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Heterotrimeric G protein-mediated signal transduction is one of the most important and highly conserved signaling pathways in eukaryotes, which involves in the regulation of many important biological processes. As compared with those in mammals and Arabidopsis thaliana, the functions of rice heterotrimeric G protein and their molecular mechanisms are largely unknown. The rice genome contains a single Gα (RGA1) and Gβ (RGB1), and five Gγ (RGG1, RGG2, GS3, DEP1/qPE9–1, and GGC2) subunits. Recent genetic studies have shown that DEP1/qPE9–1, an atypical putative Gγ protein, is responsible for the grain size as well as the dense and erect panicles, but the biochemical and molecular mechanisms underlying the control of grain size are not well understood. Here, we report that rice plants carrying DEP1/qPE9–1 have more endosperm cells per grain than plants contain the dep1/qpe9–1 allele. The DEP1/qPE9–1 line has a higher rate and more prolonged period of starch accumulation than the dep1/qpe9–1 line. Additionally, the expression of several essential genes encoding enzymes catalyzing sucrose metabolism and starch biosynthesis is higher in the DEP1/qPE9–1 line than in the dep1/qpe9–1 line, especially from the mid to late grain-filling stage. Grains of the DEP1/qPE9–1 line also have higher contents of three phytohormones, ABA, auxin and cytokinin. Exogenous application of auxin or cytokinin enhanced the starch accumulation and the expression of genes encoding grain-filling-related enzymes in the grains of dep1/qpe9–1, whereas ABA produced no effects. Based on these results, we conclude that DEP1/qPE9–1 positively regulates starch accumulation primarily through auxin and cytokinin, which enhance the expression of genes encoding starch biosynthesis during the mid to late grain-filling stage, resulting in increased duration of the grain-filling process. [ABSTRACT FROM AUTHOR]

Drought stress can affect interaction between plant cell plasma membrane and cell wall. Arabidopsis AT14A, an integrin-like protein, mediates the cell wall-plasma membrane-cytoskeleton continuum (WMC continuum). To gain further insight into the function of AT14A, the role of AT14A in response to drought stress simulated by polyethylene glycol (PEG-6000) in Arabidopsis suspension cultures was investigated. The expression of this gene was induced by PEG-6000 resulting from reverse transcription-PCR, which was further confirmed by the expression data from publically available microarray datasets. Compared to the wild-type cells, overexpression of AT14A ( AT14A-OE) in Arabidopsis cultures exhibited a greater ability to adapt to water deficit, as evidenced by higher biomass accumulation and cell survival rate. Furthermore, AT14A-OE cells showed a higher tolerance to PEG-induced oxidative damage, as reflected by less HO content, lipid peroxidation (malondialdehyde (MDA) content), and ion leakage, which was further verified by maintaining high levels of activities of antioxidant defense enzymes such as ascorbate peroxidase and guaiacol peroxidase and soluble protein. Taken together, our results suggest that overexpression of AT14A improves drought stress tolerance and that AT14A is involved in suppressing oxidative damage under drought stress in part via regulation of antioxidant enzyme activities [ABSTRACT FROM AUTHOR]

Heavy metal pollution has become a worldwide problem in aquaculture. We studied copper (Cu) accumulation and physiological responses of two red algae Gracilaria lemaneiformis and Gracilaria lichenoides from China under Cu exposure of 0-500 μg/L in concentration. Compared with G. lemaneiformis, G. lichenoides was more capable in accumulating Cu, specifically, more Cu on extracellular side (cell wall) than on intracellular side (cytoplasm) and in cell organelles (especially chloroplast, cell nucleus, mitochondria, and ribosome). In addition, G. lichenoides contained more insoluble polysaccharide in cell wall, which might promote the extracellular Cu-binding as an efficient barrier against metal toxicity. Conversely, G. lemaneiformis was more vulnerable than G. lichenoides to Cu toxin for decreases in growth, pigment (chlorophyll a, chlorophyll b, phycobiliprotein, and β-carotene) content, and photosynthetic activity. Moreover, more serious oxidative damages in G. lemaneiformis than in G. lichenoides, in accumulation of reactive oxidative species and malondialdehyde, and in electrolyte leakage, because of lower antioxidant enzyme (superoxide dismutase and glutathione reductase) activities. Therefore, G. lichenoides was less susceptible to Cu stress than G. lemaneiformis. [ABSTRACT FROM AUTHOR]

