Flowering in Pisum: the Effect of Light Quality on the Genotype If e Sn Hr

Far-red light, when given as a 16 h photoperiod extension, iamore effective than red light in reducing the flowering nodeof genotype Pisum. In contrast, when a 16 h dark period is interruptedby a 2 h light break red light is more effective than far-redlight. In addition, the stimulatory effect of a red interruptionis partially reversed by a subsequent period of far-red. However,a light interruption is not effective until over 12 h have elapsedsince the start of the previous photoperiod, regardless of whetherthe photoperiod was of 4 or 8 h duration. The results suggest that there are two light-dependent reactionscontrolling flowering in peas, one operating through the phytochromesystem with high levels of Pfr suppressing production of flowerinhibitor by the sn gene and a second requiring continuous illuminationwith wavelengths above 700 nm. The role of time measurementin the photoperiod response in peas is suggested to be filledby the proportion of time the Sn gene is effectively producinginhibitor. The photoperiod response in peas is not independentof temperature or plant age since the activity of gene Sn isalso varied by these factors.     

The Vrn-H2 locus is a major determinant of flowering time in a facultative × winter growth habit barley (Hordeum vulgare L.) mapping population

With the aim of dissecting the genetic determinants of flowering time, vernalization response, and photoperiod sensitivity, we mapped the candidate genes for Vrn-H2 and Vrn-H1 in a facultative × winter barley mapping population and determined their relationships with flowering time and vernalization via QTL analysis. The Vrn-H2 candidate ZCCT-H genes were completely missing from the facultative parent and present in the winter barley parent. This gene was the major determinant of flowering time under long photoperiods in controlled environment experiments, irrespective of vernalization, and under spring-sown field experiments. It was the sole determinant of vernalization response, but the effect of the deletion was modulated by photoperiods when the vernalization requirement was fulfilled. There was no effect under short photoperiods. The Vrn-H1 candidate gene (HvBM5A) was mapped based on a microsatellite polymorphism we identified in the promoter of this gene. Otherwise, the HvBM5A alleles for the two parents were identical. Therefore, the significant flowering time QTL effect associated with this locus suggests tight linkage rather than pleiotropy. This QTL effect was smaller in magnitude than those associated with the Vrn-H2 locus and was significant in two-way interactions with Vrn-H2. The Vrn-H1 locus had no effect on vernalization response. Our results support the Vrn-H2/Vrn-H1 repressor/structural gene model for vernalization response in barley and suggest that photoperiod may also affect the Vrn genes or tightly linked loci.     

Expression profiles of a CONSTANS homologue GmCOL11 in Glycine max

Soybean (Glycine max L.) is a typical short-day crop, and its flowering is strictly restricted by specific photoperiod conditions. CONSTANS (CO) plays a pivotal role in the photoperiod pathway of flowering regulation. CO-like genes are present in many plant species. Here we describe the isolation of the CO homologue GmCOL11 (Glycine max CO-like 11) from the soybean cv. Kennong 18. Sequence comparisons show that GmCOL11 is a group II CO-like gene with some similarity to AtCOL6 and AtCOL16. Its sequence includes a conserved B box and a CCT domain. The study of GmCOL11 expression using quantitative real time RT-PCR demonstrated that this gene was regulated in a diurnal rather than in a circadian manner. The gene was expressed throughout the plant, but mainly in adult leaves and maturing seeds; its expression was enhanced following flowering. Apparently GmCOL11 is involved in several aspects of soybean development.     

