Mapping quantitative trait loci controlling seed dormancy and heading date in rice, Oryza sativa L., using backcross inbred lines

 To detect quantitative trait loci (QTLs) controlling seed dormancy, 98 BC₁F₅ lines (backcross inbred lines) derived from a backcross of Nipponbare (japonica)/Kasalath (indica)//Nipponbare were analyzed genetically. We used 245 RFLP markers to construct a framework linkage map. Five putative QTLs affecting seed dormancy were detected on chromosomes 3, 5, 7 (two regions) and 8, respectively. Phenotypic variations explained by each QTL ranged from 6.7% to 22.5% and the five putative QTLs explained about 48% of the total phenotypic variation in the BC₁F₅ lines. Except for those of the QTLs on chromosome 8, the Nipponbare alleles increased the germination rate. Five putative QTLs controlling heading date were detected on chromosomes 2, 3, 4, 6 and 7, respectively. The phenotypic variation explained by each QTL for heading date ranged from 5.7% to 23.4% and the five putative QTLs explained about 52% of the total phenotypic variation. The Nipponbare alleles increased the number of days to heading, except for those of two QTLs on chromosomes 2 and 3. The map location of a putative QTL for heading date coincided with that of a major QTL for seed dormancy on chromosome 3, although two major heading-date QTLs did not coincide with any seed dormancy QTLs detected in this study. Received: 10 October 1997 / Accepted: 12 January 1998     

Novel QTLs for photoperiodic flowering revealed by using reciprocal backcross inbred lines from crosses between japonica rice cultivars

The rice japonica cultivars Nipponbare and Koshihikari differ in heading date and response of heading to photoperiod (photoperiod sensitivity). Using simple sequence repeat (SSR) and single nucleotide polymorphism (SNP) markers, we conducted quantitative trait locus (QTL) analyses for heading date in a set of reciprocal backcross inbred lines (BILs) from crosses between Nipponbare and Koshihikari. Under natural-day conditions, transgressive segregation in days to heading (DTH) toward both early and late heading was observed in both BIL populations. QTL analyses revealed that two QTLs-on chromosomes 3 and 6-were involved in the difference in heading date between the parental cultivars. The Nipponbare allele at the QTLs on chromosomes 3 and 6 showed, respectively, increasing and decreasing effects on DTH in both BIL populations. The transgressive segregation observed in the BILs could be accounted for mainly by the complementary action of a set of alleles with opposing effects. Both QTLs were finely mapped as single Mendelian factors in secondary mapping populations (BC(2)F(2) plants/BC(2)F(3) lines). The QTL on chromosome 3 was mapped in the 1,140-kb interval between 94O03-4 (SSR) and OJ21G19-4 (SNP) and was designated Hd16. The QTL on chromosome 6 was mapped in the 328-kb interval between P548D347 (SSR) and 0007O20 (SSR) and was designated Hd17. Both Hd16 and Hd17 were involved in photoperiod sensitivity, as revealed by observation of the DTH of nearly isogenic lines of Nipponbare under short- and long-day conditions, suggesting that allelic differences in both Hd16 and Hd17 account for most of the difference in photoperiod sensitivity between the parental cultivars.     

Identification of quantitative trait loci associated with rice eating quality traits using a population of recombinant inbred lines derived from a cross between two temperate japonica cultivars

Improved eating quality is a major breeding target in japonica rice due to market demand. In this study, we performed genetic analysis to identify quantitative trait loci (QTLs) that control rice eating quality traits using 192 recombinant inbred lines (RILs) derived from a cross between two japonica cultivars, 'Suweon365' and 'Chucheongbyeo'. We evaluated the stickiness (ST) and overall evaluation (OE) of cooked rice using a sensory test, the glossiness of cooked rice (GCR) using a Toyo-taste meter, and measured the amylose content (AC), protein content (PC), alkali digestion value (ADV), and days to heading (DH) of the RILs in the years 2006 and 2007. Our analysis revealed 21 QTLs on chromosomes 1, 4, 6, 7, 8, and 11. QTLs on chromosomes 6, 7, and 8 were detected for three traits related to eating quality in both years. QTLs for ST and OE were identified by a sensory test in the same region of the QTLs for AC, PC, ADV, GCR and DH on chromosome 8. QTL effects on the GCR were verified using QTL-NILs (near-isogenic lines) of BC(3)F(4-6) in the Suweon365 background, a low eating quality variety, and some BC(1)F(3) lines. Chucheongbyeo alleles at QTLs on chromosomes 7 and 8 increased the GCR in the NILs and backcrossed lines. The QTLs identified by our analysis will be applicable to future marker-assisted selection (MAS) strategies for improving the eating quality of japonica rice.     