The dynamic changes of the activities of enzymes involving in starch biosynthesis, including ADP-glucose pyrophosphorylase (AGPase), soluble starch synthases (SSS), starch branching enzyme (SBE) and starch debranching enzymes (DBE) were studied, and changes of fine structure of amylopectin were characterized by isoamylase treatment during rice grain development, using trans anti-waxy gene rice plants. The relationships between the activities of those key enzymes were also analyzed. The amylose synthesis was significantly inhibited in transgenic Wanjing 9522, but the total starch content and final grain weight were less affected as compared with those of non-transgenic Wanjing 9522 rice cultivar. Analyses on the changes of activities of enzymes involving in starch biosynthesis showed that different enzyme activities were expressed differently during rice endosperm development. Soluble starch synthase is relatively highly expressed in earlier stage of endosperm development, whilst maximal expression of granule-bound starch synthase (GBSS) occurred in mid-stage of endosperm development. No obvious differences in changes of the activities of AGPase and SBE between two rice cultivars investigated, except the DBEs. Distribution patterns of branches of amylopectin changed continually during the development of rice grains and varied between two rice cultivars. It was suggested that amylopectin synthesis be prior to the synthesis of amylose and different enzymes have different roles in controlling syntheses of branches of amylopectin. [ABSTRACT FROM AUTHOR]

Background: Drought stress is one of the major abiotic stresses that restrict plant growth and development. 14–3-3 proteins have been validated to regulate many biological processes in plants. Previous research demonstrated that OsGF14b plays different roles in panicle and leaf blast resistance. In this study, we researched the function of OsGF14b in drought resistance in rice. Findings: Here, we report that OsGF14b was strongly induced by soil drought stress. In comparison with wild type (WT), the osgf14b mutant exhibited improved resistance to drought and osmotic stress by changing the content of stress-relevant parameters, complementation of the osgf14b mutant restored the drought sensitivity to WT levels, whereas the OsGF14b-overexpression lines exhibited enhanced sensitivity to drought and osmotic stress. The osgf14b mutant plants were hypersensitive to abscisic acid (ABA), while the OsGF14b-overexpression plants showed reduced sensitivity to ABA. Furthermore, mutation and overexpression of OsGF14b affected the expression of stress-related genes under normal growth conditions and/or drought stress conditions. Conclusions: We have demonstrated that OsGF14b is involved in the drought resistance of rice plants, partially in an ABA-dependent manner. [ABSTRACT FROM AUTHOR]

The receptor for activated C kinase 1 (RACK1) is a WD40 type protein that is involved in multiple signaling pathways and is conserved from prokaryotes to eukaryotes. Here we report that rice RACK1A (OsRACK1A) is regulated by circadian clocks and plays an important role in the salt stress response. OsRACK1A was found to follow a rhythmic expression profile under circadian conditions at both the transcription and the translation levels, although the expression was arrhythmic under salt stress. Analysis of plant survival rates, fresh weight, proline content, malondialdehyde, and chlorophyll showed that suppression of OsRACK1A enhanced tolerance to salt stress. The ion concentration in both roots and leaves revealed that OsRACK1A-suppressed transgenic rice could maintain low Na+ and high K+ concentrations. Furthermore, OsRACK1A-suppressed transgenic rice accumulated significantly more abscisic acid (ABA) and more transcripts of ABA- and stress-inducible genes compared with the wild-type plants. Real-time quantitative polymerase chain reaction analysis revealed that many stress-related genes, including APETALA 2/Ethylene Responsive Factor (AP2/ERF) transcription factors, were upregulated in the OsRACK1A-suppressed transgenic rice line. We identified putative interactors of OsRACK1A, and found that OsRACK1A interacted with many salt stress-responsive proteins directly. These results suggest that OsRACK1A is regulated by circadian rhythm, and involved in the regulation of salt stress responses. [ABSTRACT FROM AUTHOR]

Background: Monodehydroascorbate reductase (MDAR or MDHAR), which is responsible for growth, development and stress response in plants, is a key enzyme in the maintenance of the ascorbate acid (AsA) pool through the AsA-glutathione (AsA-GSH) cycle. High temperature affects a broad spectrum of cellular components and metabolism including AsA-GSH cycle in plants. In rice, however, the detailed roles of OsMDHAR4 in resistance against heat stress remains unclear.Results: Here, we report that OsMDHAR4 protein was localized to the chloroplasts. OsMDHAR4 expression was detected in all tissues surveyed and peaked in leaf blade. OsMDHAR4 was responsive to multiple stresses and was relatively strongly induced by heat treatment. In comparison with wild type, the osmdhar4 mutant exhibited improved tolerance to heat stress, whereas OsMDHAR4 overexpression lines exhibited enhanced sensitivity to heat stress. Moreover, we found that suppression of OsMDHAR4 promoted stomatal closure and hydrogen peroxide accumulation, and overexpression of OsMDHAR4 increased stomatal opening and decreased hydrogen peroxide content in rice leaves.Conclusions: Taken together, these results indicated that OsMDHAR4 negatively regulates tolerance to heat stress by mediating H2O2-induced stomatal closure in rice. [ABSTRACT FROM AUTHOR]