The gigas mutant in pea is deficient in the floral stimulus

Identification of a gene acting in the floral stimulus pathway should provide a basis for determining the identity of this elusive substance. Our tests indicate the Gi (gigas) gene in pea (Pisum sativum L.) acts in this manner. The gigas mutant was selected by Dl M. Vassiteva following gamma radiation of the late flowering, quantitative long day cultivar Virtus. The gigas trait showed single gene recessive inheritance and the mutant allele was symbolised gi consistent with our preliminary report. Gigas plants were later flowering than the initial line in all conditions tested and they showed an enhanced response to photoperiod and vernalisation. Unvernalised gigas plants did not flower under a 24-h photoperiod comprising 8 h of daylight and 16 h of weak (3μmol m^?2 s^?1) incandescent light and they took on a phenotype similar to the vegl (vegetative) mutant in pea. However, genetic tests showed the two mutants were not allelic. Three or four weeks vernalisation at 4^?C resulted in 100% flowering of gigas plants under the 24-h photoperiod. Applied gibberellin A₃ inhibited flowering in gigas plants given partial cold induction. Grafting studies showed the promotive effect of vernalisation occurred in the shoot. Grafting studies were also used to examine the physiological basis of delayed flowering in the gigas mutant. These studies indicated that gigas plants produced normal levels of flower inhibitor and they responded in a normal manner to the floral stimulus, Reciprocal grafts were made between the gigas mutant and the wild-type initial line. Under the 24-h photoperiod, either a wild-type root-stock with cotyledons or a wild-type shoot induced flowering in a gigas graft partner. However, under a 9-h photoperiod, flowering was only induced if the wild-type partner possessed both roots and a shoot. We conclude that gigas plants are deficient in the floral stimulus or a precursor which can be supplied across a graft union by a wild-type donor. Of the 12 major flowering genes known in pea, Gi is the first found to act on the synthesis pathway for the floral stimulus.     

Natural variation in the temperature range permissive for vernalization in accessions of Arabidopsis thaliana

Vernalization is an acceleration of flowering in response to chilling, and is normally studied in the laboratory at near‐freezing (2–4 °C) temperatures. Many vernalization‐requiring species, such as Arabidopsis thaliana, are found in a range of habitats with varying winter temperatures. Natural variation in the temperature range that elicits a vernalization response in Arabidopsis has not been fully explored. We characterized the effect of intermediate temperatures (7–19 °C) on 15 accessions and the well‐studied reference line Col‐FRI. Although progressively warmer temperatures are gradually less effective at activating expression of the vernalization‐specific gene VERNALIZATION‐INSENSITIVE 3 (VIN3) and in accelerating flowering, there is substantial natural variation in the upper threshold (T_max) of the flowering‐time response. VIN3 is required for the T_max (13 °C) response of Col‐FRI. Surprisingly, even 16 °C treatment caused induction of VIN3 in six tested lines, despite the ineffectiveness of this temperature in accelerating flowering for two of them. Finally, we present evidence that mild acceleration of flowering by 19 °C exposure may counterbalance the flowering time delay caused by non‐inductive photoperiods in at least one accession, creating an appearance of photoperiod insensitivity.     

Use of field observations to characterise genotypic flowering responses to photoperiod and temperature: a soyabean exemplar

Thirty-nine accessions of soyabean [Glycine max (L.) Merrill] and 1 of wild annual soyabean (Glycine soja L.) were sown at two sites in Taiwan in 1989 and 1990 and on six occasions during 1990 at one site in Queensland, Australia. On two of the occasions in Australia additional treatments extended natural daylengths by 0.5 h and 2 h. The number of days from sowing for the first flower to appear on 50% of the plants in each treatment was recorded (f), and from these values the rate of progress towards flowering (1/f) was related to temperature and photoperiod. In photoperiod-insensitive accessions it was confirmed that the rate is linearly related to temperature at least up to about 29°C. In photoperiod-sensitive genotypes this is also the case in shorter daylengths but when the critical photoperiod (P _c) is exceeded flowering is delayed. This delay increases with photoperiod until a ceiling photoperiod (P _ce) is reached. Between P _c and P _ce, 1/f is linearly related to both temperature (positive) and photoperiod (negative), but in photoperiods longer than P _ce there is no further response to either factor. The resulting triple-intersecting-plane response surface can be defined by six genetically-determined coefficients, the values of which are environment-independent but predict time to flower in any environment, and thus quantify the genotype x environment interaction. By this means the field data were used to characterise the photothermal responses of all 40 accessions. The outcome of this characterisation in conjunction with an analysis of the world-wide range of photothermal environments in which soyabean crops are grown lead to the following conclusions: (1) photoperiod-insensitivity is essential in soyabean crops in temperate latitudes, but such genotypes flower too rapidly for satisfactory yields in the tropics; (2) photoperiod-sensitivity appears to be essential to delay flowering sufficiently to allow adequate biomass accumulation in the warm climates of the tropics; (3) contrary to a widely held view, some degree of photoperiod-sensitivity is also needed in the tropics if crop-duration homeostasis is required where there is variation in sowing dates (this is achieved through a photoperiod-controlled delay in flowering which counteracts the seasonal increase in temperature that is correlated with increase in day-length); and (4) a greater degree of photoperiod-sensitivity is necessary to provide maturity-date homeostasis for variable sowing dates — a valuable attribute in regions of uncertain rainfall. Since the triple-intersecting-plane response model used here also applies to other species, the use of field data to characterise the photothermal responses of other crops is discussed briefly.     

