Effects of short-term high temperature on grain quality and starch granules of rice (Oryza sativa L.) at post-anthesis stage

Quantifying the Individual and Combined Effects of Short-Term Heat Stress at Booting and Flowering Stages on Nonstructural Carbohydrates Remobilization in Rice

Rice production is threatened by climate change, particularly heat stress (HS). Nonstructural carbohydrates (NSCs) remobilization is a key physiological mechanism that allows rice plants to cope with HS. To investigate the impact of short-term HS on the remobilization of nonstructural carbohydrates (NSCs) in rice, two cultivars (Huaidao-5 and Wuyunjing-24) were subjected to varying temperature regimes: 32/22/27 °C as the control treatment, alongside 40/30/35 °C and 44/34/39 °C, for durations of 2 and 4 days during the booting, flowering, and combined stages (booting + flowering) within phytotrons across the years 2016 and 2017. The findings revealed that the stem's NSC concentration increased, while the panicle's NSCs concentration, the efficiency of NSCs translocation from the stem, and the stem NSC contribution to grain yield exhibited a consistent decline. Additionally, sugar and starch concentrations increased in leaves and stems during late grain filling and maturity stages, while in panicles, the starch concentration decreased and sugar concentration increased. The heat-tolerant cultivar, Wuyunjing-24, exhibited higher panicle NSC accumulation under HS than the heat-sensitive cultivar, Huaidao-5, which had more stem NSC accumulation. The flowering stage was the most vulnerable to HS, followed by the combined and booting stages. Heat degree days (HDDs) were utilized to quantify the effects of HS on NSC accumulation and translocation, revealing that the flowering stage was the most affected. These findings suggest that severe HS makes the stem the primary carbohydrate storage sink, and alleviation under combined HS aids in evaluating NSC accumulation, benefiting breeders in developing heat-tolerant rice varieties.

Comparative Effects of Heat Stress at Booting and Grain-Filling Stage on Yield and Grain Quality of High-Quality Hybrid Rice

Rice plants are highly sensitive to high-temperature stress, posing challenges to grain yield and quality. However, the impact of high temperatures on the quality of high-quality hybrid rice during the booting stage, as well as the differing effects of the booting and grain-filling stages on grain quality, are currently not well-known. Therefore, four high-quality hybrid rice were subjected to control (CK) and high-temperature stress during the booting (HT1) and grain-filling stages (HT2). Compared to the control, HT1 significantly reduced the spikelets panicle-1 (16.1%), seed setting rate (67.5%), and grain weight (7.4%), while HT2 significantly reduced the seed setting rate (6.0%) and grain weight (7.4%). In terms of quality, both HT1 and HT2 significantly increased chalkiness, chalky grain rate, gelatinization temperature, peak viscosity (PV), trough viscosity (TV), final viscosity (FV), and protein content in most varieties, and significantly decreased grain length, grain width, total starch content, and amylose content. However, a comparison between HT1 and HT2 revealed that the increase in chalkiness, chalky grain rate, PV, TV, and FV was greater under HT2. HT1 resulted in a greater decrease in grain length, grain width, total starch content, and amylose content, as well as an increase in protein content. Additionally, HT1 led to a significant decrease in amylopectin content, which was not observed under HT2. Therefore, future efforts in breeding and cultivating high-quality hybrid rice should carefully account for the effects of high temperatures at different stages on both yield and quality.

Stimulus-responsive proteins involved in multi-process regulation of storage substance accumulation during rice grain filling under elevated temperature

BACKGROUND

The intensified global warming during grain filling deteriorated rice quality, in particular increasing the frequency of chalky grains which markedly impact market value. The formation of rice quality is a complex process influenced by multiple genes, proteins and physiological metabolic processes. Proteins responsive to stimulus can adjust the ability of plants to respond to unfavorable environments, which may be an important protein involved in the regulation of quality formation under elevated temperature. However, relatively few studies have hindered our further understanding of rice quality formation under elevated temperature.

RESULTS

We conducted the actual field elevated temperature experiment and performed proteomic analysis of rice grains at the early stage of grain filling. Starting with the response to stimulus in GO annotation, 22 key proteins responsive to stimulus were identified in the regulation of grain filling and response to elevated temperature. Among the proteins responsive to stimulus, during grain filling, an increased abundance of signal transduction and other stress response proteins, a decreased abundance of reactive oxygen species-related proteins, and an increased accumulation of storage substance metabolism proteins consistently contributed to grain filling. However, the abundance of probable indole-3-acetic acid-amido synthetase GH3.4, probable indole-3-acetic acid-amido synthetase GH3.8 and CBL-interacting protein kinase 9 belonged to signal transduction were inhibited under elevated temperature. In the reactive oxygen species-related protein, elevated temperature increased the accumulation of cationic peroxidase SPC4 and persulfide dioxygenase ETHE1 homolog to maintain normal physiological homeostasis. The increased abundance of alpha-amylase isozyme 3E and seed allergy protein RA5 was related to the storage substance metabolism, which regulated starch and protein accumulation under elevated temperature.

