Time Of Flower Opening Research Articles

Timing is everything: OsMYC2 controls diurnal flower-opening time in rice.

Timing is everything: OsMYC2 controls diurnal flower-opening time in rice.

The OsMYC2-JA feedback loop regulates diurnal flower-opening time via cell wall loosening in rice.

Diurnal flower-opening time (DFOT), the time of spikelet opening during the day, is an important trait for hybrid rice (Oryza sativa L.) seed production. Hybrids between indica and japonica rice varieties have strong heterosis, but the parental lines usually have different, nonoverlapping DFOTs. This reduces the success of hybrid seed production in crosses between indica and japonica subspecies, thus hindering the utilization of indica and japonica inter-subspecies heterosis. However, little is known about the molecular mechanisms regulating DFOT in rice. Here, we obtained japonica rice lines with a DFOT 1.5 h earlier than the wild type by overexpressing OsMYC2, a gene encoding a key transcription factor in the jasmonate (JA) signaling pathway. OsMYC2 is activated by JA signaling and directly regulates the transcription of genes related to JA biosynthesis and cell wall metabolism. Overexpressing OsMYC2 led to significantly increased JA contents and decreased cellulose and hemicellulose contents in lodicule cells, as well as the softening of lodicule cell walls. This may facilitate the swelling of lodicules, resulting in early diurnal flower-opening. These results suggest that the OsMYC2-JA feedback loop regulates DFOT in rice via cell wall remodeling. These findings shed light on the understanding of regulatory mechanism of the DFOT of plants, which should promote the development of indica and japonica varieties suitable for hybrid rice breeding.

Is the time of anthesis in rice (Oryza sativa) influenced by photoperiod?

Photoperiod sensitivity in rice cultivars is defined when the cultivar begins anthesis on a relatively invariant date, varying by < 7days, regardless of the date of sowing or germination. While the date of flowering in photoperiod sensitive (PPS) rice cultivars is characteristically determined by the day length, especially during the short-day season (September-December), the response of the flower opening time (FOT) to photoperiod remains hitherto unexplored. This paper examines whether day length restrains year-to-year variation in FOT in PPS cultivars. We examined 105 PPS and 173 photoperiod insensitive (PPI) cultivars grown in different years and estimated their year-to-year FOT difference (or FOTD) and the year-to-year difference of sunrise to anthesis duration (or SADD). Wilcoxon signed rank test and bootstrap test were then performed to test whether these descriptors significantly differed between PPS and PPI groups of cultivars. The means of FOTD and SADD were detected to be significantly less in the PPS group than in the PPI group of cultivars, indicating significantly lesser variability of FOT in PPS than in PPI cultivars. This is the first report of a strong restraining influence of photoperiod on FOT variability in PPS cultivars.

Adjustments of flower opening time and duration in tropical rice (Oryza sativa ssp. indica) landraces in response to heat stress

AbstractBased on our primary database of the flower opening time (FOT) and flower exposure duration (FED) of 1114 rice (Oryza sativa ssp. indica) landraces, we examined the influences of growing season, sunrise time as well as day maximum and minimum temperatures on the anthesis behaviour of indica rice landraces of South and Southeast Asia, flowering in summer and winter in 3 consecutive years (2020–2022). We also compared the FOT and FED on sunny and cloudy days of a small set of landraces, and also during summer and winter. Our data show that rice florets tend to open later in the morning and lengthen the sunrise‐to‐anthesis duration (SAD) on hotter sunny days during tropical summer than during winter and on cloudy days. These findings contradict the widely held conjecture, based on studies conducted at colder latitudes, that rice flowers open earlier in the morning to avoid heat stress. We propose that indica rice landraces are sufficiently adapted to tropical summer because they were selected and bred over millennia to withstand heat stress during tropical summer, so their FOT and SAD are weakly influenced by high day temperatures. However, the significant reduction in FED of these landraces, whose flowers open later in mid‐day, seems to be an adaptive mechanism to avoid longer exposure to rising air temperature approaching day maximum temperature.

Controlling diurnal flower-opening time by manipulating the jasmonate pathway accelerates development of indica-japonica hybrid rice breeding.

