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        The heading-date gene Ghd7 inhibits seed germination by modulating the balance between abscisic acid and gibberellins

        2021-05-06 11:02:58YongHuSongSongXiaoyuWengAiqingYouYongzhongXing
        The Crop Journal 2021年2期

        Yong Hu , Song Song , Xiaoyu Weng , Aiqing You , Yongzhong Xing ,

        a Hubei Key Laboratory of Food Crop Germplasm and Genetic Improvement, Food Crops Research Institute, Hubei Academy of Agricultural Sciences, Wuhan 430064, Hubei, China

        b National Key Laboratory of Crop Genetic Improvement and National Center of Plant Gene Research (Wuhan), Huazhong Agricultural University, Wuhan 430070, Hubei, China

        Keywords:

        ABSTRACT Seed dormancy of cultivated rice was largely weakened during the progress of domestication.Correct timing and uniformity of seed germination are important for rapid seedling establishment and highyield production.In the present study,we found that the heading-date gene Ghd7 acted as a negative regulator of germination.A mutant of ghd7 showed low sensitivity to exogenous ABA treatment during seed germination.Further investigation revealed reduced accumulation of ABA in mature ghd7 seeds as a consequence of dampened expression of OsNCED genes.Moreover,elevated GA3 level was detected in seeds of ghd7 mutant during imbibition course,which was attributed to the induction of genes responsible for the synthesis pathways of bioactive GAs.Thus,Ghd7 inhibits seed germination by increasing the ABA/GA3 ratio.Besides revealing pleiotropic effects of Ghd7,our results indicate its role in linking seed germination to growth-phase transition in rice,which would enrich the theoretical basis for future breeding practices.

        1.Introduction

        Seed dormancy is defined as the state or condition in which seeds are prevented from germinating even under optimal environmental conditions [1].Seed dormancy is an adaptation strategy for survival in unfavorable environments.Many crops, such as rice, were domesticated and selected for fast and uniform germination, followed by rapid seedling establishment, to achieve high yield [2].Therefore, an optimal germination rate is crucial for practical crop production.

        Seed germination is a complex progress affected by both environmental and endogenous signals.Two plant hormones, abscisic acid (ABA) and gibberellins (GAs), have been extensively studied and play key roles in germination.ABA negatively regulates seed germination by inducing and maintaining dormancy.ABA accumulation is low in developing seeds in early stages.In the cultivar Zhonghua 11 (ZH11) it reached a maximum at 25–30 days after pollination, declining as the seed underwent maturation and drying [3,4].ABA-deficient lines caused by mutation of the gene encoding 9-cis-epoxycarotenoid dioxygenase (NCED), which catalyzes a key step of ABA biosynthesis, showed faster germination than the wild type (WT) [5].Similarly, aTos17-transposoninduced mutant defective inOsTATC, encoding a zeaxanthin epoxidase (ZEP, another key enzyme in the ABA-synthetic pathway)showed a viviparous seed phenotype [6].Increased ABA content resulting from constitutive expression of the ABA biosynthesis geneNCED6strongly suppressed the germination ofArabidopsisseeds [7,8].ABA synthesis during seed development led to lasting dormancy, whereas maternal ABA or exogenous ABA application during seed development was not sufficient for dormancy induction[9].ABA catabolism was accompanied by promotion of germination or dormancy release [10].CYP707Afamily members(CYP707A1toCYP707A4) encoding ABA 8′-hydroxylases inArabidopsiswere the key catabolic enzymes in ABA metabolism.cyp707a1andcyp707a2mutants both showed increases in ABA levels in dry and imbibed seeds, inhibiting germination.These studies demonstrated the key roles of ABA catabolism in control of seed germination.

        In contrast,plant hormone GAs play opposite roles in seed dormancy, promoting seed germination [11,12].Gibberellins stimulate germination by inducing hydrolytic enzymes that weaken barrier tissues such as endosperm and seed coat, inducing mobilization of seed storage reserves and stimulating embryo expansion[13].GA-deficient mutants, such asga1(encoding copalyl synthase),andga2(encodingent-kaurene synthase)show strong seed dormancy and fail to germinate without exogenous GA treatment[14,15].A GA-synthesis geneOsGA20ox2was proposed[16]to regulate germination rates by influencing accumulation of GA in rice seeds.By contrast, mutants ofGA2 oxidase(GA2ox) that deactivate bioactive GAs display lower dormancy and a faster germination phenotype [17].In a recent study [18]in rice, the miR156 target geneIdeal Plant Architecture 1affected seed dormancy by directly regulating multiple genes,OsCPS1,KAO,KO2,SD1, andGNP1, involved in GA synthesis.Though these studies shed light on the function of single plant hormones in seed dormancy, increasing evidence has shown that dynamic changes in, and the balance between, ABA and GA critically affect dormancy in seeds [2,19].In maize, an appropriate ABA/GA ratio was necessary for suppression of germination and induction of maturation [20].

