Rice Chalkiness Research Articles

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.

Relationships between the appearance quality and starch structure of soft rice under different nitrogen levels

AbstractThis study aims to explore the formation mechanism of starch structure and the relationships between the appearance quality and starch structure of soft rice under different nitrogen levels. We comprehensively investigated the physiological aspects, starch structure variations, and appearance quality of soft rice in response to different nitrogen applications. The results showed that under the moderate nitrogen application (270 N), the soft rice exhibited the highest AGPase activity, the highest large‐starch granule content, and the lowest chalkiness. Under the highest nitrogen application (360 N), the soft rice exhibited the highest GBSS and DBE activity and the lowest SBE activity, the highest content of long‐branched amylopectin, the lowest relative crystallinity, the fewest ordered structures, the most amorphous structures, the largest semi‐crystalline lamellar thicknesses, and the highest transparency of chalk‐free rice. In conclusion, moderate nitrogen fertilization (270 N) improved the AGPase activity, which leaded to fuller starch granules and more compact endosperm in soft rice. Thus, the grain chalkiness of soft rice decreased. Continuous nitrogen application (0‐360 N) constantly increased the GBSS and DBE activity and reduced the SBE activity in soft rice, leading a lower content of short‐branched amylopectin and a higher content of long‐branched amylopectin in soft rice. Thus, the relative crystallinity and ordered structures of soft rice were reduced. These structures improved the transparency phenotype of soft rice.

OsNLP3 enhances grain weight and reduces grain chalkiness in rice

Grain weight, a key determinant of yield in rice (Oryza sativa L.), is governed primarily by genetic factors, whereas grain chalkiness, a detriment to grain quality, is intertwined with environmental factors such as mineral nutrients. Nitrogen (N) is recognized for its effect on grain chalkiness, but the underlying molecular mechanisms remain to be clarified. This study revealed the pivotal role of rice NODULE INCEPTION-LIKE PROTEIN 3 (OsNLP3) in simultaneously regulating grain weight and grain chalkiness. Our investigation showed that loss of OsNLP3 leads to a reduction in both grain weight and dimension, in contrast to the enhancement observed with OsNLP3 overexpression. OsNLP3 directly suppresses the expression of OsCEP6.1 and OsNF-YA8, which were identified as negative regulators associated with grain weight. Consequently, two novel regulatory modules, OsNLP3–OsCEP6.1 and OsNLP3–OsNF-YA8, were identified as key players in grain weight regulation. Notably, the OsNLP3–OsNF-YA8 module not only increases grain weight but also mitigates grain chalkiness in response to N. This research clarifies the molecular mechanisms that orchestrate grain weight through the OsNLP3–OsCEP6.1 and OsNLP3–OsNF-YA8 modules, highlighting the pivotal role of the OsNLP3–OsNF-YA8 module in alleviating grain chalkiness. These findings reveal potential targets for simultaneous enhancement of rice yield and quality.

Response of yield and quality of Japonica rice to different gradients of moisture deficit at grain-filling stage in cold regions

Abstract Water stress significantly affects on rice yield and quality. Eight Japonica varieties from the first and second accumulated temperature zones of Heilongjiang Province were used as materials and four moisture gradients (0, −10, −25 and −40 kPa) were conducted at the grain-filling stage to clarify the effect of water stress on the rice yield and quality in cold regions. The results showed that the rice yield was reduced due to the decrease in the seed setting rate. Rice chalkiness was significantly increased by drought stress, especially under −10 kPa. The protein content of most varieties was significantly reduced and taste quality was increased under −25 to −40 kPa. The effect on protein components increased with increasing drought stress. The gel consistency decreased and the average chain length of amylopectin was less affected by drought. With an increase in moisture deficit, the rapid viscosity analyzer characteristics and chain length distribution of amylopectin showed a trend of first increasing and then decreasing or decreasing and then increasing. The response of starch to mild and severe drought varied. Our study provides a theoretical basis for the efficient utilization of water and high quality and yield of Japonica rice.

Grain Chalkiness Is Decreased by Balancing the Synthesis of Protein and Starch in Hybrid Indica Rice Grains under Nitrogen Fertilization.

