Biomedical subjects

D Sudhakar

Publications and source records attributed to D Sudhakar.

6 recordsLinked to original sources

PubMed2001

Expression of Arabidopsis GAI in transgenic rice represses multiple gibberellin responses.

Bioactive gibberellins (GAs) are essential endogenous regulators of plant growth. GA signaling is mediated via GAI, a nuclear member of the GRAS family of plant transcription factors. Previous experiments have suggested that GAI is a GA-derepressible repressor of plant growth. Here we test this hypothesis by examining the effects of the expression of Arabidopsis GAI in transgenic Basmati rice. High-level expression of GAI caused dwarfism and reduced GA responses, and the strength of this effect was correlated with the level of transgene expression. In particular, the expression of GAI abolished the GA-mediated induction of rice aleurone alpha-amylase activity, thus implicating GAI orthologs in the well-characterized cereal aleurone GA response. The GA derepressible repressor model predicts that high-level expression of GAI should confer dwarfism, and these observations are consistent with this prediction.

Arabidopsis↗

PubMed2000

The maize streak virus coat protein transcription unit exhibits tissue-specific expression in transgenic rice.

Maize streak geminivirus (MSV) is a single-stranded DNA virus that infects cereals and other grasses. A promoter region incorporating the MSV large intergenic region and movement protein gene sequence was ligated to the gus (beta-glucuronidase) reporter gene which replaced the virus coat protein (CP) gene. The CP promoter activity was analysed in transgenic rice plants (Oryza sativa L.) and was compared with that obtained in plants transformed with the gus gene downstream of the cauliflower mosaic virus (CaMV) 35S promoter. The MSV CP promoter activity varied in the five plant lines tested, but was always less than that of the CaMV promoter. Histochemistry showed that the MSV CP promoter was active in cells of regenerating callus but in regenerated plants it provided an expression pattern restricted to the vascular tissues of the root, stem, leaf and floral organs. Expression was highest in phloem-associated tissues of the vegetative organs and was absent from the tip and elongation region of seedling roots. Thus, the MSV CP promoter shows a degree of developmental regulation and can be used to confer tissue-specific expression in transgenic rice plants.

Journal Article↗

PubMed2000

Linear transgene constructs lacking vector backbone sequences generate low-copy-number transgenic plants with simple integration patterns.

Whole plasmids are used in both Agrobacterium-mediated transformation and direct DNA transfer, generally leading to the integration of vector backbone sequences into the host genome along with the transgene(s). This is undesirable, as vector backbone sequences often have negative effects on transgene or endogenous gene expression, and can promote transgene rearrangements. We, therefore, bombarded rice tissue with two constructs: a plasmid containing the bar gene, and a linear DNA fragment isolated from the same plasmid, corresponding to the minimal bar gene expression cassette (promoter, open reading frame and terminator). We recovered phosphinothricin-resistant plants from both experiments, showing that the selectable marker was efficiently expressed. Transformation with such constructs resulted in predominantly 'simple' integration events (one or two bands on Southern blots), producing low-copy-number transgenic plants with a low frequency of transgene rearrangements. Conversely, transformation with supercoiled or linearized whole plasmids generated plants with 'complex' integration patterns, that is, higher copy numbers and frequent transgene rearrangements. We monitored transgenic lines through to the R4 generation and observed no silencing in plants carrying minimal constructs. We also carried out experiments in which rice tissue was simultaneously bombarded with minimal linear hpt and gusA cassettes. We observed robust GUS activity in hygromycin-resistant plants, confirming co-expression of the selectable and nonselectable markers. Furthermore, the efficiency of cotransformation using minimal constructs was the same as that using supercoiled plasmid cointegrate vectors.

Acetyltransferases↗

PubMed1999

'Green revolution' genes encode mutant gibberellin response modulators.

World wheat grain yields increased substantially in the 1960s and 1970s because farmers rapidly adopted the new varieties and cultivation methods of the so-called 'green revolution'. The new varieties are shorter, increase grain yield at the expense of straw biomass, and are more resistant to damage by wind and rain. These wheats are short because they respond abnormally to the plant growth hormone gibberellin. This reduced response to gibberellin is conferred by mutant dwarfing alleles at one of two Reduced height-1 (Rht-B1 and Rht-D1) loci. Here we show that Rht-B1/Rht-D1 and maize dwarf-8 (d8) are orthologues of the Arabidopsis Gibberellin Insensitive (GAI) gene. These genes encode proteins that resemble nuclear transcription factors and contain an SH2-like domain, indicating that phosphotyrosine may participate in gibberellin signalling. Six different orthologous dwarfing mutant alleles encode proteins that are altered in a conserved amino-terminal gibberellin signalling domain. Transgenic rice plants containing a mutant GAI allele give reduced responses to gibberellin and are dwarfed, indicating that mutant GAI orthologues could be used to increase yield in a wide range of crop species.

Alleles↗

PubMed1998

Expression and immunolocalisation of the snowdrop lectin, GNA in transgenic rice plants.

Transgenic rice (Oryza sativa L.) plants generated through particle bombardment expressed high levels of an insecticidal protein (the snowdrop lectin, GNA) directed against sap-sucking insects. Engineered plants expressed GNA either constitutively or in a tissue specific manner, depending on the nature of the promoter used to drive expression of the gene. We used specific antibodies raised against GNA to localize its expression in phloem tissue in plants engineered with the rice sucrose synthase promoter driving GNA expression. We report here molecular, biochemical and immunological analyses for fifteen independently-derived transformants out of more than 200 plants we generated.

Gene Expression↗

PubMed1998

Expression of snowdrop lectin (GNA) in transgenic rice plants confers resistance to rice brown planthopper.

Snowdrop lectin (Galanthus nivalis agglutinin; GNA) has been shown previously to be toxic towards rice brown planthopper (Nilaparvata lugens; BPH) when administered in artificial diet. BPH feeds by phloem abstraction, and causes 'hopper burn', as well as being an important virus vector. To evaluate the potential of the gna gene to confer resistance towards BPH, transgenic rice (Oryza sativa L.) plants were produced, containing the gna gene in constructs where its expression was driven by a phloem-specific promoter (from the rice sucrose synthase RSs1 gene) and by a constitutive promoter (from the maize ubiquitin ubi1 gene). PCR and Southern analyses on DNA from these plants confirmed their transgenic status, and that the transgenes were transmitted to progeny after self-fertilization. Western blot analyses revealed expression of GNA at levels of up to 2.0% of total protein in some of the transgenic plants. GNA expression driven by the RSs1 promoter was tissue-specific, as shown by immunohistochemical localization of the protein in the non-lignified vascular tissue of transgenic plants. Insect bioassays and feeding studies showed that GNA expressed in the transgenic rice plants decreased survival and overall fecundity (production of offspring) of the insects, retarded insect development, and had a deterrent effect on BPH feeding. gna is the first transgene to exhibit insecticidal activity towards sap-sucking insects in an important cereal crop plant.

Animals↗