Proteomics of rice in response to heat stress and advances in genetic engineering for heat tolerance in rice

Rice is the most important food crop worldwide. Global warming inevitably affects the grain yields of rice. Recent proteomics studies in rice have provided evidence for better understanding the mechanisms of thermal adaptation. Heat stress response in rice is complicated, involving up- or down-regulation of numerous proteins related to different metabolic pathways. The heat-responsive proteins mainly include protection proteins, proteins involved in protein biosynthesis, protein degradation, energy and carbohydrate metabolism, and redox homeostasis. In addition, increased thermotolerance in transgenic rice was obtained by overexpression of rice genes and genes from other plants. On the other hand, heterologous expression of some rice proteins led to enhanced thermotolerance in bacteria and other easily transformed plants. In this paper, we review the proteomic characterization of rice in response to high temperature and achievements of genetic engineering for heat tolerance in rice.     

Assessment of genetic diversity and morpho-physiological traits related to drought tolerance in Stylosanthes scabra

Among the many Stylosanthes species, Stylosanthes scabra, a range fodder legume, performs better under limited water condition. In the present investigation, thirty-four accessions of S. scabra were assessed under limited water condition, for various morpho-physiological characters associated with drought. In general, S. scabra exhibited better tolerance to drought, as evidenced by high leaf thickness and greater accumulation of proline, and malondialdehyde (MDA) in water stress condition. Transpiration efficiency (TE) was high, in both control and water stress conditions and positively correlated with root, shoot, and total dry matters, in both control and stress conditions (r ² = ranged from 0.589 to 0.961 in control and from 0.351 to 0.985 in stress). Of these, 25 accessions were assessed for estimation of genetic diversity, employing random amplified polymorphic DNA (RAPD) markers. A total of 210 RAPD bands, obtained with 32 primers, revealed high polymorphic information content (0.49) and marker index (4.41). Dendrogram analysis indicated close proximity among the accessions of S. scabra. These accessions were clustered in high similarity range (84.01–98.36 %). Accession IG-366A separated from other clusters at 85.62 % similarity level. RAPD marker system revealed 13 accessions exhibiting >90 % genetic similarity while the other accessions exhibited similarity ranging from 68 to 90 %. A higher level of genetic similarity which was also evident from the similar levels of TE, biomass production, root/shoot ratio, MDA, proline contents and drought tolerance index, indicated a cause–effect relationship among them. Results also indicated that among the accessions, S. scabra rate-reducing resistance allo-tetraploid lines were better suited for hard and cracking soils, under complete rain-fed condition.     

Model development and numerical simulation of electric-stimulus-responsive hydrogels subject to an externally applied electric field

Based on a multi-phasic mixture theory with consideration of ionic diffusion and convection, a multi-physic model, called the multi-effect-coupling electric-stimulus (MECe) model, is developed for simulation of responsive behavior of the electric-sensitive hydrogels when they are immersed into a bathing solution subject to an externally applied electric field. In the developed model, with chemo-electro-mechanical coupling effects, the convection-diffusion equations for concentration distribution of diffusive ions incorporate the influence of electric potential. The electroneutrality condition is replaced by the Poisson equation for distribution of electric potential. The steady and transient analyses of hydrogel deformation are easily carried out by the continuity and momentum equations of the mixture phase. Further, the computational domain of the present model covers both the hydrogel and the surrounding solution. In order to solve the present mathematical model consisting of multi-field coupled nonlinear partial differential governing equations, a hierarchical iteration technique is proposed and a meshless Hermite-Cloud method (HCM) is employed. The steady-state simulation of the electric-stimulus responsive hydrogel is numerically conducted when it is subjected to an externally applied electric field. The hydrogel deformation and the ionic concentrations as well as electric potentials of both the hydrogel and external solution are investigated. The parameter influences on the swelling behaviors of the hydrogel are also discussed in detail. The simulating results are in good agreement with the experimental data and they validate the presently developed model.     