Inter-subspecific indica-japonica hybrid rice (Oryza sativa) has the potential for increased yields over traditional indica intra-subspecies hybrid rice, but limited yield of F1 hybrid seed production (FHSP) hinders the development of indica-japonica hybrid rice breeding. Diurnal flower-opening time (DFOT) divergence between indica and japonica rice has been a major contributing factor to this issue, but few DFOT genes have been cloned. Here, we found that manipulating the expression of jasmonate (JA) pathway genes can effectively modulate DFOT to improve the yield of FHSP in rice. Treating japonica cultivar Zhonghua 11 (ZH11) with methyl jasmonate (MeJA) substantially advanced DFOT. Furthermore, overexpressing the JA biosynthesis gene OPDA REDUCTASE 7 (OsOPR7) and knocking out the JA inactivation gene CHILLING TOLERANCE 1 (OsHAN1) in ZH11 advanced DFOT by 1- and 2-h respectively; and knockout of the JA signal suppressor genes JASMONATE ZIM-DOMAIN PROTEIN 7 (OsJAZ7) and OsJAZ9 resulted in 50-min and 1.5-h earlier DFOT respectively. The yields of FHSP using japonica male-sterile lines GAZS with manipulated JA pathway genes were significantly higher than that of GAZS wildtype. Transcriptome analysis, cytological observations, measurements of elastic modulus and determination of cell wall components indicated that the JA pathway could affect the loosening of the lodicule cell walls by regulating their composition through controlling sugar metabolism, which in turn influences DFOT. This research has vital implications for breeding japonica rice cultivars with early DFOT to facilitate indica-japonica hybrid rice breeding.

Advances on the Study of Diurnal Flower-Opening Times of Rice

The principal goal of rice (Oryza sativa L.) breeding is to increase the yield. In the past, hybrid rice was mainly indica intra-subspecies hybrids, but its yield has been difficult to improve. The hybridization between the indica and japonica subspecies has stronger heterosis; the utilization of inter-subspecies heterosis is important for long-term improvement of rice yields. However, the different diurnal flower-opening times (DFOTs) between the indica and japonica subspecies seriously reduce the efficiency of cross-pollination and yield and increase the cost of indica–japonica hybrid rice seeds, which has become one of the main constraints for the development of indica–japonica hybrid rice breeding. The DFOT of plants is adapted to their growing environment and is also closely related to species stability and evolution. Herein, we review the structure and physiological basis of rice flower opening, the factors that affect DFOT, and the progress of cloning and characterization of DFOT genes in rice. We also analyze the problems in the study of DFOT and provide corresponding suggestions.

Diversity of Flower Opening Time and Duration in Rice (Oryza sativa ssp. indica) Landraces of South and Southeast Asia in Different Cultivation Seasons

Different cultivars of rice (Oryza sativa) open at different times of the day, and the overlap of anthesis time in rice between the neighbouring cultivars is of crucial importance to the degree of cross pollination in rice. Nevertheless, none of the past experiments with cross pollination between different rice cultivars ever reported the respective flower opening time (FOT) and flower exposure duration (FED) of the parent cultivars, until recently. The authors present here the first record of FOT and FED of 1114 indica rice landraces of South and Southeast Asia, growing during summer and winter seasons in three consecutive years. The authors also present an analysis of the influences of the growing season on the anthesis behaviour, and present the first records of the FOT and FED variability on sunny and cloudy days of a large number of landraces. The data show that rice florets tend to open earlier in the morning (that is, take a shorter time to anthesis after sunrise) on sunny days than on cloudy days, and also significantly later during long day seasons (spring and summer) than during short day season (winter); and that FED is inversely related to both FOT and the length of duration from sunrise to first flower opening. The wide ranges of FOT (8:50 a.m. to 12:40 p.m.) and FED (15 to 194 minutes) also suggest the ample time window for receiving pollen from neighbouring cultivars with different FOT, enhancing the chances of cross pollination between hundreds of rice landraces with FOT and FED overlaps.

