Dissecting the genetic basis of heavy panicle hybrid rice uncovered <Emphasis Type="Italic">Gn1a</Emphasis> and <Emphasis Type="Italic">GS3</Emphasis> as key genes

Key message

Shuhui498 (R498) is an elite parent of heavy panicle hybrid rice by pyramiding the rare gn1a and null gs3 alleles. This finding reveals the genetic basis and great potential application in future breeding of R498.

Abstract

The heavy panicle trait, defined as 5 g or more of grain weight per panicle, is one of the target traits in super-high-yield rice breeding programs. The use of heavy panicle-type hybrid rice has been shown to be a successful strategy for super-high-yield breeding programs, particularly under the environmental conditions of high humidity and deficient solar radiation in southwestern China. However, the genetic components of the heavy panicle trait in hybrid rice remain elusive. Here, we report that the combination of loss-of-function mutations in Grain number 1a (Gn1a) and Grain Size 3 (GS3) is responsible for the heavy panicle phenotype of the elite hybrid rice restorer line Shuhui498 (R498). The null gn1a allele is the determinant factor for heavy panicles through increased grain number, while gs3 is associated with grain size and weight. R498 pyramided the two major null alleles, resulting in heavy panicles with a high grain number and large grains. Clustering analysis revealed that the null gn1a^R498 allele is a rare haplotype which has been innovatively utilized in R498, underscoring the great potential of R498 for breeding purposes. Our research thus sheds light on the distinct genetic compositions of heavy panicle-type rice and may potentially facilitate super-high-yield rice breeding.

     

Utilization of Stiff Culm Trait of Rice smos1 Mutant for Increased Lodging Resistance

Although the introduction of semi-dwarf trait into rice has led to improved lodging resistance making it capable of supporting high grain yield, lodging still remains a concern when attempting to further increase the grain yield of rice. However, improving the lodging resistance in rice by depending on the semi-dwarf trait alone is possible only up to a certain limit, beyond which other traits may be needed for reinforcement. To search for alternative traits relating to high lodging resistance, we identified 9 rice mutant lines possessing improved culm strength. To evaluate whether such lines can be useful for breeding lodging resistant rice, small organ size1 (smos1) mutant having increased lodging resistance but low tiller number and low grain yield, was chosen as a representative for a breeding trial. smos1 was crossed with ST-4 (from the Stock rice collection of Nagoya University Togo field #4), a cultivar with high tiller number and high grain yield, and from their progeny, LRC1 (lodging resistance candidate-1) was selected. Although the low tiller number trait of smos1 was not fully reversed in LRC1, this was compensated by an increase in grain weight per panicle, thereby resulting in high grain yield per plant. This important attribute of LRC1 was further enhanced by the improved lodging resistance trait inherited from smos1. Such improved lodging resistance in LRC1 and smos1 was revealed to be mainly due to increased culm diameter and culm thickness, which led to a high section modulus (SM) value, a parameter defining the physical strength of the culm. Since smos1 possesses high breaking-type lodging resistance which is different from semi-dwarf plants with high bending-type lodging resistance, an alternative approach of using thick culm lines for the creation of rice with increased lodging resistance is hereby proposed.     

Regulation of OsmiR156h through Alternative Polyadenylation Improves Grain Yield in Rice

Substantial increases in grain yield of cereal crops are required to feed a growing human population. Here we show that a natural variant of SEMIDWARF AND HIGH-TILLERING (SDT) increases harvest index and grain productivity in rice. Gain-of-function sdt mutation has a shortened polyadenylation tail on the OsmiR156h microRNA precursor, which cause the up-regulation of OsmiR156h. The plants carrying the semidominant sdt allele exhibit reduced plant height, enhanced lodging resistance, increased tiller numbers per plant, and resulting in an increased grain yield. We also show that combining the sdt allele with the OsSPL14^WFP allele can be effective in simultaneously improving tillering capacity and panicle branching, thereby leading to higher harvest index and grain yield. Most importantly, pyramiding of the sdt allele and the green revolution gene sd1 enhances grain yield by about 20% in hybrid rice breeding. Our results suggest that the manipulation of the polyadenylation status of OsmiR156 represents a novel strategy for improving the yield potential of rice over what is currently achievable.     