Molecular genetic diversity analysis for heat tolerance of indigenous and exotic wheat genotypes

Journal of Plant Biochemistry and Biotechnology - Four hundred and ninety-six indigenous and exotic aestivum and durum wheat accessions were phenotyped for heat tolerance at three locations during...     

5种杜鹃幼苗对高温胁迫的生理生化响应及耐热性综合评价

以杜鹃花属(Rhododendron L.)5个亚属5种杜鹃的4年生实生苗为材料,对模拟高温(30℃和38℃)条件下叶片丙二醛(MDA)、过氧化氢(H2O2)和脯氨酸(Pro)含量以及超氧化物歧化酶(SOD)、过氧化氢酶(CAT)和抗坏血酸过氧化物酶(APX)活性进行了测定分析,对各指标进行了相关性和主成分分析;在此基础上,采用隶属函数法对5种杜鹃的耐热性进行了综合评价,并通过建立最优回归方程对综合评价结果进行检验.测定结果表明:与对照( 22℃)相比,5种杜鹃幼苗的MDA、H2O2和Pro含量以及CAT和APX活性均随胁迫温度的升高而增加;SOD活性则表现为在30℃条件下小幅增加、38℃条件下下降的趋势.CAT活性与H2O2和Pro含量及APX活性均呈极显著正相关关系(P＜0.01),APX活性与Pro含量和SOD活性分别呈显著的正相关和负相关关系(P＜0.05).通过主成分分析可将测定的6个单项指标转换成3个相互独立的综合指标,累计贡献率达87.52％.根据综合评价值(D),可将5种杜鹃的耐热性分为4个等级:白花杜鹃[R.mucronatum (Blume)G.Don]的耐热性最强,毛棉杜鹃(R.moulmainense Hook.f.)和羊踯躅[R.molle (Blume)G.Don]耐热性较强,红滩杜鹃(R.chihsinanum Chun et Fang)耐热性较弱,红棕杜鹃(R.rubiginosum Franch.)的耐热性最弱.利用所建立的最优同归方程对供试种类进行耐热性预测,预测值与D值的次序完全一致,表明综合评价法可用于杜鹃苗期耐热性的评价.     

A threshold for central T cell tolerance to an inducible serum protein

We report an inducible system of self Ag expression that examines the relationship between serum protein levels and central T cell tolerance. This transgenic approach is based on tetracycline-regulated expression of a secreted form of hen egg lysozyme, tagged with a murine hemoglobin (Hb) epitope. In the absence of the tetracycline-regulated transactivator, serum levels of the chimeric protein are extremely low (< or = 0.1 ng/ml) and the mice show partial tolerance to both Hb(64-76) and lysozyme epitopes. In the presence of the transactivator, expression increases to 1.5 ng/ml and the mice are completely tolerant. Partial tolerance was further investigated by crossing these mice to strains expressing transgenic TCRs. At the lowest Ag levels, 3.L2tg T cells (specific for Hb(64-76)/I-E(k)) escape the thymus and approximately 10% of CD4(+) splenocytes express the 3.L2 TCR. In contrast, 3A9 T cells (specific for hen egg lysozyme(46-61)/I-A(k)) are completely eliminated by negative selection. These data define a tolerogenic threshold for negative selection of Ag-specific T cells by circulating self proteins that are 100-fold more sensitive than previously demonstrated. They suggest that partial tolerance at extremely low levels of self Ag exposure is the result of a restricted repertoire of responding T cells, rather than a simple reduction in precursor frequency; tolerogenic thresholds are T cell specific.     

A general model for detecting genetic determinants underlying longitudinal traits with unequally spaced measurements and nonstationary covariance structure

A mixture model for determining quantitative trait loci (QTL) affecting growth trajectories has been proposed in the literature. In this article, we extend this model to a more general situation in which longitudinal traits for each subject are measured at unequally spaced time intervals, different subjects have different measurement patterns, and the residual correlation within subjects is nonstationary. We derive an EM-simplex hybrid algorithm to estimate the allele frequencies, Hardy-Weinberg disequilibrium, and linkage disequilibrium between QTL in the original population and parameters contained in the growth equation and in the covariance structure. A worked example of head circumference growth in 145 children is used to validate our extended model. A simulation study is performed to examine the statistical properties of the parameter estimation obtained from this example. Finally, we discuss the implications and extensions of our model for detecting QTL that affect growth trajectories.     

