OPAQUE3, encoding a transmembrane bZIP transcription factor, regulates endosperm storage protein and starch biosynthesis in rice

The ankyrin repeat-containing protein OsANK3 affects grain size and quality in rice

MAIN CONCLUSION

Mutation of OsANK3 increases grain length, grain weight, and chalkiness. OsANK3 influences grain size and quality by regulating genes involved in the cell cycle and starch metabolism. Grain size and endosperm starch content are key determinants of rice yield and quality. In this study, we investigated the function of OsANK3, a gene encoding ankyrin repeats, in regulating grain development traits. This gene was initially identified through mass spectrometry analysis as a potential upstream regulator of rice chalkiness in our previous screening. Using CRISPR/Cas9 technology, we generated OsANK3 knockout mutants (cr-osank3-2, cr-osank3-6, and cr-osank3-7) and found that OsANK3 is predominantly expressed in stems and leaves, with subcellular localization in the cytoplasm and plasma membrane. Disruption of OsANK3 increased plant height, grain length, grain weight, and chalkiness while reducing total starch content, amylose content (AC), and gel consistency (GC). Cytological analysis revealed that the elongated grains in cr-osank3 mutants resulted from enhanced cell proliferation and elongation in the outer lemma. qRT-PCR data demonstrated that OsANK3 regulates cell cycle-related genes, thereby influencing cell division and expansion. In addition, starch biosynthesis genes (OsGBSSI, OsAGPL1) were down-regulated in mutants, whereas starch hydrolase genes (OsAmy1 A, OsAmy3B) were up-regulated. Our findings demonstrate that OsANK3 knockout enhances grain size but compromises grain quality by altering cell dynamics and starch metabolism. This study elucidates the molecular role of OsANK3 in grain development and provides a valuable target for rice breeding programs.

A MYB61-SWB9-KOs module regulates grain chalkiness via gibberellin biosynthesis in rice endosperm

Grain chalkiness leads to the deterioration of grain appearance quality, which affects grain processing quality and the market value of rice. Gibberellin plays a crucial role in seed germination and plant growth, but its mechanism on endosperm starch synthesis and rice grain chalkiness formation remains largely elusive. Here, we identified a grain white belly (chalkiness in the belly area of grain) gene, SWB9, which encodes a kinesin-4 protein with a conserved ATPase domain and a coiled-coil domain. The mutation of SWB9 affects the starch structure, resulting in a grain white belly. SWB9 regulates endogenous gibberellin synthesis and accumulation in endosperm by directly binding to the promoter of ent-kaurene oxidase genes (KO1, KO2 and KOL5) encoding gibberellin-biosynthetic enzymes, and negatively regulates their expression. The loss of SWB9 function resulted in higher gibberellin content in the endosperm of swb9 than that of the wild type. Besides, a MYB transcription factor, MYB61 binds to the promoter of SWB9 and activates its expression. The grain of myb61 showed the same white belly phenotype as swb9, while overexpression of SWB9 in myb61 inhibited the grain white belly phenotype. Furthermore, the exogenous GA3 treatment showed increased grain chalkiness, and high gibberellin treatment can induce the reduced expression of MYB61, and then weaken the inhibitory effect of SWB9 on the expression of KO1, KO2 and KOL5, so as to break the homeostasis of endogenous gibberellin in the endosperm. Meanwhile, MYB61 directly binds to the promoter of amylopectin synthesis-related genes, SSIIa, BEIIb, ISA1 and PUL, at the GAMYB element and activates their expression, further affecting the distribution of amylopectin chain length. Our findings uncover a new insight into the gibberellin dose-dependent feedback regulation loop in rice endosperm that determines grain chalkiness formation.

A natural gene on-off system confers field thermotolerance for grain quality and yield in rice

Rising global temperatures threaten crop grain quality and yield; however, how temperature regulates grain quality and how to achieve synergistic thermotolerance for both quality and yield remain unknown. Here, we identified a rice major locus, QT12, which negatively controls grain-quality field thermotolerance by disrupting endosperm storage substance homeostasis through over-activating unfolded protein response (UPR). Natural variations in QT12 and an NF-Y complex form a natural gene on-off system to modulate QT12 expression and thermotolerance. High temperatures weaken NF-YB9/NF-YC10 interactions with NF-YA8, releasing QT12 suppression and triggering quality deterioration. Low QT12 expression confers superior quality and increases elite rice yield up to 1.31-1.93 times under large-scale high-temperature trials. Two trait regulatory haplotypes (TRHs) from co-selected variations of the four genetically unlinked genes in NF-Ys-QT12 were identified for subspecies thermotolerance differentiation. Our work provides mechanistic insights into rice field thermotolerance and offers a proof-of-concept breeding strategy to break stress-growth and yield-quality trade-offs.

