Amylose Content,Morphology,Crystal Structure,and Thermal Properties of Starch Grains in Main and Ratoon Rice Crops

Rice ratooning,or the production of a second rice crop from stubble after the harvest of the main crop,is considered to be a green and resource-efficient rice production system.The present study was conducted to examine variance in amylose content(AC),grain morphology,crystal structure,and thermal properties of starch between main-and ratoon-season rice of seven varieties.Ratoon-season rice grains had higher ACs and significantly lower transition gelatinization temperatures(To,Tp,and Tc)than did main-season rice grains.The relative crystallinity and lamellar peak intensity of ratoon-season rice starch were 7.89%and 20.38%lower,respectively,than those of main-season rice starch.In addition,smaller granules with smoother surfaces and lower thermal parameters were observed in the starch of ratoon-season rice.The relative crystallinity and lamellar peak intensity of starch correlated negatively with the AC and positively with transition gelatinization temperatures.These results suggest that the superior cooking quality of ratoon-season rice is attributable to the moderate increase of grain AC,which reduces the relative crystallinity,weakens the crystal structure,and lead to a decrease in the gelatinization temperature.

Amylose Content and Starch Granule Size in Rice Grains are Affected By Growing Season

Amylose content and starch granule size in grains influence rice quality,which differs between the early(ES)and late season(LS).The objective of this study was to determine the variation of amylose content and starch granule size between seasons and find the main reasons(e.g.,temperature and solar radiation)for the observed variation.Field experiments with six rice varieties(three high and three low amylose content rice)planted in the ES and LS were conducted in 2016 and 2017,respectively.The mean temperatures during the filling stage were higher in ES,however,the daily temperatures at 7-10 days after flowering(DAF)in 2016,and at 5-10,13-14 DAF in 2017 were higher in LS.The results showed that amylose content in LS was lower than in ES with high amylose content rice varieties(HACV);the opposite trend occurred with low amylose content rice varieties(LACV).The mean starch granule diameter was higher in LS than ES in 2016,but the opposite result occurred in 2017 with all rice.Our results suggest that higher temperatures increased and decreased the amylose content in HACV and LACV,respectively.Temperatures at 5-15 DAF were important for the formation of starch granules:lower temperatures during 10-14 DAF increased the proportion of larger starch granules(d>6.21μm,some with d>13.3μm),and higher temperatures at 5-6 DAF increased the proportion of starch granules with diameter 4.24-6.21μm.

The kinase OsSK41/OsGSK5 negatively regulates amylose content in rice endosperm by affecting the interaction between OsEBP89 and OsBP5

Amylose content(AC) is the main factor determining the palatability, viscosity, transparency, and digestibility of rice(Oryza sativa)grains. AC in rice grains is mainly controlled by different alleles of the Waxy(Wx) gene. The AP2/EREBP transcription factor OsEBP89 interacts with the MYC-like protein OsBP5 to synergistically regulate the expression of Wx.Here, we determined that the GLYCOGEN SYNTHASE KINASE 5(OsGSK5, also named SHAGGY-like kinase 41 [OsSK41]) inhibits the transcriptional activation activity of OsEBP89 in rice grains during amylose biosynthesis. The loss of OsSK41 function enhanced Wx expression and increased AC in rice grains. By contrast, the loss of function of OsEBP89 reduced Wx expression and decreased AC in rice grains. OsSK41 interacts with OsEBP89 and phosphorylates four of its sites(Thr-28,Thr-30, Ser-238, and Thr-257), which makes OsEBP89 unstable and attenuates its interaction with OsBP5. Wx promoter activity was relatively weak when regulated by the phosphomimicvariantOsEBP89E–OsBP5but relatively strong when regulated by the nonphosphorylatable variant OsEBP89A–OsBP5.Therefore, OsSK41-mediated phosphorylation of OsEBP89 represents an additional layer of complexity in the regulation of amylose biosynthesis during rice grain development. In addition, our findings provide four possible sites for regulating rice grain AC via precise gene editing.