Field level evaluation of rice introgression lines for heat tolerance and validation of markers linked to spikelet fertility

Rice lines derived from wild species and mutants can serve as a good resource for favorable alleles for heat tolerance. In all, 48 stable lines including 17 KMR3/O. rufipogon introgression lines (KMR3 ILs), 15 Swarna/O. nivara ILs (Swarna ILs) along with their parents, Nagina 22 (N22) and its 4 EMS induced mutants and 7 varieties were evaluated for heat tolerance under irrigated conditions under field in two seasons, wet season 2012 using poly cover house method and dry season 2013 using late sown method. Spikelet fertility (SF), yield per plant (YP) and heat susceptibility index (HSI) for these two traits were considered as criteria to assess heat tolerance compared to control. Four KMR3 ILs and eight Swarna ILs were identified as heat tolerant based on SF and YP and their HSIs in both wet and dry seasons. S-65 and S-70 showed low SF and high YP consistently in response to heat in both seasons. We provide evidence that SF alone may not be the best criterion to assess heat tolerance and including YP is important as lines with low SF but high YP and vice versa were identified under heat stress. Out of 49 SSR markers linked to spikelet fertility, 18 were validated for five traits. RM229 in wet season and RM430 and RM210 in dry season were significantly associated with both SF and its HSI under heat stress. RM430 was also significantly associated with both YP and its HSI in dry season. Thirty two candidate genes were identified close to nine markers associated with traits under heat stress.     

Data and theory point to mainly additive genetic variance for complex traits

The relative proportion of additive and non-additive variation for complex traits is important in evolutionary biology, medicine, and agriculture. We address a long-standing controversy and paradox about the contribution of non-additive genetic variation, namely that knowledge about biological pathways and gene networks imply that epistasis is important. Yet empirical data across a range of traits and species imply that most genetic variance is additive. We evaluate the evidence from empirical studies of genetic variance components and find that additive variance typically accounts for over half, and often close to 100%, of the total genetic variance. We present new theoretical results, based upon the distribution of allele frequencies under neutral and other population genetic models, that show why this is the case even if there are non-additive effects at the level of gene action. We conclude that interactions at the level of genes are not likely to generate much interaction at the level of variance.     

An evaluation of nonlinearities in the motor output response to applied torque perturbations in man

Nonlinearities present in the motor output response of biceps and triceps muscles in normal human subjects to applied torque perturbations were evaluated quantitatively. When the applied perturbations were relatively continuous, consisting of a pseudo-random train of pulses, the identified nonlinearities were small, never exceeding 20% of the amplitude of the linear component of the response and usually being much less.     

Sporophytic response to pollen selection for Alachlor tolerance in maize

In order to assess the efficiency of male gametophytic selection (MGS) for crop improvement, pollen selection for tolerance to herbicide was applied in maize. The experiment was designed to test the parallel reactivity to Alachlor of pollen and plants grown in controlled conditions or in the field, the response to pollen selection in the sporophytic progeny, the response to a second cycle of MGS, and the transmission of the selected trait to the following generations. The results demonstrated that pollen assay can be used to predict Alachlor tolerance under field conditions and to monitor the response to selection. A positive response to selection applied to pollen in the sporophytic progeny was obtained in diverse genetic backgrounds, indicating that the technique can be generally included in standard breeding programs; the analysis of the data produced in a second selection cycle indicated that the selected trait is maintained in the next generation.     