The important reason for the commercial value of hybrid rice suffering is due to excessive chalkiness, and the biosynthesis of starch and proteins is critical for regulating chalkiness; however, it is currently unclear how the application of N fertilizer affects grains to reduce their chalkiness and improve their quality. The 2019, 2020, and 2021 trials were conducted in a split-plot design, with high and low chalky varieties as the main plot and N fertilizer rate as the split-plot. The effects of fertilization with 75, 150, and 225 kg N ha-1 on the dynamic synthesis of starch, protein, and endogenous hormones and on the amino acid of hybrid indica rice kernels with different degrees of chalkiness were investigated. Grain physiological activity was higher in low-chalky varieties than in high-chalky varieties, and these physiological parameters were strongly associated with chalkiness formation. Higher N fertilization (150 and 225 kg N ha-1) significantly reduced the proportion of chalky grains (8.93-28.02%) and chalkiness (8.61-33.99%) compared with 75 kg N ha-1. Increased N fertilization decreased the activities of granule-bound starch synthase and starch-debranching enzyme, but significantly increased adenosine diphosphate glucose pyrophosphorylase, soluble starch synthase, and starch-branching enzyme activities, synergistically improving glutamate synthetase and glutamine synthetase enzyme activities, which tended to support the synthesis of amylopectin, α-ketoglutarate, and 3-phosphoglyceric acid-derived amino acids in the endosperm cells of the grains; this favored starch and protein accumulation in the grains at 6-30 days after anthesis. Additionally, N application promoted the synthesis of endogenous hormones 1-aminocyclopropane-1-carboxylic acid, gibberellins, and abscisic acid in grains. Hence, N fertilization reduced the rice chalkiness in hybrid indica rice varieties by balancing grain protein and starch composition and enhancing some endogenous hormone synthesis.

Pyramiding of Low Chalkiness QTLs Is an Effective Way to Reduce Rice Chalkiness

Rice chalkiness is a key limiting factor of high-quality rice. The breeding of low chalkiness varieties has always been a challenging task due to the complexity of chalkiness and its susceptibility to environmental factors. In previous studies, we identified six QTLs for the percentage of grain chalkiness (PGC), named qPGC5, qPGC6, qPGC8.1, qPGC8.2, qPGC9 and qPGC11, using single-segment substitution lines (SSSLs) with genetic background of Huajingxian 74 (HJX74). In this study, we utilized the six low chalkiness QTLs to develop 17 pyramiding lines with 2–4 QTLs. The results showed that the PGC decreased with the increase of QTLs in the pyramiding lines. The pyramiding lines with 4 QTLs significantly reduced the chalkiness of rice and reached the best quality level. Among the six QTLs, qPGC5 and qPGC6 showed greater additive effects and were classified as Group A, while the other four QTLs showed smaller additive effects and were classified as Group B. In pyramiding lines, although the presence of epistasis, additivity remained the main component of QTL effects. qPGC5 and qPGC6 showed stronger ability to reduce rice chalkiness, particularly in the environment of high temperature (HT) in the first cropping season (FCS). Our research demonstrates that by pyramiding low chalkiness QTLs, it is feasible to develop the high-quality rice varieties with low chalkiness at the best quality level even in the HT environment of FCS.

Identification of Candidate SNPs and Genes Controlling Chalkiness in the Medium-Grain Rice (Oryza sativa L.)

Identification of Candidate SNPs and Genes Controlling Chalkiness in the Medium-Grain Rice (Oryza sativa L.)

Grain chalkiness is reduced by coordinating the biosynthesis of protein and starch in fragrant rice (Oryza sativa L.) grain under nitrogen fertilization

The synthesis of protein and starch in grain is crucial for regulating rice (Oryza sativa L.) chalkiness. However, little is known about how to coordinate them in the grain to improve the appearance quality of fragrant rice under nitrogen (N) fertilizer application. In the present study, both pot and field experiments were conducted to study the effects of N fertilization on chalkiness, starch and protein content, and enzyme activities related to carbon (C) and N metabolism in fragrant rice grains. The field experiment was carried out with five N levels of 0 (N0), 64 (N64), 128 (N128), 160 (N160), and 192 (N192) kg N ha−1, and a pot experiment was additionally performed with equivalent treatments. Compared to N0, N application significantly reduced fragrant rice chalkiness grain rate (17.54–39.47 %), chalkiness area (23.79–38.54 %), and chalkiness (35.98–61.27 %) in pot and field experiments. N fertilization decreased the mean grain filling rate (0.17 mg grain−1 d−1) and extended the effective grain filling duration (3.69 d). N fertilization significantly increased the protein content (16.17–22.63 %), which was driven by the improved activities of glutamine synthetase (GS), glutamate synthase (GOGAT), glutamic oxaloacetate transaminase (GOT), and glutamate pyruvate transaminase (GPT). Amylose and amylopectin contents, components of starch, decreased with N fertilizer application, which was associated with depression of the activities of adenosine diphosphate glucose pyrophosphorylase (AGP), granules bound starch synthase (GBSS), soluble starch synthase (SSS), and starch branching enzyme (SBE). The structural equation model (SEM) showed that N fertilization coordinated the synthesis of protein and starch and reduced the fragrant rice chalkiness by changing the process of C and N metabolism in fragrant rice grains. In short, the N fertilization decreased fragrant rice chalkiness by optimizing grain filling, balancing the protein and starch content in the grain.