Relationships between Flower Opening Time, Environmental Conditions, Corolla Opening Size and Nectar Production in Five Winter Oilseed Rape (Brassica napus L.) Cultivars in China

Abstract Oilseed rape is an economically important crop and provides a good nectar resource. In this study, the nectar secretion characteristics of five winter oilseed rape (Brassica napus L.) cultivars in China were examined throughout the daytime. The correlations of corolla opening size, air temperature and relative humidity with nectar production were also determined. Different daily patterns of nectar secretion were detected in flowers opening at different times of the day, and similar trends were observed among cultivars. The nectar volume and nectar sugar concentration in flowers that opened before 9:00 peaked on the first day. The nectar volume of flowers that opened at 11:00 peaked on the second day, and the nectar sugar concentration peaked on the first day. The total nectar yield of flowers opening before 9:00 (4.422–5.265 μl) was lower than that of flowers opening at 11:00 (7.982–10.646 μl). The average nectar sugar concentration of flowers opening before 9:00 (18.4–23.3%) was higher than that of flowers opening at 11:00 (15.3–17.5%). The nectar volume was positively correlated with air temperature and relative humidity, while the nectar sugar concentration was positively correlated with air temperature and negatively correlated with relative humidity. The nectar volume and nectar sugar concentration were positively correlated with corolla opening size. The glucose/fructose ratio ranged from 0.89 to 1.44. These results will contribute to a better understanding of the nectar secretion patterns of B. napus L. and will support further studies assessing the melliferous potential of B. napus L. and the temporal dynamics of plant-pollinator interactions.

STYLAR MOVEMENT IN Talinum fruticosum (TALINACEAE): CONTRIBUTIONS TO THE REPRODUCTIVE SUCCESS OF THE SPECIES IN POPULATIONS FROM CENTRAL-WEST BRAZIL

In plant species, the movement of reproductive structures can be an adaptive advantage in mating system studies. This phenomenon can promote outcrossing or cause a reduction in intrafloral male-female sexual interference. Consequently, this contributes to the avoidance of self-pollination and/or delayed autonomous self-pollination. The aim of this short communication is to report the results of assessments done in two natural populations of a native species from central-west Brazil that grows spontaneously and sub-spontaneously in opening and ruderal areas of Pantanal. In this study, the movement of the stigma was recorded throughout floral anthesis, and the mating system was determined. Floral measurements such as: flower opening time, pollen viability and the period that the stigma was receptive were also reported. The formation of fruits by spontaneous self-pollination and cross-pollination reinforces the hypothesis that stylar movement in Talinum fruticosum can facilitate or hinder self-pollination in some situations.

Divergent strategies of nectar secretion in two bat-pollinated Passiflora species

The secretion dynamics and chemical compositions of flower nectar can vary according to the plant physiology and the pollinator type. Bat-pollinated flowers are commonly associated with nocturnal nectar secretion as well as large amounts of nectar per flower, which is generally diluted and composed mostly of hexose sugars. The nectar traits in bat-pollinated Passiflora species are poorly understood and in this work, we describe these for two such species. We conducted field experiments to assess the nectar secretion dynamics of two species with nocturnal anthesis and similar colours and structures, performed chemical analyses of the sugar components of nectar from these two species, and combined these data with systematic observations of floral visitors. The nectar dynamics of both Passiflora species are similar to those of other bat-pollinated species. In Passiflora mucronata, nectar secretion starts before the flower opens, which occurs around 04h00, with secretion ending after 10h00. Passiflora setacea starts secreting nectar at the time of flower opening, around 22h00, finishing secretion between 04h00 and 06h00. In P. setacea, the final period of anthesis is characterised by active nectar resorption. The different blooming times of these two bat-pollinated passionflowers and the significant differences in their nectar secretion schedules suggest a divergent nectar secretion dynamics: the nectar of P. mucronata is made available only by the end of the bats’ foraging activity period, continuing throughout the morning, while P. setacea secretes nectar earlier, with very little overlap in the secretion period between the species. We hypothesise that this segregation in time helps avoid the negative effects from competition for pollinators or pollen interference between flowers with a similar structure, while the outstanding nectar traits and the constant production of flowers throughout the year make these closely related vines important nectar sources for their bat pollinators where they co-occur.

