A Farmer’s Approach to Detecting Photoperiod Sensitivity in Rice (Oryza sativa ssp. indica) Landraces

Most indigenous rice landraces are sensitive to photoperiod during short day seasons,and this sensitivity is more pronounced in indica than in japonica landraces.Attempts to identify photoperiod sensitive(PPS)cultivars based on the life history stages of the rice plant,and several models and indices based on phenology and day length have not been precise,and in some cases yield counterfactual inferences.Following the empirical method of traditional Asian rice farmers,the author has developed a robust index,based on the sowing and flowering dates of a large number of landraces grown in different seasons from 2020 to 2023,to contradistinguish PPS from photoperiod insensitive cultivars.Unlike other indices and models of photoperiod sensitivity,the index does not require the presumed duration of different life history stages of the rice plant but relies only on the flowering dates and the number of days till flowering of a rice cultivar sown on different dates to consistently identify photoperiod sensitive cultivars.

The Genetic Architecture of Flowering Time and Photoperiod Sensitivity in Maize as Revealed by QTL Review and Meta Analysis

The control of flowering is not only important for reproduction, but also plays a key role in the processes of domestication and adaptation. To reveal the genetic architecture for flowering time and photoperiod sensitivity, a comprehensive evaluation of the relevant literature was performed and followed by meta analysis. A total of 25 synthetic con- sensus quantitative trait loci （QTL） and four hot-spot genomic regions were identified for photoperiod sensitivity including 11 genes related to photoperiod response or flower morphogenesis and development. Besides, a comparative analysis of the QTL for flowering time and photoperiod sensitivity highlighted the regions containing shared and unique QTL for the two traits. Candidate genes associated with maize flowering were identified through integrated analysis of the homologous genes for flowering time in plants and the consensus QTL regions for photoperiod sensitivity in maize （Zea mays L.）. Our results suggest that the combination of literature review, meta-analysis and homologous blast is an efficient approach to identify new candidate genes and create a global view of the genetic architecture for maize photoperiodic flowering. Sequences of candidate genes can be used to develop molecular markers for various models of marker-assisted selection, such as marker-assisted recurrent selection and genomic selection that can contribute significantly to crop environmental adaptation.

Relationship between rice heading sensitivity and male-sterile sensitivity to photoperiod in view of developmental genetics

We studied the relationship between the head-ing sensitivity and the male-sterile sensitivityin photoperiod-sensitive genie males-sterile rice(PGMSR)and conventional rice.Materialsused in this study were 7001S,a late maturingPGMS japonica strain derived from Nongken58S; Akihikari and Youmang-zaojing(YMZJ),two early maturing conventional Japonica rice;and CPSLO-17,a Wide compatible convention-al indica rice.The heading date and seed-set-ting rate of Fand Fof three cross combina-tions between PGMSR and conventional riceswere examined in phytotron which was adjust-ed at 25±1℃ with day-length of 14.5 h(LD)and 12 h(SD).The segregation ratio of fertile:sterile in Funder LD was in accordance

Comparative Studies on the Changes of Microtubule Distribution and Reorganization During the Meiotic Stages of Development in Normal (IR36) and a Temperature/photoperiod Sensitive Male Sterile Line (Peiai 64S) of Rice ( Oryza sativa )

Changes in the pattern of organization of microtubules in the meiotic stages of development of pollen (i.e. from pre-meiotic interphase to more or less metaphase I) of a normal (IR36) and a temperature/photoperiod sensitive male sterile line (Peiai 64S) of rice were studied using immunofluorescence confocal microscopy. In IR36, from pre-meiotic interphase to metaphase I, the pattern of microtubule distribution in the meiocytes underwent a series of changes. Some new organizational patterns of microtubules (that have not been described before) were observed during microsporogenesis, including the existence of a broad band of perinuclear microtubules at the diakinesis stage of development. The pattern of microtubule distribution in the meiocytes of the male sterile line, Peiai 64S, was quite different front that seen in IR36. In Peiai 64S, the microtubules showed abnormal patterns of distribution from pre-meiotic interphase to metaphase I. For example the broad band of perinuclear microtubules seen at diakinesis in IR36 was much disorganized and loosened in Peiai 64S. The spindles formed were also very abnormal and different from the normal spindle. The appearance of abnormal microtubule distribution in the early stages of microsporogenesis may contribute to the malformation and ultimate abortion of pollen in Peiai 64S.