        InArabidopsis, the temperature experience of the mother plant activated the expression ofFlowering Locus T(FT) and thus influenced the germination of progeny seeds [21].Further investigation showed thatFTregulated seed dormancy viaFlowering Locus C(FLC) gene expression and regulated the chromatin state by activating antisenseFLCtranscription [22].However, in a different study [23],FLCregulated seed germination by influencing the expression ofCYP707A2andGA20ox1, thus affecting the ABA catabolic and GA biosynthesis pathways.Despite these differing findings, the flowering-time genesFLCandFTlinked two key events in the plant life: seed germination and vegetative-toreproductive phase transition.

        Grain number, plant height and heading date 7(Ghd7) was first identified [24]as a pleiotropic gene regulating heading date, plant height, and grain yield.Further investigation [25]revealed that it was involved in the regulation of multiple processes, including hormone metabolism and stress response.Faster seed germination was consistently observed in theghd7mutant than in the wild type (WT) in our annual field experiments, motivating us to investigate the effect ofGhd7on seed germination.Here, we confirm thatGhd7is associated with seed germination and found thatGhd7suppressed seed dormancy by modulating the balance of ABA and GA via regulation of their biosynthesis and catabolism.

        2.Materials and methods

        2.1.Plant materials and growing conditions

        Aghd7mutant with a G-to-A substitution in the coding region in cultivar Zhonghua 11 (ZH11,Oryza sativaL.ssp.japonica, as WT) resulting in a premature stop codon was generated in our pre-vious study [26].The rice plants were cultivated in the field in Wuhan (Huazhong Agricultural University, 3028′N, 11421′E).The mutantghd7flowered about 10 days earlier than ZH11.For comparison of fresh seeds, ZH11 was planted earlier thanghd7to ensure that they would flower on similar dates.Florets on panicles with the same heading date were marked on the day of pollination.Grains described by days after pollination (DAP) were used for specific experiments.

        2.2.Germination rate measurement and plant hormone treatments

        Fresh seeds were harvested, immediately soaked in water, and placed in a growth chamber at 30in the dark.Germination was scored visually when the radicle was ≥1 mm in length [27].Germination was recorded each day for 15 days.For ABA and GA3treatments, freshly harvested seeds were dried at 30for three days and then treated with indicated reagents.Germination rates were recorded each day for six days.

        2.3. Seed imbibition and sampling

        Fresh seeds were soaked in water and placed in darkness at 30.Seeds with indicated times of imbibition were collected and dried with tissue paper, quickly frozen in liquid nitrogen, and stored at -80for further use.

        2.4. RNA extraction from rice seeds

        RNA extraction of rice seeds followed a published protocol [28,29]with some modifications.Briefly, seeds at different devel-opmental stages or different imbibition states were ground to fine powder with a mortar and pestle in liquid nitrogen and transferred to a RNase-free tube containing 400 μL of RNA extraction buffer (100 mmol L-1Tris-HCl (pH 9.0), 2% β-ME(v/v)), then mixed thoroughly in a vortexer.A volume of 20 μL of 20% SDS was added into the suspension, which was inverted gently and centrifuged at 12,000×gfor 10 min at 4.The supernatant was transferred to a new tube containing 0.8 mL of TRIzol (TransGen Biotech, Bei-jing, China) and mixed thoroughly.RNA in the mixture was extracted with chloroform and precipitated with isopropanol fol-lowing the manufacturer’s instructions.

        2.5. Expression analysis with reverse transcription quantitative PCR

        For reverse transcription quantitative PCR (RT-qPCR), first-strand cDNA was synthesized using M-MLV reverse transcriptase (Invitrogen), and qPCR was then performed using gene-specific primers, SYBR Master Mix reagent (Roche) on a Quant-Studio 6 Flex Real-Time PCR System (Life Science), according to the manufacturer’s instructions.The PCR conditions were as follows: 10 min at 95followed by 40 cycles of 10 s at 95and 30 s at 60.PCR amplifications were performed for three independent biologi-cal replicates for each sample, and a rice ubiquitin gene (Os02g0161900) was used for normalization.Gene-specific primers are described in Table S1.