Floral biology, breeding system and pollination ecology of Justicia betonica L. (Acanthaceae): An assessment of its low reproductive success in West Bengal, India

AbstractBesides its importance as an ornamental plant, Justicia betonica L. is also used as a medicinal plant for the treatment of several human disorders. However, the population size and abundance of the plant species are very low in Indian states, including West Bengal. The breeding system and pollination ecology of J. betonica are still unclear. Therefore, some reproductive aspects were investigated in order to provide important information for the sustainability of the species. The flowering duration spanned from December to May, with its peak in February–March. Flower opening time was much earlier (5.00–8.00 a.m.) on a hot day (in April–May) than on a cold day (10.00 a.m.–12.00 p.m. in December–January). The time of anther dehiscence coincided with the flower opening time; however, the stigma became receptive later. The plant species is self‐compatible but dependent on pollinators for fruit and seed sets. Members of different insect groups like ants, bees, butterflies, flies, moths and wasps visit the flowers. Among them, Allorhynchium metallicum and Halictus acrocephalus are the primary pollinators (based on the “relative pollinator service”). The plant species showed a significant pollination deficit (coefficient of pollination deficit [D] = 0.32) in the open condition. Larvae of the florivorous moth Gatesclarkeana erotias significantly reduced reproductive success by eating their floral parts, ovules and immature seeds. In conclusion, combining the pollination deficit and the feeding activity of phytophagous insects (moth larvae) may reduce the reproductive fitness of J. betonica in the study regions.

Effect of drought stress on flowering characteristics in rice (Oryza sativa L.): a study using genotypes contrasting in drought tolerance and flower opening time

ABSTRACT Rice is most susceptible to heat and drought stress at flowering stage, but flowering characteristics under drought stress are not well characterized. This study investigated flowering characteristics of rice genotypes contrasting in their flower opening time (FOT) and level of drought tolerance. Near-isogenic lines for the early-morning flowering trait (IR64+ qEMF3) and for drought tolerance (IR87707-445-B-B-B), and their recurrent parent cultivar (IR64) were used. IR64+ qEMF3 had stable earlier FOT than IR64 and IR87707-445-B-B-B under drought stress conditions. Drought stress occasionally affects FOT depending on genotype. The number of open spikelets was higher in IR87707-445-B-B-B than in IR64 and IR64+ qEMF3, and the difference among genotypes increased as the rice plants were subjected to more severe stress levels. Panicle temperature increased under drought stress conditions and was similar among genotypes when it was measured at the same time of day, demonstrating that earlier FOT in IR64+ qEMF3 must be beneficial to avoid heat stress at flowering under drought stress conditions. However, IR64+ qEMF3 did not exhibit drought avoidance, as evidenced by the root mass at depth. To assess the potential for the EMF trait to complement ongoing drought breeding efforts, heat tolerance among 13 advanced drought breeding lines and released cultivars was tested. Wide variation in heat tolerance at flowering was observed and, notably, none of the 13 lines possessed the EMF trait. This study therefore proposes that a breeding strategy that transfers the EMF trait into drought tolerant lines could enhance the resilience of rice spikelets to the combined stresses of heat and drought at flowering. Abbreviations: Analysis of variance (ANOVA), dry season (DS), early-morning flowering (EMF), flower opening time (FOT), near-isogenic line (NIL), panicle water potential (PWP), quantitative trait locus (QTL), wet season (WS)

Better time of flower opening, a good time to improve the efficiency of hybrid seed production

The proper time of flower opening, which ensures successful pollination by exposure of stamens and gynoecia via petal movement, is locally adapted to diverse environmental changes among different plants (Cheng et al., 2021). Consequently, flower opening time may differ among divergent populations as a result of long-term adaptation, thereby promoting prezygotic reproductive isolation by preventing mating and hybridization.

Methylesterification of cell-wall pectin controls the diurnal flower-opening times in rice

Flowers are the core reproductive organ of plants, and flowering is essential for cross-pollination. Diurnal flower-opening time is thus a key trait influencing reproductive isolation, hybrid breeding, and thermostability in plants. However, the molecular mechanisms controlling this trait remain unknown. Here, we report that rice Diurnal Flower Opening Time 1 (DFOT1) modulates pectin methylesterase (PME) activity to regulate pectin methylesterification levels of the lodicule cell walls, which affect lodicule swelling to control diurnal flower-opening time. DFOT1 is specifically expressed in the lodicules, and its expression gradually increases with the approach to flowering but decreases with flowering. Importantly, a knockout of DFOT1 showed earlier diurnal flower opening. We demonstrate that DFOT1 interacts directly with multiple PMEs to promote their activity. Knockout of PME40 also resulted in early diurnal flower opening, whereas overexpression of PME42 delayed diurnal flower opening. Lower PME activity was observed to be associated with higher levels of pectin methylesterification and the softening of cell walls in lodicules, which contribute to the absorption of water by lodicules and cause them to swell, thus promoting early diurnal flower opening. Higher PME activity had the opposite effect. Collectively, our work uncovers a molecular mechanism underlying the regulation of diurnal flower-opening time in rice, which would help reduce the costs of hybrid breeding and improve the heat tolerance of flowering plants by avoiding higher temperatures at anthesis.