Uncovering of major genetic factors generating naturally occurring variation in heading date among Asian rice cultivars

To dissect the genetic factors controlling naturally occurring variation of heading date in Asian rice cultivars, we performed QTL analyses using F₂ populations derived from crosses between a japonica cultivar, Koshihikari, and each of 12 cultivars originating from various regions in Asia. These 12 diverse cultivars varied in heading date under natural field conditions in Tsukuba, Japan. Transgressive segregation was observed in 10 F₂ combinations. QTL analyses using multiple crosses revealed a comprehensive series of loci involved in natural variation in flowering time. One to four QTLs were detected in each cross combination, and some QTLs were shared among combinations. The chromosomal locations of these QTLs corresponded well with those detected in other studies. The allelic effects of the QTLs varied among the cross combinations. Sequence analysis of several previously cloned genes controlling heading date, including Hd1, Hd3a, Hd6, RFT1, and Ghd7, identified several functional polymorphisms, indicating that allelic variation at these loci probably contributes to variation in heading date. Taken together, the QTL and sequencing results indicate that a large portion of the phenotypic variation in heading date in Asian rice cultivars could be generated by combinations of different alleles (possibly both loss- and gain-of-function) of the QTLs detected in this study.     

上位性和QTL×环境互作对水稻(Oryza sativa L.)抽穗期的影响

水稻抽穗期是重要的农艺性状之一,对水稻品种的地理分布和适应性起到关键性作用。适宜的抽穗期是获得高产的前提。因此确定水稻抽穗期的遗传基础在育种计划中具有重要的意义。本研究用一套来源于亲本IR64/Azucena的双单倍体(DH)群体在两个种植季节的试验资料,用基于混合线性模型的复合区间作图方法,对水稻抽穗期QTL的加性、上位性及其与环境互作效应进行了研究。结果表明共有14个QTL影响水稻抽穗期,它们分布在除第5和第9条染色体外的10条染色体上,有8个位点携带单位点效应,5对位点携带双位点互作效应,2个单位点和1对双位点存在与环境的互作,所有效应值介于1.179～2.549天之间,相应的贡献率为1.04%～4.84%。基于所估算的QTL效应值,本研究预测了两个亲本和两个极端型品系的遗传效应值,并讨论了影响遗传效应值与实际观测值偏差的可能原因,以及研究群体所具有的遗传潜力。对水稻抽穗期QTL的定位结果与前人研究基本一致,并进一步证实了上位性和QE互作效应是水稻抽穗期的重要遗传基础。     

上位性和QTL×环境互作对水稻(Oryza sativa L.)抽穗期的影响

水稻抽穗期是重要的农艺性状之一,对水稻品种的地理分布和适应性起到关键性作用。适宜的抽穗期是获得高产的前提。因此确定水稻抽穗期的遗传基础在育种计划中具有重要的意义。本研究用一套来源于亲本IR64/Azucena的双单倍体（DH）群体在两个种植季节的试验资料,用基于混合线性模型的复合区间作图方法,对水稻抽穗期QTL的加性、上位性及其与环境互作效应进行了研究。结果表明共有14个QTL影响水稻抽穗期,它们分布在除第5和第9条染色体外的10条染色体上,有8个位点携带单位点效应,5对位点携带双位点互作效应,2个单位点和1对双位点存在与环境的互作,所有效应值介于1.179～2.549天之间,相应的贡献率为1.04%～4.84%。基于所估算的QTL效应值,本研究预测了两个亲本和两个极端型品系的遗传效应值,并讨论了影响遗传效应值与实际观测值偏差的可能原因,以及研究群体所具有的遗传潜力。对水稻抽穗期QTL的定位结果与前人研究基本一致,并进一步证实了上位性和QE互作效应是水稻抽穗期的重要遗传基础。     

