Molecular mechanisms underlying low temperature inhibition of grain filling in maize (Zea mays L.): coordination of growth and cold responses.

Low temperature (LT) greatly restricts grain filling in maize (Zea mays L.), but the relevant molecular mechanisms are not fully understood. To better understand the effect of LT on grain development, 17 hybrids were subjected to LT stress in field trials over 3 years, and two hybrids of them with contrasting LT responses were exposed to 30/20°C and 20/10°C for 7 days during grain filling in a greenhouse. At LT, thousand-kernel weight declined, especially in LT-sensitive hybrid FM985, while grain-filling rate was on average about 48% higher in LT-tolerant hybrid DK159 than FM985. LT reduced starch synthesis in kernel mainly by suppression of transcript levels and enzyme activities for sucrose synthase and hexokinase. Brassinolide (BR) was abundant in DK159 kernel, and genes involved in BR and cytokinin signals were inducible by stress. LT downregulated the genes in light-harvesting complex and photosystem I/II subunits, accompanied by reduced photosynthetic rate and Fv/Fm in ear leaf. The LT-tolerant hybrid could maintain a high soluble sugar content and fast interconversion between sucrose and hexose in the stem internode and cob, improving assimilate allocation to kernel at LT stress and paving the way for simultaneous growth and LT stress responses.

Transcription factor OsbZIP10 modulates rice grain quality by regulating OsGIF1.

Understanding and optimizing the process of grain filling helps the quest to maximize rice (Oryza sativa L.) seed yield and quality, yet the intricate mechanisms at play remain fragmented. Transcription factors (TFs) are major players in the gene networks underlying the grain filling process. Here, we employed grain incomplete filling (OsGIF1)/cell wall invertase 2, a key gene involved in grain filling, to explore its upstream TFs and identified a bZIP family TF, OsbZIP10, to be a transcriptional activator of OsGIF1. Rice grains of the knockouts of OsbZIP10 showed increased white-core rates but lower amylose content (AC), leading to better eating and cooking qualities in all genetic backgrounds investigated, though the impact of mutations in OsbZIP10 on grain weight depended on genetic background. Multi-omics analyses suggested that, in addition to OsGIF1, multiple genes involved in different biological processes contributing to grain filling were targeted by OsbZIP10, including OsAGPS1, a gene encoding the ADP-Glc pyrophosphorylase (AGPase) small subunit, and genes contributing to homeostasis of reactive oxygen species. Distinct genetic make-up was observed in OsbZIP10 between japonica and indica rice varieties, with the majority varieties of each subspecies belonging to two different haplotypes that were closely associated with AC. Overexpressing the haplotype linked to high-AC in the low-AC genetic background increased AC. Overall, this study sheds crucial light on the significance of the OsbZIP10-OsGIF1 module in the determination of rice grain quality, offering a potential avenue for genetic engineering of rice to produce seeds with tailored attributes.

Exogenous abscisic acid (ABA) improves the filling process of maize grains at different ear positions by promoting starch accumulation and regulating hormone levels under high planting density.

BACKGROUND: Higher planting densities typically cause a decline in grain weight, limiting the potential for high maize yield. Additionally, variations in grain filling occur at different positions within the maize ear. Abscisic acid (ABA) is important for grain filling and regulates grain weight. However, the effects of exogenous ABA on the filling process of maize grains at different ear positions under high planting density are poorly understood. In this study, two summer maize hybrids (DengHai605 (DH605) and ZhengDan958 (ZD958)) commonly grown in China were used to examine the effects of ABA application during the flowering stage on grain filling properties, starch accumulation, starch biosynthesis associated enzyme activities, and hormone levels of maize grain (including inferior grain (IG) and superior grain (SG)) under high planting density. RESULTS: Our results showed that exogenous ABA significantly increased maize yield, primarily owing to a higher grain weight resulting from an accelerated grain filling rate relative to the control. There was no significant difference in yield between DH605 and ZD958 in the control and ABA treatments. Moreover, applying ABA promoted starch accumulation by raising the activities of sucrose synthase, ADP-glucose pyrophosphorylase, granule-bound starch synthases, soluble starch synthase, and starch branching enzyme in grains. It also increased the levels of zeatin riboside, indole-3-acetic acid, and ABA and decreased the level of gibberellin in grains, resulting in more efficient grain filling. Notably, IG exhibited a less efficient filling process compared to SG, probably due to lower starch biosynthesis associated enzyme activities and an imbalance in hormone contents. Nevertheless, IG displayed greater sensitivity to exogenous ABA than SG, suggesting that appropriate cultural measures to improve IG filling may be a viable strategy to further increase maize yield. CONCLUSIONS: According to our results, spraying exogenous ABA could effectively improve grain filling properties, accelerate starch accumulation by increasing relevant enzyme activities, and regulate hormone levels in grains, resulting in higher grain weight and yield of maize under high planting density. Our findings offer more evidence for using exogenous hormones to improve maize yield under high planting density.