        2.6. Plant hormone measurement

        Samples of 50–100 mg were ground into fine powder and mixed with 4 mL of 99:1 isopropanol:glacial acetic acid (v/v) containing 20 ng of each deuterium-labeled internal standard ([2H2]GA3and [2H6]ABA), and placed on a shaker at 300 rpm in 4in the dark for 24 h.The samples were then centrifuged at 290×gfor 10 min and the supernatant was transferred to a clean tube.The pellets were resuspended in 500 μL of the extraction buffer and centrifuged for 10 min, and the supernatant was combined with the initial extract.The extract was then passed through a C18 Sep-Pak column which had been equilibrated with 4 mL of 100%methanol followed by 4 mL of extraction buffer.The column was rinsed with 500 μL of 80% methanol acidified with 1% glacial acetic acid.The purified extract was dried with nitrogen gas and reconsti-tuted with 200 μL of 100% methanol at 4in the dark for 16 h, followed by centrifugation at 13,000×gfor 10 min.The super-natant was transferred into the HPLC vials and subjected to liquid chromatography–mass spectrometry (LC-MS) analysis on a SCIEX-6500QTRAP LC/MS/MS system, equipped with an ESI Turbo Ion-Spray interface.

        3.Results

        3.1. Germination phenotype and responses to plant hormones ABA and GA of ghd7 seeds

        To investigate germination rate, fresh seeds were harvested 30 DAP and immediately used for germination assay.Seeds of theghd7mutant displayed significantly higher germination rates than that of the WT throughout the germination course (Fig.1A–C).Considering the close relationships betweenGhd7and plant hormones [25], and the important roles of ABA and GA in regulation of seed germination [19,30], we investigated the response ofghd7seeds to exogenous treatment of 10 μmol L-1ABA and 500 μmol L-1GA.Exogenous ABA treatment strongly inhibited germination of WT seeds especially during the fifth to seventh days of imbibition, when the difference in germination rates between ABA treatment and control (water treatment) maximized to about 30%.The germination ofghd7seeds was inhibited by ABA after 2 h of imbibition (P= 0.02,t-test).However, thereafter the difference between ABA treatment and its control was not statistically significant (P> 0.05) although the mean germination rate of ABA treatedghd7seeds was lower than that of the control.Thus, ABA treatment enlarged the difference of germination rate between theghd7mutant and WT (Fig.2A).Furthermore, we tested the responses of seeds to GA3, the most abundant bioactive GA in rice seeds [18].As expected, GA3markedly accelerated the germination of WT seeds, whereas that of theghd7mutant was similar (P> 0.05) between GA3-treated and untreated controls at all tested time points (Fig.2B).Thus, seeds ofghd7were less sensitive to ABA than the WT and were insensitive to GA3treatment.

        Fig.1.Different germination phenotypes between WT (ZH11) and the ghd7 mutant.(A and B) Germination phenotypes of fresh seeds harvested 30 days after germination (DAP) of WT (A) and the ghd7 mutant (B) at 28 °C in the dark.(C) Comparison of dynamic germination rates between WT and ghd7 in a period of 15 days.Values are mean ± standard error of mean (SEM) of three replicates.

        3.2. Ghd7 increased ABA accumulation during seed development

        To investigate the relationship betweenGhd7and plant hormone ABA, we measured the ABA levels in freshly harvested seeds.Markedly less ABA was accumulated in seeds of theghd7mutant than in those of the WT at 30 DAP (Fig.3A) when ABA accumulation reached its maximum in ZH11 [3].The differing contents of ABA could be attributed to differing expression of genes involved in the synthesis pathway.To investigate this hypothesis, expression levels of fiveOsNCEDgenes encoding 9-cis-epoxycarotenoid dioxygenases in rice [31,32]were evaluated in seeds at three development stages: 5, 15, and 30 DAP.As expected, expression levels ofOsNCED3andOsNCED5both showed significant reductions in seeds ofghd7at 15 and 30 DAP (Fig.3C and E), whereasOsNCED4showed significant differences only at 30 DAP (Fig.3D).No difference inOsNCED1was detected at any of the development stages (Fig.3B).To get further insight of the dynamic changes of ABA, we analyzed the ABA content during the progress of seed imbibition.ABA content gradually declined as imbibition time increased in both genotypes, with that inghd7mutant slightly but significantly lower than that in the WT after 12 h of imbibition.But the differences in contents betweenghd7and WT decreased steadily thereafter at 24-h, 48-h and 96-h (Fig.4A) withghd7seeds showing lower rates of ABA reduction (Fig.4A).The expression levels of three ABA 8′-hydroxylase genes (ABA8ox1,2, and3) controlling the key steps of ABA catabolism [32,33]were measured during the imbibition course.Significantly suppressed expression ofOsABA8ox2at 96-h andOsABA8ox3after 12 h of imbibition was found inghd7seeds compared with that of WT (Fig.4B–D), which is consistent with the lower rate of reduction of ABA content inghd7seeds (Fig.4A).Together, these results demonstrated the involvement ofGhd7in the regulation of ABA content in seeds via both ABA synthesis and catabolism.