Phenotypic plasticity of Daphnia life history traits in response to predator kairomones: genetic variability and evolutionary potential

Cladoceran populations can respond to changingpredation regimes by a phenotypical response as wellas by shifts in genotype frequencies. In this study,we investigated the phenotypic plasticity exhibited bylife history traits of D. galeata in response tothe presence of predator kairomones, as well as theextent to which natural selection may act on thesetraits and their phenotypic plasticity. In alife-table experiment, seven clones of a natural D. galeata population were subjected to kairomonesfrom fish (Perca), from an invertebrate predator(Chaoborus) or a mixture of both. Life historytraits were affected by the kairomones of bothpredators, but effects of Chaoborus wereneutralised by Perca in the kairomone mix. Noapparent trade-off was found between growth- andreproduction related traits: although daphnids fromthe Chaoborus treatment grew faster thandaphnids from the other treatments, no reduction inthe reproductive output was observed. Broad-senseheritabilities were found to be relatively high forsome life history traits (size at maturity, neonatesize, number of neonates) as well as for thephenotypic plasticity response of these traits. Thisreflects the evolutionary potential of life historytraits and their phenotypic response to predatorkairomones in the D. galeata population.Publication number 2334 of The Netherlands Institute of Ecology, Centre for LimnologyPublication number 2334 of The Netherlands Institute of Ecology, Centre for Limnology     

Yield response to water deficit in an upland rice mapping population: associations among traits and genetic markers

A population of recombinant inbred rice lines from a cross between the upland japonica cultivar Azucena and the upland indica cultivar Bala was evaluated in a series of upland field experiments. Water stress was imposed during the reproductive stage by managed irrigation during the dry season, while control treatments were maintained in aerobic, well-irrigated conditions. Water deficit resulted in a yield reduction of 17 to 50%. The genetic correlation between stress and control yields was quite high when stress was mild, and the heritability of yield was similar in stress and control treatments across both years of this study. Genetic correlations between secondary traits such as leaf rolling and drying and yield under stress varied from high (leaf drying) to insignificant (leaf rolling). Lines with superior yield tended to have fewer panicles and larger grain size than the high-yielding parent, Bala, even though the panicle number was positively correlated with yield and the thousand-grain weight was not associated with yield for the population as a whole. Analysis of quantitative trait loci (QTLs) for yield and yield components allowed the identification of 31 regions associated with growth or yield components. Superior alleles came from either parent. Several of the regions identified had also been reported for root mass at depth or maximum root length in this population in other studies made under controlled environments, and for leaf drying (LD) in field studies. However, the direction of the effect of QTLs was not consistent, which indicates that there was not necessarily a causal relationship between these secondary traits and performance. We conclude that mapping populations can provide novel insights on the actual relationships between yield components and secondary traits in stress and control environments and can allow identification of significant QTLs for yield components under drought stress.Abbreviations DAS Days after sowing - GPP Grains per panicle - QTL Quantitative trait locus - RWC Relative water content - SPP Spikelets per panicle - TGW Thousand-grain weight - VPD Vapor pressure deficit     

Identification of drought tolerance determinants by genetic analysis of root response to drought stress and abscisic Acid

Drought stress is a common adverse environmental condition that seriously affects crop productivity worldwide. Due to the complexity of drought as a stress signal, deciphering drought tolerance mechanisms has remained a major challenge to plant biologists. To develop new approaches to study plant drought tolerance, we searched for phenotypes conferred by drought stress and identified the inhibition of lateral root development by drought stress as an adaptive response to the stress. This drought response is partly mediated by the phytohormone abscisic acid. Genetic screens using Arabidopsis (Arabidopsis thaliana) were devised, and drought inhibition of lateral root growth (dig) mutants with altered responses to drought or abscisic acid in lateral root development were isolated. Characterization of these dig mutants revealed that they also exhibit altered drought stress tolerance, indicating that this root response to drought stress is intimately linked to drought adaptation of the entire plant and can be used as a trait to access the elusive drought tolerance machinery. Our study also revealed that multiple mechanisms coexist and together contribute to whole-plant drought tolerance.     