Overexpression of Orysa;KRP4 drastically reduces grain filling in rice.

MAIN CONCLUSION: Excess of KRP4 in the developing kernels in rice causes poor filling of the grains possibly through inhibition of CDKA;2 and CDKB;1 activity mediated by its interaction with CDKF;3. The potential yield of the rice varieties producing compact and heavy panicles bearing numerous spikelets is compromised because a high percentage of spikelets remain poorly filled, reportedly because of a high expression of KRPs that causes suppression of endosperm cell proliferation. To test the stated negative relationship between KRP expression and grain filling, Orysa;KRP4 was overexpressed under the control of seed-specific glutelin promoter in IR-64 rice variety that shows good grain filling. The transgenic lines showed more than 15-fold increase in expression of KRP4 in the spikelets concomitant with nearly 50% reduction in grain filling compared with the wild type without producing any significant changes on the other yield-related parameters like panicle length and the spikelets numbers that were respectively 30.23 ± 0.89 cm and 229.25 ± 33.72 per panicle in the wild type, suggesting a highly organ-targeted effect of the genetic transformation. Yeast two-hybrid test revealed CDKF;3 as the interacting partner of KRP4, and CDKF;3 was found to interact with CDKA;2, CDKB;1 and CDKD;1. Significant decrease in grain filling in the transgenic lines compared with the wild type due to overexpression of KRP4 could be because of suppression of the activity of CDKB;1 and CDKA;2 by inhibition of their phosphorylation directly by CDKF;3, or mediated through inhibition of phosphorylation of CDKD;1 by CDKF;3. The study thus indicated that suppression of expression of KRP(s) by genetic manipulation of their promoters could be an important way of improving the yield of the rice varieties bearing compact and heavy panicles.

OsmiR5519 regulates grain size and weight and down-regulates sucrose synthase gene RSUS2 in rice (Oryza sativa L.).

MAIN CONCLUSION: The up-regulation of OsmiR5519 results in the decrease of grain size, weight and seed setting rate. OsmiR5519 plays important roles in the process of grain filling and down-regulates sucrose synthase gene RSUS2. MicroRNAs (miRNAs) are one class of small non-coding RNAs that act as crucial regulators of plant growth and development. In rice, the conserved miRNAs were revealed to regulate the yield components, but the function of rice-specific miRNAs has been rarely studied. The rice-specific OsmiR5519 was found to be abundantly expressed during reproductive development, but its biological roles remain unknown. In this study, the function of rice-specific OsmiR5519 was characterized with the miR5519-overexpressing line (miR5519-OE) and miR5519-silenced line (STTM5519). At seedling stage, the content of sucrose, glucose and fructose was obviously lower in the leaves of miR5519-OE lines than those of wild-type (WT) line. The grain size and weight were decreased significantly in miR5519-OE lines, compared to those of WT rice. The cell width of hull in miR5519-OE was smaller than that in WT. The seed setting rate was notably reduced in miR5519-OE lines, but not in STTM5519 lines. Cytological observation demonstrated that the inadequate grain filling was the main reason for the decline of seed setting rate in miR5519-OE lines. The percentage of the defects of grain amounted to 40% in miR5519-OE lines, which almost equaled to the decreased value of seed setting rate. Furthermore, the sucrose synthase gene RSUS2 was identified as a target of OsmiR5519 via RNA ligase-mediated 3'-amplification of cDNA ends (3'-RLM-RACE), dual luciferase assays and transient expression assays. In summary, our results suggest that OsmiR5519 regulates grain size and weight and down-regulates RSUS2 in rice.

