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 < 7 days, 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.

Jasmonate-deficient mutant lox3a reveals crosstalk between jasmonate and ethylene in the differential regulation of male and female flower opening and early fruit development in Cucurbita pepo

Jasmonate (JA) has been found to be a relevant hormone in floral development in numerous species, but its function in cucurbit floral development and sex determination is unknown. Crosstalk between JA and ethylene (ET) in the differential regulation of male and female floral development was investigated by using the novel JA-deficient mutant lox3a, and the ET-deficient and -insensitive mutants, aco1a and etr2b, respectively, of Cucurbita pepo. The lox3a mutation suppresses male and female flower opening and induces the development of parthenocarpic fruit. A bulked-segregant analysis coupled with whole genome sequencing and fine mapping approach allowed the identification of lox3a mutation in CpLOX3A, a LIPOXYGENASE gene involved in JA biosynthesis. The reduced JA content and expression of JA-signalling genes in male and female flowers of lox3a, and the rescue of lox3a phenotype by external application of methyl jasmonate (MeJA), demonstrated that JA controls petal elongation and flower opening, as well as fruit abortion in the absence of fertilization. JA also rescued the phenotype of ET mutants aco1a and etr2b, which are both specifically defective in female flower opening and fruit abortion. ET, the sex determining hormone of cucurbits, is induced in female flowers towards anthesis, activating JA production and promoting the aperture of the female flower, and the abortion of the unfertilized ovary. Given the close association between flower closure and parthenocarpic fruit development, we propose that flower opening can act as a switch that triggers fruit set and development in fertilized ovaries, but may alternatively induce the abortion of the unfertilized ovary. Both ET and JA from mature and senescent petals can serve as remote signals that determine the alternative development of the ovary and fruit.

Multigenic regulation in the ethylene biosynthesis pathway during coffee flowering

Ethylene regulates different aspects of the plant's life cycle, such as flowering, and acts as a defense signal in response to environmental stresses. Changes induced by water deficit (WD) in gene expression of the main enzymes involved in ethylene biosynthesis, 1-aminocyclopropane-1-carboxylic acid synthase (ACS) and oxidase (ACO), are frequently reported in plants. In this study, coffee (Coffea arabica) ACS and ACO family genes were characterized and their expression profiles were analyzed in leaves, roots, flower buds, and open flowers from plants under well-watered (WW) and water deficit (WD) conditions. Three new ACS genes were identified. Water deficit did not affect ACS expression in roots, however soil drying strongly downregulated ACO expression, indicating a transcriptional constraint in the biosynthesis pathway during the drought that can suppress ethylene production in roots. In floral buds, ACO expression is water-independent, suggesting a higher mechanism of control in reproductive organs during the final flowering stages. Leaves may be the main sites for ethylene precursor (1-aminocyclopropane-1-carboxylic acid, ACC) production in the shoot under well-watered conditions, contributing to an increase in the ethylene levels required for anthesis. Given these results, we suggest a possible regulatory mechanism for the ethylene biosynthesis pathway associated with coffee flowering with gene regulation in leaves being a key point in ethylene production and ACO genes play a major regulatory role in roots and the shoots. This mechanism may constitute a regulatory model for flowering in other woody species.

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-022-01235-y.

DiZF-C3H1, a zinc finger transcription factor from the dove tree (Davidia involucrata Baill.), plays a negative role in seed development and plant growth in Arabidopsis and tobacco

Low seed fertility seriously limits the survival and adaption of rare plant species. Here, we identified a seed-specific gene, DiZF-C3H1, from the dove tree and verified its function. Overexpression of DiZF-C3H1 caused retarded root development, delayed anthesis, abnormal floral organs, and deformed siliques in transgenic Arabidopsis lines. No offspring were obtained in transgenic Arabidopsis lines due to serious seed abortion. Therefore, we performed further verification in tobacco. Similarly, overexpression of DiZF-C3H1 retarded root development and reduced berry size and seed yield in transgenic tobacco lines. Moreover, although transgenic tobacco offspring were obtained, the viability of transgenic seeds was reduced and their germination was delayed. In addition, faded flowers were observed in transgenic tobacco lines. Taken together, DiZF-C3H1 was verified to play a negative role in root growth, floral organ development, and especially seed development in Arabidopsis and tobacco. This appears to be a deleterious gene for these model plants with high seed fertility. However, this function might be of special significance for Davidia, whose seed dormancy period is extremely long; DiZF-C3H1 might play a critical role in the distinctive reproduction strategy adopted by this rare and endangered species.

