Effects of pre-harvest chemical application on rice desiccation and seed quality.

Pre-harvest desiccation may increase the efficiency of seed production. Field studies were conducted to determine the effects of diquat, paraquat, and ethephon applications on grain moisture, grain weight, and seed germination of hybrid rice Yanliangyou 88 (Oryza sativa ssp. indica) and conventional rice Wuyunjing 7 (Oryza sativa ssp. japonica). In 2013, we tested 12 treatments applied at four weeks (Yanliangyou 88) and six weeks (Wuyunjing 7) after heading. Results showed that reductions in moisture content were significant two and four days after chemical application. Chemical applications had no adverse effects on 1000-grain weight, germination percentage, or germination index, but there were negative effects on the percentage of normal seedlings. Desiccation effects increased with increase in the period after application, while the effect of ethephon combined with diquat or paraquat on desiccation was limited compared with that of diquat or paraquat alone in a short period after application. In 2013, chemical applications reduced the moisture content by from 0.5% to 6.4%, the germination percentage by from 0% to 3.3%, and the percentage of normal seedlings by from 13.3% to 100.0%. Among the treatments, diquat applied at 120 g/ha resulted in effective desiccation with fewer negative effects on grain weight and seed germination in 2013 and 2014. Therefore, diquat may have potential as a pre-harvest chemical desiccation treatment for rice. These results may provide a basis for developing and implementing protocols for large scale field trials.

Characterization of a vacuolar zinc transporter OZT1 in rice (Oryza sativa L.).

The CDF family is a ubiquitous family that has been identified in prokaryotes, eukaryotes, and archaea. Members of this family are important heavy metal transporters that transport metal ions out of the cytoplasm. In this research, a full length cDNA named Oryza sativa Zn Transporter 1 (OZT1) that closely related to rat ZnT-2 (Zn Transporter 2) gene was isolated from rice. The OZT1 encoding a CDF family protein shares 28.2 % ~ 84.3 % of identities and 49.3 % ~ 90.9 % of similarities with other zinc transporters such as RnZnT-2, HsZnT-8, RnZnT-8 and AtMTP1. OZT1 was constitutively expressed in various rice tissues. The OZT1 expression was significantly induced both in the seedlings of japonica rice Nipponbare and indica rice IR26 in response to Zn(2+) and Cd(2+) treatments. Besides, OZT1 expression was also increased when exposed to other excess metals, such as Cu(2+), Fe(2+) and Mg(2+). Subcellular localization analysis indicated that OZT1 localized to vacuole. Heterologous expression of OZT1 in yeast increased tolerance to Zn(2+) and Cd(2+) stress but not the Mg(2+) stress. Together, OZT1 is a CDF family vacuolar zinc transporter conferring tolerance to Zn(2+) and Cd(2+) stress, which is important to transporting and homeostasis of Zn, Cd or other heavy metals in plants.

A novel nuclear protein phosphatase 2C negatively regulated by ABL1 is involved in abiotic stress and panicle development in rice.

Type 2C protein phosphatase plays an important role in the signal transduction of stress response in plants. In this paper, we identified a novel stress-induced type 2C protein phosphatase gene OsSIPP2C1 from rice. OsSIPP2C1 contains a complete open reading frame of 1,074 bp, encoding a protein with 357 amino acids. OsSIPP2C1 expression was up-regulated by high salt, PEG6000 and exogenous ABA, and enhanced in the abl1 mutant under normal, salt, or drought condition. Interestingly, OsSIPP2C1 expression was increased during the early panicle development. Subcellular localization assay using rice protoplast cells indicated that OsSIPP2C1 was predominantly located in the nucleus. Together, it is suggested that a nuclear PP2C protein OsSIPP2C1 negatively regulated by ABL1 is involved in abiotic stress and panicle development in rice.

Overexpression of the Qc-SNARE gene OsSYP71 enhances tolerance to oxidative stress and resistance to rice blast in rice (Oryza sativa L.).

OsSYP71 is an oxidative stress and rice blast response gene that encodes a Qc-SNARE protein in rice. Qc-SNARE proteins belong to the superfamily of SNAREs (soluble N-ethylmaleimide-sensitive factor attachment protein receptors), which function as important components of the vesicle trafficking machinery in eukaryotic cells. In this paper, 12 Qc-SNARE genes were isolated from rice, and expression patterns of 9 genes were detected in various tissues and in seedlings challenged with oxidative stresses and inoculated with rice blast. The expression of OsSYP71 was clearly up-regulated under these stresses. Overexpression of OsSYP71 in rice showed more tolerance to oxidative stress and resistance to rice blast than wild-type plants. These results indicate that Qc-SNAREs play an important role in rice response to environmental stresses, and OsSYP71 is useful in engineering crop plants with enhanced tolerance to oxidative stress and resistance to rice blast.

Quantitative trait loci analysis for rice seed vigor during the germination stage.

Seed vigor is an important characteristic of seed quality, and rice cultivars with strong seed vigor are desirable in direct-sowing rice production for optimum stand establishment. In the present study, the quantitative trait loci (QTLs) of three traits for rice seed vigor during the germination stage, including germination rate, final germination percentage, and germination index, were investigated using one recombinant inbred line (RIL) population derived from a cross between japonica Daguandao and indica IR28, and using the multiple interval mapping (MIM) approach. The results show that indica rice presented stronger seed vigor during the germination stage than japonica rice. A total of ten QTLs, and at least five novel alleles, were detected to control rice seed vigor, and the amount of variation (R(2)) explained by an individual QTL ranged from 7.5% to 68.5%, with three major QTLs with R(2)>20%. Most of the QTLs detected here are likely to coincide with QTLs for seed weight, seed size, or seed dormancy, suggesting that the rice seed vigor might be correlated with seed weight, seed size, and seed dormancy. At least five QTLs are novel alleles with no previous reports of seed vigor genes in rice, and those major or minor QTLs could be used to significantly improve the seed vigor by marker-assisted selection (MAS) in rice.