CONCLUSION

Auxin synthesis and calcium signal associated with signal transduction, other stress responses, protein transport and modification, and reactive oxygen species-related proteins may be key proteins responsive to stimulus in response to elevated temperature. Alpha-amylase isozyme 3E and seed allergy protein RA5 may be the key proteins to regulate grain storage substance accumulation and further influence quality under elevated temperature. This study enriched the regulatory factors involved in the response to elevated temperature and provided a new idea for a better understanding of grain response to temperature.

Effects of increased ozone on rice panicle morphology

Ground-level ozone threatens rice production, which provides staple food for more than half of the world's population. Improving the adaptability of rice crops to ozone pollution is essential to ending global hunger. Rice panicles not only affect grain yield and grain quality but also the adaptability of plants to environmental changes, but the effects of ozone on rice panicles are not well understood. Through an open top chamber experiment, we investigated the effects of long-term and short-term ozone on the traits of rice panicles, finding that both long-term and short-term ozone significantly reduced the number of panicle branches and spikelets in rice, and especially the fertility of spikelets in hybrid cultivar. The reduction in spikelet quantity and fertility because of ozone exposure is caused by changes in secondary branches and attached spikelet. These results suggest the potential for effective adaptation to ozone by altering breeding targets and developing growth stage-specific agricultural techniques.

How rice adapts to high temperatures

High-temperature stress affects crop yields worldwide. Identifying thermotolerant crop varieties and understanding the basis for this thermotolerance would have important implications for agriculture, especially in the face of climate change. Rice (Oryza sativa) varieties have evolved protective strategies to acclimate to high temperature, with different thermotolerance levels. In this review, we examine the morphological and molecular effects of heat on rice in different growth stages and plant organs, including roots, stems, leaves and flowers. We also explore the molecular and morphological differences among thermotolerant rice lines. In addition, some strategies are proposed to screen new rice varieties for thermotolerance, which will contribute to the improvement of rice for agricultural production in the future.

Effect of climate warming on the grain quality of early rice in a double-cropped rice field: A 3-year measurement

Introduction

The threat of climate warming to global rice production has been widely addressed, but little is known about its influence on the quality of rice grains.

Methods

A free-air temperature increase (FATI) facility with two widely-planted high-quality cultivars was used to explore the impact of warming on the grain quality of early rice in subtropical China over 3 consecutive years.

Results

Compared with the control, FATI increased diurnal canopy temperature by 1.5°, and thus, rice growth duration was shortened by 4.0 d under warming. We found that warming significantly reduced both the milled rice and head rice rates relative to the control, thereby leading to a decrease in the milled rice and head rice yield by 3.9 and 8.3%, respectively. The chalky grain rate and chalkiness were increased by 19.1 and 22.2% under warming compared with the control, respectively. The content of protein, essential amino acids, and non-essential amino acids were increased by 4.1, 5.4, and 4.9% under warming, respectively. Warming reduced the amylose content and setback by 2.0 and 47.5% but increasing peak viscosity, trough viscosity, breakdown, and final viscosity by 9.5, 13.6, 5.7, and 6.0%, respectively.

Conclusion

Our results suggest that the deteriorated milling and appearance quality induced by warming may be an upcoming challenge for high-quality early rice production in the future.

Recent Advances in the Drying Process of Grains

Grain drying is a vital operation in preparing finished grain products such as flour, drinks, confectioneries and infant food. The grain drying kinetics is governed by the heat and mass transfer process between the grain and the environment. Incomplete, improper and over-drying are crucial to the grain quality and negatively influence the acceptance of the grain by the consumers. Dried grain moisture content is a critical factor for developing grain drying systems and selecting optimal performance by researchers and the grain processing industry. Many grain drying technologies such as fluidised bed dryers, fixed bed dryers, infrared dryers, microwave dryers, vacuum dryers and freeze dryers have been used in recent years. To improve the drying process of grain, researchers have combined some drying technologies such as microwave + hot air, infrared + hot air and microwave + a fluidised bed dryer. Also, they introduce some treatments such as ultrasound dielectric and dehumidification. These methods enhance the dryer performance, such as higher moisture removal, reduced processing time, higher energy efficiency and nutrient retention. Therefore, this review focused on the drying conditions, time, energy consumption, nutrient retention and cost associated with the reduction of moisture content in grain to a suitable safe level for further processing and storage.

Starch parameters and short-term temperature fluctuations - Important but not yet in focus?

Plants are regularly challenged by unfavorable environmental conditions. As climate change continues, adverse situations such as drought, heat, and cold are expected to increase and become more severe. Most starchy crops are affected by such stresses. In recent years, researchers have made many new discoveries about starch metabolism in general and also on granule structure, including effects on starch following longer-term temperature stresses. However, in this study, we focus on short-term temperature stress on storage starch granule properties. Here our knowledge is less and it is likely that also short-term temperature stresses can affect various starch parameters. Therefore, we see a need for this type of analysis and discuss the matter in more detail and we conclude that a deeper knowledge particularly of starch granule parameters could allow targeted breeding of cultivars that exhibit different starch characteristics as a result of short-term stress. For these reasons, we are convinced that more comprehensive research on the effects of short-term temperature stress on starch granule characteristics is important, necessary, and timely.