Identification of quantitative trait loci for grain size and the contributions of major grain-size QTLs to grain weight in rice

Grain weight, one of the three major components of rice yield, is largely determined by grain size, which is controlled by quantitative trait loci (QTLs). In a previous study, we identified qGS5 as a major QTL for grain width. Here, we report our identification of two more major grain-size QTLs (qGL3 and qGW2a) by using a recombinant inbred line (RIL) population from a cross of two indica varieties, ‘Zhenshan 97’ and ‘SLG’. To investigate the contribution of the three grain-size QTLs to final grain weight, we developed near-isogenic lines (NILs) NIL-qGL3, NIL-qGW2a, and NIL-qGS5 and used these to build the combined QTLs–NIL in the genetic background of ‘Zhenshan 97’ by marker-assisted selection and conventional backcrossing, respectively. A BCF₂ population of 957 individuals was developed from the combined QTLs-NIL for further study of the genetic control of grain size. The QTL analysis revealed that qGW2a and qGL3 played more important roles in grain weight gain than qGS5. All three QTLs showed additive effects with respect to grain weight, with no interaction. These results clearly indicate that pyramiding of major grain-size QTLs is a useful approach for improving rice yield.     

Transgenic rice overexpressing the Brassica juncea gamma-glutamylcysteine synthetase gene enhances tolerance to abiotic stress and improves grain yield under paddy field conditions

Glutathione (GSH), a low-molecular-weight tripeptide molecule that plays an important role in cell function and metabolism as an antioxidant, is synthesized by γ-glutamylcysteine synthetase and glutathione synthetase. To investigate the functional role of GSH in the adaptation of plants to abiotic stresses, we developed Brassica juncea L. ECS (BrECS)-expressing transgenic rice plants (BrECS1 and BrECS2) under the regulation of a stress-inducible Rab21 promoter. BrECS1 and BrECS2 transgenic rice plants with BrECS overexpression tolerated high salinity by maintaining a cellular glutathione (GSH)/glutathione disulfide redox buffer, which prevented unnecessary membrane oxidation. BrECS1 and BrECS2 rice plants also showed lower ion leakage and higher chlorophyll-fluorescence than wild-type (WT) rice plants in the presence of methyl viologen (MV) and salt, resulting in enhanced tolerance to abiotic stresses. During germination, BrECS overexpression increased growth and development, resulting in an increased germination rate in the presence of salt conditions, but not under salt-free normal conditions. Furthermore, BrECS1 and BrECS2 rice plants displayed a moderate increase in biomass and rice grain yield under general paddy field conditions when compared to WT rice plants under general paddy field conditions. Therefore, our results suggest that BrECS-overexpression was critical for cellular defense from reactive oxygen species attacks produced by salt and MV, promotion of germination, and metabolic processes involved in natural environmental stress tolerance, thereby enhancing growth development and rice grain yield.     

The effects of feeding by the rice water weevil, Lissorhoptrus oryzophilus Kuschel, on the growth and yield components of rice, Oryza sativa

Abstract 1 The effects of feeding by larvae of the rice water weevil, Lissorhoptrus oryzophilus Kuschel, on the growth and yield components of rice, Oryza sativa, were evaluated using four varieties of rice, ‘Cocodrie’, ‘Cypress’, ‘Bengal’ and ‘XP1003’, over 2 years. 2 Both adults and larvae of L. oryzophilus feed on rice plants, but it is feeding by the larval stage that causes economic losses. Feeding by L. oryzophilus larvae resulted in extensive damage to root systems. Pruning of root systems resulted in a decrease in tiller number and shoot biomass of rice plants in the vegetative stage of growth. 3 Yield losses were due to a combination of decreases in panicle densities, numbers of grains per panicle, and grain weights. Decreases in panicle densities were a direct result of the reductions in tiller numbers. Reductions in numbers of grains per panicle and grain weights probably resulted from decreases in shoot biomass. 4 Injury by rice water weevil larvae is chronic. The tillering stage of rice suffered the majority of weevil damage, but the growth effects were not manifested until later.     

