Development of transgenic rice plants expressing maize anthocyanin genes and increased blast resistance

The functional association of flavonoids with plant stress responses, though widely reported in the literature, remains to be documented in rice. Towards this end we chose a transgenic approach with well characterized regulatory and structural genes from maize involved in flavonoid biosynthesis. Activation of anthocyanin pathway in rice was investigated with the maize genes. Production of purple anthocyanin pigments were observed in transformed Tp309 (a japonica rice variety) calluses upon the introduction of the maize regulatory genes C1 (coloured-1), R (red) and the structural gene C2 (coloured-2, encoding chalcone synthase). In addition, stable transgenic plants carrying the maize C2 gene under the control of the maize Ubiquitin promoter were generated. A localized appearance of purple/red pigment in the leaf blade and leaf sheath of R₀ C2 transgenic seedlings was observed. Such a patchy pattern of the transgene expression appears to be conditioned by the genetic background of Tp309, which is homozygous for dominant color inhibitor gene(s) whose presence was unravelled by appropriate genetic crosses. Southern blot analysis of the transgenic plants demonstrated that c2 cDNA was integrated into the genome. Western blot analysis of these primary transgenics revealed the CHS protein while it was not detected in the control untransformed Tp3O9, suggesting that Tp309 might have a mutation at the corresponding C2 locus or that the expression of this gene is suppressed in Tp309. Further analysis of C2 transgenics revealed CHS protein only in three out of sixteen plants that were western-positive in the R₀ generation, suggesting gene silencing. Preliminary screening of these R₁ plants against the rice blast fungus Magnaporthe grisea revealed an increase in resistance.     

基因枪介导的籼稻遗传转化及外源基因在受体中的遗传研究

由来自水稻成熟胚的愈伤组织或由此而建立的悬浮细胞系作基因枪转化的靶材料 ,将质粒 p ILTAB2 2 7(含 hph基因和 gus基因 )导入籼稻 ,在 Basmati- 1、青油粘、新山粘 2 9、胜优 2号 ,明恢 63等品种获得了转基因植株。 T0 转化体 gus基因组织化学染色和 DNA分子杂交 ( Southern blot)证实 ,gus和 hph基因已整合到上述品种的基因组中。本实验仔细研究了hph基因在 Basmati- 1的 T1、T2 和 T3等各个世代的遗传及表达。对 T1家系中各个体核 DNA的分子检测表明 ,hph基因普遍呈 3∶ 1的分离 (转基因阳性∶阴性 ) ,表明 hph基因为单一位点的整合 ,其遗传符合单 (显性 )基因控制的孟德尔遗传规律。还发现一些株系表现 1∶ 1的不正常的分离 (阳性个体较预期的少 ) ,推测这是由于雌或雄配子之一方的 hph基因受到抑制而产生基因沉默的结果。在 T2 、T3世代获得了具 hph基因的纯合体。笔者还探讨了外源基因在核基因组中的遗传稳定性及基因的沉默与活化问题     

Improvement of somatic embryogenesis and plant recovery in cassava

Methods for improving the efficiency of plant recovery from somatic embryos of cassava (Manihot esculenta Crantz) were investigated by optimizing the maturation regime and incorporating a desiccation stage prior to inducing germination. Somatic embryos were induced from young leaf lobes of in vitro grown shoots of cassava on Murashige and Skoog medium with 2,4-dichlorophenoxy acetic acid. After 15 to 20 days of culture on induction medium, the somatic embryos were transferred to a hormone free medium supplemented with activated charcoal. In another 18 days mature somatic embryos became distinctly bipolar and easily separable as individual units and were cultured on half MS medium for further development. Subsequent desiccation of bipolar somatic embryos resulted in 92% germination and 83% complete plant regeneration. The plants were characterized by synchronized development of shoot and root axes. Of the non-desiccated somatic embryos, only 10% germinated and 2% regenerated plants. Starting from leaf lobes, transplantable plantlets were derived from primary somatic embryos within 70 to 80 days.Abbreviations 2,4-D 2,4 dichlorophenoxyacetic acid - BA Benzyl aminopurine - GA Giberellic acid - MS Murashige and Skoog - NAA Naphthalene acetic acid     

An improved rice transformation system using the biolistic method

Immature embryos and embryogenic calli of rice, both japonica and indica subspecies, were bombarded with tungsten particles coated with plasmid DNA that contained a gene encoding hygromycin phosphotransferase (HPH, conferring hygromycin resistance) driven by the CaMV 35S promoter or Agrobactenum tumefaciens NOS promoter. Putatively transformed cell clusters were identified from the bombarded tissues 2 weeks after selection on hygromycin B. By separating these cell clusters from each other, and by stringent selection not only at the callus growth stage but also during regeneration and plantlet growth, the overall transformation and selection efficiencies were substantially improved over those previously reported. From the most responsive cultivar used in these studies, an average of one transgenic plant was produced from 1.3 immature embryos or from 5 pieces of embryogenic calli bombarded. Integration of the introduced gene into the plant genome, and inheritance to the offspring were demonstrated. By using this procedure, we have produced several hundred transgenic plants. The procedure described here provides a simple method for improving transformation and selection efficiencies in rice and may be applicable to other monocots.Abbreviations bp base pairs - CaMV cauliflower mosaic virus - GUS -glucuronidase - HPH hygromycin phosphotransferase - hyg B hygromycin B - hyg^r hygromycin resistance - NOS Agrobactenum tumefaciens nopaline synthase - PCR polymerase chain reaction - X-Gluc 5-bromo-4-chloro-3-indolyl--D-glucuronide     