A novel transcription factor OsMYB73 affects grain size and chalkiness by regulating endosperm storage substances' accumulation-mediated auxin biosynthesis signalling pathway in rice

Enhanced grain yield and quality traits are everlasting breeding goals. It is therefore of great significance to uncover more genetic resources associated with these two important agronomic traits. Plant MYB family transcription factors play important regulatory roles in diverse biological processes. However, studies on genetic functions of MYB in rice yield and quality are rarely to be reported. Here, we investigated a nucleus-localized transcription factor OsMYB73 which is preferentially expressed in the early developing pericarp and endosperm. We generated targeted mutagenesis of OsMYB73 in rice, and the mutants had longer grains with obvious white-belly chalky endosperm appearance phenotype. The mutants displayed various changes in starch physicochemical characteristics and lipid components. Transcriptome sequencing analysis showed that OsMYB73 was chiefly involved in cell wall development and starch metabolism. OsMYB73 mutation affects the expression of genes related to grain size, starch and lipid biosynthesis and auxin biosynthesis. Moreover, inactivation of OsMYB73 triggers broad changes in secondary metabolites. We speculate that rice OsMYB73 and OsNF-YB1 play synergistic pivotal role in simultaneously as transcription activators to regulate grain filling and storage compounds accumulation to affect endosperm development and grain chalkiness through binding OsISA2, OsLTPL36 and OsYUC11. The study provides important germplasm resources and theoretical basis for genetic improvement of rice yield and quality. In addition, we enriches the potential biological functions of rice MYB family transcription factors.

NAC25 transcription factor regulates the degeneration of cytoplasmic membrane integrity and starch biosynthesis in rice endosperm through interacting with MADS29

Introduction

Grain filling is a crucial stage of the rice endosperm development. During this process, the endosperm accumulates abundant storage products such as starch and proteins, which determine both the yield and quality of the grain.

Methods

Here, we analyzed the expression of NAC25 transcription factor via qRT-PCR and histochemical GUS assays, and obtained its mutants by CRISPR/Cas9-based gene editing in ZH11.

Results and discussion

The results showed that NAC25 was expressed specifically in developing rice endosperm, and knockout of NAC25 led to delayed degeneration of cytoplasmic membrane integrity, reduced starch accumulation and chalky starchy endosperm. We showed that NAC25 interacted with MADS29, a MADS family transcription factor whose mutant also showed defective grain filling. These results provide novel insight into the transcriptional regulation of rice grain filling.

Genome-wide identification and expression analysis of TaFDL gene family responded to vernalization in wheat (Triticum aestivum L.)

BACKGROUND

FLOWERING LOCUS D (FD) is a basic leucine zipper (bZIP) transcription factor known to be crucial in vernalization, flowering, and stress response across a variety of plants, including biennial and winter annual species. The TaFD-like (TaFDL) gene in wheat is the functional homologue of Arabidopsis FD, yet research on the TaFDL gene family in wheat is still lacking.

RESULTS

In this study, a total of 62 TaFDL gene family members were identified and classified into 4 main subfamilies, and these genes were located on 21 chromosomes. A comprehensive analysis of the basic physicochemical properties, gene structure, conservation motif, conserved domain, and advanced protein structure of TaFDL gene family revealed the conservation among its individual subfamily. The family members underwent purifying selection. The segmental duplication events were the main driving force behind the expansion of the TaFDL gene family. The TaFDL gene family underwent differentiation in the evolution of FD genes. Additionally, the subcellular localization and transcriptional activation activities of five key TaFDL members were demonstrated. Gene Ontology (GO) annotations and promoter cis-regulatory element analysis indicated that the TaFDL members may play potential roles in regulating flowering, hormone response, low-temperature response, light response, and stress response, which were verified by transcriptome data analysis. Specifically, quantitative real-time PCR (qRT-PCR) analysis revealed that five TaFDL genes exhibited differential responses to different vernalization conditions in winter wheat seeding. Finally, the homologous genes of the five key TaFDL genes across nine different wheat cultivars highlight significant genetic diversity.

CONCLUSION

These findings enrich the research on FD and its homologous genes, providing valuable insights into the TaFDL gene family's response to vernalization.

Grain Weight and Taste Quality in Japonica Rice Are Regulated by Starch Synthesis and Grain Filling Under Nitrogen-Phosphorus Interactions

