Biochemical and genetic analysis of the effects of amylose-extender mutation in rice endosperm

New insights into cold plasma-induced starch modification: A comparative analysis of microstructure and physicochemical properties in A-type and B-type starches

With the growing demand for clean labeling in food products, cold plasma (CP) has gained attention as an eco-friendly method for starch modification. This study evaluated various effects of CP treatment on A- and B-type starches by comparing their microstructure and physicochemical properties. CP treatment caused the deposition of precipitates on the starch surfaces. While it did not alter the crystalline type, it reduced the relative crystallinity, particularly in potato starch (PS), with a 6.5 % decrease. Amylopectin chain length analysis showed depolymerization as the dominant effect in PS, while corn starh (CS) experienced cross-linking and degradation. Furthermore, the formation of smaller particles through CP enhanced water-holding capacity. CP treatment induced lower digestibility in both raw and cooked starches, especially uncooked PS showed slowly-digestible and resistant starch content with 11.59 % and 59.69 %. These effects are linked to differences in crystal cell arrangement, offering potential for CP-modified starches with tailored industrial applications.

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.

Rice with a healthier glycaemic profile: Unveiling the molecular mechanisms and breeding strategies for the future

Rice is a staple food crop consumed by billions globally. However, rice consumption is associated with a high glycaemic response, which has negative health implications. Identifying rice varieties with intrinsically lower glycaemic responses would benefit public health. Recent research has uncovered genomic loci in rice associated with glycaemic response in rice. However, diagnostic assays are needed to efficiently characterize these loci in rice germplasm and breeding populations. This review summarizes current knowledge on low glycaemic rice genetics and proposes strategies for diagnostic assay development. Specific loci implicated in modulating starch digestion and glycaemic response are highlighted. Developing robust, high-throughput molecular marker platform for low glycaemic rice loci will accelerate varietal improvement and enhance the nutritional qualities and health benefits of this essential crop. The review also explores the role of other grain components, such as lipids and proteins, and their interactions with starch in influencing the glycaemic index (GI).

Modulation of plant carbon and nitrogen metabolism by novel actinobacteria Rhodospirillum sp. to combat galaxolide toxicity in barley and maize plants

The phytotoxic effect of cosmetics such as galaxolide (HHCB) has been investigated, however, their metabolic basis of this impact is still obscure. Thus, we investigated the effect of HHCB on the biomass accumulation, photosynthesis, primary and secondary metabolites in two species from different functional groups i.e., barley (C3) and maize (C4). In addition, the metabolic bases of HHCB stress mitigating impact of the bioactive Rhodospirillum sp. JY3 were investigated. HHCB toxicity on plant growth and physiology was significantly reduced in PGPB treated plants. At metabolism level, sugars levels and metabolic enzymes (e.g., invertase, sucrose synthase, starch synthase) were increased. Consequentially, this provided a route for organic, amino and fatty acids biosynthesis. PGPB further mitigated the phytotoxic impact of HHCB upon the levels of organic acids (e.g., oxalic, citric, succinic, malic and isobutyric acids), amino acids, particularly proline, in addition to unsaturated fatty acids. Furthermore, plant growth-promoting bacteria (PGPB) treatment reduced HHCB toxicity through increasing antioxidant metabolites (e.g., polyamines and anthocyanin), their precursors (e.g., phenylalanine, naringenin, cinnamic and coumaric acids) and their related biosynthetic enzymes such as chalcone synthase and cinnamate-4-hydroxylase. Overall, this study, for the first time, significantly contributes to quenching the environmental hazards and maintaining agriculture sustainability using eco-friendly tools.

Effects of different fatty acids on the structure, physicochemical properties, and in vitro digestibility of Chinese yam resistant starch-lipid complexes

Nine CYRS-FA complexes were prepared by resistant starch in Chinese yam (CYRS) and nine fatty acids (FAs) with different chain lengths and degrees of unsaturation. CYRS-myristic acid and CYRS-palmitic acid showed higher complexing index (CI) and relative crystallinity (RC); CYRS-myristic acid and CYRS-oleic acid exhibited lower estimated glycemic index (eGI). Chain lengths of FAs showed significantly positive correlations with CI and contact angle (CA), and yet, unsaturation degree of FAs was negative correlated with both CI and CA. The eGI exhibited positive relations with solubility, and negative correlations with CI and RC. Therefore, the results indicated that chain lengths and unsaturation degrees of FAs were key factors for complexation of the CYRS-FA complexes, which influenced the structural, physicochemical and digestive properties. The findings were expected to provide a theoretical foundation for the interactions between starch and lipids in food processing, and elevate the high-tech values of Chinese yam.

TaDL interacts with TaB3 and TaNF-YB1 to synergistically regulate the starch synthesis and grain quality in bread wheat

Starch biosynthesis is a critical factor in wheat (Triticum aestivum L.) quality and yield. However, the full scope of its regulation is not fully understood. Here we report that TaDL interacts with TaB3 and TaNF-YB1 to synergistically regulate starch biosynthesis and quality in wheat. Genome-edited tadl mutant lines had smaller and lighter grains with lower total starch and amylose contents compared to wild type (WT). Correspondingly, the transcript levels of starch biosynthesis-related genes, including TaSUS1, TaSUS2, TaAGPL2, TaSBEIIa, TaGBSSII, and TaSWEET2a, were markedly lower at 15 d after flowering (DAF) in tadl mutants. TaDL physically interacted with TaB3 and TaNF-YB1 and activated the transcription of TaSUS2 and TaAGPL2 through direct binding to their promoter regions. A null mutant of TaB3 also affected grain filling, with phenotypes similar to those of tadl mutants, whereas overexpression of TaNF-YB1 promoted grain filling. Our study demonstrated that TaDL plays an essential role in starch biosynthesis and identified an elite allele (TaDL-BI) associated with starch content, providing insights into the underlying molecular mechanism of wheat grain filling, which may be useful in breeding of high-yielding wheat and quality improvement.

Priming with multiwalled carbon nanotubes improved biomass accumulation, biological activity and metabolism of four horticultural plants during the sprouting stage

BACKGROUND

It is imperative to enhance the quality of sprouts since they are a rich source of various primary and secondary metabolites. The objective of this work was to examine how multiwalled carbon nanotubes (MWCNTs) priming at various concentrations affected the nutritional qualities of four horticultural plants (T. foenum-graecum, L. grandiflorum, L. sativum and A. graveolens) and their sprouting processes.

RESULTS

Among the four applied concentrations (10-60 mgL-1), MWCNTs at 10 and 40 mg L⁻¹ induced the highest biomass accumulation in L. grandiflorum and T. foenum-graecum, respectively, while 60 mg L⁻¹ was most effective for L. sativum and A. graveolent. MWCNTs induced growth by enhancing photosynthesis, as shown by increased chlorophyll content and rubisco activity, which rose by 27%, 17%, 23% and 12% in T. foenum-graecum, L. grandiflorum, L. sativum, and A. graveolens, respectively. Enhanced photosynthesis by MWCNTs improved sugar metabolism as indicated by increased activity of sugar metabolic enzymes such as amylase, starch synthase and invertase. This also supplied the carbon necessary for the production of primary (amino acids, fatty acids and organic acids) and secondary (flavonoids and polyphenols) metabolites. There was consistently higher activity of antioxidant enzymes (catalase and peroxidase). Interestingly, species-specific reactions to MWCNT priming were observed, where L. sativum sprouts showed the highest antioxidant activity, followed by A. graveolens.

CONCLUSION

MWCNT priming improves sprout growth and nutritional quality by boosting metabolic processes and antioxidant activity, presenting a promising approach for sustainable agriculture. © 2024 Society of Chemical Industry.