普通野生稻中增产相关QTL的发掘

普通野生稻(Oryza Rufipogon)是重要的遗传资源,发掘其优良等位基因将对水稻遗传改良产生重要影响。文章从以珍汕97为轮回亲本,普通野生稻为供体的BC2F1群体中选择一个与珍汕97表型明显不同的单株BC2F1-15,经过连续自交获得回交重组自交系BC2F5群体。均匀分布于12条染色体的126个多态性SSR(Simplesequence repeats)标记基因型分析,发现BC2F1-15单株在30%的标记位点为杂合基因型;利用该群体共检测到4个抽穗期、3个株高、4个每穗颖花数、2个千粒重和1个单株产量QTL。在第7染色体RM481-RM2区间,检测到抽穗期、每穗颖花数和产量QTL,野生稻等位基因表现增效作用;其他3个每穗颖花数QTL位点,野生稻等位基因也均具有增效作用。结果表明野生稻携带有增产相关的等位基因,这些有利等位基因无疑是水稻遗传改良可资利用的新资源。     

Genetic dissection of grain traits in Yamadanishiki,an excellent sake-brewing rice cultivar

Key message

The grain traits of Yamadanishiki, an excellent sake-brewing rice cultivar in Japan, are governed by multiple QTLs, namely, a total of 42 QTLs including six major QTLs.

Abstract

Japanese rice wine (sake) is produced using brewing rice (Oryza sativa L.) that carries traits desirable for sake-brewing, such as a larger grain size and higher white-core expression rate (WCE) compared to cooking rice cultivars. However, the genetic basis for these traits in brewing rice cultivars is still unclear. We performed analyses of quantitative trait locus (QTL) of grain and days to heading over 3 years on populations derived from crosses between Koshihikari, a cooking rice, and Yamadanishiki, an excellent sake-brewing rice. A total of 42 QTLs were detected for the grain traits, and the Yamadanishiki alleles at 16 QTLs contributed to larger grain size. Two major QTLs essential for regulating both 100-grain weight (GWt) and grain width (GWh) were harbored in the same regions on chromosomes 5 and 10. An interaction was noted between the environment and the QTL associated with WCE on chromosome 6, which was detected in two of 3 years. In addition, two QTLs for WCE on chromosomes 3 and 10 overlapped with the QTLs for GWt and GWh, suggesting that QTLs associated with grain size also play an important role in the formation of white-core. Despite differences in the rate of grain growth in both Koshihikari and Yamadanishiki across 2 years, the WCE in Yamadanishiki remained consistent, thus demonstrating that the formation of white-core does not depend on grain filling speed. These data can be informative for programs involved in breeding better cooking and brewing rice cultivars.

     

水稻籼粳杂种生殖障碍的基因定位分析

籼稻(Oryza sativa L.ssp.indica)与粳稻(O.sativa ssp.japonica)杂交优势明显但存在生殖隔离。生殖障碍主要表现为胚囊败育、花粉败育、开花时花药不开裂和雌雄异熟。应用具有137个标记位点的籼、粳杂交(“窄叶青8号”/“京系17”)F_1花药培养获得的127个双单倍体(DH)群体构建的RFLP图谱,对控制籼、粳杂种小穗败育的基因座位进行了定位研究。结果在第1、3、4、5、6、7、8、12染色体上检测到10个基因座位,其中第3、12染色体上的2个不育基因位点stj-3和stj-12与同一杂交组合F_2分离群体中发现的异常分离热点处于相同的染色体区段。Ssj-6的基因加性效应为负值,有增加籼、粳亲和性的作用;其余的不育基因座位皆有增加籼、粳杂种不育性的作用。     

Genetic analysis of leaffolder resistance in rice

A double haploid(DH)population,which consists of 120 lines derived from anther culture of a typical indica and japonica hybrid'CJ06'/'TN1',was used to investigate the genetic basis for rice leaffolder resistance.Using a constructed molecular linkage map,five QTLs for rolled leaves were detected on chromosomes 1,2,3,4,and 8.The positive alleles from C J06 on chromosomes 3,4,and 8 in-creased the resistance to dee leaffolder,and the alleles from TN1 on chromosomes 1 and 2 also enhanced resistance to leaffolder.The interactions between QTLs were identified and tested,and four conditional interactions were acquired for resistance to rice leaffolder.These loci were located on chromosomes 2,9,10,and 11,respectively.QTL pyramiding indicated that the positive alleles affect resis-tance to leaffolder.The prospective application of this data in rice breeding was also discussed.     

