Rice Storage Proteins:Focus on Composition,Distribution,Genetic Improvement and Effects on Rice Quality

Rice storage proteins(RSPs)are plant proteins with high nutritional quality.As the second largest type of storage substance in rice,it is the main source of protein intake for people who consume rice as a staple food.The content and type of RSPs affect the appearance,processing quality and eating quality of rice.These effects involve the distribution of RSPs in rice grains as well as the interactions of RSPs with other components such as starch in rice grains.In the past two decades,some progress has been made in the genetic improvement of RSPs.However,the determination mechanism of protein content and composition in rice is still unclear,and the mechanism of the effect of RSPs on rice quality has not been elucidated.In this review,the composition,biosynthesis and distribution of RSPs,and quantitative trait loci mapping and cloning of RSP genes are summarized,the research progress of the influence of RSPs and their components on rice quality are reviewed,and the research directions in the future are proposed.

Changes of structure and functional properties of rice protein in the fresh edible rice during the seed development

It has been reported that fresh edible rice has more bioactive compounds and its protein is easier to digest and has lower hypoallergenic than mature rice. In this paper, the changes in structure and functional properties of proteins at five different stages, including early milky stage(EMS), middle milky stage(MMS), late milky stage(LMS), waxy ripe stage(WS)and ripening stage(RS), during the seed development were investigated. It was found that with the seed developing, the molecular weight of fresh rice protein gradually become larger while the secondary structure changed from the highest content of disordered structure at MMS to the highest content of ordered structure at RS, which affect the surface hydrophobicity and then the functional properties of proteins, including foaming properties, emulsifying properties and oil holding capacity. Fresh rice protein at MMS has the strongest surface hydrophobicity while fresh edible rice protein at RS has the strongest oil holding capability. The results of our study can provide a theoretical basis for the application of fresh rice protein in the food industry and help to develop new fresh edible rice food.

Modeling Rice rgMT as a Plant Metallothionein-Like Protein by the Distance Geometry and Homology Methods

Rice metallothionein-like protein (rgMT) shows characteristics of a three-section pattern composed of two highly conserved cysteine rich (CR) domains in the terminals and a spacer without cysteine (cys) residues in the center of the molecule. In this paper, the two CR domains and the spacer region were modeled by the distance geometry and homology methods separately. For the CR domains, twenty random models were generated for each cys combination based on the constraint conditions of CXC (C represents cys, X represents any amino acid other than cys), and CXXC motifs and a metal-sulfur chelating cluster. Four models for the N-terminal and two for C-terminal CR domain containing metal chelating structures formed by different combinations of cys were selected from 900 possible conformations. The GOR method was used to predict the secondary structure of the spacer region and its model was built by the homology method. After three parts of the protein were modeled, they were connected to form a three-dimensional structure model of rgMT. The whole conformation showed that rgMT could form two independent metal-sulfur chelating structures connected by a spacer peptide, without a structural or energy barrier for them to form two independent metal-chelating clusters just as mammalian metallothionein (MT) proteins. As all plant metallothionein-like (MT-L) proteins have the same primary structural characteristic, two CR domains connected by a spacer region, and many have the same cys arrangement pattern as rgMT, the three-dimensional structure model of rgMT will provide an important reference for the structural study of other plant MT-L proteins.

Charactering protein fraction concentrations as influenced by nitrogen application in low-glutelin rice cultivars

To optimize both grain yield and quality of low-glutelin rice cultivars under N-fertilizer strategies, two-year field experiments involving three low-glutelin rice cultivars（W1240, W1721, W025） and an ordinary rice cultivar（H9405） with five N treatments were carried out to determine the effects of N application rate and genotype on protein fractions contents and Glutelin/Prolamin ratio（Glu/Pro）. The difference of protein fraction concentrations affected by N application rate existed in genotypes. Ordinary rice cultivar had a larger increase in glutlein concentration affected by N application rate than low-glutelin rice cultivars did. Glutelin in H9405 had a increase of 30.6 and 41.0% under the N4 treatment（360 kg N ha^（–1）） when compared with N0 treatment（no fertilizer N） in 2010 and 2011 respectively, while all the low-glutelin rice cultivars showed relatively smaller increases for two years. Variance analysis showed no significant effect of N application rate on glutelin in W1240 and W025 while the effects on albumin, globulin and prolamin were significant in low-glutelin rice. What＇s more, N treatment had no significant i nfluence on Glu/Pro ratios in low-glutelin rice cultivars while a significant increase in Glu/Pro ratio was observed in ordinary rice cultivar. So low-gultelin rice cultivars showed a different pattern from ordinary rice cultivars when influenced by N application rate.