Mutation of MeMinD increased amyloplast size with a changed starch granule morphologenesis and structures in cassava storage roots

Amyloplasts are the sites of starch synthesis and accumulation. Little is known about amyloplast division and its effects on the size, structure, and physicochemical properties of starch granules. In this study, we created mutants of plastid division-related gene MeMinD by CRISPR/Cas9 technology, leading to the disruption of normal division of amyloplasts in cassava storage roots. The memind mutants exhibited significantly enlarged amyloplasts with an increased number of starch granules, and broader range of granule sizes. The loss of MeMinD function led to transcriptional reprogramming of gene expressions related to starch-synthesizing enzymes, affecting the fine structure of starch. Starch in memind mutant storage roots showed a significantly decreased proportion of shorter amylopectin chains and an increased proportion of medium and long chains, which ultimately led to a significant increase in apparent amylose content (AAC) in memind mutants compared to that in WT. The changes in starch granule size and structure resulted in a significant increase in onset temperature (To), peak temperature (Tp), and conclusion temperature (Tc) of the gelatinization process, extending the time to reach peak temperature. These data suggest that regulating amyloplast division affects starch accumulation in cassava, presenting an effective strategy for developing novel cassava starch.

Loss-of-function of SSIIa and SSIIIa confers high resistant starch content in rice endosperm

Rice (Oryza sativa L.) endosperm accumulates huge amounts of starch. Rice starch is highly digestible, potentially enhancing the occurrence of blood sugar- and intestine-related diseases such as type 2 diabetes. Resistant starch (RS) is hardly digestible in small intestine but can be converted into beneficial short-chain fatty acids in large intestine, potentially reducing the incidence of these diseases. However, it is still difficult to produce a high RS rice variety. Here, we report that simultaneous deficiency of soluble starch synthases IIa and IIIa confers high RS content in rice endosperm. The ssIIa ssIIIa exhibited higher RS content than did the ssIIIa ssIIIb, a mutant reported currently to have remarkably higher RS content than parental ssIIIa, under our experimental conditions. Loss-of-function of SSIIa and SSIIIa significantly elevated the activity of granule-bound starch synthase I and thus content of amylose. Furthermore, total lipid content increased in mutant seeds, implying that intermediate metabolites spilled out from starch biosynthesis into lipid biosynthesis. The increased amylose content and improved lipid synthesis coordinately contributed to high RS content in mutant seeds. These results further reveal the molecular mechanism of RS occurrence in rice endosperm and provide a critical genetic resource for breeding higher RS rice cultivars.

Enzymatic modification of wheat starch by a novel maltotetraose-forming amylase from Atopomonas hussainii to retard retrogradation and improve bread quality

To retard starch retrogradation and improve bread quality, a novel maltotetraose-forming amylase (AhMFA) from Atopomonas hussainii was expressed in Komagataella phaffii. After high cell density fermentation, the enzyme activity reached a maximum level of 3032 U mL-1. AhMFA showed optimal activity at pH 6.0 and 55 °C, respectively. After raw wheat starch was treated with AhMFA at 55 °C for 1 h, the relative crystallinity decreased from 24.5 % to 20.8 % without changing the A-type crystalline pattern. The side chain components with A, B1 and B2 chains were reduced to 27.5 %, 44.9 %, and 13.8 %, respectively. The retrogradation enthalpy of wheat starch decreased significantly by 67.8 %. Moreover, the decreased Mixolab parameters (C5 and C5 - C4) indicated that AhMFA reduced starch retrogradation of wheat dough. After addition of AhMFA (3 ppm), the specific volume of bread increased by 29.5 % and its hardness decreased by 46.1 % compared to the control. The AhMFA-added bread exhibited good anti-staling properties with 43.7 % less hardness than the control after storage at 4 °C for 4 days. This study provided a novel maltotetraose-forming amylase for starch modification to retard retrogradation and improve bread quality.

Structural-functional analysis of modified kudzu starch as a novel instant powder: Role of modified technology

Adopting effective methods to modify starch structure for enhanced functional properties has become a pivotal pursuit within the realm of food science. This study investigated the physicochemical and structural properties of ball milling-modified kudzu starch (BS), extrusion puffing-modified kudzu starch (ES), alcohol-alkali-modified kudzu starch (ANS), urea-alkali-modified kudzu starch (UNS), pullulanase-modified kudzu starch (PS), and extrusion puffing-pullulanase-modified kudzu starch (EPS). The d (0.5) value increasing from 10.54 μm (NS) to 83.99 μm (ANS). The Small-angle X-ray scattering (SAXS) characteristic curve of other modified kudzu starch disappeared except for the UNS. The solubility of EPS was the highest, ranging from 73 % to 80 %, significantly higher than that of NS (0 %-1 %). The agglomeration rates of ES and EPS were 0.3 % and 0.6 %, respectively, at a stirring time of 30 s. indicating favorable hydration properties. Flavonoids content in ES increased to 0.1825 mg/g. Moreover, the resistant starch content of modified kudzu starch was increased, ranging from 58.50 %-86.87 %. This study is expected to provide a scientific foundation for selecting optimal modification methods for the production of instant kudzu powder.

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.

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.

Functional nutritional rice: current progresses and future prospects

More than half of the world's population relies on rice as their staple food for three meals a day. From a dietary perspective, rice can be considered the most important grain in the world. With the continuous improvement of people's living standards, the demand for food has gradually shifted from being full and eating well to being nutritious and healthy. Developing functional nutritional rice has become an important research direction and strategic initiative for developing a major food concept. In this paper, we review the current progress in the breeding of functional nutritional rice and mineral-biofortified rice. This review focuses on the following aspects: (i) the concept, rice basic structure, nutritional components, and categorization of functional nutritional rice; (ii) genes that have been applied and identified so far, including nutritional functional rice genes, mineral bioenhancement-related genes, and their regulatory mechanisms; (iii) based on the history and technical mainline of rice breeding, research progress in nutritional functional rice using conventional breeding, a combination of conventional breeding and marker-assisted breeding, mutagenesis breeding, genetic engineering technology, and gene editing technology. Based on the current research and industrialization issues, we highlight an outlook of the problems and future developmental directions in nutritional functional rice research.

Starch molecular structure and diabetes

Starch is a primary source of food energy for human beings. Its chain-length distribution (CLD) is a major structural feature influencing physiologically-important properties, such as digestibility and palatability, of starch-containing foods. Diabetes, which is of epidemic proportions in many countries, is related to the rate of starch digestion in foods. Isoforms of three biosynthesis enzymes, starch synthase, starch branching enzymes and debranching enzymes, control the CLDs of starch, which can be measured by methods such as size-exclusion chromatography and fluorophore-assisted carbohydrate electrophoresis. Fitting observed CLDs to biosynthesis-based models based on the ratios of the activities of those isoforms yields biosynthesis-related parameters describing CLD features. This review examines CLD measurement, fitting CLDs to models, relations between CLDs, the occurrence and management of diabetes, and how plant breeders can develop varieties to optimize digestibility and palatability together, to develop starch-based foods with both a lower risk of diabetes and acceptable taste.