Maize DDK1 encoding an Importin-4 ß protein is essential for seed development and grain filling by mediating nuclear exporting of eIF1A.

Nuclear-cytoplasmic trafficking is crucial for protein synthesis in eukaryotic cells due to the spatial separation of transcription and translation by the nuclear envelope. However, the mechanism underlying this process remains largely unknown in plants. In this study, we isolated a maize (Zea mays) mutant designated developmentally delayed kernel 1 (ddk1), which exhibits delayed seed development and slower filling. Ddk1 encodes a plant-specific protein known as Importin-4 ß, and its mutation results in reduced 80S monosomes and suppressed protein synthesis. Through our investigations, we found that DDK1 interacts with eIF1A proteins in vivo. However, in vitro experiments revealed that this interaction exhibits low affinity in the absence of RanGTP. Additionally, while the eIF1A protein primarily localizes to the cytoplasm in the wild-type, it remains significantly retained within the nuclei of ddk1 mutants. These observations suggest that DDK1 functions as an exportin and collaborates with RanGTP to facilitate the nuclear export of eIF1A, consequently regulating endosperm development at the translational level. Importantly, both DDK1 and eIF1A are conserved among various plant species, implying the preservation of this regulatory module across diverse plants.

Temporal Gene Expression Profiles From Pollination to Seed Maturity in Sorghum Provide Core Candidates for Engineering Seed Traits.

Sorghum (Sorghum bicolor (L.) Moench) is a highly nutritional multipurpose millet crop. However, the genetic and molecular regulatory mechanisms governing sorghum grain development and the associated agronomic traits remain unexplored. In this study, we performed a comprehensive transcriptomic analysis of pistils collected 1-2 days before pollination, and developing seeds collected -2, 10, 20 and 30 days after pollination of S. bicolor variety M35-1. Out of 31 337 genes expressed in these stages, 12 804 were differentially expressed in the consecutive stages of seed development. These exhibited 10 dominant expression patterns correlated with the distinct pathways and gene functions. Functional analysis, based on the pathway mapping, transcription factor enrichment and orthology, delineated the key patterns associated with pollination, fertilization, early seed development, grain filling and seed maturation. Furthermore, colocalization with previously reported quantitative trait loci (QTLs) for grain weight/size revealed 48 differentially expressed genes mapping to these QTL regions. Comprehensive literature mining integrated with QTL mapping and expression data shortlisted 25, 17 and 8 core candidates for engineering grain size, starch and protein content, respectively.

ZmMPK6, a mitogen-activated protein kinase, regulates maize kernel weight.

Kernel weight is a critical agronomic trait in maize production. Many genes are related to kernel weight but only a few of them have been applied to maize breeding and cultivation. Here, we identify a novel function of maize mitogen-activated protein kinase 6 (ZmMPK6) in the regulation of maize kernel weight. Kernel weight was reduced in zmmpk6 mutants and increased in ZmMPK6-overexpressing lines. In addition, starch granules, starch content, protein content, and grain-filling characteristics were also affected by the ZmMPK6 expression level. ZmMPK6 is mainly localized in the nucleus and cytoplasm, widely distributed across various tissues, and is expressed during kernel development, which is consistent with its role in kernel weight. Thus, these results provide new insights into the role of ZmMPK6, a mitogen-activated protein kinase, in maize kernel weight, and could be applied to further molecular breeding for kernel quality and yield in maize.

Sucrose phosphate synthase 8 is required for the remobilization of carbon reserves in rice stems during grain filling.