        3.3. GA3 accumulated to higher levels in ghd7 mutant seeds during imbibition

        To investigate the involvement of GAs in regulation of germina-tion ofghd7seeds, we compared GA3contents in seeds ofghd7and WT during the imbibition course.The GA3level showed no signif-icant difference in seeds at 30 DAP (Fig.5A).During the imbibition course, fluctuations of GA3levels were observed in bothghd7and WT seeds (Fig.5B).GA3levels peaked at around 48-h in WT seeds, but were low inghd7seeds.(Fig.5B).To investigate the regulatory mechanisms, we measured the expression profiles of corresponding genes responsible for the biosynthesis of GA3.During the developing stages (0–30 DAP),KO2,KAO,GA20ox2, andGA20ox4showed similar expression patterns with peaks at 15 DAP, and the level ofGA20ox3was undetected (Fig.5C–G).No differences in the expression of these genes were detected betweenghd7and WT, except for a lower level ofKO2in seeds ofghd7at 15 DAP.In the course of imbibition, expression of these genes was relatively low in the first 6–12 h, and gradually increased thereafter (Fig.5C–G).Compared with WT, seeds of theghd7mutant displayed lower expression ofKAOandGA20ox4at 12 h of imbibition, but significantly higher expression ofKO2(48, 72, and 96 h),KAO(48, 72, and 96 h),GA20ox1(24, 48, and 72 h) andGA20ox2(48 and 96 h)(Fig.5C–G), in correspondence with the higher level of GA3inghd7seeds (Fig.5B).

        Fig.2.Germination dynamics of WT and ghd7 mutant under abscisic acid (ABA) and gibberellin 3 (GA3) treatment.Germination rates of dried seeds of WT and ghd7 mutant treated with 10 μmol L-1 of ABA (A) and 500 μmol L-1 of GA3 (B) at 28 °C in the dark.Germination rates were recorded each day for 7 days.Values are shown as mean ± SEM of three replicates.

        Fig.3.Measurement of ABA levels and expression of genes involved in biosynthesis of ABA.(A) ABA levels in fresh seeds at 30 DAP of WT and ghd7 mutant by liquid chromatography–mass spectrometry (LC-MS).Values are mean ± SEM of three replicates.(B–E) Expression of genes encoding the 9-cis-epoxycarotenoid dioxygenase(OsNCED), which catalyzes the key step of ABA biosynthesis in seeds, at 5, 15, and 30 DAP.Expression of OsNCED2 was undetectable.Values are mean ± SEM of three replicates, and a rice ubiquitin gene (Os03g0234200) was used for normalization.*, P <0.05; **, P <0.01, t-test.

        Fig.4.ABA content and expression of genes involved in ABA catabolism during seed imbibition in WT and ghd7 mutant.(A)ABA content dynamics in imbibed seeds of WT and ghd7 mutant by LC-MS analysis.Values are mean ± SEM of three replicates.(B–D) Expression of genes encoding ABA 8′-hydroxylase, which deactivates the ABA molecule in seeds, at 3, 6, 12, 24, 48, 72, and 96 h of imbibition.Values are mean ± SEM of three replicates, and a rice ubiquitin gene (Os03g0234200) was used for normalization.*, P <0.05; **, P <0.01, t-test.