Regulation of Grain Chalkiness and Starch Metabolism by FLO2 Interaction Factor 3, a bHLH Transcription Factor in Oryza sativa.

Chalkiness is a key determinant that directly affects the appearance and cooking quality of rice grains. Previously, Floury endosperm 2 (FLO2) was reported to be involved in the formation of rice chalkiness; however, its regulation mechanism is still unclear. Here, FLO2 interaction factor 3 (OsFIF3), a bHLH transcription factor, was identified and analyzed in Oryza sativa. A significant increase in chalkiness was observed in OsFIF3-overexpressed grains, coupled with a round, hollow filling of starch granules and reduced grain weight. OsFIF3 is evolutionarily conserved in monocotyledons, but variable in dicotyledons. Subcellular localization revealed the predominant localization of OsFIF3 in the nucleus. The DAP-seq (DNA affinity purification sequencing) results showed that OsFIF3 could affect the transcriptional accumulation of β-amylase 1, α-amylase isozyme 2A-like, pectinesterase 11, β-glucosidase 28 like, pectinesterase, sucrose transport protein 1 (SUT1), and FLO2 through the binding of the CACGTG motif on their promoters. Moreover, FLO2 and SUT1 with abundant OsFIF3 binding signals showed significant expression reduction in OsFIF3 overexpression lines, further confirming OsFIF3's role in starch metabolism regulation and energy material allocation. Taken together, these findings show that the overexpression of OsFIF3 inhibits the expression of FLO2 and SUT1, thereby increasing grain chalkiness and affecting grain weight.

Effects of elevated nitrogen fertilizer on the multi-level structure and thermal properties of rice starch granules and their relationship with chalkiness traits.

Chalkiness in rice reduces its market value and affects consumer acceptance. Research on the mechanism of chalkiness formation has focused primarily on the activity of key enzymes of carbon metabolism and starch accumulation. The relationship between the formation of chalkiness induced by N fertilizer and rice starch's multi-level structure and thermal properties still needs to be fully elucidated. In this study, the rates of chalky grains and degree of chalkiness decreased with the increase in N fertilizer dosage. This was attributed to an increased proportion of short chains, ordered structure carbon chains, small starch granules, and branched starches, and a higher degree of crystallinity and ΔHg in protein, and a decreased proportion of amylose, large starch granules, and weighted average diameter of starch granule surface area and volume. Application of N fertilizer promoted an increased proportion of short-branched chain amylopectin to develop a more ordered carbohydrate structure and crystalline lamella. These effects enhanced the normal development and compactness of starch granules in grains, and improved their arrangement morphology, thereby reducing the chalkiness in rice. These changes in starch multi-level structure and protein improve the physicochemical characteristics of starch and enhance the fullness, crystallinity and compactness of starch granules, while synergistically increasing the regularity and homogeneity of starch granules and thus optimizing the stacking pattern of starch granules, leading to a reduction in rice chalkiness under nitrogen fertilization and thus improving the appearance of rice. © 2023 Society of Chemical Industry.

Metagenomic Sequencing to Analyze Composition and Function of Top-Gray Chalky Grain Microorganisms from Hybrid Rice Seeds.