To reveal the regulatory effects of nitrogen and phosphorus interactions on grain-filling- and starch-synthesis-related enzymes, and grain weight of superior grains (SGs) and inferior grains (IGs) and taste quality, the japonica rice cultivar Shennong 265 was grown under field conditions with three nitrogen levels (210, 178.5, and 147 kg N ha-1; N3, N2, and N1) and two phosphorus levels (105 and 73.5 kg P ha-1; P2 and P1). At the N3 level, the yield of P1 was significantly lower (by 19.26%) compared to P2; at the N2 and N1 levels, P1 yielded higher than P2, peaking at N2P1. Spikelets per panicle showed P2 exceeding P1 at the same nitrogen level, with the highest for both SGs and IGs observed at N2P2, followed by N2P1. Reductions in nitrogen and phosphorus decreased the grain-filling rate but prolonged the duration for grain-filling. N2P1 maintained grain weight by extending the grain-filling duration across the early, middle, and late stages of IGs, and the middle and late stages of SGs. Increased nitrogen enhanced the activities of soluble starch synthase (SSS) and starch branching enzyme (SBE), whereas increased phosphorus inhibited these activities in SGs but enhanced them in IGs. Reduced nitrogen and phosphorus fertilizer diminished ADP glucose pyrophosphorylase (AGPP) and granule-bound starch synthase (GBSS) activities in SGs and IGs, inhibiting amylose accumulation while enhancing taste value. Compared with N3P2, the taste value of N2P1 increased significantly by 6.93%, attributed to a higher amylopectin/amylose ratio. N2P1 (178.5 kg N ha-1 and 73.5 kg P ha-1) optimized enzyme activity, starch composition, and grain filling, balancing both yield and taste, and thus demonstrated an effective fertilization strategy for stable rice production.

A molecular module improves rice grain quality and yield at high temperatures

Excessive temperatures during grain filling can compromise endosperm starch biosynthesis and decrease grain quality and yield in rice. However, the molecular mechanisms underlying these remain unclear. Here, we show that heat shock protein OsHsp40-1 interacts with and elevates the ATPase activity of OsHsp70-2 in rice. OsHsp40-1 also interacts with the key starch biosynthetic enzymes OsGBSSI and OsPPDKB and thereby enhances their stability and activity, which is essential for maintaining rice quality and grain yield under moderate high-temperature (HT) conditions. Overexpression of OsHsp70-2 and OsHsp40-1 in rice significantly improved grain quality and yield at HT. Furthermore, a haplotype analysis identified favorable alleles of OsHsp70-2 and OsHsp40-1, which could be used for improving thermotolerance in rice. Collectively, our findings reveal a novel mechanism by which the OsHsp70-2-OsHsp40-1 module ameliorates the effects of HT on starch biosynthesis, providing a new strategy for genetic improvement of rice quality and yield under HT conditions.

A TT1-SCE1 module integrates ubiquitination and SUMOylation to regulate heat tolerance in rice

Heat stress poses a significant threat to grain yield. As an α2 subunit of the 26S proteasome, TT1 has been shown to act as a critical regulator of rice heat tolerance. However, the heat tolerance mechanisms mediated by TT1 remain elusive. In this study, we unveiled that small ubiquitin-like modifier (SUMO)-conjugating enzyme 1 (SCE1), which interacts with TT1 and acts as a downstream component of TT1, is engaged in TT1-mediated 26S proteasome degradation. We showed that SCE1 functions as a negative regulator of heat tolerance in rice, which is associated with its ubiquitination modification. Furthermore, we observed that small heat-shock proteins (sHSPs) such as Hsp24.1 and Hsp40 can undergo SUMOylation mediated by SCE1, leading to increased accumulation of sHSPs in the absence of SCE1. Reducing protein levels of SCE1 significantly enhanced grain yield under high-temperature stress by improving seed-setting rate and rice grain filling capacity. Taken together, these results uncover the critical role of SCE1 in the TT1-mediated heat tolerance pathway by regulating the abundance of sHSPs and SUMOylation, and ultimately modulating rice heat tolerance. These findings underscore the great potential of the TT1-SCE1 module in improving the heat tolerance of crops.

Lysine 98 in NAC20/NAC26 transcription factors: a key regulator of starch and protein synthesis in rice endosperm

Starch and proteins are main storage product to determine the appearance, cooking, texture, and nutritional quality of rice (Oryza sativa L.). OsNAC20 and OsNAC26, as pivotal transcription factors, redundantly regulate the expression of genes responsible for starch and protein synthesis in the rice endosperm. Any knockout of OsNAC20 or OsNAC26 did not result in visible endosperm defects. In this study, we had isolated and characterized a mutant named as floury endosperm25 (flo25). The caryopsis of the flo25 mutant exhibits a floury endosperm, accompanied by reductions in both the 1000-grain weight and grain length, as well as diminished levels of total starch and protein. Through map-based cloning, it was determined that FLO25 encodes a NAM, ATAF, and CUC (NAC) transcription factors, namely OsNAC26, with a lysine to asparagine substitution at position 98 in the flo25 mutant. Remarkably, lysine 98 is conserved across plants species, and this mutation does not alter the subcellular localization of OsNAC26 but significantly attenuates its transcriptional activity and its ability to activate downstream target genes. Furthermore, the mutant protein encoded by OsNAC26-flo25 could interact with OsNAC20, disrupting the native interaction between OsNAC20 proteins. Additionally, when lysine 98 is substituted with asparagine in OsNAC20, the resulting mutant protein, OsNAC20(K98N), similarly disrupts the interaction between OsNAC26 proteins. Collectively, these findings underscore the pivotal role of Lysine 98 (K) in modulating the transcriptional activity of NAC20/NAC26 within the rice endosperm.