Studies on the Heredity of the Traits Related to the Photoperiod-Sensitive Phenomenon Among the Temperate ×Tropical Crosses in Maize

The genetic study of characters concerning photoperiod sensitivity of the growth and development stages, plant and ear height was carried out from 5 temperate tropical combinations by using P1 , P2, F1, F2, BC1, BC2 generations mean analysis. The results showed that the square sums of additive, of dominance and of epistatic gene effects contributed to total genetic variance were 11. 3 -53. 6%, 36.0 -78. 6% and 5.5 -27.0% respectively for five traits of the insensitive×insensitive combination to photoperiod, which suggested dominance gene effect was the most important among various gene effects. In insensitive X sensitive combination to photoperiod, the square sums of additive gene effect with 66. 9 - 84. 5 %, of dominance gene effect with 11. 6 30. 7% and of epistatic gene effect with 1.4-5. 2% were found for five tested traits, which showed additive gene effect held a dominant position, and dominance and epistatic gene effects were reduced compared with insensitive×insensitive combination. The differences existed among different insensitive×sensitive combinations. The proportion of the genetic component among the insensitive×sensitive crossbreed offspring in the temperate zone had a certain dosage effect on fading photoperiod sensitivity reaction. The sensitivity of BC1 , with 25 % of the tropical genetic component, is extremely weak, but with high application value.

Isolation and Analysis of the Promoter of OsRacD from PhotoperiodSensitive Genic Male Sterile Rice

By using OsRacD cDNA as probe to screen the genomic library of photoperiod sensitive genic male sterile rice line Nongken 58S, a positive clone containing 2 kb promoter and 396 bp coding region of OsRacD was obtained. Compared with the promoter of OsRacD cloned by reverse PCR from normal rice variety Nongken 58 （Nongken 58N）, the homology was 99.8%, and the different nucleotides were outside the predicted response elements in promoter, suggesting that the fertility between rice varieties Nongken 58S and Nongken 58N under the long-day conditions was not attributed to the difference in the structure of OsRacD upstream regulation sequences, but to the developmental regulation of gene differential expression.

The CCT domain-containing gene family has large impacts on heading date, regional adaptation, and grain yield in rice

There are 41 members of the CCT（CO, CO-like, and TOC1） domain-containing gene family in rice, which are divided into three subfamilies： COL（CONSTANS-like）, CMF（CCT motif family）, and PRR（pseudoresponse regulator）. The first flowering gene to be isolated by map-based cloning, Heading date 1（Hd1）, which is the orthologue of CO in rice, belongs to COL. The central regulator of plant development, Ghd7, belongs to CMF. The major role in controlling rice distribution to high latitudes, Ghd7.1/PRR37, belongs to PRR. Both of Hd1, Ghd7 and Ghd7.1 simultaneously control grain number, plant height, and the heading date. To date, 13 CCT family genes from these three subfamilies have been shown to regulate flowering. Some of them have pleiotropic effects on grain yield, plant height, and abiotic stresses, and others function as circadian oscillators. There are two independent photoperiod flowering pathways that are mediated by GI-Hd1-Hd3 a/RFT and GI-Ehd1-Hd3 a/RFT in rice. CCT family genes are involved in both pathways. The latest study reveals that protein interaction between Hd1 and Ghd7 integrates the two pathways. CCT family genes are rich in natural variation because rice cultivars have been subjected to natural and artificial selection for different day lengths in the process of domestication and improvement. Alleles of several crucial CCT family genes such as Hd1, Ghd7, and Ghd7.1 exhibit geographic distribution patterns and are highly associated with yield potentials. In addition, CCT family genes are probably involved in the responses to abiotic stress, which should be emphasized in future work. In general, CCT family genes play important roles in regulating flowering, plant growth, and grain yield. The functional identification and elucidation of the molecular mechanisms of CCT family genes would help construct a flowering regulatory network and maximize their contribution to rice production.

High-density genetic mapping identified a major locus for environmental sex expression in pumpkin(Cucurbita moschata Duch.)

Long-day length and high temperature inhibit sex expression in pumpkin(Cucurbita moschata Duch.),and therefore directly impact the production potential.In this study,female flowering patterns in photoperiod-insensitive(PPIS)and photoperiod-sensitive(PPS)germplasms differed significantly in a moderately long day and high temperature environment.However,both germplasms exhibited a similar response in short day with either low temperature or high temperature environment.Photoperiod sensitivity led to this difference in sex expression between the germplasms.For the traits of 1st female flowering node(FFFN)and number of female flowers(NFF),high-density linkage map construction and quantitative trait locus(QTL)mapping were performed using SLAF-seq technology and 162 F_(2) individuals generated from PPIS and PPS.In total,4655 SLAFs were selected and mapped on 20 linkage groups(LGs).The total map length was 2502.01 cM with an average interval distance of 0.75 cM.Major QTLs for both FFFN and NFF were detected on LG6 with intervals of 7.89 and 17.67 cM and PVE values of 30.5%and 22.9%,respectively.Further analyses of the major locus for FFFN revealed 73 protein-coding genes.Among them,4 were related to sex expression,photoperiod flowering,and hormone response.An InDel(insertion and deletion)marker partially correlated with FFFN of the F_(2) population was also developed.Our study identified the QTL for the sex expression response to environmental factors using the high-density linkage map.The identified candidate genes and markers will provide useful information about the molecular interaction between the environment and sex expression and for marker-assisted selection of pumpkin environment-insensitive resources.