The top-gray chalkiness of hybrid rice (Oryza sativa L.) seeds is a typical phenomenon in hybrid rice seeds. The chalky part of the grain is infected and is the inoculum to infect the normal seeds during storage and soaking. These seed-associated microorganisms were cultivated and sequenced using metagenomics shotgun sequencing to obtain more comprehensive information on the seed-associated microorganisms in this experiment. The results showed that fungi could grow well on the rice flour medium, similar to the ingredients of rice seed endosperms. After the assembly of metagenomic data, a gene catalog was established, comprising 250,918 genes. Function analysis showed that glycoside hydrolases were the dominant enzymes, and the genus Rhizopus accounted for the dominant microorganisms. The fungal species R. microspores, R. delemar, and R. oryzae were likely to be the candidate pathogens in the top-gray chalky grains of hybrid rice seeds. These results will provide a reference for improving hybrid rice processing after harvest.

Targeted mutagenesis of the vacuolar H+ translocating pyrophosphatase gene reduces grain chalkiness in rice.

Grain chalkiness is a major concern in rice production because it impacts milling yield and cooking quality, eventually reducing market value of the rice. A gene encoding vacuolar H+ translocating pyrophosphatase (V-PPase) is a major quantitative trait locus in indica rice, controlling grain chalkiness. Higher transcriptional activity of this gene is associated with increased chalk content. However, whether the suppression of V-PPase could reduce chalkiness is not clear. Furthermore, natural variation in the chalkiness of japonica rice has not been linked with V-PPase. Here, we describe promoter targeting of the japonica V-PPase allele that led to reduced grain chalkiness and the development of more translucent grains. Disruption of a putative GATA element by clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated protein 9 suppressed V-PPase activity, reduced grain chalkiness and impacted post-germination growth that could be rescued by the exogenous supply of sucrose. The mature grains of the targeted lines showed a much lower percentage of large or medium chalk. Interestingly, the targeted lines developed a significantly lower chalk under heat stress, a major inducer of grain chalk. Metabolomic analysis showed that pathways related to starch and sugar metabolism were affected in the developing grains of the targeted lines that correlated with higher inorganic pyrophosphate and starch contents and upregulation of starch biosynthesis genes. In summary, we show a biotechnology approach of reducing grain chalkiness in rice by downregulating the transcriptional activity of V-PPase that presumably leads to altered metabolic rates, including starch biosynthesis, resulting in more compact packing of starch granules and formation of translucent rice grains.

Physiological Basis of High Nighttime Temperature-Induced Chalkiness Formation during Early Grain-Filling Stage in Rice (Oryza sativa L.)

Heat stress during the grain-filling stage seriously affects grain quality in rice. However, very limited information is available regarding the effects of short-term high nighttime temperature (HNT) on grain chalkiness formation in rice. In this paper, the effects of HNT at the early grain-filling stage (7 days after ear emergence) on rice chalkiness formation and the potential causes were investigated by using two rice varieties that differed in susceptibility to high temperature. Although the HNT treatment at night dramatically increased the grain chalkiness in Jiuxiangzhan (JXZ) and Huanghuazhan (HHZ), the increase was greater in JXZ compared to HHZ. The net photosynthetic rate and SPAD value were significantly reduced by HNT treatment in the flag leaves of JXZ, while no significant differences were observed in HHZ. Furthermore, HNT treatment reduced the antioxidant enzyme activity in the flag leaves of JXZ, while the opposite was observed in HHZ, exhibiting increased antioxidant enzyme activity. Moreover, HNT treatment altered the endogenous hormone levels, enhanced the enzymatic activities related to starch biosynthesis, and accelerated the filling rate in grains of JXZ when compared to HHZ. Scanning electron microscopy (SEM) observation exhibited that the starch granules in the endosperm of JXZ were loosely packed together and more starch granules with small pits were produced after HNT treatment. Based on these data, we inferred that HNT stress during the early stage of rice grain filling accelerated the grain-filling rate but shortened the grain-filling duration by changing the endogenous hormone levels and enhancing the enzymatic activities responsible for starch biosynthesis, resulting in significant changes in the morphological structure and arrangement of starch granules and eventually causing the occurrence of grain chalkiness.

Mapping of qChalk1 controlling grain chalkiness in japonica rice.

Rice grain chalkiness is an undesirable characteristic that affects grain quality. The aim of this study was to map QTLs controlling grain chalkiness in japonica rice. In this study, two japonica rice cultivars with similar grain shapes but different grain chalkiness rates were crossed and the F2 and BC1F2 populations were subjected to QTL-seq analysis to map the QTLs controlling the grain chalkiness rate. QTL-seq analysis revealed SNP index differences on chromosome 1 in both of the segregating populations. Using polymorphic markers between the two parents, QTL mapping was conducted on 213 individual plants in the BC1F2 population. QTL mapping confined a QTL controlling grain chalkiness, qChalk1, to a 1.1Mb genomic region on chromosome 1. qChalk1 explained 19.7% of the phenotypic variation. A QTL controlling grain chalkiness qChalk1 was detected in both F2 and BC1F2 segregating populations by QTL-Seq and QTL mapping methods. This result would be helpful for further cloning of the genes controlling grain chalkiness in japonica rice.