Effects of high temperature on grain quality and enzyme activity in heat-sensitive versus heat-tolerant rice cultivars

BACKGROUND

High-temperature (HT) stress significantly affects the quality of rice (Oryza sativa L.), although the underlying the mechanism remains unknown. Therefore, in the present study, we assessed protein components, amino acids, mineral element levels, starch biosynthesis enzyme activity and gene expression of two heat-sensitive and two heat-tolerant genotypes under HT treatment during early (from 1 to 10 days, T1) and mid-filling (from 11 to 20 days, T2) after anthesis.

RESULTS

Except for one cultivar, most rice varieties exhibited increased levels of amylose, chalky degree and protein content, along with elevated cracked grains and pasting temperatures and, consequently, suppressed amino acid levels under HT stress. HT treatment also increased protein components, macro- (Mg, K, P and S) and microelements (Cu, Zn, and Mo) in the rice flour. Both HT treatments reduced the activity of ADP-glucose pyrophosphate, ground-bound starch synthase, as well as the relative ratio of amylose to total starch, at the same time increasing starch branch enzyme activity. The expression levels of OsAGPL2, OsSSS1 and OsSBE1 in all varieties exhibited the same trends as enzyme activity under HT treatment.

CONCLUSION

High temperatures negatively affected rice quality during grain filling, which is related to heat tolerance and grain shape. Altered enzymatic activity is crucial to compensate for the lowered enzyme quality under heat stress. © 2024 Society of Chemical Industry.

An Integrative Analysis of the Transcriptome and Proteome of Rice Grain Chalkiness Formation Under High Temperature

Exposure to high temperatures can impair the grain-filling process in rice (Oryza sativa L.), potentially leading to the formation of chalky endosperm, but the molecular regulation mechanism remains largely elusive. Here, we reported that high-temperature (HT) stress (day/night, 35 °C/30 °C) reduces both the grain-filling rate and grain weight of Ningjing 1 variety compared to normal temperatures (NT, day/night, 28 °C/23 °C). Grains under HT stress exhibited an opaque, milky-white appearance, alongside significant alterations in starch physicochemical properties. An integrated transcriptomic analysis of grains under HT revealed up-regulation of genes related to defense mechanisms and oxidoreductase activity, while genes involved in sucrose and starch synthesis were down-regulated, and α-amylase genes were up-regulated. Proteomic analysis of grains under HT echoed this pattern. These results demonstrate that high temperature during the grain-filling stage significantly increases rice chalkiness by down-regulating genes related to sucrose and starch synthesis, while up-regulating those involved in starch degradation.

Genome-Wide Analysis of Heat Shock Protein Family and Identification of Their Functions in Rice Quality and Yield

Heat shock proteins (Hsps), acting as molecular chaperones, play a pivotal role in plant responses to environmental stress. In this study, we found a total of 192 genes encoding Hsps, which are distributed across all 12 chromosomes, with higher concentrations on chromosomes 1, 2, 3, and 5. These Hsps can be divided into six subfamilies (sHsp, Hsp40, Hsp60, Hsp70, Hsp90, and Hsp100) based on molecular weight and homology. Expression pattern data indicated that these Hsp genes can be categorized into three groups: generally high expression in almost all tissues, high tissue-specific expression, and low expression in all tissues. Further analysis of 15 representative genes found that the expression of 14 Hsp genes was upregulated by high temperatures. Subcellular localization analysis revealed seven proteins localized to the endoplasmic reticulum, while others localized to the mitochondria, chloroplasts, and nucleus. We successfully obtained the knockout mutants of above 15 Hsps by the CRISPR/Cas9 gene editing system. Under natural high-temperature conditions, the mutants of eight Hsps showed reduced yield mainly due to the seed setting rate or grain weight. Moreover, the rice quality of most of these mutants also changed, including increased grain chalkiness, decreased amylose content, and elevated total protein content, and the expressions of starch metabolism-related genes in the endosperm of these mutants were disturbed compared to the wild type under natural high-temperature conditions. In conclusion, our study provided new insights into the HSP gene family and found that it plays an important role in the formation of rice quality and yield.

Production of grains with ultra-low heavy metal accumulation by pyramiding novel Alleles of OsNramp5 and OsLsi2 in two-line hybrid rice

Ensuring rice yield and grain safety quality are vital for human health. In this study, we developed two-line hybrid rice (TLHR) with ultra-low grain cadmium (Cd) and arsenic (As) accumulation by pyramiding novel alleles of OsNramp5 and OsLsi2. We first generated low Cd accumulation restorer (R) lines by editing OsNramp5, OsLCD, and OsLCT1 in japonica and indica. After confirming that OsNramp5 was most efficient in reducing Cd, we edited this gene in C815S, a genic male sterile line (GMSL), and screened it for alleles with low Cd accumulation. Next, we generated R and GMSL lines with low As accumulation by editing OsLsi2 in a series of YK17 and C815S lines. When cultivated in soils that were heavily polluted with Cd and As, the edited R, GMSL, and TLHR plants showed significantly reduced heavy metal accumulation, while maintaining a relatively stable yield potential. This study provides an effective scheme for the safe production of grains in As- and/or Cd-polluted paddy fields.