Comparison of grain yield and quality of different types of japonica rice cultivars in the northern Jiangsu plain,China

In recent years,an increasing number of different types of japonica rice cultivars have been released in the southern rice region of China.The grain yield and quality of these new cultivars showed significant differences in large scale planting.However,the causes of the differences remain little known.Therefore,three typical types of japonica rice cultivars were used in this study to investigate their grain yield and quality.A scanning calorimeter(DSC),X-ray powder diffractometer(XRD),rapid viscosity analyzer(RVA)and taste analyzer were used to evaluate the cooking and eating properties.The results showed that the yield of non-soft hybrid japonica rice cultivars was significantly higher than that of non-soft inbred japonica rice cultivars and soft inbred japonica rice cultivars.Soft inbred japonica rice cultivars had a low amylose content and moderate protein content,which are the main reasons for the superior cooking and eating quality.In addition,the relative crystallinity of soft inbred japonica rice cultivars was significantly higher than that of non-soft inbred and non-soft hybrid japonica rice cultivars,which is considered the major factor resulting in higher transition temperature and gelatinization enthalpy(ΔH_(gel)).Non-soft hybrid japonica rice cultivars had a higher number of large starch granules than soft inbred and non-soft inbred japonica rice cultivars.The setback value(SB)and breakdown value(BD),indirectly reflecting the cooking and eating quality of the three types of japonica rice cultivars,also confirmed that soft inbred japonica rice cultivars with a low SB value and a high BD value had better palatability than the other two types.This study provides guidance for future plantation of different types of japonica rice cultivars in large rice-producing areas.

Performance of Soft Rice (Oryza sativa L.) Grown in Early Season in China

Eating quality is of paramount importance to rice(Oryza sativa L.)consumers and soft rice with low amylose content has become popular in China.This study was conducted to evaluate the performance of soft rice grown in the early season(ES)dominated by non-soft rice.Field experiments were conducted in Yongan and Santang,Hunan Province,China from 2016-2018.Results showed that grain amylose content in soft rice cultivars was consistently lower in the ES compared to the late season(LS).The lower grain amylose content in the ES compared to the LS was partly attributed to higher average daily mean temperature during grain filling.No significant relationship was observed between grain yield and seed amylose content in ES rice.Soft rice cultivars produced a similar average grain yield to non-soft rice cultivars in the ES.These results encourage breeders to develop more ES rice cultivars with soft texture to meet the consumer demand for this type of rice.

Anaerobic biodegradation,physical and structural properties of normal and high-amylose maize starch films

Biodegradable plastics have attracted considerable attention in recent years due to their biodegradability,biocompatibility and non-toxicity.In this study,normal maize starch(containing 25%amylose)and high-amylose maize starch(containing 80%amylose)were served as model materials to prepare starch/polyvinyl alcohol(PVA)blends.To comprehensively study the effects of amylose contents on the film performances,the mechanical properties,water resistance and anaerobic biodegradability of the two films were examined.Moreover,the processes of anaerobic degradation were investigated by evolutions of biogas production,pH in reactors and the changes of film structures and compositions.The results indicated that amylose content played an important role in the microstructures of starch film as well as mechanical properties and water resistance,whereas it had no significant influence on anaerobic biodegradability of the films.Nonetheless,the structure of high-amylose maize starch/PVA film was more suitable and beneficial to the anaerobic biodegradation than that of the normal maize starch/PVA film,because it could effectively avoid accumulation of volatile fatty acids,which contributed to the stable biogas production,short fermentation period and non-souring in the reactor.

A rare Waxy allele coordinately improves rice eating and cooking quality and grain transparency

In rice(Oryza sativa), amylose content(AC) is the major factor that determines eating and cooking quality(ECQ). The diversity in AC is largely attributed to natural allelic variation at the Waxy(Wx)locus. Here we identified a rare Wx allele, Wx^(mw) ,which combines a favorable AC, improved ECQ and grain transparency. Based on a phylogenetic analysis of Wx genomic sequences from 370 rice accessions, we speculated that Wx^(mw) may have derived from recombination between two important natural Wx alleles, Wx^(in) and Wx^(b). We validated the effects of Wx^(mw) on rice grain quality using both transgenic lines and near-isogenic lines(NILs). When introgressed into the japonica Nipponbare(NIP) background, Wx^(mw) resulted in a moderate AC that was intermediate between that of NILs carrying the Wx^(b)allele and NILs with the Wx^(mp) allele. Notably, mature grains of NILs fixed for Wx^(mw) had an improved transparent endosperm relative to soft rice. Further, we introduced Wx^(mw) into a high-yielding japonica cultivar via molecular marker-assisted selection: the introgressed lines exhibited clear improvements in ECQ and endosperm transparency. Our results suggest that Wx^(mw) is a promising allele to improve grain quality, especially ECQ and grain transparency of high-yielding japonica cultivars, in rice breeding programs.

