Quantitative trait Loci for panicle layer uniformity identified in doubled haploid lines of rice in two environments.

Uniformity of stem height in rice directly affects crop yield potential and appearance, and has become a vital index for rice improvement. In the present study, a doubled haploid (DH) population, derived from a cross between japonica rice Chunjiang 06 and indica rice TN1 was used to analyze the quantitative trait locus (QTL) for three related traits of panicle-layer-uniformity; that is, the tallest panicle height, the lowest panicle height and panicle layer disuniformity in two locations: Hangzhou (HZ) and Hainan (HN). A total of 16 QTLs for three traits distributed on eight chromosomes were detected in two different environments. Two QTLs, qTPH-4 and qTPH-8 were co-located with the QTLs for qLPH-4 and qLPH-8, which were only significant in the HZ environment, whereas the qTPH-6 and qLPH-6 located at the same interval were only significant in the HN environment. Two QTLs, qPLD-10-1 and qPLD-10-2, were closely linked to qTPH-10, and they might have been at the same locus. One QTL, qPLD-3, was detected in both environments, explaining more than 23% of the phenotypic variations. The CJ06 allele of qPLD-3 could increase the panicle layer disuniformity by 9.23 and 4.74 cm in the HZ and HN environments. Except for qPLD-3, almost all other QTLs for the same trait were detected only in one environment, indicating that these three traits were dramatically affected by environmental factors. The results may be useful for elucidation of the molecular mechanism of panicle-layer-uniformity and marker assisted breeding for super-rice.

[Genetic transformation of Bt gene into sorghum (Sorghum bicolor L.) mediated by Agrobacterium tumefaciens].

Sorghum (Sorghum bicolor L.) was one of the most important crops in the world next to wheat, rice, maize, soybean and barley. Using the callus derived from immature inflorescence as the recipients, we efficiently transformed sorghum varieties 115, ICS21B and 5-27 with the insecticidal Bacillus thuringiensis (Bt) cry1Ab gene carried in the T-DNA of binary vectors which contained hygromycin resistance gene and gus gene via Agrobacterium tumefaciens. After gradient selection with hygromycin, a total of 21 independent transgenic plant lines, 52 transgenic plants were regenerated, and the average stably transformation efficiency was 1.9%. The integration and transcription of cry1Ab gene in transgenic sorghum was confirmed by PCR analysis, Southern blotting and RT-PCR analysis. The Bt proteins were expressed in most transgenic plants with different level from plant to plant by Western blotting and ELISA assay. According to insect bioassay in laboratory, the transgenic plants with a relatively high level of Bt gene expression displayed insect-resistance to pink rice borer (Sesamina inferens).

Mapping QTLs for heading synchrony in a doubled haploid population of rice in two environments.

Simultaneous heading of plants within the same rice variety, also refer to heading synchrony, is an important factor that affects simultaneous ripening of the variety. Understanding of the genetic basis of heading synchrony may contribute to molecular breeding of rice with simultaneous heading and ripening. In the present study, a doubled haploid (DH) population, derived from a cross between Chunjiang 06 and TN1 was used to analyze quantitative trait locus (QTL) for heading synchrony related traits, i.e., early heading date (EHD), late heading date (LHD), heading asynchrony (HAS), and tiller number (PN). A total of 19 QTLs for four traits distributed on nine chromosomes were detected in two environments. One QTL, qHAS-8 for HAS, explained 27.7% of the phenotypic variation, co-located with the QTLs for EHD and LHD, but it was only significant under long-day conditions in Hangzhou, China. The other three QTLs, qHAS-6, qHAS-9, and qHAS-10, were identified under short-day conditions in Hainan, China, each of which explained about 11% of the phenotypic variation. Two of them, qHAS-6 and qHAS-9, were co-located with the QTLs for EHD and LHD. Two QTLs, qPN-4 and qPN-5 for PN, were detected in Hangzhou, and qPN-5 was also detected in Hainan. However, none of them was co-located with QTLs for EHD, LHD, and HAS, suggesting that PN and HAS were controlled by different genetic factors. The results of this study can be useful in marker assisted breeding for improvement of heading synchrony.