The relationship between ecological factors and commercial quality of high-quality foxtail millet "Jingu 21"

The commercial quality of foxtail millet grain (Setaria italica L.) includes appearance quality, functional quality, and cooking and eating quality, which directly determine whether consumers will purchase the product. We studied the relationship between ecological factors and commercial quality attributes of foxtail millet "Jingu 21" from twelve production areas. The results showed that altitude, latitude, and diurnal temperature range were negatively correlated with b*, total flavones content (TFC), setback (SB), consistence (CS) and pasting temperature (PTM), but positively correlated with L/B and breakdown (BD). In contrast, average temperature, average precipitation, average humidity, available nitrogen, phosphorus, and potassium had positive effects on 1,000-grain weight (KGW), b*, TFC, CS, and PTM and had a negative impact on L/B and BD. Climate factors had a greater effect on the commercial quality of foxtail millet than soil factors, and the influence of climatic factors was particularly obvious in the early and middle growth periods. The multivariate equation between ecological factors and the comprehensive score of foxtail millet commercial quality is Y = 1,159.745-4.496X₁ (altitude) + 19.529X₅ (≥10℃ effective accumulated temperature) - 166.327X₁₀ (organic matters). In conclusion, high temperature and precipitation are conducive to high quality appearance and the accumulation of functional substances, while a high diurnal temperature range and high soil nutrients are conducive to the formation of cooking and eating quality. The impact of ecological factors on foxtail millet quality is complicated and it is essential to select a cultivation site that is matched to the intended use of the foxtail millet being produced.

Identification of QTLs for Heat Tolerance at the Flowering Stage Using Chromosome Segment Substitution Lines in Rice

High temperature is a major stress in rice production. Although considerable progress has been made in investigating heat tolerance (HT) in rice, the genetic basis of HT at the heading stage remains largely unknown. In this study, a novel set of chromosome segment substitution lines (CSSLs) consisting of 113 lines derived from a heat-resistant indica variety N22 and a heat-sensitive indica variety 9311 was developed and used for the analysis of the genetic basis of HT. The heat sensitivity index (HSI) calculated based on seed-setting rates under natural and high-temperature environments was used to evaluate the influence of HT at the rice heading stage. In total, five quantitative trait loci (QTLs) associated with HT were detected based on seed-setting rate (SSR) evaluation; these were named qSSR6-1, qSSR7-1, qSSR8-1, qSSR9-1 and qSSR11-1 located on chromosomes 6, 7, 8, 9 and 11, respectively. Heat-tolerant alleles of the QTLs were all derived from N22. Among them, qSSR9-1 overlapped with QTLs identified previously, while the remaining QTLs were found novel. In particular, qSSR7-1 explained a high phenotypic variation of 26.35% with a LOD score of 10.75, thus deserved to be further validated. These findings will increase our understanding of the genetic mechanism underlying HT and facilitate the breeding of heat-tolerant rice varieties.

Grain Quality Characterization of Hybrid Rice Restorer Lines with Resilience to Suboptimal Temperatures during Filling Stage

Rice (Oryza sativa L.) is a staple food that is consumed worldwide, and hybrid rice has been widely employed in many countries to greatly increase yield. However, the frequency of extreme temperature events is increasing, presenting a serious challenge to rice grain quality. Improving hybrid rice grain quality has become crucial for ensuring consumer acceptance. This study compared the differences in milling quality, appearance quality, and physical and chemical starch properties of rice grains of five restorer lines (the male parent of hybrid rice) when they encountered naturally unfavorable temperatures during the filling period under field conditions. High temperatures (HTs) and low temperatures (LTs) had opposite effects on grain quality, and the effect was correlated with rice variety. Notably, R751, R313, and Yuewangsimiao (YWSM) were shown to be superior restorer lines with good resistance to both HT and LT according to traits such as head rice rate, chalkiness degree, chalky rice rate, amylose content, alkali spreading value, and pasting properties. However, Huazhan and 8XR274 were susceptible to sub-optimal temperatures at the grain-filling stage. Breeding hybrid rice with adverse-temperature-tolerant restorer lines can not only ensure high yield via heterosis but also produce superior grain quality. This could ensure the quantity and taste of rice as a staple food in the future, when extreme temperatures will occur increasingly frequently.

Starch structural and functional properties of waxy maize under different temperature regimes at grain formation stage

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Excessive high temperature (>35 °C) enlarges and corrodes the starch granules.

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Heat stress increases the proportion of amylopectin long chains.

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Extremely high temperature induces the lowest pasting viscosity and the highest retrogradation of starch.

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This study provides scientific basis for the deterioration of waxy maize starch under severe high temperature.

