Adoracion P. Resurreccion

Impact of down-regulation of starch branching enzyme IIb in rice by artificial microRNA- and hairpin RNA-mediated RNA silencing

The inactivation of starch branching IIb (SBEIIb) in rice is traditionally associated with elevated apparent amylose content, increased peak gelatinization temperature, and a decreased proportion of short amylopectin branches. To elucidate further the structural and functional role of this enzyme, the phenotypic effects of down-regulating SBEIIb expression in rice endosperm were characterized by artificial microRNA (amiRNA) and hairpin RNA (hp-RNA) gene silencing. The results showed that RNA silencing of SBEIIb expression in rice grains did not affect the expression of other major isoforms of starch branching enzymes or starch synthases. Structural analyses of debranched starch showed that the doubling of apparent amylose content was not due to an increase in the relative proportion of amylose chains but instead was due to significantly elevated levels of long amylopectin and intermediate chains. Rices altered by the amiRNA technique produced a more extreme starch phenotype than those modified using the hp-RNA technique, with a greater increase in the proportion of long amylopectin and intermediate chains. The more pronounced starch structural modifications produced in the amiRNA lines led to more severe alterations in starch granule morphology and crystallinity as well as digestibility of freshly cooked grains. The potential role of attenuating SBEIIb expression in generating starch with elevated levels of resistant starch and lower glycaemic index is discussed.

Diversity of Global Rice Markets and the Science Required for Consumer-Targeted Rice Breeding

With the ever-increasing global demand for high quality rice in both local production regions and with Western consumers, we have a strong desire to understand better the importance of the different traits that make up the quality of the rice grain and obtain a full picture of rice quality demographics. Rice is by no means a ‘one size fits all’ crop. Regional preferences are not only striking, they drive the market and hence are of major economic importance in any rice breeding / improvement strategy. In this analysis, we have engaged local experts across the world to perform a full assessment of all the major rice quality trait characteristics and importantly, to determine how these are combined in the most preferred varieties for each of their regions. Physical as well as biochemical characteristics have been monitored and this has resulted in the identification of no less than 18 quality trait combinations. This complexity immediately reveals the extent of the specificity of consumer preference. Nevertheless, further assessment of these combinations at the variety level reveals that several groups still comprise varieties which consumers can readily identify as being different. This emphasises the shortcomings in the current tools we have available to assess rice quality and raises the issue of how we might correct for this in the future. Only with additional tools and research will we be able to define directed strategies for rice breeding which are able to combine important agronomic features with the demands of local consumers for specific quality attributes and hence, design new, improved crop varieties which will be awarded success in the global market.

Addressing the dilemmas of measuring amylose in rice.

ABSTRACT Amylose content is a parameter that correlates with the cooking behavior of rice. It is measured at the earliest possible stages of rice improvement programs to enable breeders to build the foundations of appropriate grain quality during cultivar development. Amylose is usually quantified by absorbance of the amylose-iodine complex. The International Network for Quality Rice (INQR) conducted a survey to determine ways that amylose is measured, reproducibility between laboratories, and sources of variation. Each laboratory measured the amylose content of a set of 17 cultivars of rice. The study shows that five different versions of the iodine binding method are in use. The data show that repeatability was high within laboratories but reproducibility between laboratories was low. The major sources of variability were the way the standard curve was constructed and the iodine binding capacity of the potato amylose used to produce the standard. Reproducibility is much lower between laboratories using ...

