Un-Sang Yeo

OsCIPK31, a CBL-Interacting Protein Kinase Is Involved in Germination and Seedling Growth under Abiotic Stress Conditions in Rice Plants

Calcineurin B-like protein-interacting protein kinases (CIPKs) are a group of typical Ser/Thr protein kinases that mediate calcium signals. Extensive studies using Arabidopsis plants have demonstrated that many calcium signatures that activate CIPKs originate from abiotic stresses. However, there are few reports on the functional demonstration of CIPKs in other plants, especially in grasses. In this study, we used a loss-of-function mutation to characterize the function of the rice CIPK gene OsCIPK31. Exposure to high concentrations of NaCl or mannitol effected a rapid and transient enhancement of OsCIPK31 expression. These findings were observed only in the light. However, longer exposure to most stresses resulted in downregulation of OsCIPK31 expression in both the presence and absence of light. To determine the physiological roles of OsCIPK31 in rice plants, the sensitivity of oscipk31::Ds, which is a transposon Ds insertion mutant, to abiotic stresses was examined during germination and seedling stages. oscipk31::Ds mutants exhibited hypersensitive phenotypes to ABA, salt, mannitol, and glucose. Compared with wild-type rice plants, mutants exhibited retarded germination and slow seedling growth. In addition, oscipk31::Ds seedlings exhibited enhanced expression of several stress-responsive genes after exposure to these abiotic stresses. However, the expression of ABA metabolic genes and the endogenous levels of ABA were not altered significantly in the oscipk31::Ds mutant. This study demonstrated that rice plants use OsCIPK31 to modulate responses to abiotic stresses during the seed germination and seedling stages and to modulate the expression of stress-responsive genes.

The identification of candidate rice genes that confer resistance to the brown planthopper (Nilaparvata lugens) through representational difference analysis

The development of rice varieties (Oryza sativa L.) that are resistant to the brown planthopper (BPH; Nilaparvata lugens Stål) is an important objective in current breeding programs. In this study, we generated 132 BC5F5 near-isogenic rice lines (NILs) by five backcrosses of Samgangbyeo, a BPH resistant indica variety carrying the Bph1 locus, with Nagdongbyeo, a BPH susceptible japonica variety. To identify genes that confer BPH resistance, we employed representational difference analysis (RDA) to detect transcripts that were exclusively expressed in one of our BPH resistant NIL, SNBC61, during insect feeding. The chromosomal mapping of the RDA clones that we subsequently isolated revealed that they are located in close proximity either to known quantitative trait loci or to an introgressed SSR marker from the BPH resistant donor parent Samgangbyeo. Genomic DNA gel-blot analysis further revealed that loci of all RDA clones in SNBC61 correspond to the alleles of Samgangbyeo. Most of the RDA clones were found to be exclusively expressed in SNBC61 and could be assigned to functional groups involved in plant defense. These RDA clones therefore represent candidate defense genes for BPH resistance.

Large-scale screening of rice accessions to evaluate resistance to bakanae disease

Bakanae disease is an important fungal disease in the world. No rice (Oryza sativa L.) varieties have been found to be completely resistant to this disease. To facilitate accurate, uniform and simultaneous screening of many rice accessions, we developed an inoculation method for microconidia of Fusarium fujikuroi using a tissue embedding cassette and seedling tray. Standards for evaluating the inoculated rice seedlings as healthy or unhealthy were also established. The method was fast and reproducible for accurately evaluating resistance to bakanae disease in rice.

A Waxy Black Giant Embryo Earley Maturing Rice Variety ‘Nunkeunheugchal’

Nunkeunheugchal (registration No. 01-0001-2014-4), a black waxy giant embryo rice cultivar, was developed by the rice breeding team of National Institute of Crop Science (NICS), RDA in 2012. This cultivar was derived from the cross between ge and Josaengheugchal in 2004/2005 winter season, and selected by a promising line, YR25277-B-B-314-2, was selected and designated as the line of Milyang263 in 2009. The local adaptability test of Milyang263 was carried out at four locations from 2010 to 2012 and it was named as Nunkeunheugchal. This variety is a early maturity cultivar. It has 65 cm in culm length and 72 spikelets per panicle, and 1,000 grain-weight of brown rice is 17.8 g which is less than that of Josaengheugchal. This variety is resistant to leaf blast, but susceptible to bacterial blight, neck blast, virus disease and insect pest. The yield potential of Nunkeunheugchal was about 3.54 MT/ha as brown rice at ordinary fertilizer level in local adaptability test for three years. Nunkeunheugchal possesses benefits to rice consumers because of high amounts of GABA, anthocyanin, calcium and iron. This variety would be adaptable to the paddy field of middle and southern plain region of Korea.