An early-morning flowering trait in rice can enhance grain yield under heat stress field conditions at flowering stage

An early-morning flowering (EMF) trait is supposed to be effective in enhancing grain yield due to mitigation of heat-induced spikelet sterility at flowering in rice. This study evaluated (i) phenotypic differences between a near-isogenic line carrying a QTL for EMF trait (designated as IR64 +qEMF3) and a recurrent parent, IR64, under wide variation in climates and (ii) whether the EMF trait can enhance grain yield under heat stress at flowering. IR64 +qEMF3 had significant earlier flower opening time (FOT) in diverse environmental conditions including temperate, subtropical, and tropical regions. FOT differentially responded to maximum and minimum air temperatures between genotypes. Under non-heat stress temperatures at flowering, IR64 +qEMF3 had similar grain yield to IR64 with minimal changes in yield components. Seven field trials in heat-vulnerable regions of Myanmar for multiple years showed that higher percentage of grain set contributed to the significantly higher grain yield in IR64 +qEMF3 when plants were exposed to daily maximum air temperatures around 36.1 °C or higher. Lower spikelet sterility in IR64 +qEMF3 was attributed to the earlier FOT during cooler early morning hours. This is the first field study that clearly demonstrates the enhancement of grain yield due to EMF trait under diverse heat stress field conditions at flowering.

Effects of different photoperiods on flower opening, flower closing and circadian expression of clock-related genes in Iris domestica and I. dichotoma.

The circadian clock can entrain to forced light-dark cycles by adjusting the phases and periods of flower opening and closing in ephemeral flowers. The responses of circadian rhythms to the same light conditions differ from species. However, the differences in internal genetic mechanisms underlying the different responses between species remain unclear. Iris domestica and I. dichotoma have ephemeral flowers and significantly divergent flower opening and closing times. The effects of different photoperiods (continuous darkness, 4L20D, 8L16D, 12L12D, 16L8D, 20L4D and continuous white light) on flower opening and closing, and expression patterns of seven genes (CRYPTOCHROME 1, PHYTOCHROME B, LATE ELONGATED HYPOCOTYL, PSEUDO RESPONSE REGULATOR 95, PHYTOCHROME INTERACTING FACTOR 4-like, SMUX AUXIN UP RNA 64-like and senescence-associated gene 39-like) involved in the circadian regulation of flower opening and closing were compared between I. domestica and I. dichotoma. Flower opening and closing in the two species exhibited circadian rhythms under continuous darkness (DD), but showed arrhythmia in continuous white light (LL). In the two species, keeping robust rhythms, strong synchronicity, rapid progressions of flower opening and closing and reaching full opening stage required a dark period longer than 4h. In light-dark cycles with dark periods longer than 4h, flower opening and closing times of the two species delayed with the delay of dawn, and the degree to which flower opening time varies with the time of dawn was greater in I. dichotoma than in I. domestica. The arrhythmia of flower opening and closing under 20L4D and LL would result from the arrhythmic output signals rather than arrhythmia of oscillators and photoreceptors. The different responses of the two species to the change of photoperiods would be caused by the transcriptional differences of genes in the output pathway of circadian clock system rather than in the input pathway or oscillators.