Genetic Analysis of Heading Date of Japonica Rice Cultivars in Southwest China

Heading date of 26 native japonica rice cultivars in southwest China was investigated,and their basic vegetative growth(BVG),photoperiod-sensitivity(PS) and temperature-sensitivity(TS) were analyzed under artificial short-day and natural long-day conditions in Nanjing,as well as artificial high-temperature and natural low-temperature conditions in winter in Hainan.The results showed that the PS and TS varied among different cultivars.The BVG of all the japonica cultivars was well situated,but differed within cultivars.Regression analysis showed a significant correlation between heading date and PS,indicating that PS was the main factor affecting heading date of japonica cultivars in southwest China.Genetic analysis was conducted on these 26 cultivars using a set of heading date near isogenic lines as test lines.All the japonica cultivars carried the dominant early-heading gene Ef-1 or Ef-1t,and most of these cultivars carried the dominant photoperiod sensitivity allele E1 or E1t,the PS of which was slightly weaker than E1.For the Se-1 locus,these cultivars mainly carried recessive photoperiod insensitivity gene Se-1e.In addition,the PS of 22 japonica cultivars could be repressed or weakened by the recessive allele hd2,inhibiting the expression of E1 and Se-1.These results indicated that the genotypes of heading date determined different PS and well situated BVG in japonica rice cultivars in southwest China.

Hd1,Ghd7,and DTH8 synergistically determine the rice heading date and yield-related agronomic traits

Heading date determines the seasonal and regional adaptation of rice(Oryza sativa L.)varieties and is mainly controlled by photoperiod sensitivity(PS).The core heading date genes Hd1,Ghd7,DTH8,and PRR37 act synergistically in regulating the PS.In this study,we systematically analyze the heading date,PS,and agronomic traits of eight homozygous lines with various combinations of Hd1,Ghd7,and DTH8 alleles in the prr37 background under long-day(LD)and short-day(SD)conditions,respectively.We find that Hd1 alone promotes heading,regardless of the day length.However,under LDs,Hd1 suppresses flowering,in coordination with functional Ghd7 or with Ghd7 and DTH8.These loci cooperate to negatively regulate the Ehd1-Hd3 a/RFT1 pathway and delay heading.Under SDs,Hd1 competes with various heading suppressors to promote heading.Therefore,the dual function of Hd1 is vital for PS.The lines carrying Hd1 alone show reduced plant height with fewer primary and secondary branches in panicles.Lines carrying Ghd7 and DTH8(with hd1)show delayed heading and improve agronomic traits.Overall,our results reveal the regulation of rice PS flowering by the core heading date genes and their effects on agronomic traits,providing valuable information for the selection of rice varieties for adaptation to different light and temperature conditions.

Validation and Characterization of Ghd7.1, a Major Quantitative Trait Locus with Pleiotropic Effects on Spikelets per Panicle, Plant Height, and Heading Date in Rice (Oryza sativa L.)

A quantitative trait locus （QTL） that affects heading date （HD） and the number of spikelets per panicle （SPP） was previously identified in a small region on chromosome 7 in rice （Oryza sativa L.）. In order to further characterize the QTL region, near isogenic lines （NILs） were quickly obtained by self-crossing recombinant inbred line 189, which is heterozygous in the vicinity of the target region. The pleiotropic effects of QTL Ghd7.1 on plant height （PH）, SPP, and HD, were validated using an NIL-F2 population. Ghd7.1 explained 50.2%, 45.3%, and 76.9% of phenotypic variation in PH, SPP, and HD, respectively. Ghd7.1 was precisely mapped to a 357-kb region on the basis of analysis of the progeny of the NIL-F2 population. Day-length treatment confirmed that Ghd7.1 is sensitive to photoperiod, with long days delaying heading up to 12.5 d. Identification of panicle initiation and development for the pair of NILs showed that Ghd7.1 elongated the photoperiod-sensitive phase more than 10 d, but did not change the basic vegetative phase and the reproductive growth phase. These findings indicated that Ghd7.1 regulates SPP by controlling the rate of panicle differentiation rather than the duration of panicle development.