Analysis of a large number of independent transgenic rice plants produced by the biolistic method

Summary Over 500 independent transgenic rice plants have been obtained by the biolistic method with an average transformation frequency of 9.7% for japonica variety Taipei 309. A tight selection procedure using 50 mg/l of hygromycin B successfully prevented the growth of nontransformed tissues. Analysis of the T0 transgenic rice plants revealed that more than 97% of the transgenic plants were morphologically normal and more than 80% were at least partially fertile. The hyg^r trait was inherited as a dominant trait in a Mendelian manner in 8 out of 11 transgenic events assayed. Thirty-seven out of fifty transgenic plants were estimated to contain no more than five copies of the transgenes. In six out of seven transformation events, unlinked, co-transformed genes co-segregated in the T1 generation. The hyg^r trait has been stably inherited to the T4 generation. No chimerical transgenic plant has been found in an intensive search. Novel phenomena observed in transgenic rice plants are also reported.     

Transient gene expression in cassava using high-velocity microprojectiles

The bacterial gene encoding -glucuronidase (GUS) was transiently expressed in cassava leaves following the introduction of the gene by microparticle bombardment. The DNA expression vector used to introduce the reporter gene is a pUC 19 derivative and consisted of a CaMV 35S promoter (P35S), the GUS coding region and 7S polyadenylation region. Several other promoters and regulating sequences were tested for efficiency in cassava leaves. Two derivatives of the P35S, one including a partial duplication of the upstream region of the P35S and the other containing a tetramer of the octopine synthase enhancer, were found to be expressed at three times the level of the P35S in cassava leaves. The ubiquitin 1 promoter fromArabidopsis thaliana was expressed at the same level as the P35S. No influence on the level of expression was observed when different 3 ends were used. The biolistic transient gene expression system in cassava leaves allows rapid analysis of gene constructs and can serve as a preliminary screen for chimeric gene function in the construction of transgenic cassava plants.     

DNA double helix destabilizing properties of cyclobisintercaland compounds and competition with a single strand binding protein

The DNA helix destabilizing activity of a series of cyclobisintercaland compounds (CBIs) has been evaluated by measuring their ability to displace a 32P-labelled oligonucleotide primer (17-mer) hybridized to the single stranded DNA of M13. This destabilizing activity appears to be strongly dependent on the cyclic structure (the linear acyclic references are inactive) and the size of the macrocycle; both features being known to determine the preferential binding of the compound to ssDNA. Interestingly, CBIs induced the dissociation of the duplex template in a concentration range (0.5-1 microM) close to that required for the destabilizing activity of single stranded DNA binding proteins (SSBs). Therefore competition experiments between CBIs and an SSB protein (Eco SSB) for binding to a single stranded oligonucleotide target (36-mer) have been performed through gel electrophoresis and nitrocellulose binding assays and strong inhibitory effects on the formation of the SSB:36-mer complex have been observed.     

A High-throughput Platform for the Production and Analysis of Transgenic Cassava (Manihot esculenta) Plants

A platform for high-throughput production and analysis of transgenic cassava (Manihot esculenta) has been developed for the variety 60444 and implemented to generate plants expressing traits for nutritional enhancement, modified metabolism, promoter analysis and disease resistance. Over a three and a half year period this system has been utilized to produce more than 3500 independent transgenic plant lines from 50 different genetic constructs within a single laboratory. Plants recovered through this system have proven robust and efficacious for engineered traits under greenhouse conditions and within the first confined field trials of transgenic cassava carried out in Uganda, Kenya, Nigeria and Puerto Rico. Detailed procedures are described for the operation of this platform, including all steps in tissue culture, genetic transformation, copy number estimation, greenhouse establishment for shoot and storage root formation and systems for centralized quality control, transgenic plant tracking and regulatory compliance. In addition to providing reliable transgenic plant production for proof of concept studies in the variety 60444, the systems implemented and described here form the structure for high throughput production of transgenic farmer-preferred cultivars of cassava.     

Expression of the oligomerization domain of the replication-associated protein (Rep) of Tomato leaf curl New Delhi virus interferes with DNA accumulation of heterologous geminiviruses

The minimal DNA binding domain of the replication-associated protein (Rep) of Tomato leaf curl New Delhi virus was determined by electrophoretic mobility gel shift analysis and co-purification assays. DNA binding activity maps to amino acids 1-160 (Rep-(1-160)) of the Rep protein and overlaps with the protein oligomerization domain. Transient expression of Rep protein (Rep-(1-160)) was found to inhibit homologous viral DNA accumulation by 70-86% in tobacco protoplasts and in Nicotiana benthamiana plants. The results obtained showed that expression of N-terminal sequences of Rep protein could efficiently interfere with DNA binding and oligomerization activities during virus infection. Surprisingly, this protein reduced accumulation of the African cassava mosaic virus, Pepper huasteco yellow vein virus and Potato yellow mosaic virus by 22-48%. electrophoretic mobility shift assays and co-purification studies showed that Rep-(1-160) did not bind with high affinity in vitro to the corresponding common region sequences of heterologous geminiviruses. However, Rep-(1-160) formed oligomers with the Rep proteins of the other geminiviruses. These data suggest that the regulation of virus accumulation may involve binding of the Rep to target DNA sequences and to the other Rep molecules during virus replication.