PAY1 improves plant architecture and enhances grain yield in rice

Plant architecture, a complex of the important agronomic traits that determine grain yield, is a primary target of artificial selection of rice domestication and improvement. Some important genes affecting plant architecture and grain yield have been isolated and characterized in recent decades; however, their underlying mechanism remains to be elucidated. Here, we report genetic identification and functional analysis of the PLANT ARCHITECTURE AND YIELD 1 (PAY1) gene in rice, which affects plant architecture and grain yield in rice. Transgenic plants over‐expressing PAY1 had twice the number of grains per panicle and consequently produced nearly 38% more grain yield per plant than control plants. Mechanistically, PAY1 could improve plant architecture via affecting polar auxin transport activity and altering endogenous indole‐3‐acetic acid distribution. Furthermore, introgression of PAY1 into elite rice cultivars, using marker‐assisted background selection, dramatically increased grain yield compared with the recipient parents. Overall, these results demonstrated that PAY1 could be a new beneficial genetic resource for shaping ideal plant architecture and breeding high‐yielding rice varieties.     

Nicotianamine,a Novel Enhancer of Rice Iron Bioavailability to Humans

Background

Polished rice is a staple food for over 50% of the world''s population, but contains little bioavailable iron (Fe) to meet human needs. Thus, biofortifying the rice grain with novel promoters or enhancers of Fe utilization would be one of the most effective strategies to prevent the high prevalence of Fe deficiency and iron deficiency anemia in the developing world.

Methodology/Principal Findings

We transformed an elite rice line cultivated in Southern China with the rice nicotianamine synthase gene (OsNAS1) fused to a rice glutelin promoter. Endosperm overexpression of OsNAS1 resulted in a significant increase in nicotianamine (NA) concentrations in both unpolished and polished grain. Bioavailability of Fe from the high NA grain, as measured by ferritin synthesis in an in vitro Caco-2 cell model that simulates the human digestive system, was twice as much as that of the control line. When added at 1∶1 molar ratio to ferrous Fe in the cell system, NA was twice as effective when compared to ascorbic acid (one of the most potent known enhancers of Fe bioavailability) in promoting more ferritin synthesis.

Conclusions

Our data demonstrated that NA is a novel and effective promoter of iron utilization. Biofortifying polished rice with this compound has great potential in combating global human iron deficiency in people dependent on rice for their sustenance.     

Effect of silicon on grain yield of rice under cadmium-stress

Many publications indicated various beneficial effects of the addition of silicon (Si) in soil on the physiology of rice plants. The gene responsible for the Si-uptake in rice, low Si-influx 1 (Lsi1), was identified and cloned for this study. The photosynthetic rate (Pn), grain yield, and resistance to Cadmium (Cd)-stress of the wild-type (WT) and Lsi1-transgenic Lemont rice lines under Cd-stress were examined in an attempt to better understand the mechanism associated with the Si-addition, Cd-stress, and rice physiology. Si-fertilization significantly reduced the Cd-content in rice under Cd-stress. The effect was most significant in the Lsi1-overexpression transgenic Lemont rice (Lsi1-OE line) under high Cd-stress. Conversely, Cd in soil lowered the Si-uptake of the plants indicating a significant interaction between the two elements. During the grain-filling period, Cd-stress greatly reduced the chlorophyll content and Pn of the rice resulting in a diminished grain output. However, Lsi1-OE line with a higher chlorophyll content and Pn than either WT or Lsi1-RNAi transgenic Lemont rice (Lsi1-RNAi line) maintained a high photo-assimilate transportation for high yield potential. At harvest, Lsi1-OE line contained more Si and less Cd than WT, whereas the Lsi1-RNAi line showed an opposite result. In general, Cd-stress reduced, while Si-fertilization significantly increased, the grain yield on rice. However, no significant difference on the grain yields existed between WT and Lsi1-RNAi line. This might be due to a compensation effect generated by Lsi1-RNAi line. It appeared that Si in the soil, as well as the enhancing or inhibiting Lsi1 expression and the resistance to Cd-toxicity of the plants, could significantly affect the rice yield making alternations on these factors a plausible approach for production improvement.     

