stable QTL (qSn-7A.2, qSc-7A, and qFsn-7A.3) might be one of the valuable candidate regions for further genetic improvement. In addition, the R7A was found to show syntenic with R7B, indicating the possibly exsting homoeologous candidate genes in both regions. The SNP markers involved with the above highlighted regions will eventually facilitate positional cloning or marker-assisted selection for the optimal spike characteristics under various N input conditions.

Early heading 7 interacts with DTH8, and regulates flowering time in rice.

EH7/Ghd7 interacts with DTH8, and regulates heading date by controlling the expression of Ehd1 in rice. Heading date, or flowering time, an important agronomic trait, influences regional adaptability and yield of crops. Many genes related to heading date in rice have been identified, and a preliminary regulatory network has been established, but the relationships between proteins involved are poorly understood. We identified a flowering suppressor EH7 (Early heading 7) that represses flowering under long-day (LD) conditions. The eh7 allele caused earlier heading, shorter plant height and less grain per main panicle than did the wild type (WT), but the tiller number and 1000-grain weight were not significantly affected under natural long-day conditions. Biochemical assays showed that EH7 interacts with DTH8. Quantitative PCR showed that EH7 inhibited heading date by downregulating the expression of Ehd1, Hd3a and RFT1. We propose that EH7 interacts with DTH8 to control flowering time by regulating the expression of Ehd1, Hd3a and RFT1.