Natural variation in GmGBP1 promoter affects photoperiod control of flowering time and maturity in soybean

The present study screened for polymorphisms in coding and non‐coding regions of the GmGBP1 gene in 278 soybean accessions with variable maturity and growth habit characteristics under natural field conditions in three different latitudes in China. The results showed that the promoter region was highly diversified compared with the coding sequence of GmGBP1. Five polymorphisms and four haplotypes were closely related to soybean flowering time and maturity through association and linkage disequilibrium analyses. Varieties with the polymorphisms SNP_‐796G, SNP_‐770G, SNP_‐307T, InDel_‐242normal, SNP_353A, or haplotypes Hap‐3 and Hap‐4 showed earlier flowering time and maturity in different environments. The shorter growth period might be largely due to higher GmGBP1 expression levels in soybean that were caused by the TCT‐motif with SNP_‐796G in the promoter. In contrast, the lower expression level of GmGBP1 in soybean caused by RNAi interference of GmGBP1 resulted in a longer growth period under different day lengths. Furthermore, the gene interference of GmGBP1 also caused a reduction in photoperiod response sensitivity (PRS) before flowering in soybean. RNA‐seq analysis on GmGBP1 underexpression in soybean showed that 94 and 30 predicted genes were significantly upregulated and downregulated, respectively. Of these, the diurnal photoperiod‐specific expression pattern of three significant flowering time genes GmFT2a, GmFT5a, and GmFULc also showed constantly lower mRNA levels in GmGBP1‐i soybean than in wild type, especially under short day conditions. Together, the results showed that GmGBP1 functioned as a positive regulator upstream of GmFT2a and GmFT5a to activate the expression of GmFULc to promote flowering on short days.     

Ecotype-Specific Expression of a Flowering Mutant Phenotype in Arabidopsis thaliana

The majority of mutations that delay flowering in Arabidopsis thaliana have been identified in studies of the Landsberg erecta (Ler) ecotype. In this report we describe a gene (referred to as FLD) that, when mutated, delays flowering in the Columbia ecotype but has a minimal phenotype in the Ler genetic background. The late-flowering phenotype of fld mutants requires a non-Ler allele of another gene involved in the control of flowering time, Flowering Locus C. fld mutants retain a photoperiod response, and the flowering time of fld mutants can be reduced by cold treatment and low red/far-red light ratios.     

