Rice Soluble Starch Synthase I: Allelic Variation, Expression, Function, and Interaction With Waxy

Starch, which is composed of amylose and amylopectin, is the key determinant of rice quality. Amylose is regulated by the Waxy (Wx) gene, whereas amylopectin is coordinated by various enzymes including eight soluble starch synthases (SSSs), of which SSSI accounts for ∼70% of the total SSS activity in cereal endosperm. Although great progress has been made in understanding SSSI gene expression and function, allelic variation and its effects on gene expression, rice physicochemical properties and qualities, and interactions with the Wx gene remain unclear. Herein, SSSI nucleotide polymorphisms were analyzed in 165 rice varieties using five distinct molecular markers, three of which reside in an SSSI promoter and might account for a higher expression of the SSSIi allele in indica ssp. than of the SSSIj allele in japonica ssp. The results of SSSI promoter-Beta-Glucuronidase (β-GUS) analysis were consistent with the expression results. Moreover, analysis of near isogenic lines (NILs) in the Nipponbare (Nip) background showed that Nip (SSSIi) and Nip (SSSIj) differed in their thermal properties, gel consistency (GC), and granule crystal structure. Knockdown of SSSI expression using the SSSI-RNA interference (RNAi) construct in both japonica and indica backgrounds caused consistent changes in most tested physicochemical characteristics except GC. Moreover, taste value analysis (TVA) showed that introduction of the SSSI allele in indica or knockdown of SSSI expression in japonica cultivars significantly reduced the comprehensive taste value, which was consistent with the superior taste of japonica against indica. Furthermore, to test the potential interaction between SSSI and different Wx alleles, three NILs within the Wx locus were generated in the indica cv. Longtefu (LTF) background, which were designated as LTF (Wxa), LTF (Wxb), and LTF (wx). The SSSI-RNAi construct was also introduced into these three NILs, and physiochemical analysis confirmed that the knockdown of SSSI significantly increased the rice apparent amylose content (AAC) only in the Wxa and Wxb background and caused different changes in GC in the NILs. Therefore, the effect of SSSI variation on rice quality also depends on its crosstalk with other factors, especially the Wx gene. These findings provide fundamental knowledge for future breeding of rice with premium eating and cooking qualities

CHARACTERISATION OF HORDEUM VULGARE CELLULOSE SYNTHASE-LIKE F6 PROMOTER VIA TRANSGENE EXPRESSION IN RICE

Beta-glucan in cereal crops is known as a functional food, which can reduce cardiovascular diseases by lowering blood cholesterol levels. However, beta-glucan content is relatively low in rice grains, despite being relatively abundant in barley and oat grains. Taking advantage of rice as the staple food for Asians, increasing beta-glucan content in rice for their consumption may help to reduce cardiovascular-related diseases among them. Previous attempts in increasing beta-glucan content in rice via transgene expression of betaglucan synthase genes from barley into rice were unsuccessful due to the use of non-tissue specific as well as constitutively expressing promoter. The current transgenic expression study was performed to characterise the promoter of beta-glucan synthase gene in barley using betaglucuronidase (GUS) reporter gene. Two fragments of HvCslF6 promoter (2771 bp and 1257 bp) were successfully fused with GUS reporter gene and integrated into rice plants, demonstrated that the promoter was functional in the heterologous plant system. The presence of blue GUS staining was observed on the leaf, root, stem, and grain of the transgenic rice regardless of the promoter length used and stayed functional up to the next generation. GUS qualitative analysis confirmed that the shorter promoter length generated a stronger GUS activity in comparison to the longer one. This indicated that the presence of repressor elements in between the -2771 bp and -1257 bp regions. The preliminary results shed light on the strong promoter activity in the rice endosperm tissue. It can become an alternative to the collection of plant promoters that can be used for grain quality improvement and biofortification

Comparison of Physicochemical Characteristics of Starch Isolated from Sweet and Grain Sorghum

