He Guangcun

Mapping of two new brown planthopper resistance genes from wild rice

A brown planthopper (BPH) resistance line, B5, derived its resistance genes from the wild riceOryza officinalis Wall exwatt, was hybridized with Taichung Native 1, a cultivar highly susceptible to BPH. A mapping population composed of randomly selected 167 F2 individuals was used for determining the BPH resistance genes by the restriction fragment length polymorphism analysis (RFLP). Bulked segregant analysis was conducted to identify RFLP makers linked to the BPH resistance genes in B5. The results indicated that the markers linked to BPH resistance are located at two genomic regions on the long arm of chromosome 3 and the short arm of chromosome 4, respectively. The existence of the two loci was further assessed by the quantitative trait locus (QTL) analysis. We located the two loci at a 3.2 cM interval between G1318 and R1925 on chromosome 3 and a 1.2 cM interval between C820 and S11182 on chromosome 4. Comparison with the BPH genes that have been reported indicated that the BPH resistance genes in B5 are novel. These two genes may be useful BPH resistance resource for rice breeding. Furthermore, the mapping of the two genes is useful for cloning the BPH resistance genes.

The breeding of two polyploid rice lines with the characteristic of polyploid meiosis stability.

Polyploidization is a basic feature of plant evolution. Nearly all of the main food, cotton and oil crops are polyploid. When ploidy levels increase, yields double; this phenomenon suggested a new strategy of rice breeding that utilizes wide crosses and polyploidization dual advantages to breed super rice. Because low seed set rates in polyploid rice usually makes it difficult to breed, the selection of Ph-liked gene lines was emphasized. After progenies of indica-japonica were identified and selected, two polyploid lines, PMeS-1 and PMeS-2 with Polyploid Meiosis Stability (PMeS) genes were bred. The procedure included seven steps: selecting parents, crossing or multiple crossing, back-crossing, doubling chromosomes, identifying the polyploid, and choosing plants with high seed set rates that can breed themselves into stable lines. The characteristics of PMeS were determined by observing meiotic behaviors and by cross-identification of seed sets. PMeS-1 and PMeS-2, (japonica rice), have several characteristics different from other polyploid rice lines, including a higher rate of seed set (more than 65%, increasing to more than 70% in their F1 offspring); and stable meiotic behaviors (pairing with bivalents and quarivalents nearly without over-quarivalent in prophase, nearly without lagging chromosomes in metaphase and without micronuclei in anaphase and telophase). The latter was obviously different from control polyploid line Dure-4X, which displayed abnormal meiotic behaviors including a higher rate of multivalents, univalents and trivalents in prophase, lagging chromosomes in metaphase and micronuclei in anaphase and telophase. There were also three differences of the breeding method between PMeS lines and normal diploid lines: chromosomes doubling, polyploidism identifying and higher seed set testing. The selection of PMeS lines is the first step in polyploid rice breeding; their use will advance the progress of polyploid rice breeding, which will in turn offer a new way to breed super rice.

Comparative analysis of genomes in Oryza sativa, O. officinalis and O. meyeriana with C0t-1 DNA and genomic DNA of cultivated rice