The novel quantitative trait locus GL3.1 controls rice grain size and yield by regulating Cyclin-T1;3

Increased crop yields are required to support rapid population growth worldwide. Grain weight is a key component of rice yield, but the underlying molecular mechanisms that control it remain elusive. Here, we report the cloning and characterization of a new quantitative trait locus (QTL) for the control of rice grain length, weight and yield. This locus, GL3.1, encodes a protein phosphatase kelch (PPKL) family — Ser/Thr phosphatase. GL3.1 is a member of the large grain WY3 variety, which is associated with weaker dephosphorylation activity than the small grain FAZ1 variety. GL3.1-WY3 influences protein phosphorylation in the spikelet to accelerate cell division, thereby resulting in longer grains and higher yields. Further studies have shown that GL3.1 directly dephosphorylates its substrate, Cyclin-T1;3, which has only been rarely studied in plants. The downregulation of Cyclin-T1;3 in rice resulted in a shorter grain, which indicates a novel function for Cyclin-T in cell cycle regulation. Our findings suggest a new mechanism for the regulation of grain size and yield that is driven through a novel phosphatase-mediated process that affects the phosphorylation of Cyclin-T1;3 during cell cycle progression, and thus provide new insight into the mechanisms underlying crop seed development. We bred a new variety containing the natural GL3.1 allele that demonstrated increased grain yield, which indicates that GL3.1 is a powerful tool for breeding high-yield crops.     

The ubiquitin-interacting motif-type ubiquitin receptor HDR3 interacts with and stabilizes the histone acetyltransferase GW6a to control the grain size in rice

For grain crops such as rice (Oryza sativa), grain size substantially affects yield. The histone acetyltransferase GRAIN WEIGHT 6a (GW6a) determines grain size and yield in rice. However, the gene regulatory network underlying GW6a-mediated regulation of grain size has remained elusive. In this study, we show that GW6a interacts with HOMOLOG OF DA1 ON RICE CHROMOSOME 3 (HDR3), a ubiquitin-interacting motif-containing ubiquitin receptor. Transgenic rice plants overexpressing HDR3 produced larger grains, whereas HDR3 knockout lines produce smaller grains compared to the control. Cytological data suggest that HDR3 modulates grain size in a similar manner to GW6a, by altering cell proliferation in spikelet hulls. Mechanistically, HDR3 physically interacts with and stabilizes GW6a in an ubiquitin-dependent manner, delaying protein degradation by the 26S proteasome. The delay in GW6a degradation results in dramatic enhancement of the local acetylation of H3 and H4 histones. Furthermore, RNA sequencing analysis and chromatin immunoprecipitation assays reveal that HDR3 and GW6a bind to the promoters of and modulate a common set of downstream genes. In addition, genetic analysis demonstrates that HDR3 functions in the same genetic pathway as GW6a to regulate the grain size. Therefore, we identified the grain size regulatory module HDR3–GW6a as a potential target for crop yield improvement.

A ubiquitin receptor ubiquitylates and stabilizes a histone acetyltransferase; this module regulates downstream gene expression, altering rice grain size by modulating cell proliferation.     

Fine mapping SPP1, a QTL controlling the number of spikelets per panicle, to a BAC clone in rice (Oryza sativa)