Maintaining the yield of edible rice in a warming world

High temperature increases the amount of chalk in rice (Oryza sativa L.) grains, which causes grains to break during polishing, lowering the amount of rice for consumption. Here, we examined the effect of elevated temperature on substrate supply to the panicle, the capacity of the panicle to produce edible grains, and underlying factors affecting yield of edible grain in two varieties. During grain-filling, substrate supply followed a bell shaped curve, and high temperature significantly shortened supply time. The rate of grain-filling did not change and paddy yield fell in both varieties. In high temperature, yield loss in IR8 was due to lighter grains relative to those grown in cool temperature, but in IR60, it was due to the early sacrifice of 30% of the spikelets. The yield of edible rice was zero for IR8 and ~60% for IR60 for the high temperature treatments, and 100% for IR60 and 70% for IR8 in the cool temperature. IR60 differs from IR8 in regulation of substrate supply, architecture of the panicles and the capacity of the panicles to alter sink size in response to the stress and these factors may be responsible for the difference in edible rice in the two varieties.

Important Sensory Properties Differentiating Premium Rice Varieties

In rice-consuming countries, specific varieties are recognized as premium, “gold standard” varieties, while others are recognized as being superior but second best, despite being identical using the current suite of tools to evaluate quality. The objectives of this study were to determine if there are distinguishable differences in sensory properties of premium and second best varieties and whether these differences are common to premium varieties. Color, an important sensory property, was determined on the raw and cooked rice using a colorimeter. As raw rice, some of the premium varieties were whiter than their second best counterparts while others were not. However, when cooked, with two exceptions, the premium varieties were of the same or greater whiteness than their counterparts. A trained sensory panel employed descriptive sensory analysis, an objective tool, to characterize and analytically measure the flavor (aromatics, taste, mouthfeel) and texture of premium and second best varieties collected from nine rice-consuming countries. Sweet taste, popcorn aroma/flavor, and water-like metallic mouthfeel showed significant differences in intensity between the premium–second best variety pairs. Slickness, roughness, and springiness were the major traits that distinguished the texture of varieties. Quality evaluation programs do not routinely measure these texture and flavor traits, but the fact that they distinguished the varieties in most pairs indicates that their measurement should be added to the suite of grain quality tests in the development of new higher-yielding, stress-tolerant varieties. The incorporation of premium quality will ensure that quality is no impediment to widespread adoption leading to enhanced productivity and food security.

Identification of a Major Genetic Determinant of Glycaemic Index in Rice

Type II diabetes is a major chronic disease. In developing countries, the prevalence of type II diabetes is increasing enormously. Much research indicates that choice of carbohydrates, particularly those with low glycaemic index (GI) is able to assist in the management or prevention of type II diabetes. Most developing countries consume rice as the staple. The objectives of this study were to determine the variability in the GI of popular improved and traditional varieties of rice and to find the genetic basis of GI. A method to predict GI using an in vitro system was compared to the in vivo system using a range of rice varieties differing in GI. Large variability in GI, ranging from low to high GI, was found using a set of 235 varieties. The major gene that associated with GI in the 235 varieties was the Waxy gene. This paper reports the first large-scale phenotyping of this trait, provides important information for nutritionists to identify and quantify the impact of low GI rices on blood sugar status and offers a mechanism for breeding programmes to select for GI based on amylose content. Furthermore, it allows rice consumers to select particular varieties of rice as their choice of carbohydrate.

Biomolecular Analyses of Starch and Starch Granule Proteins in the High-Amylose Rice Mutant Goami 2