Global warming affects crop productivity, but the influence is uncertain under different temperature regimes. The impact of growth temperatures (T0, 28 °C/20 °C; T1, 32 °C/24 °C; T2, 36 °C/28 °C; T3, 40 °C/32 °C) at grain formation stage on the waxy maize starch physicochemical properties of Suyunuo5 (heat-sensitive hybrid) and Yunuo7 (heat-tolerant hybrid) was studied. Compared with T0, T2 and T3 resulted in a higher number of starch granules with more pitted or uneven surface due to the enhanced enzymatic activities of α-amylase and β-amylase. Meanwhile, large starch granule size, long amylopectin chain-length, and high relative crystallinity under T2 and T3 resulted in low pasting viscosities and gelatinization enthalpy and high retrogradation percentage, especially under T3. The low coefficient variation of gelatinization temperatures indicated that the differences were meaninglessness. The influence of T1 on the pasting viscosities were more obvious in Suyunuo5. In conclusion, high temperatures at grain formation stage deteriorated the starch pasting and retrogradation properties.

Low Light Stress Increases Chalkiness by Disturbing Starch Synthesis and Grain Filling of Rice

Low light stress increases the chalkiness of rice; however, this effect has not been fully characterized. In this study, we demonstrated that low light resulted in markedly decreased activity of ADP-glucose pyrophosphorylase in the grains and those of sucrose synthase and soluble starch synthase in the early period of grain filling. Furthermore, low light also resulted in decreased activities of granule-bound starch synthase and starch branching enzyme in the late period of grain filling. Therefore, the maximum and mean grain filling rates were reduced but the time to reach the maximum grain filling rates and effective grain filling period were increased by low light. Thus, it significantly decreased the grain weight at the maximum grain filling rate and grain weight and retarded the endosperm growth and development, leading to a loose arrangement of the amyloplasts and an increase in the chalkiness of the rice grains. Compared to the grains at the top panicle part, low light led to a greater decrease in the grain weight at the maximum grain filling rate and time to reach the grain weight at the maximum grain filling rate at the bottom panicle part, which contributed to an increase in chalkiness by increasing the rates of different chalky types at the bottom panicle part. In conclusion, low light disturbed starch synthesis in grains, thereby impeding the grain filling progress and increasing chalkiness, particularly for grains at the bottom panicle part.

Comprehensive Impacts of Climate Change on Rice Production and Adaptive Strategies in China

The rice production system is one of the most climate change sensitive agro-ecosystems. This paper reviews the effects of current and future climate change on rice production in China. In recent decades, thermal resources have increased during the rice growing season, while solar radiation resources have decreased, and precipitation heterogeneity has increased. The increasing frequency of high-temperature stress, heavy rainfall, drought, and flood disasters may reduce the utilization efficiency of hydrothermal resources. Climate change, thus far, has resulted in a significant northward shift in the potential planting boundaries of single- and double-cropping rice production systems, which negatively affects the growth duration of single-, early-, and late-cropping rice. Studies based on statistical and process-based crop models show that climate change has affected rice production in China. The effects of climate change on the yield of single rice (SR), early rice (ER), and late rice (LR) were significant; however, the results of different methods and different rice growing areas were different to some extent. The trend of a longer growth period and higher yield of rice reflects the ability of China’s rice production system to adapt to climate change by adjusting planting regionalization and improving varieties and cultivation techniques. The results of the impact assessment under different climate scenarios indicated that the rice growth period would shorten and yield would decrease in the future. This means that climate change will seriously affect China’s rice production and food security. Further research requires a deeper understanding of abiotic stress physiology and its integration into ecophysiological models to reduce the uncertainty of impact assessment and expand the systematicness of impact assessment.

Extreme Low-Temperature Stress Affects Nutritional Quality of Amino Acids in Rice

Global climate change has increased the frequency of extreme climate events, and their effects on the nutritional quality, especially on amino acids in rice, have not been quantified. The data from a 3-year low temperature stress (LTS) experiment including two rice varieties (Huaidao 5 and Nanjing 46), seven minimum/maximum temperature levels (one optimal 21/27°C and six LTS levels from 17/23 to 6/12°C), and three LTS durations (3, 6, and 9 days) after flowering, revealed significant interactive effects of LTS at different stages, durations, and temperature levels on the content and accumulation of amino acids. LTS increased rice total amino acid content, while decreasing its accumulation, with higher sensitivities to LTS at the flowering stage than at the grain filling stage. In most treatments, the lysine (the first limiting amino acid) and phenylalanine content were increased under LTS at early and peak flowering stages but decreased at the grain filling stage in both varieties, and only leucine content was increased at all three stages after flowering, while the content of other essential amino acids differed among the two varieties. With an increase of 1°C·d per day in the accumulated cold degree days, the relative content of the essential amino acids was increased by 0.01-0.41%, depending on the rice variety and growth stage. Our results suggest that LTS can improve nutritional quality of amino acids of rice grains in terms of amino acids content, especially at flowering stage. These results provide critical insights for assessing the potential impact of extreme climates on the nutrient quality of rice under future climate change.