Novel Wx alleles generated by base editing for improvement of rice grain quality

Amylose content(AC),which is regulated by the Waxy(Wx)gene,is a major indicator of eating and cooking quality(ECQ)in rice(Oryza sativa).Thus far,only a limited number of mutations in the N-terminal domain of Wx were found to have a major impact on the AC of rice grains and no mutations with such effects were reported for other regions of the Wx protein.Here,nucleotide substitutions in the middle region of Wx were generated by adenine and cytosine base editors.The nucleotide substitutions led to changes in 15 amino acid residues of Wx,and a series of novel Wx alleles with ACs of 0.3%-29.43%(wild type with AC of 19.87%)were obtained.Importantly,the waxy~(abe2)allele showed a"soft rice"AC,improved ECQ,favorable appearance,and no undesirable agronomic traits.The transgenes were removed from the waxy~(abe2)progeny,generating a promising breeding material for improving rice grain quality.

Effects of soluble starch synthase genes on eating and cooking quality in semi waxy japonica rice with Wx^(mp)

The purpose of this study is to reveal the genetic mechanism of the variation of amylose content among different semi waxy or glutinous japonica rice in the background of Wxmp gene.Sixty-four semi waxy lines derived from the hybrid progenies of Wujing 13 and Milky Princess(Kantou 194)with polymorphism in soluble starch synthase gene SSIIa(SSII-3)and SSIIIa(SSIII-2)but no polymorphism in other starch synthase related genes were used as test materials.The genotypes of SSIIa and SSIIIa allele were identified by molecular markers,and the allelic effects of SSIIa and SSIIIa gene on amylose content(AC),gel consistency(GC),gelatinization temperature(GT)and rapid visco analyzer(RVA)profile characteristics were analyzed.The significant effects of SSIIa and SSIIIa alleles and the interactive effects between two genes on AC,GT,GC and RVA profile characteristics were found.The SSIIa and SSIIIa alleles from Wujing13 shown positive effects on AC with an average increase of 1.87 and 1.23%in 2 years respectively.There was no significant effect on GT for SSIIa or SSIIIa allele but remarkable influence on GT when the co-existence of the two genes.The genotype SSIIa^(mp)SSIIIa^(mp) shown 1.34℃higher GT than genotype SSIIawjSSIIIawj(mp and wj indicated that the gene was derived from Milky Princess and Wujing 13 respectively,the same as in the below).Different genes and alleles resulted in significant different GC.The genetic effect of SSIIawj and SSIIIamp on GC was 8.74 and 9.62mm respectively.The GC of SSIIa^(wj)SSIIIa^(mp) was 10.64 and 16.95mm higher than that of SSIIa^(mp)SSIIIa^(wj) and SSIIawjSSIIIawj,respectively.The allele SSIIa^(wj) could increase the peak viscosity(PKV),hot paste viscosity(HPV),cool paste viscosity(CPV)and breakdown viscosity(BDV),while decrease the consistency viscosity(CSV)and setback viscosity(SBV).However for the allele SSIIIa^(wj) the opposite was true.The genotype SSIIa^(wj)SSIIIa^(mp) had the largest PKV,HPV and CPV,the genotype SSIIa^(wj)SSIIIa^(wj) had the largest BDV and CSV,but the genotype SSIIa^(wj)SSIIIa^(mp) had the least SBV.According to the comprehensive effect of each trait,the genotype SSIIawjSSIIIamp was the best.The allelic variation and interaction effect of SSIIa and SSIIIa genes have important reference value for improving cooking and eating quality of semi waxy japonica rice.