Carbon reserve remobilization in stems is closely related to rice grain filling. Sucrose phosphate synthase (SPS) is highly associated with carbon reserve remobilization. In this study, we investigated the expression pattern of SPS genes in various rice tissues, and found that SPS8 is the major SPS isoform in rice stems during the grain-filling stage. We then constructed sps8 mutants using the CRISPR/Cas9 system. The SPS activity of the sps8 mutants was markedly reduced in the stems. In addition, the sps8 mutants exhibited significant starch accumulation in stems. 14C-labelling experiments revealed that the remobilization of non-structural carbohydrates from rice stems to grains was impaired in the sps8 mutants. In the sps8 mutants, grain filling was delayed and yield decreased by 15% due to a reduced percentage of ripened grains. RNA sequencing and quantitative PCR analyses indicated that the genes involved in starch synthesis and degradation were up-regulated in the sps8 mutant stems. In addition, the activity of the enzymes involved in starch synthesis and degradation was increased in the sps8 stems. These results demonstrate that SPS8 is required for carbon reserve remobilization from rice stems to grains, and that its absence may enhance 'futile cycles' of starch synthesis and degradation in rice stems.

Identification of the mechanistic basis of nitrogen responsiveness in two contrasting Setaria italica accessions.

Nitrogen (N) is a macronutrient limiting crop productivity with varied requirements across species and genotypes. Understanding the mechanistic basis of N responsiveness by comparing contrasting genotypes could inform the development and selection of varieties with lower N demands, or inform agronomic practices to sustain yields with lower N inputs. Given the established role of millets in ensuring climate-resilient food and nutrition security, we investigated the physiological and genetic basis of nitrogen responsiveness in foxtail millet (Setaria italica L.). We had previously identified genotypic variants linked to N responsiveness, and here we dissect the mechanistic basis of the trait by examining the physiological and molecular behaviour of N responsive (NRp-SI58) and non-responsive (NNRp-SI114) accessions at high and low N. Under high N, NRp-SI58 allocates significantly more biomass to nodes, internodes and roots, more N to developing grains, and is more effective at remobilizing flag leaf N compared with NNRp-SI114. Post-anthesis flag leaf gene expression suggests that differences in N induce much higher transcript abundance in NNRp-SI114 than NRp-SI58, a large proportion of which is potentially regulated by APETALA2 (AP2) transcription factors. Overall, the study provides novel insights into the regulation and manipulation of N responsiveness in S. italica.

Sodium stress-induced oxidative damage and antioxidant responses during grain filling in Indica rice.

KEY MESSAGE: Sodium treatment caused the sodium ion accumulation at the milk stage of immature rice grains which in turn triggered the overproduction of reactive oxygen species and oxidative damage. The tolerant cultivar showed an enhanced antioxidative response and induced expressions of OsNHX and OsHKT ion-transporters. Sodium chloride-(NaCl) induced soil salinity is a major constraint hindering global rice production. Amongst its constituent ions, sodium (Na+) is known to be the main driver of toxicity under salt stress. The present investigation aims to measure the impacts of excess Na+ during rice grain filling using two Indica rice cultivars with opposite tolerances to salt (salt tolerant: Panvel-3, salt-sensitive: Sahyadri-3) mainly via oxidative and responsive antioxidative pathways. Plants were treated with Na+-specific treatments and NaCl with equimolar Na+ levels (100 mM) at the initiation of the reproductive phase. Stressed and control plants were harvested at three different grain-filling stages- early milk, milk, and dough and assessed for ion accumulation and oxidative damage/antioxidant responses under Na+ stress. Na+ toxicity triggered reactive oxygen species (ROS) production and upregulated the responsive enzymatic antioxidants. Na+ stress also increased the nitric oxide (NO) levels and the activity of nitrate reductase in immature grains. Differential expression levels of OsNHX and OsHKT transporters were observed in response to Na+ stress. Mature grains displayed a high accumulation of Na+ along with reduced K+ content and elevated Na+/K+ under high Na+ availability. The alterations in mature grains' sugar, starch, and protein content were also observed in response to the Na+ stress. Overall, the salt-tolerant cultivar displayed higher antioxidant activities and a lower rate of ROS generation in response to the Na+ stress. Results suggested a link between Na+ accumulation, Na+-mediated stress responses via anti/-oxidant pathways, and the grain-filling process in both rice cultivars.