Effects of Biochar Amendment and Nitrogen Fertilizer on RVA Profile and Rice Grain Quality Attributes

Improving rice production in modern agriculture relies heavily on the overuse of chemical fertilizer, which adversely affects grain quality. Biochar (BC) application is well known for enhancing rice yield under reduced nitrogen (N) application. Therefore, we conducted a two-year field experiment in 2019 and 2020 to evaluate RVA profile characteristics, grain milling, and appearance qualities under four BC rates (0, 10, 20, 30 t ha⁻¹) in combination with two N levels (135 and 180 kg ha⁻¹). The results showed that BC at 30 t ha⁻¹ along with 135 kg N ha⁻¹ improved rapid visco-analyzer (RVA) profile attributes, including peak viscosity (4081.3), trough viscosity (3168.0), break down (913.3), final viscosity (5135.7), and set back (1967.7). Grain yield, grain rain length, milled rice rate, percent grains with chalkiness, amylose, and starch content were improved by 27%, 23%, 37%, 24%, 14%, and 8%, respectively, in the plots treated with the combination of 30 t BC ha⁻¹ and 180 kg N ha⁻¹. A positive coefficient of correlation was observed in RVA profile, milling, and apparent quality of rice with soil properties. These results suggested that BC at 20 to 30 t ha⁻¹ in combination with 135 kg N ha⁻¹ is a promising option for enhancing grain yield, RVA profile, appearance, and milling quality.

Identification and Pleiotropic Effect Analysis of GSE5 on Rice Chalkiness and Grain Shape

Chalkiness is one of several major restricting factors for the improvement of rice quality. Although many chalkiness-related quantitative trait loci have been mapped, only a small number of genes have been cloned to date. In this study, the candidate gene GSE5 of a major quantitative trait locus (QTL) for rice chalkiness, qDEC5, was identified by map-based cloning. Phenotyping and haplotype analysis of proActin:GSE5 transgenic line, gse5-cr mutant, and 69 rice varieties further confirmed that GSE5 had the pleiotropic effects and regulated both chalkiness and grain shape. Genetic analysis showed GSE5 was a dominant gene for grain length and a semi-dominant gene for grain width and chalkiness. The DNA interval closely linked to GSE5 was introgressed to Zhenshan 97B (ZB) based on molecular marker-assisted selection, and the improved ZB showed lower chalkiness and longer but smaller grains, which showed that GSE5 played an important role in breeding rice varieties with high yield and good quality. Transcriptomics, proteomics, and qRT-PCR analyses showed that thirty-nine genes associated with carbon and protein metabolism are regulated by GSE5 to affect the formation of chalkiness, including some newly discovered genes, such as OsCESA9, OsHSP70, OsTPS8, OsPFK04, OsSTA1, OsERdj3A, etc. The low-chalkiness lines showed higher amino sugar and nucleotide sugar metabolism at 10 days after pollination (DAP), lower carbohydrate metabolism at 15 DAP, and lower protein metabolism at 10 and 15 DAP. With heat shock at 34/30°C, rice chalkiness increased significantly; OsDjC10 and OsSUS3 were upregulated at 6 and 12 DAP, respectively, and OsGSTL2 was downregulated at 12 DAP. Our results identified the function and pleiotropic effects of qDEC5 dissected its genetic characteristics and the expression profiles of the genes affecting the chalkiness formation, and provided a theoretical basis and application value to harmoniously pursue high yield and good quality in rice production.

Multiomics analysis of kernel development in response to short-term heat stress at the grain formation stage in waxy maize

Understanding the adaptive changes in maize kernels under high-temperature stress during grain formation stage is critical for developing strategies to alleviate the negative effects on yield and quality. In this study, we subjected waxy maize (Zea mays L. sinensis Kulesh) to four different temperature regimes from 1-15 d after pollination (DAP), namely normal day/normal night (control), hot day/normal night, normal day/hot night, and hot day/hot night. Compared to the control, the three high-temperature treatments inhibited kernel development and starch deposition. To understand how the kernels responded to high-temperature stress, their transcriptomes, proteomes, and metabolomes were studied at 10 DAP and 25 DAP. This showed that genes and proteins related to kernel development and starch deposition were up- and down-regulated, respectively, at 10 DAP, but this pattern was reversed at 25 DAP. Metabolome profiling under high-temperature stress showed that the accumulation patterns of metabolites at 10 DAP and 25 DAP were inversely related. Our multiomics analyses indicated that the response to high-temperature stress of signaling pathways mediated by auxin, abscisic acid, and salicylic acid was more active at 10 DAP than at 25 DAP. These results confirmed that high-temperature stress during early kernel development has a carry-over effect on later development. Taken together, our multiomics profiles of developing kernels under high-temperature stress provide insights into the processes that underlie maize yield and quality under high-temperature conditions.

Emerging cold plasma treatment on rice grains: A mini review

Future demand of rice is projected to increase with the increase of global population. However, the presence of bacteria, insects, and fungi has resulted in various changes in the physical and chemical characteristics of rice grain. To make it worse, the overuse of post-harvest chemicals (fungicide and pesticide) has caused possible risks to human health through either occupational or non-occupational exposure. For the last few years, cold plasma has been developed as an alternative non-thermal emerging technology for rice grains treatment due to its ability to inactivate or decontaminate pathogens without causing thermal damage and free of any harmful residues. Therefore, this review describes the operational mechanism of cold plasma treatment technology on rice grains, existing reactor system designs, and parameters influenced by the treatment technology (reactor design parameters and treatment process parameters). Possible advanced investigation on future reactor design modification as well as standard operating range of influenced parameters were suggested for improved efficiency and effectiveness of cold plasma treatment.