Genome-wide association mapping and gene expression analysis reveal candidate genes for grain chalkiness in rice.

Grain chalkiness is the main factor determining the market value of rice. Reducing chalkiness is an important breeding goal for genetic improvement of high quality rice. Identification of QTLs or genes controlling chalkiness is the prerequisite for molecular breeding in rice. Here, we conducted a genome-wide association study to identify QTLs associated with grain chalkiness including percentage of grains with chalkiness (PGWC) and degree of endosperm chalkiness (DEC) in 450 rice accessions consisting of 300 indica and 150 japonica rice in two environments. A total of 34 QTLs were identified, including 14 QTLs for PGWC and 20 QTLs for DEC. Among them, seven QTLs were commonly identified in two environments, and eight QTLs were simultaneously related to two traits. Based on the haplotype analysis, LD decay analysis, RNA-sequencing, qRT-PCR confirmation and haplotype comparisons, four genes (LOC_Os10g36170, LOC_Os10g36260, LOC_Os10g36340 and LOC_Os10g36610) were considered as the candidate genes for qDEC-10c1w,2wj , which could be identified in both environments and had the most significant p-value among the newly identified QTLs. These results provided new insight into the genetic basis of grain chalkiness and gene resources for improving quality by molecular breeding in rice.

Fine mapping of the grain chalkiness quantitative trait locus qCGP6 reveals the involvement of Wx in grain chalkiness formation.

Grain chalkiness is an important index of rice appearance quality and is negatively associated with rice processing and eating quality. However, the genetic mechanism underlying chalkiness formation is largely unknown. To identify the genetic basis of chalkiness, 410 recombinant inbred lines (RILs) derived from two representative indica rice varieties, Shuhui498 (R498) and Yihui3551 (R3551), were used to discover quantitative trait loci (QTLs). The two parental lines and RILs were grown in three locations in China under three controlled fertilizer application levels. Analyses indicated that chalkiness was significantly affected by genotype, the environment, and the interaction between the two, and that heritability was high. Several QTLs were isolated, including the two stable QTLs qCGP6 and qCGP8. Fine mapping and candidate gene verification of qCGP6 showed that Wx may play a key role in chalkiness formation. Chromosomal segment substitution lines (CSSLs) and near-isogenic lines (NILs) carrying the Wxa or Wxin allele produced more chalky grain than the R498 parent. A similar result was also observed in the 3611 background. Notably, the effect of the Wx genotype on rice chalkiness was shown to be dependent on environmental conditions, and Wx alleles exhibited different sensitivities to shading treatment. Using clustered regularly interspaced short palindromic repeats (CRISPR)/CRISPR-associated 9 (Cas9), the Wxa promoter region was successfully edited; down-regulating Wx alleviates chalkiness formation in NILR498-Wxa. This study developed a new strategy for synergistic improvement of eating and appearance qualities in rice, and created a novel Wx allele with great potential in breeding applications.

A mitochondrion-associated PPR protein, WBG1, regulates grain chalkiness in rice.

Rice kernel quality has vital commercial value. Grain chalkiness deteriorates rice's appearance and palatability. However, the molecular mechanisms that govern grain chalkiness remain unclear and may be regulated by many factors. In this study, we identified a stable hereditary mutant, white belly grain 1 (wbg1), which has a white belly in its mature grains. The grain filling rate of wbg1 was lower than that of the wild type across the whole filling period, and the starch granules in the chalky part were oval or round and loosely arranged. Map-based cloning showed that wbg1 was an allelic mutant of FLO10, which encodes a mitochondrion-targeted P-type pentatricopeptide repeat protein. Amino acid sequence analysis found that two PPR motifs present in the C-terminal of WBG1 were lost in wbg1. This deletion reduced the splicing efficiency of nad1 intron 1 to approximately 50% in wbg1, thereby partially reducing the activity of complex I and affecting ATP production in wbg1 grains. Furthermore, haplotype analysis showed that WBG1 was associated with grain width between indica and japonica rice varieties. These results suggested that WBG1 influences rice grain chalkiness and grain width by regulating the splicing efficiency of nad1 intron 1. This deepens understanding of the molecular mechanisms governing rice grain quality and provides theoretical support for molecular breeding to improve rice quality.