Transcription factor GmAlfin09 regulates endoplasmic reticulum stress in soybean via peroxidase GmPRDX6

Soybean (Glycine max [L.] Merr.) is a valuable oil crop but is also highly susceptible to environmental stress. Thus, developing approaches to enhance soybean stress resistance is vital to soybean yield improvement. In previous studies, transcription factor Alfin has been shown to serve as an epigenetic regulator of plant growth and development. However, no studies on Alfin have yet been reported in soybean. In this study, the endoplasmic reticulum (ER) stress- and reactive oxygen species (ROS)-related GmAlfin09 was identified. Screening of genes co-expressed with GmAlfin09 unexpectedly led to the identification of soybean peroxidase 6 (GmPRDX6). Further analyses revealed that both GmAlfin09 and GmPRDX6 were responsive to ER stress, with GmPRDX6 localizing to the ER under stress. Promoter binding experiments confirmed the ability of GmAlfin09 to bind to the GmPRDX6 promoter directly. When GmAlfin09 and GmPRDX6 were overexpressed in soybean, enhanced ER stress resistance and decreased ROS levels were observed. Together, these findings suggest that GmAlfin09 promotes the upregulation of GmPRDX6, and GmPRDX6 subsequently localizes to the ER, reduces ROS levels, promotes ER homeostasis, and ensures the normal growth of soybean even under ER stress. This study highlights a vital target gene for future molecular breeding of stress-resistant soybean lines.

BTA2 regulates tiller angle and the shoot gravity response through controlling auxin content and distribution in rice

Tiller angle is a key agricultural trait that establishes plant architecture, which in turn strongly affects grain yield by influencing planting density in rice. The shoot gravity response plays a crucial role in the regulation of tiller angle in rice, but the underlying molecular mechanism is largely unknown. Here, we report the identification of the BIG TILLER ANGLE2 (BTA2), which regulates tiller angle by controlling the shoot gravity response in rice. Loss-of-function mutation of BTA2 dramatically reduced auxin content and affected auxin distribution in rice shoot base, leading to impaired gravitropism and therefore a big tiller angle. BTA2 interacted with AUXIN RESPONSE FACTOR7 (ARF7) to modulate rice tiller angle through the gravity signaling pathway. The BTA2 protein was highly conserved during evolution. Sequence variation in the BTA2 promoter of indica cultivars harboring a less expressed BTA2 allele caused lower BTA2 expression in shoot base and thus wide tiller angle during rice domestication. Overexpression of BTA2 significantly increased grain yield in the elite rice cultivar Huanghuazhan under appropriate dense planting conditions. Our findings thus uncovered the BTA2-ARF7 module that regulates tiller angle by mediating the shoot gravity response. Our work offers a target for genetic manipulation of plant architecture and valuable information for crop improvement by producing the ideal plant type.

Deciphering the Transcriptional Regulatory Network Governing Starch and Storage Protein Biosynthesis in Wheat for Breeding Improvement

Starch and seed storage protein (SSP) composition profoundly impact wheat grain yield and quality. To unveil regulatory mechanisms governing their biosynthesis, transcriptome, and epigenome profiling is conducted across key endosperm developmental stages, revealing that chromatin accessibility, H3K27ac, and H3K27me3 collectively regulate SSP and starch genes with varying impact. Population transcriptome and phenotype analyses highlight accessible promoter regions' crucial role as a genetic variation resource, influencing grain yield and quality in a core collection of wheat accessions. Integration of time-serial RNA-seq and ATAC-seq enables the construction of a hierarchical transcriptional regulatory network governing starch and SSP biosynthesis, identifying 42 high-confidence novel candidates. These candidates exhibit overlap with genetic regions associated with grain size and quality traits, and their functional significance is validated through expression-phenotype association analysis among wheat accessions and loss-of-function mutants. Functional analysis of wheat abscisic acid insensitive 3-A1 (TaABI3-A1) with genome editing knock-out lines demonstrates its role in promoting SSP accumulation while repressing starch biosynthesis through transcriptional regulation. Excellent TaABI3-A1Hap1 with enhanced grain weight is selected during the breeding process in China, linked to altered expression levels. This study unveils key regulators, advancing understanding of SSP and starch biosynthesis regulation and contributing to breeding enhancement.