The worldwide interest about sweet sorghum (Sorghum bicolor L. Moench) goes towards stem sugar, but little has been focused on its grain. The starches were isolated from the grains of eight sweet and four grain sorghum varieties, and their physical, chemical, and morphological properties were carefully compared. The results reflected that starch from sweet varieties usually had larger granule size than that from grain ones, especially from two sweet varieties GL-4 and GL-6 with the granule size of 15.49 μm and 15.67 μm, respectively. The amylose content of sweet varieties starch was lower than that of grain ones. For water solubility index, starch from sweet varieties ranked top, whereas that from grain varieties ranked top for swelling power. The starch from both sweet and grain had A-type crystalline pattern, while the data from 13C NMR reflected pattern differences for C1 and C6 resonance between sweet and grain varieties. Chains length distribution from sweet varieties debranched starch was found a little different from grain one. The starch particles surface of sweet sorghum was smooth with some dents, while that from grain was smooth without appearance of dents. As sweet sorghum has ability to withstand harsh environments where other crops do not and is characterized by low production cost, the extensive potential existed for starch from sweet varieties to be used in starch industries

In situ Degradation and Characterization of Endosperm Starch in Waxy Rice with the Inhibition of Starch Branching Enzymes during Seedling Growth

High-resistant starch cereal crops with the inhibition of the starch branching enzyme (SBE) have been widely studied. However, the effects of the inhibition of SBE on waxy cereal crops are unclear. A transgenic rice line (GTR) derived from a japonica waxy rice cultivar Guang-ling-xiang-nuo (GLXN) has been developed through antisense RNA inhibition of both SBEI and SBEIIb. In this study, GLXN and GTR were cultivated in the dark only in deionized H2O, and their shoot and root growth, starch in situ degradation, and starch property changes were investigated during seedling growth. Compared with GLXN, GTR showed a significantly slow seedling growth, which was not due to the embryo size and vitality. The slow degradation of starch in the seed restrained the seedling growth. GLXN starch was completely degraded gradually from the proximal to distal region of the embryo and from the outer to inner region in the endosperm, but GTR starch in the peripheral region of the endosperm was not completely degraded, and the starch residual was located in the outside of the compound starch though its degradation pattern was similar to GLXN. During seedling growth, GLXN starch had the same A-type crystallinity and a similar ordered structure, but the crystallinity changed from the CA-type to B-type and the ordered structure gradually increased in the GTR starch. The above results indicated that GTR had a heterogeneous starch distributed regionally in the endosperm. The starch in the peripheral region of the endosperm had a B-type crystallinity, which was located in the outside of the compound starch and significantly increased the resistance to in situ degradation, leading to the seedling slow growth

Characterization of the time evolution of starch structure from rice callus

Callus (formed when a plant tissue is wounded) is a promising system for studying starch biosynthesis and bioengineering; however the molecular structure of callus starch has been poorly characterized. Size-exclusion chromatography was used in this study to characterize the starch structure in rice calli from two cultivars and a mutant of one cultivar lacking starch branching enzyme IIb. There were major qualitative differences in the chain-length and whole-molecule size distributions between starch from grain and from callus. However callus starch was found to be able to simulate the starch metabolism from both leaves and endosperm and reveal the structural development of starch granules, and this was dependent on the culture system. During synthesis, trans-lamellar amylopectin chains in callus are synthesized earlier than single-lamella chains, while enzymatic degradation starts from outer to inner amylopectin chains. The outer layers of the callus–starch granules have larger molecules with lower amylose content and shorter amylopectin chains compared to further inside the callus–starch granules. Controlling starch granular number and size thus has potential for improving both the quantity and quality of plant starch

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Not AvailableBackground: The global shift in food consumption patterns accompanied by a sedentary lifestyle has been driving the upsurge of non-communicable diseases, projected to remain as a global health challenge for the coming decades. Sustainable food-centric interventions should be developed and strengthened to mitigate the growing health concerns with huge socio-economic implications. Scope and approach: Milled white rice is typically starch-rich, serves as the major daily caloric source for a majority of the world population especially in Asia. Most rice varieties are of high glycemic index (GI), a food quality inferenced to contribute to the health problems surrounding high-calorie intake and dysregulated glucose metabolism. Manipulation of GI through various approaches will significantly help in the fight against diabetes and related diseases. Key findings and conclusions: A multidisciplinary approach of (a) introducing low to moderate GI property to modern varieties of rice through genetic manipulations, and (b) diet-based diversification solutions in a healthy plate of well-balanced portions of macronutrients with low GI food matrix together with elevated nutrient density and dietary fibre (DF) offers a sustainable solution to address the growing concern in meeting double burden nutritional challenges