Investigation of starch hierarchical structure in relation to physicochemical properties and digestive behavior under different high hydrostatic pressure treatment time

Changes and causal relationships in the hierarchical structure, thermal, pasting and rheological properties, as well as the digestive behavior of starch under different high hydrostatic pressure (HHP) treatment time were investigated. At 5 min, the thickness of amorphous lamellae increased (2.76 nm) and the content of B2 and B3 chains in the amorphous lamellae decreased significantly (10.78 % and 9.08 %). As the treatment time increased, the crystalline lamellae swelled and tightly arranged double helices located in the crystalline lamellae were disturbed, resulting in a decrease in the content of double helices (12.16 %) and relative crystallinity (16.96 %). Helix dissociation, crystal disruption, lamellar collapse and granule deformation were observed at 20 min. These structural changes were closely linked to variations in the physicochemical behaviors. The thermal parameters decreased gradually, accompanied by a decrease in double helix stability. The swollen crystalline lamellae provided more space for molecular stretching, thus enhancing the pasting characteristics. Regarding the digestive behavior, the swollen amorphous lamellae facilitated the invention of enzyme molecules to hydrolyze the starch at 5 min. The digestion rate coefficient and rapidly digestible starch content increased significantly until 15 min, which demonstrated that starch was more easily digested while retaining its intact granular form.

Structure and physicochemical properties of starches from six accessions of the genus Pueraria in China

Kudzu (Pueraria lobata) root contains abundant starch, but the physicochemical properties of kudzu starch are not well understood. In this study, we compared the compositions and physicochemical properties of starches isolated from six Pueraria accessions in China. Caige starch exhibited the highest purity (96.99 %) and amylose content (24.76 %), while Yege starch contained higher levels of puerarin (493.37 μg/g) and daidzein (38.68 μg/g). All kudzu starches were rich in resistant starch, with RS2 content ranging from 38.61 % to 46.22 % and RS3 content from 3.59 % to 6.04 %. The granules of kudzu starches varied in morphology, with Yege starch featuring larger polygonal granules. The kudzu starches presented either A-type or A-type-like C-type diffraction patterns. Caige starch had a higher IR2 value (1.28), higher gelatinization temperatures, wider temperature ranges, and greater enthalpy changes. Yege (JX) starch exhibited the highest peak viscosity but the lowest setback viscosity and pasting temperature. Fenge starch showed the highest final viscosity, with Fenge (ZJ) starch demonstrating the highest crystallinity (25.7 %) and IR1 value (0.80). These results indicated that kudzu starches derived from various Pueraria species possess unique structural and physicochemical properties, which provide significant potential for applications in food and other industrial fields.

Starch-related structural basis and enzymatic mechanism of the different appearances of soft rice

To investigate the fine starch structure characteristics and formation mechanism of high-quality appearance soft rice, two high-quality and low-quality soft rice varieties (HA-SR and LA-SR, respectively) were selected. Differences in appearance quality, fine starch structure, and activity of key enzymes involved in starch synthesis during the grain-filling stage were compared. The results showed that compared with LA-SR, HA-SR were less chalky, more transparent, had larger starch grains, a lower content of shorter chains (DP 6-24), a higher content of longer chains (DP ≥ 25), lower relative crystallinity, fewer ordered structures, more amorphous structures and larger thicknesses of semi-crystalline lamellae. In terms of amylase activity during the grain-filling stage, the AGPase and GBSS activities of HA-SR were higher, and the SBE activity of HA-SR was lower compared to LA-SR. In conclusion, higher AGPase activity can produce a higher filling rate resulting in fuller starch grain in soft rice. Fuller starch grains reduce the chalkiness of soft rice. Higher AGPase and GBSS activities and lower SBE activity can result in soft rice with more long-branched and less short-branched amylopectin. Thus, soft rice has lower relative crystallinity and less ordered structure. These structures may facilitate reduce grain chalkiness and improve grain transparency.

NnSBE1 encodes a starch branching enzyme involved in starch biosynthesis in lotus seeds

Lotus seed starch holds vast potential for utilization across various industries, with its content and structure directly influencing the commercial value of lotus seeds. However, there has been limited information available on the molecular mechanisms underlying lotus seed starch biosynthesis. In this study, three starch branching enzyme homologs were identified in the lotus genome, designated as NnSBE1 to NnSBE3, which possess conserved CBM_48 and α_Aamy domains. Among them, NnSBE1 exhibited predominant expression, with abundant transcript levels observed in lotus seeds and flower-related organs. Expression of NnSBE1 remained consistently up-regulated in lotus cotyledons from 6 to 21 days after pollination. Additionally, a C2H2-type finger protein encoding gene, NnLOL1, co-expressed with NnSBE1 in lotus cotyledons. As a seed-predominantly expressed transcription factor, NnLOL1 was confirmed to activate NnSBE1 expression. Transient overexpression of NnSBE1 in lotus cotyledons resulted in a significant increase in both amylopectin and total starch content compared to the control. Furthermore, multiple variation sites within the NnSBE1 gene gave rise to diverse haplotypes between seed-lotus and other lotus varieties. These findings contribute to our understanding of the regulation mechanisms involved in lotus seed starch biosynthesis, offering valuable theoretical insights for the genetic improvement of lotus seed starch by molecular breeding strategies.

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.

Zn-Al and Mg-Al layered double hydroxide nanoparticles improved primary and secondary metabolism of geranium plants

Layer double hydroxide (LDH) nanoparticles (NPs) have been applied to enhance plant growth and productivity. However, their effects on carbon and nitrogen metabolism of aromatic plants, are not well understood. Therefore, we investigated the impact of foliar application of Zn-Al LDH and Mg-Al LDH NPs (10 ppm) on the growth and metabolism of geranium plants. Zn-Al LDH and Mg-Al LDH NPs significantly increased the dry biomass, photosynthetic pigment, and Zn and Mg uptake by treated plants. These increases were consistent with increased primary metabolism such as soluble sugars and their metabolic enzymes (invertase and amylase). The supply of high sugar levels induced TCA organic accumulation, providing a pathway for amino acid biosynthesis. Among amino acids, proline level and its biosynthetic enzymes such as pyrroline-5-carboxylate reductase (P5CR), ornithine aminotransferase (OAT), and pyrroline-5-carboxylate synthetase (P5CS), glutamine synthetase (GS), and arginase were increased. Increased primary metabolites can then be channeled into secondary metabolic pathways, leading to higher levels of secondary metabolites including tocopherols, phenolics, and flavonoids. These observed increases in primary and secondary metabolites also improve the biological value of geranium plants. Overall, our research highlights the potential of Zn-Al LDH and Mg-Al LDH NPs as elicitors to enhance metabolism in geranium plants, thereby improving their growth bioactivity.

Multiomics of a rice population identifies genes and genomic regions that bestow low glycemic index and high protein content

To counter the rising incidence of diabetes and to meet the daily protein needs, we created low glycemic index (GI) rice varieties with protein content (PC) surpassing 14%. In the development of recombinant inbred lines using Samba Mahsuri and IR36 amylose extender (IR36ae) as parental lines, we identified quantitative trait loci and genes associated with low GI, high amylose content (AC), and high PC. By integrating genetic techniques with classification models, this comprehensive approach identified candidate genes on chromosome 2 (qGI2.1/qAC2.1 spanning the region from 18.62 Mb to 19.95 Mb), exerting influence on low GI and high amylose. Notably, the phenotypic variant with high value was associated with the recessive allele of the starch branching enzyme 2b (sbeIIb). The genome-edited sbeIIb line confirmed low GI phenotype in milled rice grains. Further, combinations of alleles created by the highly significant SNPs from the targeted associations and epistatically interacting genes showed ultralow GI phenotypes with high amylose and high protein. Metabolomics analysis of rice with varying AC, PC, and GI revealed that the superior lines of high AC and PC, and low GI were preferentially enriched in glycolytic and amino acid metabolisms, whereas the inferior lines of low AC and PC and high GI were enriched with fatty acid metabolism. The high amylose high protein recombinant inbred line (HAHP_101) was enriched in essential amino acids like lysine. Such lines may be highly relevant for food product development to address diabetes and malnutrition.