Genetic analysis of leaffolder resistance in rice

A double haploid(DH)population,which consists of 120 lines derived from anther culture of a typical indica and japonica hybrid 'CJ06'/'TN1',was used to investigate the genetic basis for rice leaffolder resistance.Using a constructed molecular linkage map,five QTLs for rolled leaves were detected on chromosomes 1,2,3,4,and 8.The positive alleles from CJ06 on chromosomes 3,4,and 8 in-creased the resistance to rice leaffolder,and the alleles from TN1 on chromosomes 1 and 2 also enhanced resistance to leaffolde...     

Detection of QTLs for heading time and photoperiod response in wheat using a doubled-haploid population.

The genetic basis of heading time in wheat (Triticum aestivum L.) was investigated through the study of flowering under normal autumn sown field conditions as well as photoperiod responses under a controlled environment. Quantitative trait loci (QTLs) for these traits were mapped in a doubled-haploid (DH) population derived from a cross between the wheat cultivars 'Courtot' and 'Chinese Spring'. A molecular marker linkage map of this cross that was previously constructed based on 187 DH lines and 380 markers was used for QTL mapping. The genome was well covered (85%) except for chromosomes 1D and 4D, and a set of anchor loci regularly spaced over the genome (one marker each 15.5 cM) was chosen for marker regression analysis. The presence of a QTL was declared at a significance threshold of alpha = 0.005. The population was grown under field conditions in Clermont-Ferrand, France during two years (1994-1995), in Norwich, U.K. over one year (1998), and also under controlled environments in Norwich. For each trait, between 2 and 4 QTLs were identified with individual effects ranging between 6.3% and 44.4% of the total phenotypic variation. Two QTLs were detected that simultaneously affected heading time and photoperiod response. For heading time, these two QTLs were detected in more than one year. One QTL located on chromosome arm 2BS near the locus Xfbb121-2B, co-segregated with the gene Ppd-B1 known to be involved in photoperiod response. This chromosome region explained a large part of the variation (23.4-44.4% depending on the years or the traits). Another region located on chromosome arm 7BS between the loci Xfbb324-7B and Xfbb53-7B also had a strong effect (7.3-15.3%). This region may correspond to a QTL for earliness per se.     

Detection of quantitative trait loci controlling pre-harvest sprouting resistance by using backcrossed populations of japonica rice cultivars

Backcrossed inbred lines (BILs) and a set of reciprocal chromosome segment substitution lines (CSSLs) derived from crosses between japonica rice cultivars Nipponbare and Koshihikari were used to detect quantitative trait loci (QTLs) for pre-harvest sprouting resistance. In the BILs, we detected one QTL on chromosome 3 and one QTL on chromosome 12. The QTL on the short arm of chromosome 3 accounted for 45.0% of the phenotypic variance and the Nipponbare allele of the QTL increased germination percentage by 21.3%. In the CSSLs, we detected seven QTLs, which were located on chromosomes 2, 3 (two), 5, 8 and 11 (two). All Nipponbare alleles of the QTLs were associated with an increased rate of germination. The major QTL for pre-harvest sprouting resistance on the short arm of chromosome 3 was localized to a 474-kbp region in the Nipponbare genome by the SSR markers RM14240 and RM14275 by using 11 substitution lines to replace the different short chromosome segments on chromosome 3. This QTL co-localized with the low-temperature germinability gene qLTG3-1. The level of germinability under low temperature strongly correlated with the level of pre-harvest sprouting resistance in the substitution lines. Sequence analyses revealed a novel functional allele of qLTG3-1 in Nipponbare and a loss-of-function allele in Koshihikari. The allelic difference in qLTG3-1 between Nipponbare and Koshihikari is likely to be associated with differences in both pre-harvest sprouting resistance and low-temperature germinability.     