Potential benefits of promoting snowmelt by artificial snow blacking on the growth of winter wheat and their dependence upon regional climate

An earlier onset of regrowth after snow disappearance can enable wheat cultivars to avoid the hotter grain-filling period, without the need for early sowing in snowy regions. A blackened snow surface easily accelerates snow melting by absorbing solar radiation. In this study, we compare the yield components associated with snowmelt acceleration over 4 years and in 2 locations (Sapporo, SP, and Memuro, MM) in Japan, which exhibit contrasting autumn and spring climates. Early snow melting by snow-blackening accelerated wheat growth in MM by a maximum of 4 days for heading and 3 days for anthesis. Moreover, accelerating wheat phenological growth improved the grain yield in MM in 2016. This is because wheat plants were less likely to experience the localised cool and rainy weather that typically occurs during anthesis in mid-June. Early anthesis would decrease the likelihood that wheat plants experiencing lower sunlight intensity during the grain-filling period owing to exposure to rainy weather. However, warmer autumn conditions in SP likely hindered the development of high-level cold resistance in overwintering wheat. Accelerating snowmelt is one possible tool for mitigating the fluctuations in regional wheat production; however, the effectiveness of snow-blackening depends on the regional climate.

Flowering in Persian walnut: patterns of gene expression during flower development

BACKGROUND

Flower development and sufficient fruit set are important parameters with respect to walnut yield. Knowledge about flowering genes of fruit trees can help to conduct better molecular breeding programs. Therefore, this study was carried out to investigate the expression pattern of some flowering genes (FT, SOC1, CAL, LFY and TFL1) in Persian walnut (cv. Chandler) during the growing season and winter dormancy.

RESULTS

The results showed that walnut flower induction and initiation in Shahmirzad, Iran occurred in early June and late September, respectively. After meeting chilling and heat requirement, flower differentiation and anthesis occurred in late-March and mid-April to early-May, respectively. Study of flowering gene expression showed that the expression of the FT gene increased in three stages including before breaking of bud dormancy, from late March to late April (coincided with flower differentiation and anthesis) and from late May to mid-June (coincided with flower induction). Like FT, the expression of SOC1 gene increased during flower induction and initiation (mid-May to early-August) as well as flower anthesis (mid-April to early-May). LFY and CAL genes as floral meristem identity genes are activated by FT and SOC1 genes. In contrast with flowering stimulus genes, TFL1 showed overexpression during winter dormancy which prevented flowering.

CONCLUSION

The expression of FT gene activated downstream floral meristem identity genes including SOC1, CAL and LFY which consequently led to release bud dormancy as well as flower anthesis and induction. Also, TFL1 as a flowering inhibitor gene in walnut showed overexpression during the bud dormancy. Chilling accumulation reduced TFL1 gene expression and increased the expression of flowering genes which ultimately led to overcome dormancy.

Detecting flowering phenology in oil seed rape parcels with Sentinel-1 and -2 time series

A novel methodology is proposed to robustly map oil seed rape (OSR) flowering phenology from time series generated from the Copernicus Sentinel-1 (S1) and Sentinel-2 (S2) sensors. The time series are averaged at parcel level, initially for a set of 229 reference parcels for which multiple phenological observations on OSR flowering have been collected from April 21 to May 19, 2018. The set of OSR parcels is extended to a regional sample of 32,355 OSR parcels derived from a regional S2 classification. The study area comprises the northern Brandenburg and Mecklenburg-Vorpommern (N) and the southern Bavaria (S) regions in Germany. A method was developed to automatically compute peak flowering at parcel level from the S2 time signature of the Normalized Difference Yellow Index (NDYI) and from the local minimum in S1 VV polarized backscattering coefficients. Peak flowering was determined at a temporal accuracy of 1 to 4 days. A systematic flowering delay of 1 day was observed in the S1 detection compared to S2. Peak flowering differed by 12 days between the N and S. Considerable local variation was observed in the N-S parcel-level flowering gradient. Additional in-situ phenology observations at 70 Deutscher Wetterdienst (DWD) stations confirm the spatial and temporal consistency between S1 and S2 signatures and flowering phenology across both regions. Conditions during flowering strongly determine OSR yield, therefore, the capacity to continuously characterize spatially the timing of key flowering dates across large areas is key. To illustrate this, expected flowering dates were simulated assuming a single OSR variety with a 425 growing degree days (GDD) requirement to reach flowering. This GDD requirement was calculated based on parcel-level peak flowering dates and temperatures accumulated from 25-km gridded meteorological data. The correlation between simulated and S2 observed peak flowering dates still equaled 0.84 and 0.54 for the N and S respectively. These Sentinel-based parcel-level flowering parameters can be combined with weather data to support in-season predictions of OSR yield, area, and production. Our approach identified the unique temporal signatures of S1 and S2 associated with OSR flowering and can now be applied to monitor OSR phenology for parcels across the globe.