Screening and identification of genes affecting grain quality and spikelet fertility during high-temperature treatment in grain filling stage of rice

BACKGROUND

Recent temperature increases due to rapid climate change have negatively affected rice yield and grain quality. Particularly, high temperatures during right after the flowering stage reduce spikelet fertility, while interfering with sugar energy transport, and cause severe damage to grain quality by forming chalkiness grains. The effect of high-temperature on spikelet fertility and grain quality during grain filling stage was evaluated using a double haploid line derived from another culture of F1 by crossing Cheongcheong and Nagdong cultivars. Quantitative trait locus (QTL) mapping identifies candidate genes significantly associated with spikelet fertility and grain quality at high temperatures.

RESULTS

Our analysis screened OsSFq3 that contributes to spikelet fertility and grain quality at high-temperature. OsSFq3 was fine-mapped in the region RM15749-RM15689 on chromosome 3, wherein four candidate genes related to the synthesis and decomposition of amylose, a starch component, were predicted. Four major candidate genes, including OsSFq3, and 10 different genes involved in the synthesis and decomposition of amylose and amylopectin, which are starch constituents, together with relative expression levels were analyzed. OsSFq3 was highly expressed during the initial stage of high-temperature treatment. It exhibited high homology with FLOURY ENDOSPERM 6 in Gramineae plants and is therefore expected to function similarly.

CONCLUSION

The QTL, major candidate genes, and OsSFq3 identified herein could be effectively used in breeding rice varieties to improve grain quality, while tolerating high temperatures, to cope with climate changes. Furthermore, linked markers can aid in marker-assisted selection of high-quality and -yield rice varieties tolerant to high temperatures.

Detrimental effects of heat stress on grain weight and quality in rice (Oryza sativa L.) are aggravated by decreased relative humidity

There is concern over the impact of global warming on rice production due increased heat stress, coupled with decreased relative humidity (RH). It is unknown how rice yield and quality are affected by heat stress and decreased RH during the grain filling stage. We conducted experiments in controlled growth chambers on six rice cultivars, varying in heat tolerance using 12 combinative treatments of three factors: two RH levels (75% and 85%), three temperature levels (the daily maximum temperature at 33 °C, 35 °C, and 37 °C), and two durations (8 d and 15 d after anthesis). Results showed that RH75% with temperature treatments significantly reduced grain weight, which was higher than RH85%. The same trend was also observed for both head rice rate and chalkiness. R168 was the most heat-tolerant cultivar, but it still had some differences in grain weight, head rice rate, and chalkiness between the two RH regimes. The lower RH was most detrimental at 35 °C, and to a lesser extent at 33 °C, but had a negligible effect at 37 °C. Our results provide a better understanding of temperature and RH’s interaction effects on rice quality during the grain filling stage, suggesting that RH should be considered in heat tolerance screening and identification to facilitate rice breeding and genetic improvement.

Effect of yam (Dioscorea spp.) starch on the physicochemical, rheological, and sensory properties of yogurt

This study investigated the effect of the addition of starch from “hawthorn” yam (Dioscorea rotundata) and “creole” yam (Dioscorea alata) at different concentrations (0.1%, 0.3%, and 0.5% w/w) on the physicochemical and sensory properties of stirred-type yogurt. Pectin (0.3% w/w) was used as a reference stabilizer. Yogurt with yam starch presented 13.38% less syneresis than yogurts with pectin. At the sensory level, the most accepted treatment was yogurt with “creole” yam starch at 0.1% w/w. During 21 days of storage, yogurt with yam starch (“creole” and “hawthorn”) at 0.1% w/w showed a decrease in syneresis between 7% and 8%, while in those with pectin, syneresis remained practically constant in this period. Yogurt with yam starch was characterized as a pseudoplastic fluid, with a lactic acid bacterial count according to NTC 805. Yam starch can be used as stabilizer because it improves the physicochemical, sensory, and rheological characteristics of stirred-type yogurt. Especially the “creole” yam starch (0.1% w/w), which presents the best preference by consumers.

iTRAQ-based quantitative proteomic analysis reveals the metabolic pathways of grain chalkiness in response to nitrogen topdressing in rice

Grain chalkiness is a highly undesirable trait that adversely affects rice quality. This chalkiness is easily influenced by the application of chemical nitrogen (N) fertilizer at the late growth stage. However, on the molecular mechanism underlying grain chalkiness caused by late N fertilization is not fully clear. In this study, proteomic differences in expression were determined in developing grains exposed to N topdressing (108 kg N ha^-1, N+) and a control (0 kg N ha^-1, N0), using the rice variety OM052, which has a high level of chalkiness. A total of 198 differentially expressed proteins (DEPs) were detected between the N+ and N0 treatments, including 9 up-regulated proteins and 189 down-regulated proteins. Of these DEPs, approximately half were associated with carbohydrate metabolism (glycolysis, tricarboxylic acid cycle, pentose phosphate pathway, fermentation and starch metabolism) and N metabolism (protein synthesis, folding, degradation and storage, amino acid synthesis and catabolism). A detailed pathway dissection revealed that multiple metabolic pathways during the grain filling stage were involved in the N-induced grain chalkiness. Reduced abundances of proteins associated with respiratory metabolism and energy metabolism drastically impaired the biosynthesis and deposition of starch in the developmental endosperms, which might be a crucial trigger for the increase in grain chalkiness. The disturbed N metabolism and differential expression of storage proteins up-regulated during the grain filling stage are able to partially explain the occurrence of grain chalkiness in rice.