        Unlike genes of GA synthesis,OsGA2oxgenes responsible for GA catabolism showed a more complicated expression profile during seed imbibition.Relative lower expression levels ofOsGA2ox1(12 h),OsGA2ox2(3 h and 6 h) andOsGA2ox3(12 h) were detected in theghd7mutant at the beginning of imbibition, whereasOsGA2ox3showed higher expression at 72 h and 96 h in seeds ofghd7(Fig.6A–C).The expression of the GA signaling geneOsGAMYB, which reflects the capability of endosperm starch degradation and germination [34,35], showed relatively low levels during the seed developing period and the first 6 h of imbibition and increased to constant steady levels during the rest of the imbibition course.In agreement with the observation of higher GA3content inghd7seeds,OsGAMYBexpression was significantly higher inghd7than in the WT (Fig.6D).Taken together, these results demonstrated thatghd7mutation increased GA3levels in the imbibition process.

        Fig.5.GA3 levels and expression of genes in biosynthesis pathway of bioactive GAs during seed development and seed imbibition in WT and ghd7 mutant.(A–B)GA3 levels in fresh seeds at 30 DAP (A) and dynamic changes in imbibed seeds (B) of WT and ghd7 mutant by LC-MS analysis.Values are mean ± SEM of three replicates.(C–G)Expression of genes involved in the biosynthesis pathway that includes KO2, KAO and GA20ox family members during seed development stage (5, 15, and 30 DAP) and imbibition course.Dotted lines separate the developing stages and imbibition course.Expression of GA20ox3 is undetectable.Values are mean±SEM of three replicates,and a rice ubiquitin gene (Os03g0234200) was used for normalization.*, P <0 0.05; **, P <0.01, t-test.

        3.4. Dynamic changes in ABA/GA ratio controlled by Ghd7

        The ABA/GA ratio is critical for the maintenance and release of dormancy [1,19].Generally, the ABA/GA ratios of both WT andghd7mutant declined as the time of imbibition increased, with a peak at 24 h (Fig.7).The highest ABA/GA ratio in WT was detected at the beginning of imbibition (12 h) (Fig.7), which was consistent with the lower germination rate in WT (Fig.1C).This result suggested thatGhd7modulated the ABA/GA3ratio to regulate seed germination rate.

        Fig.6.Expression of OsGA2ox members and OsGAMYB.(A–C)Expression of OsGA2ox members encoding GA2-oxidases catalyzing the deactivation step of GA catabolism in the imbibition course of seeds.(D)Comparison of expression levels of OsGAMYB in developing seeds and seed imbibition course.Dotted lines separate developing stages and imbibition course.Values are mean ± SEM of three replicates, and a rice ubiquitin gene (Os03g0234200) was used for normalization.*, P <0.05; **, P <0.01, t-test.

        Fig.7.Comparison of ABA/GA3 ratio between seeds of ghd7 and WT during the time course of imbibition.

        4.Discussion

        ABA and GA are major players in the regulation of seed dormancy and germination [36].Numerous studies have shed light on the roles of genes responsible for the synthesis and catabolism of both plant hormones [32].Both the accumulation and the turnover of ABA play key roles in seed germination [19,30].

        ABA accumulation in seeds of variety ZH11 was characterized during the entire progress of seed development, revealing one peak of ABA level at 25–30 DAP [3].Exactly in this developing stage, our results indicated that mutation ofghd7significantly reduced the accumulation of ABA in the seeds (Fig.3A), which was attributed to the impaired expression ofOsNCEDfamily genes (Fig.3C–E).The striking reduction of ABA in bothghd7and WT seeds during imbibition(Fig.4A)indicates that catabolism played the dominant role in the regulation of ABA content in this process.Slower catabolism inghd7seeds, represented by lower expression ofOsABA8ox2at 96-h (Fig.4C) andOsABA8ox3at 12-h (Fig.4D), may have slowed the reduction of ABA content, resulting finally in levels comparable to those of the WT (24-h to 96-h, Fig.4A).Multiple ABA-responsive elements (ABRE) were identified within 1 kb upstream ofGhd7, and expression ofGhd7was repressed by ABA treatment [25].Thus, the alteration of ABA content may reversely change the expression ofGhd7,in a form of feedback regulation circuit.Germination capacity was also negatively correlated with sensitivity of seeds to ABA[2].Seeds of rice plants overexpressingPYL/RCAR5showed hypersensitivity to ABA and delayed germination[37].In the present study,theghd7mutant exhibited low sensitivity to ABA treatment (Fig.2A).Thus, low ABA content and lower sensitivity together contributed to the higher germination rate ofghd7seeds.