Molecular mapping of the photoperiod response gene ea7 in barley

 The gene ea ₇ determining photoperiod insensitivity under short day length was mapped on the short arm of chromosome 6H near the centromere. The gene was linked to the two flanking markers Xmwg2264 and Xmwg916 by 6.7 and 13.0 cM, respectively. Compared to Ppd-H1 (chromosome 2H) and Ppd-H2 (chromosome 1H), ea ₇ determines the strongest effect on flowering time with 55 and 18 days difference compared to photoperiod sensitive genotypes grown under short and long photoperiods, respectively. Allelic and homoeologous relationships to major genes and quantitative trait loci controlling flowering time in barley and wheat are discussed. Received: 10 March 1998 / Accepted: 7 April 1998     

Flowering and branching in Lathyrus odoratus L.: loci sp and b

Summary A second flowering gene, Sp, which influences sensitivity to photoperiod, is identified in the sweet pea, Lathyrus odoratus L. Genes Sp and Dn ^h act in a complementary manner to confer the summer-flowering phenotype and a near obligate long day requirement for flowering in the unvernalized state. Mutations sp and Dn ⁱ each diminish the response to photoperiod, and genotypes sp Dn ^h and Sp Dn ⁱ confer a spring-flowering phenotype. Response to photoperiod is further reduced in genotype sp Dn ⁱ, which flowers only marginally later than the day-neutral or winter-flowering phenotype characterized by genotypes Sp dn and sp dn (gene dn is epistatic to the gene pair Sp/sp). Like Dn ⁱ, gene sp reduces basal branching, while a branching gene, here resymbolized b, is shown to delay flowering in certain circumstances. Gene dn largely prevents basal branching in either b or B plants, but dn b plants do produce lateral shoots from the upper nodes, leading to a novel phenotype. The implications of the interactions between genes sp, Dn ⁱ, dn and b are discussed with respect to the control of flowering and branching.     

Effect of Photoperiod on the Regulation of Wheat Vernalization Genes VRN1 and VRN2

Wheat is usually classified as a long day (LD) plant because most varieties flower earlier when exposed to longer days. In addition to LD, winter wheats require a long exposure to low temperatures (vernalization) to become competent for flowering. Here we show that in some genotypes this vernalization requirement can be replaced by interrupting the LD treatment by 6 weeks of short day (SD), and that this replacement is associated with the SD down-regulation of the VRN2 flowering repressor. In addition, we found that SD down-regulation of VRN2 at room temperature is not followed by the up-regulation of the meristem identity gene VRN1 until plants are transferred to LD. This result contrasts with the VRN1 up-regulation observed after the VRN2 down-regulation by vernalization, suggesting the existence of a second VRN1 repressor. Analysis of natural VRN1 mutants indicated that a CArG-box located in the VRN1 promoter is the most likely regulatory site for the interaction with this second repressor. Up-regulation of VRN1 under SD in accessions carrying mutations in the CArG-box resulted in an earlier initiation of spike development, compared to other genotypes. However, even the genotypes with CArG box mutations required LD for a normal and timely spike development. The SD acceleration of flowering was observed in photoperiod sensitive winter varieties. Since vernalization requirement and photoperiod sensitivity are ancestral traits in Triticeae species we suggest that wheat was initially a SD–LD plant and that strong selection pressures during domestication and breeding resulted in the modification of this dual regulation. The down-regulation of the VRN2 repressor by SD is likely part of the mechanism associated with the SD–LD regulation of flowering in photoperiod sensitive winter wheat. These authors contributed equally to this work     