OPEN GLUME1: a key enzyme reducing the precursor of JA, participates in carbohydrate transport of lodicules during anthesis in rice

OG1 is involved in JA-regulated anthesis by modulating carbohydrate transport of lodicules in rice. Flowering plants have evolved a sophisticated regulatory network to coordinate anthesis and maximize reproductive success. In addition to various environmental conditions, the plant hormone jasmonic acid and its derivatives (JAs) are involved in anthesis. However, the underlying mechanism remains largely unexplored. Here, we report a JA-defective mutant in rice (Oryza sativa), namely open glume 1, which has dysfunctional lodicules that lead to open glumes following anthesis. Map-based cloning and subsequent complementation tests confirmed that OG1 encodes a peroxisome-localized 12-oxo-phytodienoic acid reductase-a key enzyme that reduces the precursor of JA. Loss-of-function of OG1 resulted in almost no JA accumulation. Exogenous JA treatment completely rescued the defects caused by the og1 mutation. Further studies revealed that intracellular metabolism was disrupted in the lodicules of og1 mutant. At the mature plant stage, most seeds of the mutant were malformed with significantly reduced starch content. We speculate that JA or JA signaling mediates the carbohydrate transport of lodicules during anthesis, and signal the onset of cell degradation in lodicules after anthesis. We conclude that the OPEN GLUME 1 gene that produces a key enzyme involved in reducing the precursor of JA in JA biosynthesis and is involved in carbohydrate transport underlying normal lodicule function during anthesis in rice.

Gene expression of an arabinogalactan lysine-rich protein CaAGP18 during vegetative and reproductive development of bell pepper (Capsicum annuum L.)

Lysine-rich (Lys-rich) proteins encoded by AGP17, AGP18, and AGP19 genes are cell wall-associated glycopeptides related to sexual reproduction in flowering plants. This subclass belongs to classical arabinogalactan proteins (AGPs) widely studied in model plants like Arabidopsis. In this study, we identified the CaAGP18 cDNA from bell pepper (Capsicum annuum L.), as well as its expression pattern during vegetative and reproductive development. The deduced amino acid sequence revealed a Lys-rich AGP18 protein of 238 amino acids residues in length with an estimated molecular mass of 22.85 kDa and an isoelectric point of 9.7. The protein is predicted as canonical AGP due to the presence of a small Lys-rich region and a C-terminal sequence essential for posttranslational modification with a glycosylphosphatidylinositol (GPI). Phylogenetic analysis showed that CaAGP18 is clustered together with NtAGP18, SpAGP18, StAGP18 and NaAGP18 from Solanaceae species. CaAGP18 expression through plant phenological stages had the highest transcription level in leaves at the seedling stage, whereas in reproductive organs there was a significant up-regulation in pistils during anthesis, also in petals 2 days post-anthesis (DPA), and in fruit at the expansion stage. Our results open future research for possible roles of CaAGP18 in cell expansion as a wall-associated plasticizer and reproductive processes like pistil interactions and petal cell death.

Floral nectary, nectar production dynamics and chemical composition in five nocturnal Oenothera species (Onagraceae) in relation to floral visitors