Analysis of genotype x environment interaction effects for starch pasting viscosity characteristics in Indica rice.

Milled rice (Oryza sativa L.) is composed of approximately 90% starch. The properties of starch have considerable effects on cooked rice palatability and consumer acceptability. Starch pasting viscosity parameters serve as important indices in the estimation of eating, cooking, and processing qualities of rice. In the present study, four cytoplasmic male-sterile (CMS) lines and eight restorer (R) lines have been used in an incomplete diallel cross to analyze seed effects, cytoplasmic effects, maternal gene effects, and their genotype x environment (GE) effects on the following starch pasting viscosity parameters: breakdown (BD), consistency (CS), and setback (SB). The results demonstrated that the total main genetic variances (V(G)) accounted for over 64% of the total genetic variance (V(G) +V(GE)) for the three traits, indicating that these traits were mainly controlled by the main genetic effects in addition to the GE interaction effects. The estimated total narrow-sense heritability were 67.8%, 79.5%, and 79.5% for BD, CS, and SB, respectively. The general heritability (h(2)(G)) accounted for over 75% of the total heritability (h(2)(G) +h(2)(GE)), indicating that early selection would be effective for those traits and the selection efficiencies were relatively stable in different environments.

Rice Pi-ta gene Confers Resistance to the Major Pathotypes of the Rice Blast Fungus in the United States.

ABSTRACT The Pi-ta gene in rice prevents the infection by Magnaporthe grisea strains containing the AVR-Pita avirulence gene. The presence of Pi-ta in rice cultivars was correlated completely with resistance to two major pathotypes, IB-49 and IC-17, common in the U.S. blast pathogen population. The inheritance of resistance to IC-17 was investigated further using a marker for the resistant Pi-ta allele in an F(2) population of 1,345 progeny from a cross of cv. Katy with experimental line RU9101001 possessing and lacking, respectively, the Pi-ta resistance gene. Resistance to IC-17 was conferred by a single dominant gene and Pi-ta was not detected in susceptible individuals. A second F(2) population of 377 individuals from a reciprocal cross between Katy and RU9101001 was used to verify the conclusion that resistance to IC-17 was conferred by a single dominant gene. In this cross, individuals resistant to IC-17 also were resistant to IB-49. The presence of Pi-ta and resistance to IB-49 also was correlated with additional crosses between 'Kaybonnet' and 'M-204', which also possess and lack Pi-ta, respectively. A pair of primers that specifically amplified a susceptible pi-ta allele was developed to verify the absence of Pi-ta. We suggest that Pi-ta is responsible for resistance to IB-49 and IC-17 and that both races contain AVR-Pita genes.

[Impact of root exudates from transgenic plants on soil micro-ecosystems].

With the commercialization of transgenic plants, ecological risk assessment of transgenic plants has been scheduled. Many problems such as gene transfer from transgenic plants to related wild species, production of super weeds and super virus, tolerance to insect-resistant transgenic plants, and distruption of biodiversity have been taken place in some transgenic plants. The influences of root exudates from transgenic plants on soil micro-ecosystems were reviewed.

[Mapping of fertility-restoring genes with main effects and epistatic effects for CMS-DA in rice].