Near isogenic lines (NILs) can be used to efficiently handle a target quantitative trait locus (QTL) by blocking genetic background noise. One QTL, SPP1, which controls the number of spikelets per panicle (SPP), was located on chromosome 1, near Gn1a, a cloned gene for rice production in a recombinant inbred line population. NILs of the SPP1 regions were quickly obtained by self-crossing recombinant inbred line 30 which is heterozygous around SPP1. Using a random NIL-F₂ population of 210 individuals, we mapped SPP1 to a 2.2-cM interval between RM1195 and RM490, which explained 51.1% of SPP variation. The difference in SPP between the two homozygotes was 44. F₂-1456, one NIL-F₂ plant, was heterozygous in the SPP1 region but was fixed in the region of Gn1a gene. This plant F₃ family showed a very wide variation in SPP, which suggested that it was SPP1 but Gn1a affected the variation of SPP in this population. In a word, SPP1 is a novel gene distinct from Gn1a. Four newly developed InDel markers were used for high-resolution mapping of SPP1 with a large NIL-F₂ population. Finally, it was narrowed down to a bacterial artificial chromosome clone spanning 107 kb; 17 open reading frames have been identified in the region. Of them, LOC_Os01g12160, which encodes an IAA synthetase, is the most interesting candidate gene.     

Tillering and panicle branching genes in rice

Rice (Oryza sativa L.) is one of the most important staple food crops in the world, and rice tillering and panicle branching are important traits determining grain yield. Since the gene MONOCULM 1 (MOC 1) was first characterized as a key regulator in controlling rice tillering and branching, great progress has been achieved in identifying important genes associated with grain yield, elucidating the genetic basis of yield-related traits. Some of these important genes were shown to be applicable for molecular breeding of high-yielding rice. This review focuses on recent advances, with emphasis on rice tillering and panicle branching genes, and their regulatory networks.     