Combined gas exchange characteristics,chlorophyll fluorescence and response curves as selection traits for temperature tolerance in maize genotypes

Maize is a low-temperature (LT)-sensitive plant and its physiological responses towards LT of temperate regions developed is an adaptive trait. To further our understanding about the response of maize to LT at the physiological and photosynthesis level, we conducted Infrared Gas Analysis (IRGA using LICOR6400-XT in 45-day-old grown two maize genotypes, one from temperate region (Gurez-Kashmir Himalayas), viz., Gurez local (Gz local), and another from tropics (Gujarat), viz., GM6. This study was carried out to evaluate the underlying physiological mechanisms in the two differentially temperature-tolerant maize genotypes. Net photosynthetic rate (A/P_N), 18.253 in Gz local and 25.587 (µmol CO₂ m^?2 s^?1) in GM6; leaf conductance (gs), 0.0102 in Gz local and 0.0566 (mmol H₂O m^?2 s^?1) in GM6; transpiration rate (E), 0.5371 in Gz local and 2.9409 (mmol H₂O m^?2 s^?1) in GM6; and water use efficiency (WUE), 33.9852 in Gz local and 8.7224 (µmol CO₂ mmol H₂O^?1) in GM6, were recorded under ambient conditions. Also, photochemical efficiency of photosystem II (PSII) (F_v/F_m), 0.675 in Gz local and 0.705 in GM6; maximum photochemical efficiency (F_v′/F_m′), 0.310234 in Gz local and 0.401391 in GM6; photochemical quenching (qP), 0.2375 in Gz local and 0.2609 in GM6; non-photochemical quenching (NPQ), 2.0036 in Gz local and 1.1686 in GM6; effective yield of PSII (ФPSII), 0.0789 in Gz local and 0.099 in GM6; and electron transport rate (ETR), 55.3152 in Gz local and 68.112 in GM6, were also evaluated in addition to various response curves, like light intensities and temperature. We observed that light response curves show the saturation light intensity requirement of 1600 µmol for both the genotypes, whereas temperature response curves showed the optimum temperature requirement for Gz local as 20 °C and for GM6 it was found to be 35 °C. The results obtained for each individual parameter and other correlational studies indicate that IRGA forms a promising route for quick and reliable screening of various stress-tolerant valuable genotypes, forming the first study of its kind.

     

Role of heat tolerance and cone protection of seeds in the response of three pine species to wildfires

The post-fire regenerative ability of Pinus halepensis, Pinus nigra and Pinus sylvestris, three of the most important pine species present in the West Mediterranean basin, has been analyzed in the light of seed tolerance to different temperatures and times of exposure, and of seed position during the fire event (seeds inside cones versus free seeds). The combination of different fire intensities and degrees of seed protection allows us to draw different scenarios during the fire event: canopy scenarios (seeds inside cones), surface scenarios (seeds on the ground surface), and soil scenarios (seeds in the top soil layers). There were interspecific differences in the pattern of cone opening under the different heat treatments: cones of P. nigra and P. sylvestris showed similar percentages of opening, but considerably higher than those of P. halepensis. In the three species, seeds inside cones showed higher percentages of germination than those that were free, emphasizing the important role of cones in the protection of pine seeds from high temperatures. The percentage of germination decreased when both the temperature and the time of exposure increased, and there was also a significant species effect: P. halepensis showed higher germination rates than P. nigra, and both were higher than P. sylvestris. The overall scores of seed germination of these three pine species under the conditions tested suggests that their regeneration after fire should come either from the soil bank, or from the canopy bank, but rarely from the ground surface. As the existence of a permanent seed bank in Mediterranean pines is probably limited or nil, pine recruitment after fire appears to be mainly controlled by the existence of a canopy seed bank. The contribution of this canopy bank to the differences in postfire regeneration success of the three pine species is discussed in the light of their seeding phenology and the effects of fire severity on cone opening. The results obtained in this study contribute to explain the successful regeneration of P. halepensis, and the failure of P. nigra and P. sylvestris after fire.