Main conclusion The floral nectars were sucrose-dominant; however, nectar protein and amino acid contents differed, indicating that composition of nitrogenous compounds may vary considerably even between closely related plant species, irrespectively of nectary structure. Numerous zoophilous plants attract their pollinators by offering floral nectar; an aqueous solution produced by specialized secretory tissues, known as floral nectaries. Although many papers on nectaries and nectar already exist, there has been a little research into the structure of nectaries and/or nectar production and composition in species belonging to the same genus. To redress this imbalance, we sought, in the present paper, to describe the floral nectary, nectar production, and nectar composition in five nocturnal Oenothera species with respect to their floral visitors. The structure of nectaries was similar for all the species investigated, and comprised the epidermis (with nectarostomata), numerous layers of nectary parenchyma, and subsecretory parenchyma. Anthesis for a single flower was short (ca. 10-12 h), and flowers lasted only one night. The release of floral nectar commenced at the bud stage (approx. 4 h before anthesis) and nectar was available to pollinators until petal closure. Nectar concentration was relatively low (ca. 27%) and the nectar was sucrose-dominant, and composed mainly of sucrose, glucose and fructose. The protein content of the nectar was also relatively low (on average, 0.31 µg ml-1). Nevertheless, a great variety of amino acids, including both protein and non-protein types, was detected in the nectar profile of the investigated taxa. We noted both diurnal and nocturnal generalist, opportunistic floral insect visitors.

[Bacillus isolates from rhizosphere of cacti improve germination and bloom in Mammillaria spp. (Cactaceae)]

Cacti are the most representative vegetation of arid zones in Mexico where rainfall is scarce, evapotranspiration is high and soil fertility is low. Plants have developed physiological strategies such as the association with microorganisms in the rhizosphere zone to increase nutrient uptake. In the present work, four bacterial isolates from the rhizosphere of Mammillaria magnimamma and Coryphantha radians were obtained and named as QAP3, QAP19, QAP22 and QAP24, and were genetically identified as belonging to the genus Bacillus, exhibiting in vitro biochemical properties such as phosphate solubilization, indoleacetic acid production and ACC deaminase activity related to plant growth promotion, which was tested by inoculating M. magnimamma seeds. It was found that all isolates increased germination from 17 to 34.3% with respect to the uninoculated control seeds, being QAP24 the one having the greatest effect, accomplishing the germination of viable seeds (84.7%) three days before the control seeds. Subsequently, the inoculation of Mammillari zeilmanniana plants with this isolate showed a positive effect on bloom, registering during two months from a one year period, an increase of up to 31.0% in the number of flowering plants compared to control plants. The characterized Bacillus spp. isolates have potential to be used in conservation programs of plant species from arid zones.

RhVI1 is a membrane-anchored vacuolar invertase highly expressed in Rosa hybrida L. petals

Invertases are a widespread group of enzymes that catalyse the conversion of sucrose into fructose and glucose. Plants invertases and their substrates are essential factors that play an active role in primary metabolism and in cellular differentiation and by these activities they sustain development and growth. Being naturally present in multiple isoforms, invertases are known to be highly differentiated and tissue specific in such a way that every isoform is characteristic of a specific part of the plant. In this work, we report the identification of the invertase RhVI1 that was found to be highly expressed in rose petals. A characterization of this protein revealed that RhVI1 is a glycosylated membrane-anchored protein associated with the cytosolic side of the vacuolar membrane which occurs in vivo in a monomeric form. Purification yields have shown that the levels of expression decreased during the passage of petals from buds to mature and pre-senescent flowers. Moreover, the activity assay indicates RhVI1 to be an acidic vacuolar invertase. The physiological implications of these findings are discussed, suggesting a possible role of this protein during anthesis.

Genome-Wide Transcriptome Analysis During Anthesis Reveals New Insights into the Molecular Basis of Heat Stress Responses in Tolerant and Sensitive Rice Varieties

Rice is one of the main food crops in the world. In the near future, yield is expected to be under pressure due to unfavorable climatic conditions, such as increasing temperatures. Therefore, improving rice germplasm in order to guarantee rice production under harsh environmental conditions is of top priority. Although many physiological studies have contributed to understanding heat responses during anthesis, the most heat-sensitive stage, molecular data are still largely lacking. In this study, an RNA-sequencing approach of heat- and control-treated reproductive tissues during anthesis was carried out using N22, one of the most heat-tolerant rice cultivars known to date. This analysis revealed that expression of genes encoding a number of transcription factor families, together with signal transduction and metabolic pathway genes, is repressed. On the other hand, expression of genes encoding heat shock factors and heat shock proteins was highly activated. Many of these genes are predominantly expressed at late stages of anther development. Further physiological experiments using heat-tolerant N22 and two sensitive cultivars suggest that reduced yield in heat-sensitive plants may be associated with poor pollen development or production in anthers prior to anthesis. In parallel, induction levels of a set of heat-responsive genes in these tissues correlated well with heat tolerance. Altogether, these findings suggest that proper expression of protective chaperones in anthers is needed before anthesis to overcome stress damage and to ensure fertilization. Genes putatively controlling this process were identified and are valuable candidates to consider for molecular breeding of highly productive heat-tolerant cultivars.