Elevated proportions of amylose in cereals are commonly associated with either the loss of starch branching or starch synthase activity. Goami 2 is a high-amylose mutant of the temperate japonica rice variety Ilpumbyeo. Genotyping revealed that Goami 2 and Ilpumbyeo carry the same alleles for starch synthase IIa and granule-bound starch synthase I genes. Analyses of granule-bound proteins revealed that SSI and SSIIa accumulate inside the mature starch granules of Goami 2, which is similar to the amylose extender mutant IR36ae. However, unlike the amylose extender mutants, SBEIIb was still detectable inside the starch granules of Goami 2. Detection of SBEIIb after protein fractionation revealed that most of the SBEIIb in Goami 2 accumulates inside the starch granules, whereas most of it accumulates at the granule surface in Ilpumbyeo. Exhaustive mass spectrometric characterisations of granule-bound proteins failed to detect any peptide sequence mutation or major post-translational modifications in Goami 2. Moreover, the signal peptide was found to be cleaved normally from the precursor protein, and there is no apparent N-linked glycosylation. Finally, no difference was found in the SBEIIb structural gene sequence of Goami 2 compared with Ilpumbyeo. In contrast, a G-to-A mutation was detected in the SBEIIb gene of IR36ae located at the splice site between exon and intron 11, which could potentially introduce a premature stop codon and produce a truncated form of SBEIIb. It is suggested that the mutation responsible for producing high amylose in Goami 2 is not due to a defect in SBEIIb gene as was observed in IR36ae, even though it produces a phenotype analogous to the amylose extender mutation. Understanding the molecular genetic basis of this mutation will be important in identifying novel targets for increasing amylose and resistant starch contents in rice and other cereals.

Effect of light intensity on the growth and photosynthesis of rice under different sulfur concentrations

Abstract Rice (Oryza sativa L. cv IR 72) plants were grown hydroponically in 1.0 mm SO4 2− for 1 week and transferred to 0, 0.01, 0.03, 0.1, 0.3, or 3 mm SO4 2− under two light treatments, 1,200 (high light) and 550 (low light) µmol quanta m−2 s−1. When the plants were grown under S-deficient conditions, the biomass production of the shoot was more strongly suppressed in the high-light-grown plants than in the plants grown under low light conditions. The low-light-grown plants showed a lower relative growth rate (RGR), higher leaf area ratio (LAR), and a low net assimilation rate (NAR) that was not affected by S nutrition. Although total S contents of the leaf blades under both light treatments were similar, S allocation to the leaf blades under low light conditions was greater. A large decrease in the Rubisco content was observed in the high-light-grown, S-deficient plants. In contrast, the low-light-grown plants showed relatively high contents of Rubisco even under S-deficient conditions. Chlorophyll content was significantly higher in the plants grown under low light conditions. Irrespective of S and light treatments, leaf photosynthesis could be accounted for by the Rubisco content. The results indicated that S-deficient effects were relatively small in the low-light-grown plants and that high light conditions stimulated S-deficiency.

Effects of sulfur nutrition on the growth and photosynthesis of rice

Abstract Rice plants (Oryza sativa L. cv. IR72) were grown hydroponically in 1.0 mM SO4 2- for one week and transferred to 0, 0.01, 0.03, 0.1, 0.3, or 3 mM SO4 2-. An increase in the sulfate concentration in the medium up to 0.03 mM resulted in a significant increase in the relative growth rate (RGR) due to the increase in the net assimilation rate (NAR). The leaf blade and leaf sheath showed a linear increase in the total S content at 0 to 0.1 mM SO4 2- in the growth solution. Total 8 content in the roots continued to increase with increased 8 supply. Changes in the soluble 8 content followed the same pattern as the total 8 content but increased proportionally in the leaf sheath and roots. Total N content and N allocation to the leaves also decreased below 0.1 mM 8. However, the decrease in the N content was not appreciable, compared with that of the 8 content. 8-deficiency strongly decreased the leaf photosynthesis, which was caused by large decreases in the contents of chlorophyll and ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) below 0.1 mM SO4 2- in the growth solution.

Properties of poorly digestible fraction of protein bodies of cooked milled rice

Pepsin-treated protein bodies and human fecal protein particles from IR480-5-9 cooked milled rice (Oryza sativa L.) consisted mainly of giutelin-type polypeptides with a mean molecular weight (MW) of 16 000. They had similar MW, amino acid pattern, and isoelectric focusing characteristics as the 70% 2-propanol—0.6% β-mercaptoethanol soluble fraction of rice glutelin. The lipids of the pepsin-treated protein bodies had an identical lipid fraction ratio and fatty acid composition as the lipids of whole protein bodies.