Genome-wide identification of bZIP transcription factors in 12 Rosaceae species and modeling of novel mechanisms of EjbZIPs response to salt stress

In plantae, basic leucine zipper (bZIP) transcription factors (TFs) are widespread and regulate a variety of biological processes under abiotic stress. However, it has not been extensively studied in Rosaceae, and the functional effects of bZIP on Eriobotrya japonica under salt stress are still unknown. Therefore, in this study, the bZIP TF family of 12 species of Rosaceae was analyzed by bioinformatics method, and the expression profile and quantitative real-time polymerase chain reaction of E. japonica under salt stress were analyzed. The results showed that a total of 869 bZIP TFs were identified in 12 species of Rosaceae and divided into nine subfamilies. Differences in promoter cis-elements between subfamilies vary depending on their role. Species belonging to the same subfamily have a similar number of chromosomes and the number of genes contained on each chromosome. Gene duplication analysis has found segmental duplication to be a prime force in the evolution of Rosaceae species. In addition, nine EjbZIPs were significantly different, including seven up-regulated and two down-regulated in E. japonica under salt stress. Especially, EjbZIP13 was involved in the expression of SA-responsive proteins by binding to the NPR1 gene. EjbZIP27, EjbZIP30, and EjbZIP38 were highly expressed in E. japonica under salt stress, thus improving the salt tolerance capacity of the plants. These results can provide a theoretical basis for exploring the characteristics and functions of the bZIP TF family in more species and breeding salt-tolerant E. japonica varieties. It also provides a reference for resolving the response mechanism of bZIP TF in 12 Rosaceae species under salt stress.

QTL Mapping and Candidate Gene Analysis for Starch-Related Traits in Tartary Buckwheat (Fagopyrum tataricum (L.) Gaertn)

Starch is the main component that determines the yield and quality of Tartary buckwheat. As a quantitative trait, using quantitative trait locus (QTL) mapping to excavate genes associated with starch-related traits is crucial for understanding the genetic mechanisms involved in starch synthesis and molecular breeding of Tartary buckwheat varieties with high-quality starch. Employing a recombinant inbred line population as research material, this study used QTL mapping to investigate the amylose, amylopectin, and total starch contents across four distinct environments. The results identified a total of 20 QTLs spanning six chromosomes, which explained 4.07% to 14.41% of the phenotypic variation. One major QTL cluster containing three stable QTLs governing both amylose and amylopectin content, qClu-4-1, was identified and located in the physical interval of 39.85-43.34 Mbp on chromosome Ft4. Within this cluster, we predicted 239 candidate genes and analyzed their SNP/InDel mutations, expression patterns, and enriched KEGG pathways. Ultimately, five key candidate genes, namely FtPinG0004897100.01, FtPinG0002636200.01, FtPinG0009329200.01, FtPinG0007371600.01, and FtPinG0005109900.01, were highlighted, which are potentially involved in starch synthesis and regulation, paving the way for further investigative studies. This study, for the first time, utilized QTL mapping to detect major QTLs controlling amylose, amylopectin, and total starch contents in Tartary buckwheat. The QTLs and candidate genes would provide valuable insights into the genetic mechanisms underlying starch synthesis and improving starch-related traits of Tartary buckwheat.

Phenotypic and transcriptomic responses of diverse rice accessions to transient heat stress during early grain development

Heat stress (HS) occurring during the grain-filling period has a detrimental effect on grain yield and quality in rice (Oryza sativa). The development of heat-resilient cultivars could partly solve this issue if tolerant alleles can be identified and incorporated into the germplasm. In this study, we posit that some of the phenotypic variations for heat resilience during grain development could be due to variations in gene expression among accessions. To test this, we characterized the HS response of 10 diverse rice accessions from three major sub-populations using physiological and transcriptome analyses. At a single-grain level, grain width and grain thickness emerged as the most heat-sensitive traits. During a transient HS, IND-3 was categorized as highly sensitive, while five accessions exhibited moderate heat sensitivity, and four accessions were tolerant. Only a core set of 29.4% of the differentially expressed genes was common to the three rice sub-populations. Heat-tolerant accession TEJ-5 uniquely triggered an unfolded protein response (UPR) under HS, as evident from the induction of OsbZIP50 and downstream UPR genes. OsbZIP58, a gene that positively regulates grain filling, was more highly induced by HS in IND-2 despite its moderate heat sensitivity. Collectively, our analysis suggests that both unique gene expression responses and variation in the level of responses for a given pathway distinguish diverse accessions. Only some of these responses are associated with single-grain phenotypes in a manner consistent with the known roles of these genes and pathways.

Effect of Subsoiling on the Nutritional Quality of Grains of Maize Hybrids of Different Eras

To achieve high maize (Zea mays L.) yields and quality grain, it is necessary to develop stress-resistant cultivars and related cultivation practices, aiming to maximize efficiency. Thus, our objectives were (i) to investigate the impact of tillage practices and maize hybrids (which have improved over time) on yield and its components, and (ii) to characterize the response pattern of maize hybrid grain nutrient quality components to subsoiling. To achieve this, we conducted field trials with five maize hybrids from different eras under two tillage practices: rotary tillage and subsoiling. We compared grain yield, nutritional quality, and other indicators across different tillage conditions from the 1970s to the 2010s. The main results of this study are as follows: under rotary tillage conditions, the 2010s hybrid (DH618) significantly increased yields (9.37-55.89%) compared to hybrids from the 1970s-2000s. After subsoiling, the physiologically mature grains of all hybrids exhibited minimal changes in crude protein and fat content, while there was a significant reduction in the total soluble sugar content of the grains. After subsoiling, there was a substantial 8.14 to 12.79 percent increase in total starch accumulation in the grain for all hybrids during the period of 47-75 days post-anthesis. Furthermore, during the period of 47-75 days after anthesis, the consumption of grain crude protein significantly contributed to the accumulation of total starch in the grains. Ultimately, subsoiling significantly increased the yield of each hybrid and enhanced the total grain starch content at physiological maturity of all hybrids, with the 2010s hybrid (DH618) performing exceptionally well.