As(III)-oxidizing and plant growth-promoting bacteria increase the starch biosynthesis-related enzyme activity, 2-AP levels, and grain quality of arsenic-stressed rice plants

BACKGROUND

Grain quality is an important index of rice production, particularly when plants are grown under stress. Arsenic (As) contamination in paddy fields severely affects rice grain yield and quality. Here, the effects of As and combinations of As(III)-oxidizing bacteria (Pseudomonas stutzeri 4.25, 4.27, and 4.44) and plant growth-promoting bacteria (Delftia acidovorans KKU2500-12 and Cupriavidus taiwanensis KKU2500-3) on enzymes related to starch accumulation in grains and the grain quality of Khao Dawk Mali 105 rice cultivated in As-contaminated soil under greenhouse conditions were investigated.

RESULTS

Arsenic affected the activities of starch biosynthesis-related enzymes, and decreases of up to 76.27%, 71.53%, 49.74%, 73.39%, and 47.46% in AGPase, SSS, GBSS, SBE, and SDBE activities, respectively, and 9.42-61.07% in starch accumulation in grains were detected after growth in As-contaminated soil. However, the KKU2500-3/4.25 and KKU2500-3/4.44 combinations yielded the greatest enzyme activities in grains, and compared with the results observed in uninoculated seedlings, increases in starch accumulation of up to 51.16% and 23.81% were found in the inoculated seedlings after growth in medium- and high-As-contaminated soils, at 10-17 and 10-24 days after anthesis, respectively. The bacteria increased the 2-AP content in rice under As stress, possibly via the induction of proline, a 2-AP substrate. Bacterium-inoculated rice had significantly greater 2-AP levels than uninoculated rice, and 2.16-9.93% and 26.57-42.04% increases were detected in rice plants grown in medium- and high-As-contaminated soils, respectively.

CONCLUSIONS

Arsenic toxicity can be mitigated in rice growing under greenhouse conditions by maintaining starch biosynthesis, accumulating amylose, and increasing 2-AP content. The effectiveness of these bacteria should be validated in paddy fields; hence, safe rice grains with a good starch content and aroma could be produced.

Changes of crystalline structure and physicochemical properties of Pueraria lobata var. thomsonii starch under water deficit

Crystal type is an important physicochemical property of starch. However, it is currently unclear whether changes in crystal type affect other properties of starch. This study discovered that water deficit resulted in an increase in small starch granules and transparency in Pueraria lobata var. thomsonii, while causing a decrease in amylose content and swelling power. Additionally, the crystal type of P. Thomsonii starch changed from CB-type to CA-type under water deficit, without significantly altering the short-range ordered structure and chain length distribution of starch. This transformation in crystal type led to peak splitting in the DSC heat flow curve of starch, alterations in gelatinization behavior, and an increase in resistant starch content. These changes in crystalline structure and physicochemical properties of starch granules are considered as adaptive strategies employed by P. Thomsonii to cope with water deficit.

Effects of Binding between Ca in Hard Water and Phosphorus in Amylopectin on the Qualities of Boiled Rice and Rice Noodle Prepared by Soaking and Boiling in Hard Water

Recently, global warming has led to an increase in chalky rice grains. This has consequently resulted in the deterioration in quality of rice products. Although we previously reported that hard water, rich in Ca, is useful for the quality improvement of high-temperature-damaged rice grains, the mechanism was not elucidated sufficiently. Therefore, we used various kinds of rice cultivars, from waxy to high-amylose ones, for soaking and boiling in hard water and compared physical and chemical properties of the products. It was shown that the degree of quality improvement, such as final viscosities in pasting property, and textural properties of boiled rice, was more remarkable for high-amylose rice than low-amylose rice. As we found that the phosphorus contents showed positive correlations with amylose and long chains of amylopectin, we estimate that the effects are mainly due to binding of calcium and phosphorus. Because that high-amylose or long-chain-rich amylopectin rice cultivars showed high calcium contents in rice products, these rice cultivars would be very useful to supply calcium through dietary intake via hard water cooking.

The Waxy Gene Has Pleiotropic Effects on Hot Water-Soluble and -Insoluble Amylose Contents in Rice (Oryza sativa) Grains

Rice (Oryza sativa) is a cereal crop with a starchy endosperm. Starch is composed of amylose and amylopectin. Amylose content (AC) is the principal determinant of rice quality, but varieties with similar ACs can still vary substantially in their quality. In this study, we analyzed the total AC (TAC) and its constituent fractions, the hot water-soluble amylose content (SAC) and hot water-insoluble amylose content (IAC), in two sets of related chromosome segment substitution lines of rice with a common genetic background grown in two years. We searched for quantitative trait loci (QTLs) associated with SAC, IAC, and TAC and identified one common QTL (qSAC-6, qIAC-6, and qTAC-6) on chromosome 6. Map-based cloning revealed that the gene underlying the trait associated with this common QTL is Waxy (Wx). An analysis of the colors of soluble and insoluble starch-iodine complexes and their λmax values (wavelengths at the positions of their peak absorbance values) as well as gel permeation chromatography revealed that Wx is responsible for the biosynthesis of amylose, comprising a large proportion of the soluble fractions of the SAC. Wx is also involved in the biosynthesis of long chains of amylopectin, comprising the hot water-insoluble fractions of the IAC. These findings highlight the pleiotropic effects of Wx on the SAC and IAC. This pleiotropy indicates that these traits have a positive genetic correlation. Therefore, further studies of rice quality should use rice varieties with the same Wx genotype to eliminate the pleiotropic effects of this gene, allowing the independent relationship between the SAC or IAC and rice quality to be elucidated through a multiple correlation analysis. These findings are applicable to other valuable cereal crops as well.

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.

Rheological properties of indica rice determined by starch structure related enzymatic activities during after-ripening

The processing quality of indica rice must undergo ripening after harvest to achieve stability and improvement. However, the mechanism underlying this process remains incompletely elucidated. Starch, the predominant component in indica rice, plays a crucial role in determining its properties. This study focused on analyzing the rheological properties and starch fine structure, as well as the related biosynthetic enzymes of indica rice during the after-ripening process. The results showed that after-ripened rice exhibited increased elastic modulus (G') and viscous modulus (G″), accompanied by a decrease in the loss tangent (Tan δ), indicating an enhancement in viscoelasticity and the gel network structure. Moreover, the proportions of amylopectin super long chains (DP 37-60) decreased, while those of medium chains (DP 13-24 and DP 25-36) or short chains (DP 6-12) of amylopectin increased. Additionally, the activities of starch branching enzyme (SBE) and starch debranching enzyme (DBE) declined over the after-ripening period. Pearson correlation analysis revealed that the rheological properties of after-ripened rice were correlated with the chain length distribution (CLD) of starch, which, in turn, was associated with its related endogenous enzymes. These findings provied new insights into understanding the quality changes of after-ripened indica rice.