Transformation of Sucrose to Starch and Protein in Rice Leaves and Grains under Two Establishment Methods

Six rice varieties, PR120, PR116, Feng Ai Zan, PR115, PAU201 and Punjab Mehak 1 were raised under aerobic and transplanting conditions to assess the effects of planting conditions on sucrose metabolising enzymes in relation to the transformation of free sugars to starch and protein in flag leaves and grains. Activities of sucrose synthase, sucrose phosphate synthase and acid invertase increased till flowering stage in leaves and mid-milky stage（14 d after flowering） in grains and thereafter declined in concomitant with the contents of reducing sugar. Under aerobic conditions, the activities of acid invertase and sucrose synthase（cleavage） significantly decreased in conjunction with the decrease in non-reducing sugars and starch content in all the varieties. Disruption of starch biosynthesis under the influence of aerobic conditions in both leaves and grains and the higher build up of sugars possibly resulted in their favoured utilization in nitrogen metabolism. Feng Ai Zan, PR115 and PR120 maintained higher levels of sucrose synthase enzymes in grains and leaves and contents of metabolites（amino acid, protein and non-reducing sugar） under aerobic conditions, while PR116, Punjab Mehak 1 and PAU201 performed better under transplanting conditions, thus showing their adaptation to environmental stress. Yield gap between aerobic and transplanting rice is attributed primarily to the difference in sink activity and strength. Overall, it appear that up-regulation of sucrose synthase（synthesis） and sucrose phosphate synthase under aerobic conditions might be responsible in enhancing growth and productivity of rice varieties.

Overexpression of rice F-box phloem protein gene OsPP12-A13 confers salinity tolerance in Arabidopsis

Salinity is a serious challenge for agriculture production by limiting the arable land.Rice is a major staple food crop but very sensitive to salt stress.In this study,we used Arabidopsis for the functional characterization of a rice F-box gene LOC_Os04g48270(OsPP12-A13)under salinity stress.OsPP12-A13 is a nuclear-localized protein that is strongly upregulated under salinity stress in rice and showed the highest expression in the stem,followed by roots and leaves.Two types of transgenic lines for OsPP12-A13 were generated,including constitutive tissue over-expression using the CaMV35S promoter and phloem specific over-expression using the pSUC2 promoter.Both types of transgenic plants showed salinity tolerance at the seedling stage through higher germination percentage and longer root length,as compared to control plants under salt stress in MS medium.Both the transgenic plants also exhibited salt tolerance at the reproductive stage through higher survival rate,plant dry biomass,and seed yield per plant as compared to control plants.Determination of Na+concentration in leaves,stem and roots of salt-stressed transgenic plants showed that Na^(+) concentration was less in leaf and stem as compared to roots.The opposite was observed in wild type stressed plants,suggesting that OsPP12-A13 may be involved in Na+transport from root to leaf.Transgenic plants also displayed less ROS levels and higher activities of peroxidase and glutathione S-transferase along with upregulation of their corresponding genes as compared to control plants which further indicated a role of OsPP12-A13 in maintaining ROS homeostasis under salt stress.Further,the non-significant difference between the transgenic lines obtained from the two vectors highlighted that OsPP12-A13 principally works in the phloem.Taken together,this study showed that OsPP12-A13 improves salt tolerance in rice,possibly by affecting Na^(+) transport and ROS homeostasis.