Variation of rice starch structure and physicochemical properties in response to high natural temperature during the reproductive stage.

Climate warming affects rice growth at different phenological stages, thereby increasing rice chalkiness and protein content and reducing eating and cooking quality (ECQ). The structural and physicochemical properties of rice starch played important roles in determining rice quality. However, differences in their response to high temperature during the reproductive stage have been rarely studied. In the present study, they were evaluated and compared between two contrasting natural temperature field conditions, namely, high seasonal temperature (HST) and low seasonal temperature (LST), during the reproductive stage of rice in 2017 and 2018. Compared with LST, HST significantly deteriorated rice quality, including increased grain chalkiness, setback, consistence, and pasting temperature and reduced taste values. HST considerably reduced the total starch and increased the protein content. Likewise, HST significantly reduced the short amylopectin chains [degree of polymerization (DP) <12] and increased the long amylopectin chains (DP > 12) and relative crystallinity. The starch structure, total starch content, and protein content explained 91.4%, 90.4%, and 89.2% of the total variations in pasting properties, taste value, and grain chalkiness degree, respectively. In conclusion, we suggested that rice quality variations were closely associated with the changes in chemical composition content (total starch and protein content) and starch structure in response to HST. These results indicated that we should improve the resistance of rice to high temperature during the reproductive stage to improve the fine structure of rice starch in further breeding and practice.

GF14f gene is negatively associated with yield and grain chalkiness under rice ratooning.

Ratoon rice cropping has been shown to provide new insights into overcoming the current challenges of rice production in southern China. However, the potential mechanisms impacting yield and grain quality under rice ratooning remain unclear. In this study, changes in yield performance and distinct improvements in grain chalkiness in ratoon rice were thoroughly investigated, using physiological, molecular and transcriptomic analysis. Rice ratooning induced an extensive carbon reserve remobilization in combination with an impact on grain filling, starch biosynthesis, and ultimately, an optimization in starch composition and structure in the endosperm. Furthermore, these variations were shown to be associated with a protein-coding gene: GF14f (encoding GF14f isoform of 14-3-3 proteins) and such gene negatively impacts oxidative and environmental resistance in ratoon rice. Our findings suggested that this genetic regulation by GF14f gene was the main cause leading to changes in rice yield and grain chalkiness improvement of ratoon rice, irrespective of seasonal or environmental effects. A further significance was to see how yield performance and grain quality of ratoon rice were able to be achieved at higher levels via suppression of GF14f.

OsAAP3 Gene Mutation Promotes the Chalkiness Character in Rice

Rice chalkiness is one of the most important appearance quality traits and has a great impact on its processing quality, nutritional quality, cooking, and eating quality traits. It has important theoretical significance and application value to clarify the genetic mechanism of rice chalkiness. To reveal the relationship between chalkiness of OsAAP3 mutant rice and the shape, structure and arrangement of endosperm cells and starch grains, which will lay a foundation for further research on the formation mechanism of chalkiness character of rice and the cultivation of new high-quality rice varieties. The results showed that the chalkiness, chalkiness rate, and chalkiness area of OsAAP3 mutant rice significantly increased compared with the control ZH11, and there were significant variations in the arrangement, morphology, and cross-section starch grain distribution of the endosperm cells of the mutant rice: the white heart area of the mutant increased, and the white belly almost distributed in the edge of the whole rice cross-section. The chalky part and transparent part of the OsAAP3 mutant chalky rice also have obvious variations in the shape, structure, and arrangement of starch grains, but there is no significant difference between the transparent part of the mutant chalky rice and the starch grains of the non-chalky rice. The starch grains in the endosperm center of the OsAAP3 mutant of rice are well developed, but the starch grains in the abdomen and back are loosely arranged, and the starch grains are poorly developed. Therefore, the chalkiness character of OsAAP3 mutant rice increased significantly. The chalkiness character of its mutant mainly occurred in the abdomen, and the rest occurred in the center of the endosperm of rice. Moreover, the arrangement of starch grains in OsAAP3 mutant rice was loose, the grain shape was mostly irregular polyhedrons, and the starch development was poor.