Rice LIKE EARLY STARVATION1 cooperates with FLOURY ENDOSPERM6 to modulate starch biosynthesis and endosperm development

In cereal grains, starch is synthesized by the concerted actions of multiple enzymes on the surface of starch granules within the amyloplast. However, little is known about how starch-synthesizing enzymes access starch granules, especially for amylopectin biosynthesis. Here, we show that the rice (Oryza sativa) floury endosperm9 (flo9) mutant is defective in amylopectin biosynthesis, leading to grains exhibiting a floury endosperm with a hollow core. Molecular cloning revealed that FLO9 encodes a plant-specific protein homologous to Arabidopsis (Arabidopsis thaliana) LIKE EARLY STARVATION1 (LESV). Unlike Arabidopsis LESV, which is involved in starch metabolism in leaves, OsLESV is required for starch granule initiation in the endosperm. OsLESV can directly bind to starch by its C-terminal tryptophan (Trp)-rich region. Cellular and biochemical evidence suggests that OsLESV interacts with the starch-binding protein FLO6, and loss-of-function mutations of either gene impair ISOAMYLASE1 (ISA1) targeting to starch granules. Genetically, OsLESV acts synergistically with FLO6 to regulate starch biosynthesis and endosperm development. Together, our results identify OsLESV-FLO6 as a non-enzymatic molecular module responsible for ISA1 localization on starch granules, and present a target gene for use in biotechnology to control starch content and composition in rice endosperm.

Morphological, Molecular Structural and Physicochemical Characterization of Starch Granules Formed in Endosperm of Rice with Ectopic Overexpression of α-Amylase

The objective of this study was to characterize the endosperm starch in rice that ectopically overexpressed the α-amylase. Transgenic rice plants, transformed with cauliflower mosaic virus 35S promoter driven AmyI-1 (35S::AmyI-1) and AmyII-4 (35S::AmyII-4), and 10 kDa prolamin promoter driven AmyI-1 (P10::AmyI-1), were cultivated under standard conditions (23 °C, 12 h in the dark/ 26 °C, 12 h in the light), and brown grains were subsequently harvested. Each grain displayed characteristic chalkiness, while electron microanalyzer (EPMA)-SEM images disclosed numerous small pits on the surface of the starch granules, attributable to α-amylase activity. Fluorescence labeling and capillary electrophoresis analysis of starch chain length distribution revealed no significant alterations in the starches of 35S::AmyI-1 and 35S::AmyII-4 transgenic rice compared to the wild-type. Conversely, the extremely short α-glucan chains (DP 2-8) exhibited a dramatic increase in the P10::AmyI-1 starch. Rapid visco-analyzer analysis also identified variations in the chain length distribution of P10::AmyI-1 starch, manifesting as changes in viscosity. Moreover, 1H-NMR analysis uncovered dynamic modifications in the molecular structure of starch in rice grain transformed with P10::AmyI-1, which was found to possess unprecedented structural characteristics.

Interaction between genetic regions responsible for the starch properties in non-glutinous rice varieties in Hokkaido, Japan

Starch properties are the major determinants of grain quality and food characteristics in rice (Oryza sativa L.). Understanding the interactions between genetic regions responsible for starch properties will lead to the development of rice cultivars with desirable characteristics. This study investigated the genetic effect and interaction between qAC9.3, a low-amylose quantitative trait locus (QTL), and the genetic region around Starch branching enzyme IIb (SbeIIb). Both these factors are responsible for the starch properties of the Hokkaido breeding population. The amylose content, pasting temperature, and amylopectin chain-length distribution were compared using F5 lines derived from the cross between the lower amylose content and lower pasting temperature strain 'Hokkai332 (qAC9.3, SbeIIb)' and the higher amylose content and higher pasting temperature variety 'Kitagenki (-, SbeIIbsr )'. The qAC9.3 genotype exhibited low amylose content and reduced the hardness of boiled rice but increased the ratio of amylopectin long chains and did not alter the pasting temperature. In contrast, the SbeIIb genotype was associated with pasting temperature but did not affect the amylose content and hardness of boiled rice. It was suggested that appropriately selecting genotypes of these genetic regions and QTL would allow the fine-tuning of starch properties of cooked rice suitable for future demand.

Characterization of the starch molecular structure of wheat varying in the content of resistant starch

Resistant starch (RS) is the total amount of starch that is incompletely or not digested and absorbed in the small intestine. It plays a role similar to dietary fibre with beneficial effects for human health. In this study, the RS content of 129 wheat accessions was determined, and the relationship between the several starch physical properties and resistant starch content were analyzed. By comparing the total starch content, amylose starch content, starch chain length distribution, starch crystallization type, starch branching degree, and starch granule morphology between the high RS and low RS content wheat accessions, it was found that the amylose content and RS content were significantly positively correlated. However, in the range of chain length fb 3 (DP ≥ 37), there was a significant negative correlation between amylopectin content and RS content. The surface of starch granules became increasingly smooth as the content of RS increased.

Dynamics of starch formation and gene expression during grain filling and its possible influence on grain quality

In rice, grain filling is a crucial stage where asynchronous filling of the pollinated spikelet's of the panicle occurs. It can influence both grain quality and yield. In rice grain, starch is the dominant component and contains amylose and amylopectin. Amylose content is the chief cooking quality parameter, however, rice varieties having similar amylose content varied in other parameters. Hence, in this study, a set of varieties varying in yield (04) and another set (12) of varieties that are similar in amylose content with variation in gel consistency and alkali spreading value were used. Panicles were collected at various intervals and analysed for individual grain weight and quantities of amylose and amylopectin. Gas exchange parameters were measured in varieties varying in yield. Upper branches of the panicles were collected from rice varieties having similar amylose content and were subjected to gene expression analysis with fourteen gene specific primers of starch synthesis. Results indicate that grain filling was initiated simultaneously in multiple branches. Amylose and amylopectin quantities increased with the increase in individual grain weight. However, the pattern of regression lines of amylose and amylopectin percentages with increase in individual grain weight varied among the varieties. Gas exchange parameters like photosynthetic rate, stomatal conductance, intercellular CO2 and transpiration rate decreased with the increase in grain filling period in both good and poor yielding varieties. However, they decreased more in poor yielders. Expression of fourteen genes varied among the varieties and absence of SBE2b can be responsible for medium or soft gel consistency.

Discrepancies in resistant starch and starch physicochemical properties between rice mutants similar in high amylose content

The content of resistant starch (RS) was considered positively correlated with the apparent amylose content (AAC). Here, we analyzed two Indica rice mutants, RS111 and Zhedagaozhi 1B, similar in high AAC and found that their RS content differed remarkably. RS111 had higher RS3 content but lower RS2 content than Zhedagaozhi 1B; correspondingly, cooked RS111 showed slower digestibility. RS111 had smaller irregular and oval starch granules when compared with Zhedagaozhi 1B and the wild type. Zhedagaozhi 1B showed a B-type starch pattern, different from RS111 and the wild type, which showed A-type starch. Meantime, RS111 had more fa and fb1 but less fb3 than Zhedagaozhi 1B. Both mutants showed decreased viscosity and swelling power when compared with the parents. RS111 had the lowest viscosity, and Zhedagaozhi 1B had the smallest swelling power. The different fine structures of amylopectin between RS111 and Zhedagaozhi 1B led to different starch types, gelatinization properties, paste viscosity, and digestibility. In addition to enhancing amylose content, modifications on amylopectin structure showed great potent in breeding rice with different RS2 and RS3 content, which could meet the increasing needs for various rice germplasms.