TaMIR397-6A and -6B Homoeologs Encode Active miR397 Contributing to the Regulation of Grain Size in Hexaploid Wheat.

Wheat is one of the most important food crops globally, and understanding the regulation of grain size is crucial for wheat breeding to achieve a higher grain yield. MicroRNAs (miRNAs) play vital roles in plant growth and development. However, the miRNA-mediated mechanism underlying grain size regulation remains largely elusive in wheat. Here, we report the characterization and functional validation of a miRNA, TamiR397a, associated with grain size regulation in wheat. The function of three TaMIR397 homoeologs was determined through histochemical ß-glucuronidase-dependent assay. MiRNA expression was detected using quantitative reverse transcription polymerase chain reaction (qRT-PCR), and the function of TamiR397a was validated through its transgenic overexpression and repression in wheat. It was found that TaMIR397-6A and TaMIR397-6B encode active TamiR397a. The expression profiling indicated that TamiR397a was differentially expressed in various tissues and gradually up-regulated during grain filling. The inhibition of TamiR397a perturbed grain development, leading to a decrease in grain size and weight. Conversely, the overexpression of TamiR397a resulted in increased grain size and weight by accelerating the grain filling process. Transcriptome analysis revealed that TamiR397a regulates a set of genes involved in hormone response, desiccation tolerance, regulation of cellular senescence, seed dormancy, and seed maturation biological processes, which are important for grain development. Among the down-regulated genes in the grains of the TamiR397a-overexpressing transgenic plants, 11 putative targets of the miRNA were identified. Taken together, our results demonstrate that TamiR397a is a positive regulator of grain size and weight, offering potential targets for breeding wheat with an increased grain yield.

Response of rice yield, grain quality to chilling at grain filling stages.

BACKGROUND: This study aims to quantify the impacts of chilling at the grain filling stage on rice yield and grain quality. A factorial experiment with four levels of temperature and duration of chilling treatments at the early and late grain filling stages was conducted in 2017, 2018 and 2019. RESULTS: Per 10 °C·day increase in the accumulated cooling degree day at the early and late grain filling stages, the rice emergence-maturity duration was delayed by 0.8% (0.6%) and rice yield decreased by 2.2% (1.7%). Chilling at the early grain filling stage decreased the rice heading rate, while chilling at the late grain filling stage increased rice amylose but decreased protein content. For chilling treatment at the early grain filling stage, rice yield and grain quality were mainly correlated with seed-setting rate, whereas for chilling treatment at the late grain filling stage the rice yield and grain quality were mainly correlated with 1000-grain weight. CONCLUSION: This study improved the understanding of how chilling at the grain filling stages affects rice phenology, yield and grain quality, providing a theoretical basis for maintaining rice yield while ensuring grain quality. The results could be used to guide the rice-growing community in combating chilling at grain filling stages. © 2024 Society of Chemical Industry.

Limiting factors for panicle photosynthesis at the anthesis and grain filling stages in rice (Oryza sativa L.).

Panicle photosynthesis is crucial for grain yield in cereal crops; however, the limiting factors for panicle photosynthesis are poorly understood, greatly impeding improvement in this trait. In the present study, pot experiments were conducted to investigate the limiting factors for panicle photosynthesis at the anthesis stage in seven rice genotypes and to examine the temporal variations in photosynthesis during the grain filling stage in the Liangyou 287 genotype. At the anthesis stage, leaf and panicle photosynthesis was positively correlated with stomatal conductance and maximum carboxylation rate, which were in turn associated with hydraulic conductance and nitrogen content, respectively. Panicle hydraulic conductance was positively correlated with the area of bundle sheaths in the panicle neck. During grain filling, leaf and panicle photosynthesis remained constant at the early stage but dramatically decreased from 8 to 9 days after anthesis. The trends of variations in panicle photosynthesis were consistent with those in stomatal conductance but not with those in maximum carboxylation rate. At first, the maximum carboxylation rate and respiration rate in the panicle increased, through elevated panicle nitrogen content, but then drastically decreased, as a result of dehydration. The present study systematically investigated the limiting factors for panicle photosynthesis, which are vital for improving photosynthesis and crop yield.

