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Near-isogenic lines Nip(Wx b /SSII-2), Nip(Wx b /ss2-2), Nip(Wx mw /SSII-2), Nip(Wx mw /ss2-2), Nip(Wx mp /SSII-2) and Nip(Wx mp /ss2-2) in the Nipponbare (Nip) background containing the SSII-2RNAi cassette combined with different Waxy (Wx) alleles were investigated in terms of rice grain transparency and quality profiles. Rice lines carrying the SSII-2RNAi cassette displayed downregulation of SSII-2, SSII-3 and Wx genes. Introduction of the SSII-2RNAi cassette decreased apparent amylose content (AAC) in all transgenic lines, but grain transparency differed between low AAC rice lines. Grains from Nip(Wx b /SSII-2) and Nip(Wx b /ss2-2) were transparent, while those of rice were increasingly translucent with decreasing moisture due to cavities within starch granules. Rice grain transparency was positively correlated with grain moisture and AAC, but negatively correlated with cavity area within starch granules. Starch fine structure analysis revealed a marked increase in short amylopectin chains with DP 6-12, but a decrease in intermediate chains with DP 13-24, resulting in decreased gelatinisation temperature. Starch crystalline structure analysis showed that the transgenic rice starches have lower crystallinity and lamellar repeat distance than controls due to differences in starch fine structure. The results highlight the molecular basis underpinning rice grain transparency, and provide strategies for improving rice grain transparency., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2023 Elsevier Ltd. All rights reserved.)

This study examined the effects of the combinations of Waxy (Wx) and starch branching enzyme IIb (BEIIb) alleles on starch fine structure and functional properties in indica rice cultivars. The results showed that be2b mutant starches with BEIIb deficiency had higher amylose content, shorter amylose long chains, a higher proportion of amylopectin long chains and molecular order, but a lower proportion of amylopectin short chains and relative crystallinity, resulting in higher gelatinization temperature but lower enthalpy and paste viscosity. Compared with the rice lines carrying Wx b allele, Wx a allele contributed to relatively higher amylose content, longer amylopectin chains, less short-range ordered structure and lower relative crystallinity, leading to a little lower gelatinization enthalpy. This study provides new insight into structure-function relations among rice lines with different allele combinations of starch synthesis related genes, which is a useful strategy for rice quality breeding., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

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., (© 2021 Institute of Botany, Chinese Academy of Sciences.)

The Wx gene encodes a granule-bound starch synthase (GBSS) and plays a key role in determining rice eating and cooking qualities (ECQs). SSIII-2 (SSIIIa), a member of the soluble starch synthases, is responsible for the synthesis of long chains of amylopectin. To investigate the effects of Wx and its interaction with SSIII-2 on grain ECQs, a population from a hybrid combination was established as a research material. The genotypes of SSIII-2 and the single nucleotide polymorphisms (SNPs) on intron1, exon6, and exon10 of Wx, and the physicochemical indicators and rapid visco analyzer (RVA) profile characteristics were analyzed. The results revealed various effects of SSIII-2 on rice quality under different backgrounds of Wx alleles. There was no obvious difference between different SSIII-2 alleles under the same background of Wxa, whereas there was a significant diversity under the same background of Wxb. Wxa had a dominant epistasis to SSIII-2 because the effect of SSIII-2 was masked by the massive synthesis of GBSS under Wxa. The apparent amylose content (AAC) was mainly controlled by the In1G/T SNP, and rice gel consistency (GC) was regulated by the Ex10C/T SNP. The combined effects of three SNPs had a significant influence on all ECQs and RVA profile parameters, except for gelatinization temperature. In1T-Ex6A-Ex10C and In1T-Ex6A-Ex10T were classified as being low AAC type. TT-AA-CC and TT-AA-TT had a low AAC and a soft GC. The combined effects of different SNPs of Wx are very important for rice quality breeding. [ABSTRACT FROM AUTHOR]

A glutinous texture of endosperm is one of the important traits of rice (Oyza sativa L.). Northern Laos is known as a center of glutinous rice diversity. We genotyped INDEL, SSR and SNP markers in a sample of 297 rice landraces collected in northern Laos. These glutinous varieties were confirmed to share a loss-of-function mutation in Granule bound starch synthase I (Wx). INDEL markers revealed a high frequency of recombinant genotypes between indica and japonica. Principal component analysis using SSR genotypes of Wx flanking region revealed that glutinous indica landraces were scattered between non-glutinous indica and glutinous-japonica types. High ratios of heterozygosity were found especially in glutinous indica. Haplotype analysis using SNP markers around Wx locus revealed that glutinous indica landraces would have a few chromosome segments of glutinous japonica. Frequent recombinations were confirmed outside of this region in glutinous indica. This intricate genetic structure of landraces suggested that glutinous indica landraces in Laos were generated through repeated natural crossing with glutinous-japonica landraces and severe selection by local farmers. [ABSTRACT FROM AUTHOR]

The Wx gene encoding granule-bound starch synthase is responsible for the biosynthesis of amylose, which plays an important role in determining rice eating and cooking quality. However, the functional evaluation of different Wx alleles remains unclear. In the present study, a set of near-isogenic lines (NILs) carrying four different Wx alleles- Wx , Wx , Wx, and wx-was developed in the genetic background of indica rice cv. Yangfunuo 4 (YFN 4), and designated NIL- Wx, NIL- Wx, NIL- Wx, and NIL- wx, respectively. These NILs show great variations in amylose content (AC), gel consistency (GC), starch viscosity, and thermodynamic property. AC showed the following trend among different NILs: NIL- Wx > NIL- Wx > NIL- Wx > NIL- wx, but the opposite trend for GC. NIL- Wx and NIL- Wx had lower starch thermodynamic properties, such as onset temperature, peak temperature, and conclusion temperature, when compared with both NIL- Wx and NIL- wx. The transcript and protein of Wx gene were not detectable in the NIL- wx line. The accumulation levels of Wx transcript and Wx protein were higher in NIL- Wx than those in NIL- Wx and NIL- Wx. Therefore, Wx gene was closely related to starch quality parameters, such as AC, GC, starch paste viscosity, and starch thermodynamic property. Our results provide a solid foundation for rice grain quality improvement through marker-assistant selection. [ABSTRACT FROM AUTHOR]

The diversity of the physical and consequently the functional behaviour of starches, isolated from different rice varieties, is related to their specific structures. The latter are directly related to the starch biosynthetic pathway. To fully take advantage of the different functionalities of starches from different rice varieties and to design tailor-made starches, it is important to gain insight into biosynthesis–structure–physical behaviour–functionality relations. In a first part of this review, starch composition is described with a focus on rice starch. Secondly, current knowledge on starch biosynthesis is discussed. This more specifically includes (i) the function of the rice biosynthetic enzymes (i.e. adenosine diphosphate glucose pyrophosphorylases, synthases, branching and debranching enzymes), (ii) the effect of mutations on rice starch structure and, (iii) models for amylose and amylopectin synthesis. Thirdly, starch structure [i.e. from granule (2–100 μm), to growth ring (120–500 nm), blocklet (20–500 nm), amorphous and crystalline lamellae (9 nm), and amylopectin and amylose chain levels (0.1–1.0 nm)] is dealt with. Finally, relations between rice starch structural aspects [i.e. amylopectin (core) chain length distributions] and physical behaviour (i.e. gelatinisation and amylopectin retrogradation as measured by differential scanning calorimetry) are studied. [Copyright &y& Elsevier]