Yield-enhancing quantitative trait loci (QTLs) from wild species

Wild species of crop plants are increasingly being used to improve various agronomic traits including yield in cultivars. Dense molecular maps have enabled mapping of quantitative trait loci (QTLs) for complex traits such as yield. QTLs for increased yield have been identified from wild relatives of several crop plants. Advanced backcross QTL analysis has been used to identify naturally occurring favorable QTL alleles for yield and minimize the effect of unwanted alleles from wild species. Yield QTLs from wild species are distributed on almost all chromosomes but more often in some regions. Many QTLs for yield and related traits derived from different wild accessions or species map to identical chromosomal regions. QTLs for highly correlated yield associated traits are also often co-located implying linkage or pleiotropic effects. Many QTLs have been detected in more than one environment and in more than one genetic background. The overall direction of effect of some QTLs however, may vary with genetic context. Thus, there is evidence of stable and consistent major effect yield-enhancing QTLs derived from wild species in several crops. Such QTLs are good targets for use in marker assisted selection though their context-dependency is a major constraint. Literature on yield QTLs mapped from wild species is summarized with special reference to rice and tomato.     

Quantitative trait loci for rice yield-related traits using recombinant inbred lines derived from two diverse cultivars

The thousand-grain weight and spikelets per panicle directly contribute to rice yield. Heading date and plant height also greatly influence the yield. Dissection of genetic bases of yield-related traits would provide tools for yield improvement. In this study, quantitative trait loci (QTL) mapping for spikelets per panicle, thousand-grain weight, heading date and plant height was performed using recombinant inbred lines derived from a cross between two diverse cultivars, Nanyangzhan and Chuan7. In total, 20 QTLs were identified for four traits. They were located to 11 chromosomes except on chromosome 4. Seven and five QTLs were detected for thousand-grain weight and spikelets per panicle, respectively. Four QTLs were identified for both heading date and plant height. About half the QTLs were commonly detected in both years, 2006 and 2007. Six QTLs are being reported for the first time. Two QTL clusters were identified in regions flanked by RM22065 and RM5720 on chromosome 7 and by RM502 and RM264 on chromosome 8, respectively. The parent, Nanyangzhan with heavy thousand-grain weight, carried alleles with increased effects on all seven thousand-grain weight QTL, which explained why there was no transgressive segregation for thousand-grain weight in the population. In contrast, Chuan7 with more spikelets per panicle carried positive alleles at all five spikelets per panicle QTL except qspp5. Further work on distinction between pleiotropic QTL and linked QTL is needed in two yield-related QTL clusters.     

Identification of QTLs for Yield and Associated Traits in F₂ Population of Rice

Identification of quantitative trait loci (QTLs) controlling yield and yield-related traits in rice was performed in the F₂ mapping population derived from parental rice genotypes DHMAS and K343. A total of 30 QTLs governing nine different traits were identified using the composite interval mapping (CIM) method. Four QTLs were mapped for number of tillers per plant on chromosomes 1 (2 QTLs), 2 and 3; three QTLs for panicle number per plant on chromosomes 1 (2 QTLs) and 3; four QTLs for plant height on chromosomes 2, 4, 5 and 6; one QTL for spikelet density on chromosome 5; four QTLs for spikelet fertility percentage (SFP) on chromosomes 2, 3 and 5 (2 QTLs); two QTLs for grain length on chromosomes 1 and 8; three QTLs for grain width on chromosomes1, 3 and 8; three QTLs for 1000-grain weight (TGW) on chromosomes 1, 4 and 8 and six QTLs for yield per plant (YPP) on chromosomes 2 (3 QTLs), 4, 6 and 8. Most of the QTLs were detected on chromosome 2, so further studies on chromosome 2 could help unlock some new chapters of QTL for this cross of rice variety. Identified QTLs elucidating high phenotypic variance can be used for marker-assisted selection (MAS) breeding. Further, the exploitation of information regarding molecular markers tightly linked to QTLs governing these traits will facilitate future crop improvement strategies in rice.     

Genetic dissection of heading time and its components in rice

Heading time (HT, days from sowing to heading) is an important agronomic trait in rice. Physiologically, HT can be divided into two stages: vegetative growth time (VGT) and reproductive growth time (RGT). A number of studies for mapping QTLs conferring HT in rice have been reported, but none of them has tried to map HT-related QTLs based on their component traits (VGT and RGT). The present study aims to map HT-related QTLs in rice according not only to the performance of HT, but also the performances of VGT and RGT. A method based on an empirical equation of leaf age growth was developed to partition HT into VGT and RGT. An indica/japonica DH population and a corresponding RFLP map were constructed for the study. The methods of composite interval mapping and multiple-trait composite interval mapping were used to map QTLs. A total of 19 QTLs were mapped on all 12 rice chromosomes with the exception of chromosomes 1 and 4. Results showed that: (1) more QTLs could be detected by partitioning HT into VGT and RGT; (2) the genetic variation of HT was largely attributed to VGT; and (3) the two component stages were relatively independent in terms of QTL effects, suggesting that the ratio between VGT and RGT could be genetically adjusted without apparently altering HT. Received: 1 June 2000 / Accepted: 16 October 2000     