OsLESV and OsESV1 promote transitory and storage starch biosynthesis to determine rice grain quality and yield

Transitory starch is an important carbon source in leaves, and its biosynthesis and metabolism are closely related to grain quality and yield. The molecular mechanisms controlling leaf transitory starch biosynthesis and degradation and their effects on rice (Oryza sativa) quality and yield remain unclear. Here, we show that OsLESV and OsESV1, the rice orthologs of AtLESV and AtESV1, are associated with transitory starch biosynthesis in rice. The total starch and amylose contents in leaves and endosperms are significantly reduced, and the final grain quality and yield are compromised in oslesv and osesv1 single and oslesv esv1 double mutants. Furthermore, we found that OsLESV and OsESV1 bind to starch, and this binding depends on a highly conserved C-terminal tryptophan-rich region that acts as a starch-binding domain. Importantly, OsLESV and OsESV1 also interact with the key enzymes of starch biosynthesis, granule-bound starch synthase I (GBSSI), GBSSII, and pyruvate orthophosphote dikiase (PPDKB), to maintain their protein stability and activity. OsLESV and OsESV1 also facilitate the targeting of GBSSI and GBSSII from plastid stroma to starch granules. Overexpression of GBSSI, GBSSII, and PPDKB can partly rescue the phenotypic defects of the oslesv and osesv1 mutants. Thus, we demonstrate that OsLESV and OsESV1 play a key role in regulating the biosynthesis of both leaf transitory starch and endosperm storage starch in rice. These findings deepen our understanding of the molecular mechanisms underlying transitory starch biosynthesis in rice leaves and reveal how the transitory starch metabolism affects rice grain quality and yield, providing useful information for the genetic improvement of rice grain quality and yield.

Improving resilience to high temperature in drought: water replenishment enhances sucrose and amino acid metabolisms in maize grain

Heat stress poses a significant threat to maize, especially when combined with drought. Recent research highlights the potential of water replenishment to ameliorate grain weight loss. However, the mitigating mechanisms of heat in drought stress, especially during the crucial early grain-filling stage, remain poorly understood. We investigated the mechanism for mitigating heat in drought stress by water replenishment from the 12th to the 32nd days after silking in a controlled greenhouse experiment (Exp. I) and field trial (Exp. II). A significant reduction in grain weight was observed in heat stress compared to normal conditions. When water replenishment was applied to increase soil water content (SWC) under heat stress, the grain yield exhibited a notable increase ranging from 28.4 to 76.9%. XY335 variety was used for transcriptome sequencing to analyze starch biosynthesis and amino acid metabolisms in Exp. I. With water replenishment, the transcripts of genes responsible for trehalose 6-phosphate phosphates (TPP), alpha-trehalase (TRE), ADP-glcpyrophosphorylase, and starch synthase activity were stimulated. Additionally, the expression of genes encoding TPP and TRE contributed to an enhanced conversion of trehalose to glucose. This led to the conversion of sucrose from glucose-1-phosphate to ADP-glucose and ADP-glucose to amylopectin, ultimately increasing starch production by 45.1%. Water replenishment to boost SWC during heat stress also elevated the levels of essential amino acids in maize, including arginine, serine, tyrosine, leucine, glutamic acid, and methionine, providing valuable support to maize plants in adversity. Field trials further validated the positive impact of water replenishment on SWC, resulting in a notable increase in grain yield ranging from 7.1 to 9.2%. This study highlights the vital importance of adapting to abiotic stress and underscores the necessity of developing strategies to counteract its adverse effects on crop yield.

FLOURY ENDOSPERM24, a heat shock protein 101 (HSP101), is required for starch biosynthesis and endosperm development in rice

Endosperm is the main storage organ in cereal grain and determines grain yield and quality. The molecular mechanisms of heat shock proteins in regulating starch biosynthesis and endosperm development remain obscure. Here, we report a rice floury endosperm mutant flo24 that develops abnormal starch grains in the central starchy endosperm cells. Map-based cloning and complementation test showed that FLO24 encodes a heat shock protein HSP101, which is localized in plastids. The mutated protein FLO24T296I dramatically lost its ability to hydrolyze ATP and to rescue the thermotolerance defects of the yeast hsp104 mutant. The flo24 mutant develops more severe floury endosperm when grown under high-temperature conditions than normal conditions. And the FLO24 protein was dramatically induced at high temperature. FLO24 physically interacts with several key enzymes required for starch biosynthesis, including AGPL1, AGPL3 and PHO1. Combined biochemical and genetic evidence suggests that FLO24 acts cooperatively with HSP70cp-2 to regulate starch biosynthesis and endosperm development in rice. Our results reveal that FLO24 acts as an important regulator of endosperm development, which might function in maintaining the activities of enzymes involved in starch biosynthesis in rice.