[Preparation, characterization and application of rice Qb-SNARE protein OsNPSN11 polyclonal antibody].

Membrane fusion in vesicle trafficking in the cells of eukaryotic organisms is mediated by soluble-N-ethyl- maleimide-sensitive fusion protein attachment protein receptor (SNARE) proteins. OsNPSN11 is a member of Qb-SNARE gene family isolate from rice. The cDNA of OsNPSN11 was subcloned into pET-30a and fusion to the 6 × His tag. Induced by 0.5 mmol/L IPTG for four hours, the recombinant protein was highly expressed in Escherichia coli, which was purified by Ni2+ -NTA His-bind resin affinity chromatography column to be used as an antigen to raise the antibody in New Zealand rabbits. Western blotting analysis showed that the antibody can specifically recognize the expressed antigen and the OsNPSN11 in plasma membrane protein from various rice tissues. This indicated that the antibody can be used for expres-sion analysis in transgenic rice.

[Mapping of QTLs of Cd2+ content in brown rice under Cd2+ stress in rice].

A population of F8 recombinant inbred lines (RILs), derived from a cross between IR26 (Oryza sativa L. spp. indica) and Jiucaiqing (japonica), were used to identify the quantitative trait loci (QTLs) for Cd2+ content in brown rice under 5 mg/kg Cd2+ stress. Two QTLs, qCCBR-11a and qCCBR-11b, associated with the Cd2+ content in brown rice, were detected on chromosome 11. qCCBR-11a was located at the position between markers RM6288 and RM6544, accounting for 11.17% of the phenotypic variance with an additive effect value of 0.089. qCCBR-11b at the interval between markers RM167 and RM5704 explained 7.66% of the phenotypic variance with an additive effect value of 0.075. In addition, the correlation coefficients between Cd2+ content of brown rice and plant height, spikelets per panicle, filled grains per panicle, seed setting rate, and 1 000-grain weight were not significant. This suggested that the Cd2+ content in brown rice under Cd2+ stress was an independent genetic trait.

Increased tolerance of rice to cold, drought and oxidative stresses mediated by the overexpression of a gene that encodes the zinc finger protein ZFP245.

ZFP245 is a cold- and drought-responsive gene that encodes a zinc finger protein in rice. The ZFP245 protein localizes in the nucleus and exhibits trans-activation activity. Transgenic rice plants overexpressing ZFP245 were generated and found to display high tolerance to cold and drought stresses. The transgenic plants did not exhibit growth retardation, but showed growth sensitivity against exogenous abscisic acid, increased free proline levels and elevated expression of rice pyrroline-5-carboxylatesynthetase and proline transporter genes under stress conditions. Overproduction of ZFP245 enhanced the activities of reactive oxygen species-scavenging enzymes under stress conditions and increased the tolerance of rice seedlings to oxidative stress. Our data suggest that ZFP245 may contribute to the tolerance of rice plants to cold and drought stresses by regulating proline levels and reactive oxygen species-scavenging activities, and therefore may be useful for developing transgenic crops with enhanced tolerance to abiotic stress.

Relationships between changes of kernel nutritive components and seed vigor during development stages of F1 seeds of sh2 sweet corn.

The changes of kernel nutritive components and seed vigor in F1 seeds of sh2 sweet corn during seed development stage were investigated and the relationships between them were analyzed by time series regression (TSR) analysis. The results show that total soluble sugar and reducing sugar contents gradually declined, while starch and soluble protein contents increased throughout the seed development stages. Germination percentage, energy of germination, germination index and vigor index gradually increased along with seed development and reached the highest levels at 38 d after pollination (DAP). The TSR showed that, during 14 to 42 DAP, total soluble sugar content was independent of the vigor parameters determined in present experiment, while the reducing sugar content had a significant effect on seed vigor. TSR equations between seed reducing sugar and seed vigor were also developed. There were negative correlations between the seed reducing sugar content and the germination percentage, energy of germination, germination index and vigor index, respectively. It is suggested that the seed germination, energy of germination, germination index and vigor index could be predicted by the content of reducing sugar in sweet corn seeds during seed development stages.

Isolation and expression analysis of plastidic glucose-6-phosphate dehydrogenase gene from rice (Oryza sativa L.).

Glucose-6-phosphate dehydrogenase is a rate-limiting enzyme of pentose phosphate pathway, existing in cytosolic and plastidic compartments of higher plants. A novel gene encoding plastidic glucose-6-phosphate dehydrogenase was isolated from rice (Oryza sativa L.) and designated OsG6PDH2 in this article. Through semiquantitative RT-PCR approach it was found that OsG6PDH2 mRNA was weakly expressed in rice leaves, stems, immature spikes or flowered spikes, and a little higher in roots. However, the expression of OsG6PDH2 in rice seedlings was significantly induced by dark treatment. The complete opening reading frame (ORF) of OsG6PDH2 was inserted into pET30a (+), and expressed in Escherichia coli strain BL21 (DE3). The enzyme activity assay of transformed bacterial cells indicated that OsG6PDH2 encoding product had a typical function of glucose-6-phosphate dehydrogenase.