Loss of ADP-glucose transporter in barley sex1 mutant caused shrunken endosperm but with elevated protein and β-glucan content in whole meal

Grain shape and plumpness affect barley yield. Despite numerous studies on shrunken endosperm mutants in barley, their molecular mechanism and application potential in the food industry are largely unknown. Here, map-based cloning, co-segregation analyses, and allelic variant validation revealed that the loss of HORVU6Hr1G037950 encoding an ADP-glucose transporter caused the shrunken endosperm in sex1. Haplotype analysis suggested that hap4 in the promoter sequence was positively related to the hundred-grain weight showing a breeding potential. A pair of near-isogenic lines targeting HORVU6Hr1G037950 was produced and characterized to investigate molecular mechanisms that SEX1 regulates endosperm development. Results presented that the absence of the SEX1 gene led to the decrease of starch content and A-type granules size, the increase of β-glucan, protein, gelatinization temperature, soluble sugar content, amylopectin A chains, and B1 chains. Enzymatic activity, transcriptome and metabolome analyses revealed the loss of SEX1 results in an impaired ADP-glucose-to-starch conversion process, consequently leading to higher soluble sugar contents and lower starch accumulation, thereby inducing a shrunken-endosperm phenotype in sex1. Taken together, this study provides new insights into barley grain development, and the elevated protein and β-glucan contents of the whole meal in sex1 imply its promising application in the food industry.

Inactivation of SSIIIa enhances the RS content through altering starch structure and accumulating C18:2 in japonica rice

SSIIIa was the key gene responsible for RS formation in rice endosperm. The higher RS content in ssIIIa mutant has been proposed to be majorly due to the increased amylose-lipid complexes (RS5). However, the formation of RS5 elicited by ssIIIa mutation and the importance of RS5 for total RS content in rice are still unclear. With japonica ssIIIa loss-of-function mutants created by CRISPR/Cas9 gene editing, the effects of SSIIIa mutation on RS5 were furtherly evaluated through investigating the transcriptome and metabolites. Inactivation of SSIIIa caused significant enhancement in amylose and RS content but without depletion in starch reserves. SSIIIa mutation modulated the genes involved in carbohydrate and lipid metabolisms and the redistribution of substances, led to accumulated protein, glucose, fructose, and C18:2. Besides the increased amylose content and altered amylopectin structure, the increased C18:2 contributed greatly to the enhancement in RS content in japonica ssIIIa mutants through complexing with amylose to form RS5, while the existence of lipid counted against the enhancement of RS content in indica rice. RS5 showed discrepant contributions for the total RS in rice with different genetic background. Inactivation of SSIIIa has great potential in improving RS5 content in japonica rice without great yield loss.

Starch Properties and Morphology of Eight Floury Endosperm Mutants in Rice

Besides increasing grain yield, improving rice (Oryza sativa L.) quality has been paid more and more attention recently. Cooking and eating quality (CEQ) is an important indicator of rice quality. Since CEQs are quantitative traits and challenging for measurement, efforts have mainly focused on two major genes, Wx and SSIIa. Chalkiness and floury endosperm significantly affect the eating quality of rice, leading to noticeable changes in CEQ. Due to the easily observable phenotype of floury endosperm, cloning single gene mutations that cause floury endosperm and evaluating changes in CEQs indirectly facilitate the exploration of the minor genes controlling CEQ. In this study, eight mutants with different degrees of floury endosperm, generated through ethylmethane sulfonate (EMS) mutagenesis, were analyzed. These mutants exhibited wide variation in starch morphology and CEQs. Particularly, the z2 mutant showed spherical starch granules significantly increased rapid visco analyzer (RVA) indexes and urea swelling, while the z4 mutant displayed extremely sharp starch granules and significantly decreased RVA indexes and urea swelling compared to the wild type. Additionally, these mutants still maintained correlations with certain RVA profiles, suggesting that the genes PUL, which affect these indexes, may not undergo mutation. Cloning these mutated genes in the future, especially in z2 and z4, will enhance the genetic network of rice eating quality and hold significant importance for molecular marker-assisted breeding to improve rice quality.

Origin and evolution of the main starch biosynthetic enzymes

Starch, a semi-crystalline energy storage form primarily found in plant plastids plays a crucial role in various food or no-food applications. Despite the starch biosynthetic pathway's main enzymes have been characterized, their origin and evolution remained a subject of debate. In this study, we conducted the comprehensive phylogenetic and structural analysis of three types of starch biosynthetic enzymes: starch synthase (SS), starch branching enzyme (SBE) and isoamylase-type debranching enzyme (ISA) from 51,151 annotated genomes. Our findings provide valuable insights into the possible scenario for the origin and evolution of the starch biosynthetic pathway. Initially, the ancestor of SBE can be traced back to an unidentified bacterium that existed before the formation of the last eukaryotic common ancestor (LECA) via horizontal gene transfer (HGT). This transfer event likely provided the eukaryote ancestor with the ability to synthesize glycogen. Furthermore, during the emergence of Archaeplastida, one clade of SS was transferred from Deltaproteobacteria by HGT, while ISA and the other clade of SS originated from Chlamydiae through endosymbiosis gene transfer (EGT). Both these transfer events collectively contributed to the establishment of the original starch biosynthetic pathway. Subsequently, after the divergence of Viridiplantae from Rhodophyta, all three enzymes underwent multiple duplications and N-terminus extension domain modifications, resulting in the formation of functionally specialized isoforms and ultimately leading to the complete starch biosynthetic pathway. By shedding light on the evolutionary origins of key enzymes involved in the starch biosynthetic pathway, this study provides important insights into the evolutionary events of plants.

A model for the reproduction of amylopectin cluster by coordinated actions of starch branching enzyme isoforms

Amylopectin is a highly branched glucan which accounts for approximately 65-85% of starch in most plant tissues. It is crucially important to understand the biosynthetic process of this glucan in regulating the structure and functional properties of starch granules. Currently, the most accepted ideas of structural feature and biosynthesis of amylopectin are that amylopectin is composed of a branched element called "cluster" and that the essential process of amylopectin biosynthesis is to reproduce a new cluster from the existing cluster. The present paper proposes a model explaining the whole process of amylopectin biosynthesis as to how the new cluster is reproduced by concerted actions of multiple isoforms of starch biosynthetic enzymes, particularly by combinations of distinct roles of starch branching enzyme (BE) isoforms. This model proposes for the first time the molecular mechanism as to how the formation of a new cluster is initiated, and the reason why BEI can play a major role in this step. This is because BEI has a rather broad chain-length preference compared to BEIIb, because a low preference of BEI for the substrate chain-length is advantageous for branching a couple of elongated chains that are not synchronously formed and thus these chains having varied lengths could be safely attacked by this isoform. On the contrary, it is unlikely that BEIIb is involved in this reaction because it can react to only short chains having degree of polymerization of 12-14. BEIIa is possibly able to complement the role of BEI to some extent, because BEIIa can attack basically short chains but its chain-length preference is lower compared with BEIIb. The model implies that the first branches mainly formed by BEI to construct the amorphous lamellae whereas the second branches predominantly formed by BEIIb are located mainly in the crystalline lamellae. This paper provides new insights into the roles of BEI, BEIIb, and BEIIa in amylopectin biosynthesis in cereal endosperm.

Effects of the Molecular Structure of Starch in Foods on Human Health

Starch provides approximately half of humans' food energy, and its structural features influence human health. The most important structural feature is the chain length distribution (CLD), which affects properties such as the digestibility of starch-containing foods. The rate of digestion of such foods has a strong correlation with the prevalence and treatment of diseases such as diabetes, cardiovascular disease and obesity. Starch CLDs can be divided into multiple regions of degrees of polymerization, wherein the CLD in a given region is predominantly, but not exclusively, formed by a particular set of starch biosynthesis enzymes: starch synthases, starch branching enzymes and debranching enzymes. Biosynthesis-based models have been developed relating the ratios of the various enzyme activities in each set to the CLD component produced by that set. Fitting the observed CLDs to these models yields a small number of biosynthesis-related parameters, which, taken together, describe the entire CLD. This review highlights how CLDs can be measured and how the model-based parameters obtained from fitting these distributions are related to the properties of starch-based foods significant for health, and it considers how this knowledge could be used to develop plant varieties to provide foods with improved properties.