Enhanced Sucrose Loading Improves Rice Yield by Increasing Grain Size

Yield in cereals is a function of grain number and size. Sucrose (Suc), the main carbohydrate product of photosynthesis in higher plants, is transported long distances from source leaves to sink organs such as seeds and roots. Here, we report that transgenic rice plants (Oryza sativa) expressing the Arabidopsis (Arabidopsis thaliana) phloem-specific Suc transporter (AtSUC2), which loads Suc into the phloem under control of the phloem protein2 promoter (pPP2), showed an increase in grain yield of up to 16% relative to wild-type plants in field trials. Compared with wild-type plants, pPP2::AtSUC2 plants had larger spikelet hulls and larger and heavier grains. Grain filling was accelerated in the transgenic plants, and more photoassimilate was transported from the leaves to the grain. In addition, microarray analyses revealed that carbohydrate, amino acid, and lipid metabolism was enhanced in the leaves and grain of pPP2::AtSUC2 plants. Thus, enhancing Suc loading represents a promising strategy to improve rice yield to feed the global population.Rice (Oryza sativa) is a staple food for nearly one-half of the global population. Given the rapid growth of the world’s population, there is an urgent need to increase rice yield. Rice yield is a complex trait that is directly associated with grain size, panicle number, and the number of grains per panicle (Xing and Zhang, 2010). Increasing grain size is a prime breeding target, and several genes known to control rice grain size, such as GRAIN SIZE3 (GS3), GS5, GW2 QTL for rice grain width and weight (GW2), GW8, and rice seed width5, have been identified (Fan et al., 2006; Song et al., 2007; Shomura et al., 2008; Li et al., 2011a; Wang et al., 2012). However, our knowledge of the mechanisms that control rice yield is limited. Thus, further improving rice yield remains a challenge for breeders (Sakamoto and Matsuoka, 2008). Identifying and characterizing unique genes or targets that regulate yield traits would improve our understanding of the molecular mechanisms that regulate yield traits and facilitate the breeding of new rice varieties with higher yields.The carbohydrates in rice grains originate from photosynthesis that is carried out predominantly in leaves (sources). Therefore, grain filling and rice yield depend on the efficient transport of carbohydrates from the leaves to seeds (sinks). In most plants, Suc is the main carbohydrate transported long distance in the veins to support the growth and development of roots, flowers, fruits, and seeds (Baker et al., 2012; Braun, 2012). Recently, the entire pathway for the export of Suc from leaves has been elucidated (Baker et al., 2012; Braun, 2012). Suc is synthesized in leaf mesophyll cells and diffuses from cell to cell through plasmodesmata until it reaches the phloem parenchyma cells (Slewinski and Braun, 2010). The SWEET transporters mediate Suc efflux from the phloem parenchyma cells into the apoplast, where Suc is subsequently loaded into the phloem sieve element-companion cell (SE/CC) complexes by Suc transporters (SUTs; Braun and Slewinski, 2009; Ayre, 2011; Chen et al., 2012). The resultant accumulation of Suc in sieve elements produces a hydrostatic pressure gradient that results in the bulk flow of Suc through a conduit of contiguous sieve elements, leading to its arrival and unloading in sink tissues (Lalonde et al., 2004; Baker et al., 2012).Genetic evidence has demonstrated that apoplastic Suc phloem loading is critical for growth, development, and reproduction in Arabidopsis (Arabidopsis thaliana). AtSWEET11 and AtSWEET12 are localized to the plasma membrane of the phloem and are expressed in a subset of phloem parenchyma cells in minor veins. These transporters mediate Suc efflux from phloem parenchyma cells into the apoplast prior to Suc uptake by SE/CC (Chen et al., 2012). The atsweet11 or atsweet12 single mutants exhibit no aberrant phenotypes, possibly due to genetic redundancy. However, atsweet11;12 double mutants are mildly chlorotic and display slower growth and higher levels of starch and sugar accumulation in the leaves than do wild-type plants (Chen et al., 2012). Arabidopsis phloem-specific sucrose transporter (AtSUC2) is a phloem-specific SUT that is expressed specifically in companion cells (Stadler and Sauer, 1996). AtSUC2 plays an essential role in phloem Suc loading and is necessary for efficient Suc transport from source to sink tissues in Arabidopsis (Stadler and Sauer, 1996; Gottwald et al., 2000; Srivastava et al., 2008). The atsuc2 mutants show stunted growth, retarded development, and sterility. Furthermore, these mutants accumulate excess starch in the leaves and fail to transport sugar efficiently to the roots and inflorescences (Gottwald et al., 2000).The proper control of carbohydrate partitioning is fundamental to crop yield (Braun, 2012). It has been reported that increasing sink grain strength by improving assimilate uptake capacity could be a promising approach toward obtaining higher yield. For example, seed-specific overexpression of a potato (Solanum tuberosum) SUT increased Suc uptake and growth rates of developing pea (Pisum sativum) cotyledons (Rosche et al., 2002). In addition, the Suc uptake capacity of grains and storage protein biosynthesis was increased in transgenic wheat (Triticum aestivum) plants expressing the barley (Hordeum vulgare) SUT HvSUT1 under the control of an endosperm-specific promoter (Weichert et al., 2010). Moreover, it was recently found that these transgenic wheat plants had a higher thousand grain weight and grain width and length, as well as a 28% increase in grain yield (Saalbach et al., 2014).Since the carbohydrates in rice grains originate from photosynthesis in source leaves, and carbohydrate partitioning from source leaves to heterotrophic sinks (e.g. seeds) is mediated by Suc transport in plants (Lalonde et al., 2004; Ayre, 2011), enhancing the capacity for Suc transport from leaves to seeds theoretically could increase crop yield. However, until now, enhancing Suc transport from leaves to seeds has not been shown to improve yield (Ainsworth and Bush, 2011).Here, we tested the hypothesis that enhancing Suc transport from leaves to seeds would increase rice yield. We expressed Arabidopsis SUC2 under control of the phloem protein2 promoter (pPP2) in rice and found that enhancing Suc loading did indeed increase rice yield. The pPP2::AtSUC2 plants produced larger grain than the wild type and showed grain yield increases of up to 16% in field trials. Our results suggest that manipulating phloem Suc transport is a useful strategy for increasing grain yield in rice and other cereal crops.     