Differential Tolerance of Rice Cultivars to Mesotrione-Contained Herbicides

Greenhouse experiment was conducted to evaluate tolerance of six rice cultivars, three IndicaJaponica rice (long grain, cv. Dasanbyeo, Segejinmi and Hanareumbyeo) and three Japonica rice (short grain, Nampyung, Ilpumbyeo and Junamjosaeng) cultivars, to mesotrione+pretilachlor (MP) and bensulfuron-methyl+mesotrione+pretilachlor+pyriftalid (BMPP) in transplanting rice. Two herbicides were applied at 90 g and 180 g a.i. to three to four leaf stage rice at 5 and 15 days after transplanting, respectively. Related study was also conducted to compare for IndicaJaponica and Japonica rice cultivars at different MP rates. Response to two herbicides varied with respect to rice cultivars and herbicide rates. All IndicaJaponica rice cultivars exhibited susceptible to both MP and BMPP as reflected by increased visual injury, shorter plant height and higher plant dry matter reduction when compared with nontreated rice cutlivars. The degree of foliar chlorosis by MP at 90 g a.i. was 5~6 at 7 days after treatment(DAT) but it was decreased to 3~6 at 14DAT. The degree of leaf chlorosis treated with 180 g a.i. MP was 6~7 at 7DAT and it was also decreased to 3~8 at 14 DAT. The plant hight of IndicaJaponica rices was inhibited by 18~43% at application of 90 g a.i. MP and 30~50% at 180 g a.i. MP. The dry matter reduction was greater than that of plant height inhibition, showing 46~73% at 90 g a.i. MP and 65~82% at 180 g a.i. MP. Similar leaf chlorosis injury and growth inhibition of rice cultivars was observed in the BMPP treatment. The injury and growth inhibition by MP and BMPP increased with increase in herbicide rate from 90 g a.i. to 180 g a.i. . However, most of the Japonica cultivars are tolerant to MP and BMPP at both rates. There was no visible leaf chlorosis but plant height and dry matter production were slightly reduced at 180 g a.i. . Based on value determined in reduction of shoot dry weight for MP, the IndicaJaponica rice showed 12.9 fold lower compared with the Japonica rice. The result indicates that rice cultivars vary in tolerance to herbicides of MP and BMPP and IndicaJaponica rices were more susceptible than the Japonica rices to the MP and BMPP.

Evaluation of Optimum Rice Heading Period under Recent Climatic Change in Yeongnam Area

This study was conducted to analyze the optimum heading period according to the recent climatic change for improvement of rice yield and grain quality in the Yeongnam area. We analyzed climatic elements including daily mean air temperature, daily range of air temperature, sunshine hours, and amount of precipitation from 1996 to 2005 in comparison with those of the 1971 to 2000 normal. Daily mean air temperature and amount of precipitation in the recent 10 years increased, but daily range of air temperature and sunshine hours decreased in comparison with the norm. Also, monthly mean air temperature was lowered remarkably in July and August. The monthly amount of precipitation largely increased in August and September. The daily range of air temperature and sunshine hours were greatly decreased from August to October, Possible cultivation periods for rice in the recent 10 years ranged from 171 days in Boughwa to 228 days in Busan and was expanded about days in comparison with the normal. Optimum heading date by local regions for the maximum climatic yield potential was estimated as July 31 at Bonghwa to September 7 at Busan, Masan, and Tongyeong in the recent 10 years. There was a wide difference in optimum heading date according to local legions of the Yeongnam area. Compared to the normal, optimum heading date in the recent 10 years was delayed about I~8 days in most local regions except Bonghwa, Mungyeong, and Yeongdeok. These results suggested that it is necessary to develop late maturity rice cultivars for producing high yield and quality rice grain due to the recent climatic change. Moreover, it is still more important to select the most suitable cultivation period appropriate to the changed climate of each local region in Yeongnam area.

Effect of light on endogenous levels of gibberellin and abscisic acid in seed germination of photoblastic weedy rice (Oryza sativa L.)

The effect of red (R) and R/far-red (FR) lights on endogenous gibberellin (GA) and abscisic acid (ABA) content was first investigated during the germination of photoblastic black-hulled weedy rice (PBWR) seeds. The R light-treated PBWR seeds germinated after 36–48 h and germination was increased to 63% at 72 h. However, the FR light-treated seeds after R light treatment, suppressed the R light effect showing only 11% germination even at 72 h after the light treatment. The PBWR seed treated with R light rapidly increased the endogenous level of GA1 to about 200 times at 12 h before seed germination as compared with R/FR (control) which suppressed the effect of R light. The contents of other GAs like GA12, GA53, GA19, GA20, and GA8 were not affected by the R light irradiation. These results showed that the major biosynthetic pathway of GAs in PBWR seeds is the early 13-hydroxylation pathway leading to GA1, which was suggested to be physiologically active in the PBWR seed germination. The decrease in the level of ABA in the R light-treated seeds was greater than the R/FR light-treated seeds, indicating that the balance of endogenous GA1 and ABA is responsible for the induction of germination in the PBWR seed.

Molecular re-confirmation and floral characteristics of drooping leaf (DL) mutants generated by insertional mutagenesis in rice

Transposon tagging and insertional mutagenesis provide one of the most powerful tools in gene function studies. Here, we report a comparison between two novel drooping leaf (DL) mutants from transposon and T-DNA insertion lines of rice. DL is distinct from well-known ABC genes and a member of the YABBY gene family, and it is closely related to the CRABS CLAW (CRC) gene of Arabidopsis thaliana. Based on phenotypic analysis, DL regulated midrib formation by promoting cell proliferation in the central region of rice leaf and was necessary for the specification of carpel identity. We identified two DL mutants by screening the Ac/Ds and T-DNA insertional mutant pool of rice. Flanking sequence tag analysis indicated that both Ds and T-DNA segments were inserted in the promoter region at 3.4 kbs and 5.4 kb upstream, respectively, of the previously known OsYABBY domain. Interestingly, the progenies of DL lines of two different pools showed various degrees of leaf drooping and abnormal carpel formation. Flower structures revealed that there were more than two stigmas with normal stamens and pistils per panicle in the Ds-induced mutants. However, T-DNA induced mutant had extra stamens with staminoid carpels. These results indicate that the promoter region of DL plays an important function in regulating anther and carpel formation.