Main Characteristics of Processed Grain Starch Products and Physicochemical Features of the Starches from Maize (Zea mays L.) with Different Genotypes

To understand the relationship between the genotype of maize plants and differences in their origin and the ploidy of the genome, which carry gene alleles programming the biosynthesis of various starch modifications, the thermodynamic and morphological features of starches from the grains of these plants have been studied. This study investigated the peculiarities of starch extracted from subspecies of maize (the dry matter mass (DM) fraction, starch content in grain DM, ash content in grain DM, and amylose content in starch) belonging to different genotypes within the framework of the program for the investigation of polymorphism of the world collection of plant genetic resources VIR. Among the starch genotypes of maize studied, four groups comprised the waxy (wx), conditionally high amylose ("ae"), sugar (su), and wild (WT) genotypes. Starches with an amylose content of over 30% conditionally belonged to the "ae" genotype. The starches of the su genotype had fewer starch granules than other investigated genotypes. An increase in amylose content in the investigated starches, accompanied by a decrease in their thermodynamic melting parameters, induced the accumulation of defective structures in the starches under study. The thermodynamic parameters evaluated for dissociation of the amylose-lipid complex were temperature (T_aml) and enthalpy (H_aml); for the su genotype, temperature and enthalpy values of dissociation of the amylose-lipid complex were higher than in the starches from the "ae" and WT genotypes. This study has shown that the amylose content in starch and the individual features of the maize genotype determine the thermodynamic melting parameters of the starches under study.

Identification of a new allele of soluble starch synthase IIIa involved in the elongation of amylopectin long chains in a chalky rice mutant

A chalky endosperm mutant (GM03) induced from an indica rice GLA4 was used to investigate the functional gene in starch biosynthesis. Bulked segregant analysis and sanger sequencing determined that a novel mutation in soluble starch synthase IIIa (SSIIIa) is responsible for the chalky phenotype in GM03. Complementary test by transforming the active SSIIIa gene driven by its native promoter to GM03 recovered the phenotype to its wildtype. The expression of SSIIIa was significantly decreased, while SSIIIa protein was not detected in GM03. The mutation of SSIIIa led to increased expression of most of starch synthesis related genes and elevated the levels of most of proteins in GM03. The CRISPR/Cas9 technology was used for targeted disruption of SSIIIa, and the mutant lines exhibited chalky endosperm which phenocopied the GM03. Additionally, the starch fine structure in the knockout mutant lines ss3a-1 and ss3a-2 was similar with the GM03, which showed increased amylose content, higher proportions of B1 and B2 chains, much lower proportions of B3 chains and decreased degree of crystallinity, leading to altered thermal properties with lower gelatinization temperature and enthalpy. Collectively, these results suggested that SSIIIa plays an important role in starch synthesis by elongating amylopectin long chains in rice.

Chitosan nanoparticles support the impact of arbuscular mycorrhizae fungi on growth and sugar metabolism of wheat crop

Arbuscular mycorrhizae fungi (AMF) symbiosis is an indispensable approach in sustainable agriculture. AMF-plant association is likely to be enhanced by the nanoparticle's application. Herein, the impact of chitosan nanoparticles (CSNPs) on the mycorrhizal colonization in wheat has been investigated. The provoked changes in wheat growth, physiology and metabolism were assessed. CSNPs treatment improved AMF colonization (52 %) by inducing the levels of auxins and strigolactones in roots by 32 and 21 %, respectively besides flavonoids exudation into the rhizosphere (9 %). Such supporting action of CSNPs was associated with improved plant biomass production (21 %) compared to AMF treatment. Both treatments synergistically enhanced the photochemical efficiency of photosystem II and stomatal conductance, therefore the photosynthetic rate was increased. The combined application of CSNPs and AMF enhanced accumulation of glucose, fructose, sucrose, and starch (12, 22, 31 and 13 %, respectively), as well as the activities of sucrose-p-synthase, invertases and starch synthase compared to AMF treatment. The synchronous application of CSNPs and AMF promoted the levels of polyphenols, carotenoids, and tocopherols therefore, improved antioxidant capacity (33 %), in the roots. CSNPs can be applied as an efficient biofertilization strategies to enhance plant growth and fitness, beside improvement of health promoting compounds in wheat.

Genetic Engineering of Starch Biosynthesis in Maize Seeds for Efficient Enzymatic Digestion of Starch during Bioethanol Production

Maize accumulates large amounts of starch in seeds which have been used as food for human and animals. Maize starch is an importantly industrial raw material for bioethanol production. One critical step in bioethanol production is degrading starch to oligosaccharides and glucose by α-amylase and glucoamylase. This step usually requires high temperature and additional equipment, leading to an increased production cost. Currently, there remains a lack of specially designed maize cultivars with optimized starch (amylose and amylopectin) compositions for bioethanol production. We discussed the features of starch granules suitable for efficient enzymatic digestion. Thus far, great advances have been made in molecular characterization of the key proteins involved in starch metabolism in maize seeds. The review explores how these proteins affect starch metabolism pathway, especially in controlling the composition, size and features of starch. We highlight the roles of key enzymes in controlling amylose/amylopectin ratio and granules architecture. Based on current technological process of bioethanol production using maize starch, we propose that several key enzymes can be modified in abundance or activities via genetic engineering to synthesize easily degraded starch granules in maize seeds. The review provides a clue for developing special maize cultivars as raw material in the bioethanol industry.

Applications and Prospects of CRISPR/Cas9-Mediated Base Editing in Plant Breeding

The clustered regularly interspaced short palindromic repeats (CRISPR)/associated protein 9 system (Cas9) has been used at length to optimize multiple aspects of germplasm resources. However, large-scale genomic research has indicated that novel variations in crop plants are attributed to single-nucleotide polymorphisms (SNPs). Therefore, substituting single bases into a plant genome may produce desirable traits. Gene editing by CRISPR/Cas9 techniques frequently results in insertions-deletions (indels). Base editing allows precise single-nucleotide changes in the genome in the absence of double-strand breaks (DSBs) and donor repair templates (DRTs). Therefore, BEs have provided a new way of thinking about genome editing, and base editing techniques are currently being utilized to edit the genomes of many different organisms. As traditional breeding techniques and modern molecular breeding technologies complement each other, various genome editing technologies have emerged. How to realize the greater potential of BE applications is the question we need to consider. Here, we explain various base editings such as CBEs, ABEs, and CGBEs. In addition, the latest applications of base editing technologies in agriculture are summarized, including crop yield, quality, disease, and herbicide resistance. Finally, the challenges and future prospects of base editing technologies are presented. The aim is to provide a comprehensive overview of the application of BE in crop breeding to further improve BE and make the most of its value.