Towards the adaptation of grapevine varieties to climate change: QTLs and candidate genes for developmental stages

The genetic determinism of developmental stages in grapevine was studied in the progeny of a cross between grapevine cultivars Riesling and Gewurztraminer by combining ecophysiological modelling, genetic analysis and data mining of the grapevine whole genome sequence. The dates of three phenological stages, budbreak, flowering and veraison, were recorded during four successive years for 120 genotypes in the vineyard. The phenotypic data analysed were the duration of three periods expressed in thermal time (degree-days): 15 February to budbreak (Bud), budbreak to flowering (Flo) and flowering to veraison (Ver). Parental and consensus genetic maps were built using 153 microsatellite markers on 188 individuals. Six independent quantitative trait loci (QTLs) were detected for the three phases. They were located on chromosomes 4 and 19 for Bud, chromosomes 7 and 14 for Flo and chromosomes 16 and 18 for Ver. Interactions were detected between loci and also between alleles at the same locus. Using the available grapevine whole-genome sequences, candidate genes underlying the QTLs were identified. VvFT, on chromosome 7, and a CONSTANS-like gene, on chromosome 14, were found to colocalise with the QTLs for flowering time. Genes related to the abscisic acid response and to sugar metabolism were detected within the confidence intervals of QTLs for veraison time. Their possible roles in the developmental process are discussed. These results raise new hypotheses for a better understanding of the physiological processes governing grapevine phenology and provide a framework for breeding new varieties adapted to the future predicted climatic conditions.     

Genetic architecture underlying the evolutionary change of competitive ability in Asian cultivated and wild rice

Breeding of competitive cultivars has long been fraught with difficulty owing to limited knowledge of the genetic basis of competitive ability. In this study, we examined the diversity of competitive ability in Asian rice and the genetic basis of this variation. Cultivated strains and wild perennial strains have higher competitive ability than wild annual strains. Quantitative trait locus (QTL) analysis of competitive ability for three weed species was conducted in the cross between cultivated and wild annual strains, and three QTLs for general competitive ability (GCA) were identified. GCA-QTLs conferred higher competitive ability by the cultivated rice alleles and were co-located with QTLs for plant architecture and root growth, detected in the same mapping population. Furthermore, a significant change in GCA was achieved by accumulation and epistatic interaction of three QTLs. Further studies on the genetic control of competitive ability would facilitate the breeding of competitive cultivars in rice.     

Allelic interaction at seed-shattering loci in the genetic backgrounds of wild and cultivated rice species

It is known that the common cultivated rice (Oryza sativa) was domesticated from Asian wild rice, O. rufipogon. Among the morphological differences between them, loss of seed shattering is one of the striking characters specific for the cultivated forms. In order to understand the genetic control on shattering habit, QTL analysis was carried out using BC(2)F(1) backcross population between O. sativa cv. Nipponbare (a recurrent parent) and O. rufipogon acc. W630 (a donor parent). As a result, two strong QTLs were detected on chromosomes 1 and 4, and they were found to be identical to the two major seed-shattering loci, qSH1 and sh4, respectively. The allelic interaction at these loci was further examined using two sets of backcross populations having reciprocal genetic backgrounds, cultivated and wild. In the genetic background of cultivated rice, the wild qSH1 allele has stronger effect on seed shattering than that of sh4. In addition, the wild alleles at both qSH1 and sh4 loci showed semi-dominant effects. On the other hand, in the genetic background of wild rice, non-shattering effects of Nipponbare alleles at both loci were examined to inspect rice domestication from a viewpoint of seed shattering. It was serendipitous that the backcross plants individually having Nipponbare homozygous alleles at either shattering locus (qSH1 or sh4) shed all the seeds. This fact strongly indicates that the non-shattering behavior was not obtained by a single mutation in the genetic background of wild rice. Probably, some other minor genes are still associated with the formation or activation of abscission layer, which enhance the seed shattering.