Effects of Post-Anthesis High-Temperature Stress on Carbon Partitioning and Starch Biosynthesis in a Spring Wheat (Triticum aestivum L.) Adapted to Moderate Growth Temperatures.

This study investigates carbon partitioning in the developing endosperm of a European variety of spring wheat subjected to moderately elevated daytime temperatures (27°C/16°C d/night) from anthesis to grain maturity. Elevated daytime temperatures caused significant reductions in both fresh and dry weights and reduced the starch content of harvested grains compared to plants grown under a 20°C/16°C d/night regimen. Accelerated grain development caused by elevated temperatures was accounted for by representing plant development as thermal time (°C DPA). We examined the effects of high-temperature stress (HTS) on the uptake and partitioning of [U-14C]-sucrose supplied to isolated endosperms. HTS caused reduced sucrose uptake into developing endosperms from the second major grain-filling stage (approximately 260°C DPA) up to maturity. Enzymes involved in sucrose metabolism were unaffected by HTS, whereas key enzyme activities involved in endosperm starch deposition such as ADP-glucose pyrophosphorylase and soluble isoforms of starch synthase were sensitive to HTS throughout grain development. HTS caused a decrease in other major carbon sinks such as evolved CO2, ethanol-soluble material, cell walls and protein. Despite reductions in the labeling of carbon pools caused by HTS, the relative proportions of sucrose taken up by endosperm cells allocated to each cellular pool remain unchanged, except for evolved CO2, which increased under HTS and may reflect enhanced respiratory activity. The results of this study show that moderate temperature increases can cause significant yield reductions in some temperate wheat cultivars chiefly through three effects: reduced sucrose uptake by the endosperm, reduced starch synthesis and increased partitioning of carbon into evolved CO2.

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.

Exogenous abscisic acid improves grain filling capacity under heat stress by enhancing antioxidative defense capability in rice.

BACKGROUND: Heat stress is a major restrictive factor that causes yield loss in rice. We previously reported the priming effect of abscisic acid (ABA) on rice for enhanced thermotolerance at the germination, seedling and heading stages. In the present study, we aimed to understand the priming effect and mechanism of ABA on grain filling capacity in rice under heat stress. RESULTS: Rice plants were pretreated with distilled water, 50 µM ABA and 10 µM fluridone by leaf spraying at 8 d or 15 d after initial heading (AIH) stage and then were subjected to heat stress conditions of 38 °C day/30 °C night for 7 days, respectively. Exogenous ABA pretreatment significantly super-activated the ABA signaling pathway and improved the SOD, POD, CAT and APX enzyme activity levels, as well as upregulated the ROS-scavenging genes; and decreased the heat stress-induced ROS content (O2- and H2O2) by 15.0-25.5% in rice grain under heat stress. ABA pretreatment also increased starch synthetase activities in rice grain under heat stress. Furthermore, ABA pretreatment significantly improved yield component indices and grain yield by 14.4-16.5% under heat stress. ABA pretreatment improved the milling quality and the quality of appearance and decreased the incidence of chalky kernels and chalkiness in rice grain and improved the rice grain cooking quality by improving starch content and gel consistence and decreasing the amylose percentage under heat stress. The application of paraquat caused overaccumulation of ROS, decreased starch synthetase activities and ultimately decreased starch content and grain yield. Exogenous antioxidants decreased ROS overaccumulation and increased starch content and grain yield under heat stress. CONCLUSION: Taken together, these results suggest that exogenous ABA has a potential priming effect for enhancing rice grain filling capacity under heat stress at grain filling stage mainly by inhibiting ROS overaccumulation and improving starch synthetase activities in rice grain.

TaTPP-7A positively feedback regulates grain filling and wheat grain yield through T6P-SnRK1 signalling pathway and sugar-ABA interaction.