Research on the Relationship between the Amylopectin Structure and the Physicochemical Properties of Starch Extracted from Glutinous Rice

Glutinous rice has very low amylose content and is a good material for determining the structure and physicochemical properties of amylopectin. We selected 29 glutinous rice varieties and determined the amylopectin structure by high-performance anion exchange chromatography with the pulsed amperometric detection method. We also determined the correlation between amylopectin structure and the physicochemical properties of starch extracted from these varieties. The results showed that the amylopectin chain ratio Σdegree of polymerization (DP) ≤ 11/ΣDP ≤ 24 of 29 glutinous rice varieties was greater than 0.26, signifying that these varieties contained type II amylopectin. The results of the correlation analysis with gelatinization temperature showed that ΣDP 6-11 was significantly negatively correlated with the onset gelatinization temperature (GT) (T_O), peak GT (T_P), and conclusion GT (T_C). Among the thermodynamic properties, ΣDP 12-24 was significantly positively correlated with To, Tp, and Tc, ΣDP 25-36 was significantly negatively correlated with To, Tp, and Tc, and ΣDP ≥ 37 had no correlation with the thermodynamic properties. The results of correlation analysis with RVA spectrum characteristic values showed that ΣDP 6-11 was significantly negatively correlated with hot paste viscosity (HPV), cool paste viscosity (CPV), consistency viscosity (CSV), peak time (PeT), and pasting temperature (PaT) among the Rapid Visco Analyzer (RVA) profile characteristics, ΣDP 12-24 was significantly positively correlated with HPV, CPV, CSV, PeT, and PaT, and ΣDP ≥ 25 had no correlation with the viscosity characteristics. Therefore, we concluded that the amylopectin structure had a greater effect on the T_O, T_P, T_C, ΔH and peak viscosity, HPV, CPV, CSV, PeT, and PaT. The glutinous rice varieties with a higher distribution of short chains and a lower distribution of medium and long chains in the amylopectin structure resulted in lower GT and RVA spectrum characteristic values.

The new isolated Archaea strain improved grain yield, metabolism and quality of wheat plants under Co stress conditions

Heavy metal (e.g. cobalt) pollution causes a serious of environmental and agricultural problems. On the other hand, plant growth-promoting microorganisms enhance plant growth and mitigate heavy metal stress. Herein, we isolated and identified the unclassified species strain NARS9, belong to Haloferax,. Cobalt (Co, 200 mg/kg soil) stress mitigating impact of the identified on wheat grains yield, primary and secondary metabolism and grain quality was investigated. Co alone significantly induced Co accumulation in wheat grain (260%), and consequently reduced wheat yield (130%) and quality. Haloferax NARS9 alone significantly enhanced grain chemicals composition (i.e., total sugars (89%) and organic acids (e.g., oxalic and isobutyric acids), essential amino acids (e.g., threonine, lysine, and histidine) and unsaturated fatty acids (e.g. eicosenoic, erucic and tetracosenoic acids). Interestingly, Co stress induced wheat grain yield, reduction were significantly mitigated by Haloferax NARS9 treatment by 26% compared to Co stress alone. Under Co stress, Haloferax NARS9 significantly increased sugar metabolism including sucrose and starch levels and their metabolic enzymes (i.e. invertases, sucrose synthase, starch synthase). This in turn increased organic acid (e.g. oxalic (70%) and malic acids (60%)) and amino acids. levels and biosynthetic enzymes, e.g. glutamine synthetase and threonine synthase. Increased sugars levels by Haloferax NARS9 under Co treatment also provided a route for the biosynthesis of saturated fatty acids, particularly palmitic and stearic acids. Furthermore, Haloferax NARS9 treatment supported the wheat nutritive value through increasing minerals (Ca, Fe, Mn, Zn) and antioxidants i.e., polyphenol, flavonoids, ASC and GSH and total polyamines by 50%, 110%, 400%, 30%, and 90% respectively). These in parallel with the increase in the activity of (phenylalanine ammonia-lyase (110%) in phenolic metabolism). Overall, this study demonstrates the potentiality of Haloferax NARS9 in harnessing carbon and nitrogen metabolism differentially in wheat plants to cope with Co toxicity. Our results also suggested that the use of Haloferax NARS9 in agricultural fields can improve growth and nutritional value of wheat grains.

Combined Effects of BEIIb and SSIIa Alleles on Amylose Contents, Starch Fine Structures and Physicochemical Properties of Indica Rice

Starch branching enzyme IIb (BEIIb) and soluble starch synthase IIa (SSIIa) play important roles in starch biosynthesis in cereals. Deficiency in the BEIIb gene produces the amylose extender (ae) mutant rice strain with increased amylose content (AC) and changes in the amylopectin structure. The SSIIa gene is responsible for the genetic control of gelatinization temperature (GT). The combined effects of BEIIb and SSIIa alleles on the AC, fine structures, and physicochemical properties of starches from 12 rice accessions including 10 recombinant inbred lines (RIL) and their two parents were examined in this study. Under the active BEIIb background, starches with the SSIIa-GC allele showed a higher GT than those with the SSIIa-TT allele, resulting from a lower proportion of A chain and a larger proportion of B1 chains in the amylopectin of SSIIa-GC. However, starch with the BEIIb mutant allele (be2b) in combination with any SSIIa genotype displayed more amylose long chains, higher amylose content, B2 and B3 chains, and molecular order, but smaller relative crystallinity and proportion of amylopectin A and B1 chains than those with BEIIb, leading to a higher GT and lower paste viscosities. These results suggest that BEIIb is more important in determining the structural and physicochemical properties than SSIIa. These results provide additional insights into the structure-function relationship in indica rice rather than that in japonica rice and are useful for breeding rice with high amylose content and high resistant starch.

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

Starch and storage proteins are the main components of rice (Oryza sativa L.) grains. Despite their importance, the molecular regulatory mechanisms of storage protein and starch biosynthesis remain largely elusive. Here, we identified a rice opaque endosperm mutant, opaque3 (o3), that overaccumulates 57-kDa proglutelins and has significantly lower protein and starch contents than the wild type. The o3 mutant also has abnormal protein body structures and compound starch grains in its endosperm cells. OPAQUE3 (O3) encodes a transmembrane basic leucine zipper (bZIP) transcription factor (OsbZIP60) and is localized in the endoplasmic reticulum (ER) and the nucleus, but it is localized mostly in the nucleus under ER stress. We demonstrated that O3 could activate the expression of several starch synthesis-related genes (GBSSI, AGPL2, SBEI, and ISA2) and storage protein synthesis-related genes (OsGluA2, Prol14, and Glb1). O3 also plays an important role in protein processing and export in the ER by directly binding to the promoters and activating the expression of OsBIP1 and PDIL1-1, two major chaperones that assist with folding of immature secretory proteins in the ER of rice endosperm cells. High-temperature conditions aggravate ER stress and result in more abnormal grain development in o3 mutants. We also revealed that OsbZIP50 can assist O3 in response to ER stress, especially under high-temperature conditions. We thus demonstrate that O3 plays a central role in rice grain development by participating simultaneously in the regulation of storage protein and starch biosynthesis and the maintenance of ER homeostasis in endosperm cells.

LSL1 controls cell death and grain production by stabilizing chloroplast in rice

Lesion mutants can be valuable tools to reveal the interactions between genetic factors and environmental signals and to improve grain production. Here we identified a rice (Oryza sativa) mutant, lesion spotleaf1 (lsl1), which produces necrotic leaf lesions throughout its life cycle. LSL1 encodes a protein of unknown function and belongs to a grass-specific clade. The lesion phenotype of the lsl1 mutant was sharply induced by shading, and its detached leaves incubated in 6-benzylamino purine similarly formed lesions in the dark. In addition, the lsl1 mutant exhibited reactive oxygen species accumulation and cell death. The terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) and comet assays revealed that the lsl1 mutant contained severe DNA damage, resulting in reduced grain yield and quality. RNA sequencing, gene expression, and protein activity analyses indicate that LSL1 is required for chloroplast function. Furthermore, LSL1 interacts with PsaD and PAP10 to form a regulatory module that functions in chlorophyll synthesis and chloroplast development to maintain redox balance. Our results reveal that LSL1 maintains chloroplast structure, redox homeostasis, and DNA stability, and plays important roles in the interaction between genetic factors and environmental signals and in regulating grain size and quality.