A test-cross population was established for mapping genes conditioning fertility restoration for dwarf-wild-abortive cytoplasmic male sterility(CMS-DA) in rice. A recombinant inbred line(RIL) population consisting of 210 lines was derived from the cross Xieqingzao B/Miyang 46, in which Xieqingzao B is the maintainer line of CMS-DA Xieqingzao A, and Miyang 46 is the restorer line. Each of the RILs was crossed to Xieqingzao A, and the resulting F1s were used for phenotyping of the spikelet fertility in 1999 and 2000. A linkage map consisting of 129 RFLP and SSLP markers was constructed. QTLs having significant main effects and/or epistatic effects for spikelet fertility were determined with QTLMAPPER 1.0 of mixed linear model. Background genetic variation due to main and epistatic effects of important markers was controlled. Four QTLs having significant main effects for fertility restoration were detected. A major gene qRf-10-2 was located in interval RM258-RZ811 on the long arm of chromosome 10, and QTL qRf-1 displaying a moderate main effect was located in a position close to RG532 on chromosome 1. Two other QTLs were located on chromosome 5 (qRF-5) and the short arm of chromosome 10 (qRf-10-1), in which the main effect of qRf-5 bacame significant only in the absence of qRf-10-2. A significant digenic interaction was detected, which occurred between QTLs qRf-1 and qRf-5. No significant QTL by environmental interactions and epistasis by environmental interactions were detected. Analyses on the gene effects based on markers closest to the Rf genes were made, and multi-locus interactions were implied. The present results were also compared to a previous study on mapping fertility restoration genes in Milyang 46 for wild-abortive CMS Zhenshan 97A, and to other published reports. It was indicated that differences on the genetic control of fertility restoration among different rice populations were mainly attributed to variations on genes with minor main effects and epistatic effects.

Transcriptional silencing and developmental reactivation of cry1Ab gene in transgenic rice.

One transgenic rice line lacking Cry1Ab expression product was screened in the progenies of Agrobacterium-transformed transgenic rice variety Zhong 8215 with a cry1Ab gene under field releasing conditions by using GUS histochemical assay and Western blot. Molecular hybridization results revealed that the cry1Ab gene was silenced in the transgenic rice variety Zhong 8215 and two copies of ubiquitin promoter were integrated into the rice genome. The silencing of cry1Ab gene in transgenic rice was found to be due to the methylation of the ubiquitin promoter as revealed by methylation analysis. Meanwhile, different concentrations of demethylation reagent 5-azacytidine combining with different treatment time were employed to treat the silenced transgenic rice seeds. The results indicated that 5-azacytidine could reactivate 8%-30% of the silenced transgenic rice plants and the expression level of the reactivated cry1Ab transgene could reach as high as 0.147% of the total soluble protein. Treatment with low concentration of 5-azacytidine (45 mg/L for 1 d and 2 d) could lead to the highest reactivation ratio and the highest expression level of the cry1Ab gene.

[Studies on the distorted segregation of foreign genes in transgenic rice progenies].

The segregation mode of transgenes was investigated in the transgenic progenies of three rice varieties (lines) produced by Agrobacterium-mediated transformation. The transgenic lines all contained the Bacillus thuringiensis cry1Ab gene, under the control of a maize ubiquitin promoter, and linked in tandem with gusA and hpt genes. PCR analysis showed the transgenes cry1Ab and gusA co-segregated in all self and crossed progenies tested. Therefore, GUS bio-assay of leaf or endosperm tissues was used to monitor transgene segregation in the experiment. It was found that the ratio of positive to negative plants was significantly smaller than 3:1 in all heterozygous plants derived progenies, which implied the segregation biased from typical Mendelian mode for a single dominant gene. Less GUS positive plants, and consequently less homozygous transgenic lines than expected were recovered from the self progenies. Transgenic heterozygous plants (+/-) were crossed as female or male parent to conventional rice varieties (-/-), and the ratio of gusA positive (+/-) to negative (-/-) plants was investigated in test F1 population. When used as female parent, the segregation fit to 1:1, but significantly smaller than 1:1 when used as male parent. The seed-set of transgenic Nipponbare progeny was investigated individually for GUS positive and negative plants. It was found that the positive plants had an average seed-set of 64.5%, significantly lower than that of negative plants (77.9%). The biological and genetic basis of distorted segregation of transgenes was discussed and deduced on the basis of above results, and the authors are inclined to ascribe these phenomena to the poor competitive ability of pollens carrying transgenes.