水浮莲对水稻竞争效应、产量与土壤养分的影响

为了解入侵植物水浮莲在稻田生产中的扩散规律和对水稻农业性状的影响,通过田间水稻田实验,按照de Wit 取代试验方法和添加系列设计方法研究水浮莲与水稻(云稻2 号)混种对植株形态和生物量影响、种间竞争效应、水稻产量以及对土壤养分的影响。结果表明,混种条件下水浮莲母株株高、分蘖数、生物量和开花株数均受到水稻的明显抑制,受到的抑制率显著高于其对水稻的抑制率。水浮莲的种间竞争大于种内竞争(RY 小于1.0)而水稻的种内竞争大于种间竞争(RY 大于1.0),水浮莲混种比例大于和等于1:1 时(RYT大于1.0)与水稻不存在竞争作用,而小于1:1时(RYT 小于1.0)其存在着竞争作用,水浮莲对水稻的竞争力(CB 小于0)小于水稻。混种条件下水稻有效穗数和产量有明显提高,增产比例为3.54%-13.38%。生长过程中水浮莲对土壤钾、磷元素消耗大于水稻,而有机质和氮元素消耗小于水稻;混种条件下水稻明显降低水浮莲对土壤养分消耗,且二者在土壤养分上没有竞争关系。所有这些表明,入侵稻田的水浮莲与水稻生长过程中其形态、生物量等方面都处于劣势,而且一定的水浮莲密度有利于抑制水浮莲对土壤养分的消耗和促进水稻生长繁殖及其产量的提高,因此为满足饲料利用和环境净化,建议在正常耕作稻田中可对水浮莲进行适当的应用。     

Concurrent activation of OsAMT1;2 and OsGOGAT1 in rice leads to enhanced nitrogen use efficiency under nitrogen limitation

Nitrogen (N) is a major factor for plant development and productivity. However, the application of nitrogenous fertilizers generates environmental and economic problems. To cope with the increasing global food demand, the development of rice varieties with high nitrogen use efficiency (NUE) is indispensable for reducing environmental issues and achieving sustainable agriculture. Here, we report that the concomitant activation of the rice (Oryza sativa) Ammonium transporter 1;2 (OsAMT1;2) and Glutamate synthetase 1 (OsGOGAT1) genes leads to increased tolerance to nitrogen limitation and to better ammonium uptake and N remobilization at the whole plant level. We show that the double activation of OsAMT1;2 and OsGOGAT1 increases plant performance in agriculture, providing better N grain filling without yield penalty under paddy field conditions, as well as better grain yield and N content when plants are grown under N llimitations in field conditions. Combining OsAMT1;2 and OsGOGAT1 activation provides a good breeding strategy for improving plant growth, nitrogen use efficiency and grain productivity, especially under nitrogen limitation, through the enhancement of both nitrogen uptake and assimilation.     

Homologous expression of γ-glutamylcysteine synthetase increases grain yield and tolerance of transgenic rice plants to environmental stresses

Various environmental stresses induce reactive oxygen species (ROS), causing deleterious effects on plant cells. Glutathione (GSH), a critical antioxidant, is used to combat ROS. GSH is produced by γ-glutamylcysteine synthetase (γ-ECS) and glutathione synthetase (GS). To evaluate the functional roles of the Oryza sativa L. Japonica cv. Ilmi ECS (OsECS) gene, we generated transgenic rice plants overexpressing OsECS under the control of an inducible promoter (Rab21). When grown under saline conditions (100 mM) for 4 weeks, 2-independent transgenic (TGR1 and TGR2) rice plants remained bright green in comparison to control wild-type (WT) rice plants. TGR1 and TGR2 rice plants also showed a higher GSH/GSSG ratio than did WT rice plants in the presence of 100 mM NaCl, which led to enhanced redox homeostasis. TGR1 and TGR2 rice plants also showed lower ion leakage and higher chlorophyll-fluorescence when exposed to 10 μM methyl viologen (MV). Furthermore, the TGR1 and TGR2 rice seeds had approximately 1.5-fold higher germination rates in the presence of 200 mM salt. Under paddy field conditions, OsECS-overexpression in transgenic rice plants increased rice grain yield (TGW) and improved biomass. Overall, our results show that OsECS overexpression in transgenic rice increases tolerance and germination rate in the presence of abiotic stress by improving redox homeostasis via an enhanced GSH pool. Our findings suggest that increases in grain yield by OsECS overexpression could improve crop yields under natural environmental conditions.