A Model of Photoperiod × Temperature Interaction Effects on Plant Development

The recent whole-plant research reviewed suggests the commonly applied paradigms about vernalization and photoperiodism should be replaced. A simple equation based on new paradigms predictively models with excellent fit the published days to flowering of at least six plant species. The paradigm that the response to photoperiod of the days to flowering (DTF) of crop plants is revealed adequately by comparing a range of photoperiods at just one temperature should be replaced with the following concepts. There is a base (lowest) temperature below which photoperiod gene activity does not occur, and, when the temperature is high enough to allow activity, there is always a photoperiod × temperature × genotype interaction effect on the days to flowering. Similarly, the paradigm that vernalization gene activity occurs at low temperature and promotes development should be replaced as follows. Vernalization gene activity occurs only if the temperature is above a base (lowest) temperature that allows activity of the vernalization gene(s), and this activity delays development to flowering. Development to flowering is accelerated by low-temperature vernalization, because the low temperature prevents vernalization gene activity, thereby preventing delay of the DTF. The phenomena called long-day (LD) vernalization and short-day (SD) vernalization are reinterpreted as follows. The apparent replacement by short or long daylength of a requirement for low-temperature vernalization is actually a replacement by the low temperature of a requirement for long or short day. Just as true low-temperature vernalization results from prevention of vernalization gene activity, these SD and LD promotions of the DTF occur because the photoperiod gene activity is prevented by the low temperature. Rather than requiring an environment that induces flowering, an inherent capability for rapid development to flowering is expressed, if there is no delay of the DTF by the activity of either or both of the vernalization and photoperiod gene(s). All the above-mentioned effects of temperature are due to the Q₁₀ effect on the specified photoperiod or vernalization gene activity. The effect of thermal time (due to the accumulated growing degree days) is the integrated Q₁₀ effect on all additional genes that partially control the rate of development to the reproductive stage.     

A whole-system reconsideration of paradigms about photoperiod and temperature control of crop yield

Summary Effects by photoperiod gene(s) and daylength on crop yield and its three major physiological components (aerial biomass, harvest index, and days to harvest maturity) are reviewed for bean (Phaseolus vulgaris L.) and peanut (Arachis hypogaea L.). In these plus many other cited crops, photoperiod sensitive gene(s) delay days to flowering and/or days to maturity in non-promotive daylength while simultaneously lowering the harvest index. Thus, for many crops, earlier maturity is associated with higher harvest index, and/or it has been shown that photoperiod gene(s) control partitioning of photosynthate toward reproductive growth versus toward competitive partitioning to continued vegetative growth. Our conclusion is that photoperiod gene control over this partitioning precedes and is causal of the photoperiodgene control over days to flowering and maturity. This implies shifts from commonly accepted paradigms about effects by photoperiod and about breeding for higher yield. These paradigm shifts suggest more efficient ways to breed for cultivar adaption to the specific growing season duration and environment of each geographical site and for higher crop yield.     

水稻开花期调控的分子机理研究进展

水稻准确地感知外部环境信号,通过内部复杂的基因网络做出反应,在一年中最适合的时候开花繁殖。与长日促进长日模式植物拟南芥开花相反,短日促进短日模式植物水稻开花。通过对水稻和拟南芥的开花期调控机理的对比分析,发现水稻和拟南芥有着一些相对保守的开花期控制基因,其调控机理也是相似的。另外,水稻也有一些独特的开花期控制基因和开花途径。本文着重从光周期对水稻开花期的调控途径和作用机理角度进行了阐述,并对水稻开花期的自然变异与其育种应用、生物钟关联基因、光中断现象和临界日长现象以及开花期与产量的关系进行了总结。     

Photoperiod insensitive Ppd-A1a mutations in tetraploid wheat (Triticum durum Desf.)

Variation in photoperiod response plays an important role in adapting crops to agricultural environments. In hexaploid wheat, mutations conferring photoperiod insensitivity (flowering after a similar time in short or long days) have been mapped on the 2B (Ppd-B1) and 2D (Ppd-D1) chromosomes in colinear positions to the 2H Ppd-H1 gene of barley. No A genome mutation is known. On the D genome, photoperiod insensitivity is likely to be caused by deletion of a regulatory region that causes misexpression of a member of the pseudo-response regulator (PRR) gene family and activation of the photoperiod pathway irrespective of day length. Photoperiod insensitivity in tetraploid (durum) wheat is less characterized. We compared pairs of near-isogenic lines that differ in photoperiod response and showed that photoperiod insensitivity is associated with two independent deletions of the A genome PRR gene that cause altered expression. This is associated with induction of the floral regulator FT. The A genome deletions and the previously described D genome deletion of hexaploid wheat remove a common region, suggesting a shared mechanism for photoperiod insensitivity. The identification of the A genome mutations will allow characterization of durum wheat germplasm and the construction of genotypes with novel combinations of photoperiod insensitive alleles.