Fluorescence in situ hybridization (FISH) and comparative genomic hybridization (CGH) were applied to somatic chromosome preparations of Oryza sativa, O. officinalis and O. meyeriana with labeled probes of C0t-1 DNA and genomic DNA from cultivated rice. The coverage percentage (%) and size (Mb) of C0t-1 DNA in O. sativa, O. officinalis and O. meyeriana were 47.1 ± 0.16, 38.61 ± 0.13, 44.38 ± 0.13 and 212.33 ± 1.21, 269.42 ± 0.89, 532.56 ± 1.68, respectively. The coverage percentage and size of probe signals with genomic DNA from O. sativa in O. officinalis and O. meyeriana were 91.0%, 93.6% and 634 Mb, 1 123 Mb respectively, in which there were 365 and 591 Mb in O. officinalis and O. meyeriana which came from O. sativa genomic DNA not from repetitive sequences of O. sativa, and the uncovered genome size in O. officinalis and O. meyeriana was 64 and 78 Mb, respectively. In addition, karyotype analysis was conducted based on the signal bands of C0t-1 DNA in O. sativa, O. officinalis and O. meyeriana. The results showed that highly and moderately repetitive sequences in Oryza genus were conserved as the functional genes during the evolution process. The repetitive sequence reduplication might be one of the important causes of genome enlargement in O. officinalis and O. meyeriana; the O. officinalis genome enlarged more slowly compared with O. meyeriana. Based on the above results, it is concluded that O. officinalis and O. meyeriana formed by reduplication, rearrangement and gene selective loss during the evolution process.

Study on Young Panicle Culture in vitro From Wild Rice of Different Genomes

Researches have been made on young panicle culturein vitro from wild rice of different genomes. Main results are as follows: 1. The induction frequencies of young panicle culturedin vitro from wild rice varied largely a relation to its genome. The optimal induction period of callus is the stamen and pistil differentiation stage of young panicle development. 2. Plantlets were regenerated through two ways: first, culture method, the induced calli were transferred onto differentiation medium; second, regenerate plantlets directly from young panicles of wild rice that were cultured on the differentiation medium. 3. The regeneration rate of green plantlets that obtained through cryopreservated calli inO. meyeriana was 10 times higher than that of control.

Effect of exogenous ammonium on glutamine synthetase, glutamate synthase, and glutamate dehydrogenase in the root of rice seedling

Root biomass of rice seedlings was increased at lower concentration of exogenous NH4+, but it was decreased at higher concentration of exogenous NH4+. The level of free NH4+ in the roots was accumulated gradually with the increase of NH4+ concentration in the nutrient solution. The content of the soluble proteins was essentially constant at higher NH4+. The activities of glutamine synthetase (GS), NADH-dependent glutamate synthase (NADH-GOGAT), and NADH-dependent glutamate dehydrogenase (NADH-GDH) were risen with exogenous NH4+ concentration at the lower NH4+ concentration range. But the activities of GS and NADH-GOGAT were declined, and the level of NADH-GDH activity was kept constant under higher NH4+ concentration. The GS/GDH ratio suggested that NH4+ was assimilated by GS-GOGAT cycle under lower NH4+ concentration, but NADH-GDH was more important for NH4+ assimilation and detoxifying NH4+ to the tissue cells at the higher NH4+ level. According to the growth and the activity changes of these ammonium-assimilating enzymes of rice seedling roots, 10. 0 μg/mL NH4+-N in nutrient solution was more suitable to the rice growth.

Comparative physical map of linked markers ofPi-2(t) gene inOryza officinalis andOryza sativa with BAC-FISH

A FISH procedure was adopted to physically localize rice BAC clone 38D17 linked with Pi-2(t) gene in O.sativa and O.officinalis. The FISH results showed that both the RG64 and BAC clone 38D17 were localized on the chromosome 6 in O.officinalis and O.sativa, the percentage distances from the centromere to the hybridization sites were 44.87±5.33, 46.50±4.67 (O.officinalis), and 35.85±3.06, 36.05±2.44(O.sativa), the detection rates were 7.14%, 42.53% and 8.09%, 40.78% respectively. The results suggested that the RG64 of cultivated rice and its homologous sequence of O.officinalis were in the same BAC clone. We observed many background signals when probe was not blocked with Cot-Ⅰ DNA. It demonstrated that highly repetitive sequences were possibly homologous in a certain degree between cultivated rice and O.officinalis. The identification of chromosome 6 of O.officinalis was based on the comparative genetics map of Jena et al. (1994) and our research results. In our study, the feasibility of physical mapping in O.officinalis with rice BAC clones and preparation of Cot-Ⅰ DNA were discussed.