Integration of molecular and physiological models to explain time of anthesis in wheat

BACKGROUND AND AIMS

A model to predict anthesis time of a wheat plant from environmental and genetic information requires integration of current concepts in physiological and molecular biology. This paper describes the structure of an integrated model and quantifies its response mechanisms.

METHODS

Literature was reviewed to formulate the components of the model. Detailed re-analysis of physiological observations are utilized from a previous publication by the second two authors. In this approach measurements of leaf number and leaf and primordia appearance of near isogenic lines of spring and winter wheat grown for different durations in different temperature and photoperiod conditions are used to quantify mechanisms and parameters to predict time of anthesis.

KEY RESULTS

The model predicts the time of anthesis from the length of sequential phases: 1, embryo development; 2, dormant; 3, imbibed/emerging; 4, vegetative; 5, early reproductive; 6, pseudo-stem extension; and 7, ear development. Phase 4 ends with vernalization saturation (VS), Phase 5 with terminal spikelet (TS) and Phase 6 with flag leaf ligule appearance (FL). The durations of Phases 4 and 5 are linked to the expression of Vrn genes and are calculated in relation to change in Haun stage (HS) to account for the effects of temperature per se. Vrn1 must be expressed to sufficient levels for VS to occur. Vrn1 expression occurs at a base rate of 0·08/HS in winter 'Batten' and 0·17/HS in spring 'Batten' during Phases 1, 3 and 4. Low temperatures promote expression of Vrn1 and accelerate progress toward VS. Our hypothesis is that a repressor, Vrn4, must first be downregulated for this to occur. Rates of Vrn4 downregulation and Vrn1 upregulation have the same exponential response to temperature, but Vrn4 is quickly upregulated again at high temperatures, meaning short exposure to low temperature has no impact on the time of VS. VS occurs when Vrn1 reaches a relative expression of 0·76 and Vrn3 expression begins. However, Vrn2 represses Vrn3 expression so Vrn1 must be further upregulated to repress Vrn2 and enable Vrn3 expression. As a result, the target for Vrn1 to trigger VS was 0·76 in 8-h photoperiods (Pp) and increased at 0·026/HS under 16-h Pp as levels of Vrn2 increased. This provides a mechanism to model short-day vernalization. Vrn3 is expressed in Phase 5 (following VS), and apparent rates of Vrn3 expression increased from 0·15/HS at 8-h Pp to 0·33/HS at 16-h Pp. The final number of leaves is calculated as a function of the HS at which TS occurred (TS(HS)): 2·86 + 1·1 × TS(HS). The duration of Phase 6 is then dependent on the number of leaves left to emerge and how quickly they emerge.

CONCLUSIONS

The analysis integrates molecular biology and crop physiology concepts into a model framework that links different developmental genes to quantitative predictions of wheat anthesis time in different field situations.

Gibberellin metabolism in Vitis vinifera L. during bloom and fruit-set: functional characterization and evolution of grapevine gibberellin oxidases

Gibberellins (GAs) are involved in the regulation of flowering and fruit-set in grapes (Vitis vinifera L.), but the molecular mechanisms behind this process are mostly unknown. In this work, the family of grapevine GA oxidases involved in the biosynthesis and deactivation of GAs was characterized. Six putative GA 20-oxidase (GA20ox), three GA 3-oxidase (GA3ox), and eight GA 2-oxidase (GA2ox) proteins, the latter further divided into five C19-GA 2ox and three C20-GA2ox proteins, were identified. Phylogenetic analyses suggest a common origin of the GA3ox and C19-GA2ox groups and challenge previous evolutionary models. In vitro analysis revealed that all GA3ox and GA20ox enzymes prefer substrates of the non-13-hydroxylation pathway. In addition, ectopic expression of GA2ox genes in Arabidopsis thaliana confirmed the activity of their encoded proteins in vivo. The results show that bioactive GA1 accumulates in opening grapevine flowers, whereas at later developmental stages only GA4 is detected in the setting fruit. By studying the expression pattern of the grapevine GA oxidase genes in different organs, and at different stages of flowering and fruit-set, it is proposed that the pool of bioactive GAs is controlled by a fine regulation of the abundance and localization of GA oxidase transcripts.