Orchestrating seed storage protein and starch accumulation toward overcoming yield-quality trade-off in cereal crops

Achieving high yield and good quality in crops is essential for human food security and health. However, there is usually disharmony between yield and quality. Seed storage protein (SSP) and starch, the predominant components in cereal grains, determine yield and quality, and their coupled synthesis causes a yield-quality trade-off. Therefore, dissection of the underlying regulatory mechanism facilitates simultaneous improvement of yield and quality. Here, we summarize current findings about the synergistic molecular machinery underpinning SSP and starch synthesis in the leading staple cereal crops, including maize, rice and wheat. We further evaluate the functional conservation and differentiation of key regulators and specify feasible research approaches to identify additional regulators and expand insights. We also present major strategies to leverage resultant information for simultaneous improvement of yield and quality by molecular breeding. Finally, future perspectives on major challenges are proposed.

Jacalin-related lectin 45 (OsJRL45) isolated from 'sea rice 86' enhances rice salt tolerance at the seedling and reproductive stages

BACKGROUND

Rice (Oryza sativa L.) is one of the most widely cultivated grain crops in the world that meets the caloric needs of more than half the world's population. Salt stress seriously affects rice production and threatens food security. Therefore, mining salt tolerance genes in salt-tolerant germplasm and elucidating their molecular mechanisms in rice are necessary for the breeding of salt tolerant cultivars.

RESULTS

In this study, a salt stress-responsive jacalin-related lectin (JRL) family gene, OsJRL45, was identified in the salt-tolerant rice variety 'sea rice 86' (SR86). OsJRL45 showed high expression level in leaves, and the corresponding protein mainly localized to the endoplasmic reticulum. The knockout mutant and overexpression lines of OsJRL45 revealed that OsJRL45 positively regulates the salt tolerance of rice plants at all growth stages. Compared with the wild type (WT), the OsJRL45 overexpression lines showed greater salt tolerance at the reproductive stage, and significantly higher seed setting rate and 1,000-grain weight. Moreover, OsJRL45 expression significantly improved the salt-resistant ability and yield of a salt-sensitive indica cultivar, L6-23. Furthermore, OsJRL45 enhanced the antioxidant capacity of rice plants and facilitated the maintenance of Na+-K+ homeostasis under salt stress conditions. Five proteins associated with OsJRL45 were screened by transcriptome and interaction network analysis, of which one, the transmembrane transporter Os10g0210500 affects the salt tolerance of rice by regulating ion transport-, salt stress-, and hormone-responsive proteins.

CONCLUSIONS

The OsJRL45 gene isolated from SR86 positively regulated the salt tolerance of rice plants at all growth stages, and significantly increased the yield of salt-sensitive rice cultivar under NaCl treatment. OsJRL45 increased the activity of antioxidant enzyme of rice and regulated Na+/K+ dynamic equilibrium under salinity conditions. Our data suggest that OsJRL45 may improve the salt tolerance of rice by mediating the expression of ion transport-, salt stress response-, and hormone response-related genes.

The hot science in rice research: How rice plants cope with heat stress

Global climate change has great impacts on plant growth and development, reducing crop productivity worldwide. Rice (Oryza sativa L.), one of the world's most important food crops, is susceptible to high-temperature stress from seedling stage to reproductive stage. In this review, we summarize recent advances in understanding the molecular mechanisms underlying heat stress responses in rice, including heat sensing and signalling, transcriptional regulation, transcript processing, protein translation, and post-translational regulation. We also highlight the irreversible effects of high temperature on reproduction and grain quality in rice. Finally, we discuss challenges and opportunities for future research on heat stress responses in rice.

Regulation of seed storage protein synthesis in monocot and dicot plants: A comparative review

Seeds are a major source of nutrients for humans and animal livestock worldwide. With improved living standards, high nutritional quality has become one of the main targets for breeding. Storage protein content in seeds, which is highly variable depending on plant species, serves as a pivotal criterion of seed nutritional quality. In the last few decades, our understanding of the molecular genetics and regulatory mechanisms of storage protein synthesis has greatly advanced. Here, we systematically and comprehensively summarize breakthroughs on the conservation and divergence of storage protein synthesis in dicot and monocot plants. With regard to storage protein accumulation, we discuss evolutionary origins, developmental processes, characteristics of main storage protein fractions, regulatory networks, and genetic modifications. In addition, we discuss potential breeding strategies to improve storage protein accumulation and provide perspectives on some key unanswered problems that need to be addressed.