Root Growth Adaptation to Climate Change in Crops

Climate change is threatening crop productivity worldwide and new solutions to adapt crops to these environmental changes are urgently needed. Elevated temperatures driven by climate change affect developmental and physiological plant processes that, ultimately, impact on crop yield and quality. Plant roots are responsible for water and nutrients uptake, but changes in soil temperatures alters this process limiting crop growth. With the predicted variable climatic forecast, the development of an efficient root system better adapted to changing soil and environmental conditions is crucial for enhancing crop productivity. Root traits associated with improved adaptation to rising temperatures are increasingly being analyzed to obtain more suitable crop varieties. In this review, we will summarize the current knowledge about the effect of increasing temperatures on root growth and their impact on crop yield. First, we will describe the main alterations in root architecture that different crops undergo in response to warmer soils. Then, we will outline the main coordinated physiological and metabolic changes taking place in roots and aerial parts that modulate the global response of the plant to increased temperatures. We will discuss on some of the main regulatory mechanisms controlling root adaptation to warmer soils, including the activation of heat and oxidative pathways to prevent damage of root cells and disruption of root growth; the interplay between hormonal regulatory pathways and the global changes on gene expression and protein homeostasis. We will also consider that in the field, increasing temperatures are usually associated with other abiotic and biotic stresses such as drought, salinity, nutrient deficiencies, and pathogen infections. We will present recent advances on how the root system is able to integrate and respond to complex and different stimuli in order to adapt to an increasingly changing environment. Finally, we will discuss the new prospects and challenges in this field as well as the more promising pathways for future research.

Seed filling under different temperatures improves the seed vigor of hybrid rice (Oryza sativa L.) via starch accumulation and structure

Seed filling is crucial for seed vigor and starch accumulation and structure. Differences in hybrid rice seed vigor were evaluated in field experiments, conducted across two sites in 2017 and 2018, under different seed filling temperatures along with the underlying mechanisms related to the seed filling characteristics and starch accumulation and structure. Significant differences in the seed vigor parameters were revealed, with different seed filling characteristics observed under different temperatures. When averaged across cultivars, the seeds with a low seed filling rate and long seed filling duration obsessed 11.9% higher germination percentage (GP) and 22.7% higher vigor index (VI) than those with a high seed filling rate and short seed filling duration. Moreover, a high seed filling rate and short seed filling duration significantly decreased the total starch and amylose contents and increased the amylopectin content. Additionally, when averaged across cultivars, the relative crystallinity and starch granule diameter obtained with a high seed filling rate and short seed filling duration were 3.8% and 15.1% higher, respectively, than those with a low seed filling rate and long seed filling duration. In summary, it can be speculated that seed filling characteristics determine hybrid rice seed vigor by affecting starch accumulation and structure.

Anthocyanin Accumulation in Black Kernel Mutant Rice and its Contribution to ROS Detoxification in Response to High Temperature at the Filling Stage

Effect of high temperature (HT) on anthocyanin (ANS) accumulation and its relationship with reactive oxygen species (ROS) generation in color rice kernel was investigated by using a black kernel mutant (9311bk) and its wildtype (WT). 9311bk showed strikingly higher ANS content in the kernel than WT. Just like the starch accumulation in rice kernels, ANS accumulation in the 9311bk kernel increased progressively along with kernel development, with the highest level of ANS at kernel maturity. HT exposure evidently decreased ANS accumulation in 9311bk kernel, but it increased ROS and MDA concentrations. The extent of HT-induced decline in kernel starch accumulation was genotype-dependent, which was much larger for WT than 9311bk. Under HT exposure, 9311bk had a relatively lower increase in ROS and MDA contents than its WT. This occurrence was just opposite to the genotype-dependent alteration in the activities of antioxidant enzymes (SOD, CAT and APX) in response to HT exposure, suggesting more efficiently ROS detoxification and relatively stronger heat tolerance for 9311bk than its WT. Hence, the extent of HT-induced declines in grain weight and kernel starch content was much smaller for 9311bk relative to its WT. HT exposure suppressed the transcripts of OsCHS, OsF3’H, OsDFR and OsANS and impaired the ANS biosynthesis in rice kernel, which was strongly responsible for HT-induced decline in the accumulation of ANS, C3G, and P3G in 9311bk kernels. These results could provide valuable information to cope with global warming and achieving high quality for color rice production.