Grain size and filling are two key determinants of grain thousand-kernel weight (TKW) and crop yield, therefore they have undergone strong selection since cereal was domesticated. Genetic dissection of the two traits will improve yield potential in crops. A quantitative trait locus significantly associated with wheat grain TKW was detected on chromosome 7AS flanked by a simple sequence repeat marker of Wmc17 in Chinese wheat 262 mini-core collection by genome-wide association study. Combined with the bulked segregant RNA-sequencing (BSR-seq) analysis of an F2 genetic segregation population with extremely different TKW traits, a candidate trehalose-6-phosphate phosphatase gene located at 135.0 Mb (CS V1.0), designated as TaTPP-7A, was identified. This gene was specifically expressed in developing grains and strongly influenced grain filling and size. Overexpression (OE) of TaTPP-7A in wheat enhanced grain TKW and wheat yield greatly. Detailed analysis revealed that OE of TaTPP-7A significantly increased the expression levels of starch synthesis- and senescence-related genes involved in abscisic acid (ABA) and ethylene pathways. Moreover, most of the sucrose metabolism and starch regulation-related genes were potentially regulated by SnRK1. In addition, TaTPP-7A is a crucial domestication- and breeding-targeted gene and it feedback regulates sucrose lysis, flux, and utilization in the grain endosperm mainly through the T6P-SnRK1 pathway and sugar-ABA interaction. Thus, we confirmed the T6P signalling pathway as the central regulatory system for sucrose allocation and source-sink interactions in wheat grains and propose that the trehalose pathway components have great potential to increase yields in cereal crops.

MATE transporter GFD1 cooperates with sugar transporters, mediates carbohydrate partitioning and controls grain-filling duration, grain size and number in rice.

More than half of the world's food is provided by cereals, as humans obtain >60% of daily calories from grains. Producing more carbohydrates is always the final target of crop cultivation. The carbohydrate partitioning pathway directly affects grain yield, but the molecular mechanisms and biological functions are poorly understood, including rice (Oryza sativa L.), one of the most important food sources. Here, we reported a prolonged grain filling duration mutant 1 (gfd1), exhibiting a long grain-filling duration, less grain number per panicle and bigger grain size without changing grain weight. Map-based cloning and molecular biological analyses revealed that GFD1 encoded a MATE transporter and expressed high in vascular tissues of the stem, spikelet hulls and rachilla, but low in the leaf, controlling carbohydrate partitioning in the stem and grain but not in the leaf. GFD1 protein was partially localized on the plasma membrane and in the Golgi apparatus, and was finally verified to interact with two sugar transporters, OsSWEET4 and OsSUT2. Genetic analyses showed that GFD1 might control grain-filling duration through OsSWEET4, adjust grain size with OsSUT2 and synergistically modulate grain number per panicle with both OsSUT2 and OsSWEET4. Together, our work proved that the three transporters, which are all initially classified in the major facilitator superfamily family, could control starch storage in both the primary sink (grain) and temporary sink (stem), and affect carbohydrate partitioning in the whole plant through physical interaction, giving a new vision of sugar transporter interactome and providing a tool for rice yield improvement.

Nutrient accumulation and transcriptome patterns during grain development in rice.

Rice is an important source of calories and mineral nutrients for more than half of the world's population. The accumulation of essential and toxic mineral elements in rice grain affects its nutritional quality and safety. However, the patterns and processes by which different elements progressively accumulate during grain filling remain largely unknown. In the present study, we investigated temporal changes in dry matter, elemental concentrations, and the transcriptome in the grain of field-grown rice. We also investigated the effects of seed setting rate and the position of the grain within the rice panicle on element accumulation. Three different patterns of accumulation were observed: (i) elements including K, Mn, B, and Ca showed an early accumulation pattern; (ii) dry matter and elements including N, P, S, Mg, Cu, Zn, Mo, As, and Cd showed a mid accumulation pattern; and (iii) elements such as Fe showed a gradual increase pattern. These different accumulation patterns can be explained by the differences in the biogeochemical behavior of the various elements in the soil, as well as differences in plant nutrient redistribution, gene expression, and the sink-source relationship. These results improve our knowledge of the dynamics of elemental accumulation in rice grain and are helpful for identification of functional genes mediating the translocation of elements to grain.