Warming and soil water availability affect plant–flower visitor interactions for Stylosanthes capitata, a tropical forage legume

The reproductive success of a zoophilous plant species depends on biological interaction with pollinators, which involves both the provision and exploitation of flower resources. Currently, there is little information about how future climate change scenarios will impact interactions between plants and their flower visitors in the tropics. This study analyzes the effects of warming and two soil water conditions on interactions between the tropical forage legume species Stylosanthes capitata and its floral visitors during the flowering period. We used a temperature-free air-controlled enhancement (T-FACE) facility to simulate future warming scenarios by increasing canopy temperature. The tested treatments were: irrigated and ambient canopy temperature (Control); non-irrigated and ambient canopy temperature (wS); irrigated and elevated canopy temperature (eT, +2 °C above ambient canopy temperature); and non-irrigated and elevated canopy temperature (wSeT). The effects of treatments on the time of flower opening and closing, sugar concentration in the nectar, and plant–flower visitor interactions were assessed. In the warmed treatments, S. capitata flower opening occurred ~45 min earlier compared to non-warmed treatments, and flowers remained opened for only ~3 h. Further, the sugar concentration in the nectar from eT was 39% higher than in the Control. The effects of warming on floral biology and flower resource production in S. capitata had an impact on the plant–floral visitor relationships with the bees Apis mellifera and Paratrigona lineata, the most abundant potential pollinating floral visitors, and the butterfly visitor Hemiargus hanno. Additionally, around noon, the interactive and additive effects of the combined wS and eT treatments decreased insect visiting frequency. These results suggest that warming and soil water deficiency could affect flower–visitor interactions and thus the reproductive success of S. capitata in tropical belts.

Use of timelapse photography to determine flower opening time and pattern in banana (Musa spp.) for efficient hand pollination

Sterility and low seed set in bananas is the main challenge to their conventional genetic improvement. The first step to seed set in a banana breeding program depends on pollination at the right time to ensure effective fertilization. This study aimed at determining bract opening time (BOT) to enhance efficient pollination and seed set in bananas. A Nikon D810 digital camera was set-up to take pictures of growing banana inflorescences at five-minute intervals and time-lapse movies were developed at a speed of 30 frames per second to allow real-time monitoring of BOT. Genotypes studied included wild banana (1), Mchare (2), Matooke (4), Matooke hybrid (1), and plantain (1). Events of bract opening initiated by bract lift for female flowers (P < 0.01) started at 16:32 h and at 18:54 h for male flowers. Start of bract rolling was at 18:51 h among female flowers (P < 0.001) and 20:48 h for male flowers. Bracts ended rolling at 02:33 h and 01:16 h for female and flowers respectively (P < 0.05). Total time of bract opening (from lift to end of rolling) for female flowers was significantly longer than that of male flowers (P < 0.001). On average, the number of bracts subtending female flowers opening increased from one on the first day, to between one and four on the fourth day. The number regressed to one bract on day eight before start of opening of bracts subtending male flowers. There was a longer opening interval between bracts subtending female and male flowers constituting spatial and temporal separation. Bract rolling increased from partial to complete rolling from proximal to the distal end of the inflorescence among female flower. On the other hand, bracts subtending male flowers completely rolled. Differences in BOT of genotypes with the same reference time of assessment may be partly responsible for variable fertility. Hand pollination time between 07:00 and 10:00 h is slightly late thus an early feasible time should be tried.

Morning and evening alarm of the circadian clock for flower opening times in Hemerocallis

Previous studies demonstrated that flower opening time (FOT) is a stable trait and precisely controlled by a circadian clock responsive to the environment. It plays a vital role in improving fertility. Hemerocallis spp. has different FOTs divided into two types: nocturnal and diurnal. To explore the regulatory mechanisms of their FOTs, we carried out a transcriptome sequencing experiment at different developmental stages of an F1 population with different FOTs. 55,883 unigenes were obtained, and 9234 differential genes were identified. Co-expression was analyzed by K-means clustering and weighted gene co-expression network analysis. Results showed that after entering reproductive growth, two FOT types of Hemerocallis had increased expression of genes related to photosynthetic metabolism and sensitivity to environmental response such as light and hormone signal transmission. Circadian rhythm-related activities were enriched in hub genes during the flowering stage. Genes showing differential expression between the two Hemerocallis groups were related to environmental response and photosynthesis pathways. Putative circadian clock genes displayed differences in expression across the flower opening stage in both groups of Hemerocallis. Twenty-three key circadian clock genes were identified, which related to sensitivity to light signal input and gating. These genes might closely relate to FOTs in Hemerocallis.

Unusually High Frequency of Cross-Pollination Between Rice Landraces Shiuli and Kharah with Coincident Flower-Opening Times

Unusually High Frequency of Cross-Pollination Between Rice Landraces Shiuli and Kharah with Coincident Flower-Opening Times