Integrating Molecular Markers and Environmental Covariates To Interpret Genotype by Environment Interaction in Rice (Oryza sativa L.) Grown in Subtropical Areas

Understanding the genetic and environmental basis of genotype × environment interaction (G×E) is of fundamental importance in plant breeding. If we consider G×E in the context of genotype × year interactions (G×Y), predicting which lines will have stable and superior performance across years is an important challenge for breeders. A better understanding of the factors that contribute to the overall grain yield and quality of rice (Oryza sativa L.) will lay the foundation for developing new breeding and selection strategies for combining high quality, with high yield. In this study, we used molecular marker data and environmental covariates (EC) simultaneously to predict rice yield, milling quality traits and plant height in untested environments (years), using both reaction norm models and partial least squares (PLS), in two rice breeding populations (indica and tropical japonica). We also sought to explain G×E by differential quantitative trait loci (QTL) expression in relation to EC. Our results showed that PLS models trained with both molecular markers and EC gave better prediction accuracies than reaction norm models when predicting future years. We also detected milling quality QTL that showed a differential expression conditional on humidity and solar radiation, providing insight for the main environmental factors affecting milling quality in subtropical and temperate rice growing areas.

The different influences of drought stress at the flowering stage on rice physiological traits, grain yield, and quality

Seasonal drought is a major threat to rice production. However, the sensitivity of rice to drought stress (DS) at different growth periods remains unclear. The objective of this study was to reveal the different impacts of DS at the flowering stage on rice physiological traits, grain yield, and quality. Field experiments were conducted with two rice cultivars, Yangliangyou 6 (YLY6) and Hanyou 113 (HY113) under two water treatments (traditional flooding (CK) and DS at flowering stage) in 2013 and 2014. Compared with CK, grain yield (GY) under DS was significantly reduced by 23.2% for YLY6 and 24.0% for HY113 while instantaneous water use efficiency (IWUE) was significantly increased by 39% for YLY6 and 37% for HY113, respectively. All physiological traits were significantly decreased under DS and physiological activities did not revert to normal levels at grain filling stage. There was no significant effect on the appearance and nutritional quality except for the significant increase in chalky kernel and chalkiness under DS. Our data suggest that drought stress at flowering stage has a strong influence on rice physiological traits and yield. Stronger recovery capability contributes to maintaining relatively high grain production, which could be a great target for the breeder in developing drought-tolerant rice cultivars.

Amino acid content in rice grains is affected by high temperature during the early grain-filling period

Amino acid content in grains is an important nutritional quality trait in rice. High temperature can affect rice quality by accelerating grain filling. However, there is limited information available on the influence of high temperature on amino acid content in rice grains, especially under natural conditions. In this study, grain-filling traits and amino acid content in the grain of two rice cultivars (Luliangyou 996 and Lingliangyou 268) were compared between two years (2016 and 2017) with contrasting temperatures during the early grain-filling period under field conditions. Average daily mean temperature during the period of 0–5 days after full heading in 2016 (30.1 °C) was 5.4 °C higher than that in 2017. Initial, maximum, and mean grain-filling rates were 42–307% higher in 2016 than in 2017 for Luliangyou 996 and Lingliangyou 268. The time taken to reach the maximum grain-filling rate and active grain-filling duration were 6.3–10.7 d shorter in 2016 compared to 2017 for Luliangyou 996 and Lingliangyou 268. Grain weight was equal to or significantly higher in 2016 than in 2017 for Luliangyou 996 and Lingliangyou 268. N accumulation and N content in the grain were significantly lower in 2016 than in 2017 for both cultivars. The grain contents of all detected amino acids, except for methionine in Luliangyou 996, were significantly lower in 2016 than in 2017. Our study suggests that high temperature during the early grain-filling period can result in an accelerated grain-filling process, reduced N accumulation and content in rice grains, and consequently reduced amino acid content in the grain.

Genetic Dissection of qPCG1 for a Quantitative Trait Locus for Percentage of Chalky Grain in Rice (Oryza sativa L.)

Rice is a pivotal cereal crop that provides the staple food for more than half of the world's population. Along with improvements in the standard of living, people not only pay attention to the grain yield but also to the grain quality. Chalkiness is one of the most important index of grain quality. In this study, qPCG1, a QTL for percentage of chalky grain, was mapped in an interval with a physical distance about 139 kb on chromosome 1 by residual heterozygous line (RHL) method. qPCG1 was incomplete dominant and the additive effect plays a major role and explained 6.8-21.9% of phenotypic variance within the heterogeneous region on chromosome 1. The effect of allele from Zhonghui9308 was decreasing the percentage of chalky grains (PCG). Microscope observation results indicated that there are great differences in the shape, structure and arrangement of starch granule between the chalky part and transparent part. Analysis of starch physicochemical properties showed that the total starch content, amylose content and chain length distribution of amylopectin changed while the protein contents were not apparently affected with the changed chalkiness. qPCG1 had little influence on main agronomic traits and it might be useful in rice breeding for it did not bring negative effect on grain yield while reducing the chalkiness.