Protein changes in rice seedlings during the enhancement of chilling resistance by different stress pretreatment

The changes of proteins in the rice (Oryzasativa L.) Tesanai 2 seedling under salt (NaCl,4 g/L), heat shock (42℃, 3h ), and cold(14℃, 3d ) pretreatments were compared toexplore the mechanism of the cross adaptationto different environmental stresses. The chill-ing resistance of rice seedling after 1℃, 150pmol·msPFD(photo flux density) for 2d was enhanced distinctly by salt, heat shock,

Expression of a barley ABA-responsive protein gene in transgenic rice

A cDNA clone encoding an ABA-responsiveprotein HVA1,was isolated by differentialscreening from barley aleurone layers(Hong etal.).Expression of the HVA1 gene is shownto be developmentally regulated,organ-specif-ic,and ABA-and stress-induced(Hong et

Effects of 4PU-30 on leaf senescence and degration of protein and nucleic acid in rice

4PU—30[N—phenyl—’N—(2—chloro—4—pyridyl) urea] is a new type of plant growth regulator with cytokinin properties. It has been confirmed to delay rice leaf senescence effectively. In order to elucidate the physiological role of 4PU—30 in delaying senescence, the changes of protein, nucleic acid contents, and the related activities of degradative enzymes were studied. Shanyou 63, an indica hybrid rice was used for this experiment. In the in vitro experiment, two full—developed leaves from the top during heading stage were collected and cut into 5.0cm segments, They were floated on the surface of distilled water containing 0.1mg/14PU—30 and incubated in darkness at 30 C. The leaves floated on distilled water were used as control.It was observed that chlorophyll content in controlled leaves declined rapidly started from the second day and dropped by 93.4% on the 6th day while that in leaves treated with 4PU—30 declined by 41.4% only. During senescence, specific activities of hemoglobin—digesting

A putative 6-transmembrane nitrate transporter OsNRT1.1b plays a key role in rice under low nitrogen

OsNRT1.1a is a low-affinity nitrate（NO_3^-） transporter gene. In this study, another mRNA splicing product, OsNRT1.1b,putatively encoding a protein with six transmembrane domains, was identified based on the rice genomic database and bioinformatics analysis. OsNRT1.1a/OsNRT1.1b expression in Xenopus oocytes showed OsNRT1.1a-expressing oocytes accumulated ^（15）N levels to about half as compared to OsNRT1.1bexpressing oocytes. The electrophysiological recording of OsNRT1.1b-expressing oocytes treated with 0.25 mM NO_3^- confirmed ^（15）N accumulation data. More functional assays were performed to examine the function of OsNRT1.1b in rice. The expression of both OsNRT1.1a and OsNRT1.1b was abundant in roots and downregulated by nitrogen（N） deficiency. The shoot biomass of transgenic rice plants with OsNRT1.1a or OsNRT1.1b overexpression increased under various N supplies under hydroponic conditions compared to wild-type（WT）. The OsNRT1.1a overexpression lines showed increased plant N accumulation compared to the WT in 1.25 mM NH_4NO_3 and 2.5 mM NO_3^- or NH_4~＋ treatments, but not in 0.125 mM NH_4NO_3.However, OsNRT1.1b overexpression lines increased total N accumulation in all N treatments, including 0.125 m M NH_4NO_3,suggesting that under low N condition, OsNRT1.1b would accumulate more N in plants and improve rice growth, but also that OsNRT1.1a had no such function in rice plants.

PREPARATION AND PROPERTIES OF WHEAT GLUTEN/RICE PROTEIN COMPOSITES PLASTICIZED WITH GLYCEROL

Environment friendly thermosetting composites were prepared by blending wheat gluten （WG） and rice protein （RP） at different weight ratios with glycerol as plasticizer followed by compression molding the mixture at 120℃ to crosslink the proteins. Reducing agent of sodium bisulfate and sodium sulfite and crosslinking agent formaldehyde were used to adjust the properties of the composites. Morphology, moisture absorption and tensile properties were evaluated. The results showed that formaldehyde could increase tensile strength of the composites without significant influence on Young＇s modulus and elongation at break. On the other hand, reducing agents could improve tensile strength and extensibility simultaneously, which was much marked at WG/RP ratios from 7/3 to 3/7.