        In contrast to the effect of ABA,the accumulation of GAs is associated with the promotion of rice germination [19,30].Apart from its effects on ABA accumulation,Ghd7did not affect GA3levels in the seed development stage(Fig.5A),but dampened its accumulation during the imbibition course (Fig.5B), which could be explained by the diminution of expression ofKO2,KAO,GA20ox1,GA20ox2,andGA20ox3,genes responsible for synthesis of bioactive GA in the later stages of imbibition (Fig.5C–F).However,KAO,GA20ox1, andGA20ox4at 12 h of imbibition were more highly expressed in WT than inghd7.This difference may not have influenced the final GA content,given that their expression levels were far lower at 12 h than at later time points(Fig.5D, E,G).Although both repression (OsGA2ox1at 12 h,OsGA2ox2at 3 h and 6 h andOsGA2ox3at 12 h) and activation (OsGA2ox3at 72 h and 96 h) of catabolic genes of GAs byGhd7were observed (Fig.6A–C),significant inhibition of GA signal transduction represented by the marker geneOsGAMYBwas detected (Fig.6D).Thus, by regulation of the accumulation of ABA and GA3at different stages,Ghd7increased the ABA/GA3ratio (Fig.7), in turn slowing seed germination.

        The contents of GA3decreased in the first 24 h of imbibition and then peaked at 48 h.These results are consistent with those of a previous study [3]in which the same cultivar, ZH11, was used as the experimental material.But the content of GA3and the expression of GA3synthesis-related genes did not follow the same time course, owing possibly to the time delay between gene expression and protein synthesis [38,39].The relatively high expression ofKO2,KAO, andGA20ox4during seed development (5–30 DAP)(Fig.5C, D, G) may have contributed to the accumulation of GA3in mature seeds (Fig.5A).This GA3pre-accumulated before maturing decreased in the first 24 h of imbibition, owing possibly to the relatively high expression ofOsGA2ox2(Fig.6B), which deactivates bioactive GA3.Thereafter, thede novosynthesis of GA3followed from the increased expression ofKO2,KAO,GA20ox1, andGA20ox2, leading to the reduction of the ABA/GA3ratio.

        Ghd7was first identified as a quantitative trait locus for heading date, plant height, and grain yield [24], and further characterized as a central regulator of growth, development, and stress response [25].In the present study,Ghd7acted as a regulator of germination, the first stage of the plant life cycle.Similarly, the pleiotropic geneIdeal Plant Architecture 1(IPA1) which regulated plant architecture, and panicle size, and grain yield was recently reported [18]to modulate seed dormancy via direct regulation of multiple genes in the GA pathway.Together with our finding ofGhd7, these results provide further evidence that the mechanism of pleiotropy is the involvement of a single molecular function in multiple biological processes [40].

        Plants sense environmental changes and adjust their growth rate to maximize their fitness.Flowering-time genes controlling germination have also been reported inArabidopsis[21].Flowering Locus T, the florigen gene, was shown to be a messenger transducing maternal past temperature experience and controlling seed dormancy.In rice,Ghd7functions as a strong suppressor of heading date under long daylength conditions [24,41].Abundant natural variations in the loci ofGhd7result in a wide range of heading date in different cultivars [24].Cultivars carrying functional alleles ofGhd7with late heading date are preferred in low latitudes, while those carrying weak and null alleles with short vegetative stage are cultivated predominantly in northern areas with long day length conditions [24].Considering the effect ofGhd7on germination phenotype in this study (Fig.1A–C), we speculate that functionalGhd7also has the effect of preventing seed germination under the relatively hot and humid environment suitable for germination in low latitudes.In contrast, the relatively cold and dry environment in northern cultivation areas is sufficient to inhibit germination even if cultivars grown in those areas carry weak or null alleles ofGhd7.Thus, our results reveal the role ofGhd7in linking two key events in the plant life cycle, seed germination to growth-phase transition in rice, and enrich the theoretical basis for future breeding practice.

        CRediT authorship contribution statement

        Yongzhong Xing conceived the study.Xiaoyu Weng and Yongzhong Xing designed the experiments.Yong Hu and Song Song performed the experiments.Yongzhong Xing and Aiqing You supervised the study.Yongzhong Xing, Yong Hu, and Song Song wrote the manuscript.

        Declaration of competing interest

        The authors declare that they have no known competing finan-cial interests or personal relationships that could have appeared to influence the work reported in this paper.

        Acknowledgments

        This work was supported by the National Key Research and Development Program of China (2017YFD0100406) and China Postdoctoral Science Foundation (2019M652606).

        Appendix A.Supplementary data

        Supplementary data for this article can be found online at https://doi.org/10.1016/j.cj.2020.09.004.

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