Influence of Ethylene Inhibitors and Ethrel on Production of Protocorm Like Bodies in Orchid-Dendrobium 'Sonia'

To increase the efficiency of production of protocorm like bodies, ethylene inhibitors like silver nitrate, salicylic acid and cobalt chloride at three concentrations, viz., 2, 5 and 20 μM and ethrel at 0.7, 1.4 and 14.0 μM were tested, by supplementing MS basal with BAP 4.44 μM. The explant used was fractionated protocorm like bodies (plb). Ethylene and methane gases evolved by the explant in the culture container were measured at 20 and 40 days after inoculation (DAI). Among various ethylene inhibitors tested, the maximum number of plb's were produced in media containing silver nitrate (5 μM), cobalt chloride (2 μM) and salicylic acid (20 μM). All ethrel treatments produced succulent, vitrified and deformed plb's. No ethylene evolution was observed in any of the ethylene inhibitor treatments. Only in ethrel treatments was evolution of ethylene observed. Methane evolution was observed in all the ethylene inhibitor treatments. Absolute amounts of methane evolved could not be related to the observed plb production. However, when the evolution of methane was more than 1 nano mole g-1 FW h-1, poor plb production was observed

Regulation of Plant Developmental Processes by a Novel Splicing Factor

Serine/arginine-rich (SR) proteins play important roles in constitutive and alternative splicing and other aspects of mRNA metabolism. We have previously isolated a unique plant SR protein (SR45) with atypical domain organization. However, the biological and molecular functions of this novel SR protein are not known. Here, we report biological and molecular functions of this protein. Using an in vitro splicing complementation assay, we showed that SR45 functions as an essential splicing factor. Furthermore, the alternative splicing pattern of transcripts of several other SR genes was altered in a mutant, sr45-1, suggesting that the observed phenotypic abnormalities in sr45-1 are likely due to altered levels of SR protein isoforms, which in turn modulate splicing of other pre-mRNAs. sr45-1 exhibited developmental abnormalities, including delayed flowering, narrow leaves and altered number of petals and stamens. The late flowering phenotype was observed under both long days and short days and was rescued by vernalization. FLC, a key flowering repressor, is up-regulated in sr45-1 demonstrating that SR45 influences the autonomous flowering pathway. Changes in the alternative splicing of SR genes and the phenotypic defects in the mutant were rescued by SR45 cDNA, further confirming that the observed defects in the mutant are due to the lack of SR45. These results indicate that SR45 is a novel plant-specific splicing factor that plays a crucial role in regulating developmental processes

Rapid report Extensive coupling of alternative splicing of pre-mRNAs of serine⁄arginine (SR) genes with nonsense-mediated decay

Summary • In Arabidopsis, pre-mRNAs encoding serine ⁄ arginine (SR) proteins, key regulators of constitutive and alternative splicing, are extensively alternatively spliced. In seedlings, 13 SR genes are alternatively spliced to generate 75 transcripts, of which 53 contain a premature termination codon (PTC). However, it is not known if any of the PTC-containing splice variants are the targets of nonsense-mediated decay (NMD) and if there is any link between NMD and the abundance of functional transcripts. • Here, we analyzed the abundances of all splice variants for each alternatively spliced gene in an Arabidopsis mutant that lacks UPF3, one of the core components of NMD machinery, to determine if the PTC-containing transcripts are degraded by NMD. • Our results show that about half of the 53 splice variants with a PTC are the targets of degradation by NMD. The accumulation of PTC-containing transcripts resulted in concomitant reduction in the amount of functional transcript. • These results show widespread coupling of alternative splicing with NMD in the SR gene family, suggesting a strong link between unproductive splicing and the abundance of functional transcripts

Differential response of tomato and tobacco to <i style="">Agrobacterium </i>mediated transformation with c<i style="">ytokinin independent -1</i> (<i style="">CKI-1</i>) gene as influenced by cytokinin levels

909-918Cytokinin independent-1 (CKI-1) gene was identified through its ability to confer cytokinin independent growth in Arabidopsis which has led to this gene being advocated as a selectable marker in plant transformation. Keeping this in view, CKI-1 gene was assessed as a selectable marker by transformation of tobacco (Nicotiana tabacum) and tomato (Lycopersicon esculentum L.). Overexpression of CKI-1 gene through Agrobacterium mediated transformation in tobacco and tomato conferred cytokinin independent shoot regeneration (in media devoid of cytokinin/plant growth regulators) in tobacco, but not in tomato wherein this ability (cytokinin independence) was conferred to T1 explants of CKI-1 transgenic tomato plant (T0) regenerated on cytokinin medium. Analysis of cytokinin levels revealed that cytokinin independent growth upon transformation with CKI-1 gene in tobacco (T0) and tomato (T1) was achieved through maintaining/regulating higher endogenous cytokinin levels and CKI-1 gene expression. Levels of CKI-1 transcripts assayed through quantitative RT-PCR suggested that there seemed to be a threshold level of endogenous cytokinin level, regulated due to external or internal supply via CKI-1 gene upto which CKI-1 gene expression correlated with endogenous cytokinin content and beyond that, either the gene expression was not induced or it remains same. With the incorporation of CKI-1 gene, it appeared that this threshold level of endogenous cytokinin might be reduced in crops like tomato to support shoot regeneration at lower concentration of cytokinin, but could not be made independent of external supply of cytokinin as in tobacco suggesting that use of CKI-1 gene as an effective alternate selection marker could not be universally applicable across the species. The results of the present study revealed that CKI-1 gene in addition to enhancing cytokinin levels, was also involved in contributing to the sensitivity to cytokinin and thus served as a positive regulator of cytokinin signal transduction

Isolation and characterization of mRNAs differentially expressed during ripening of mango fruits

533-537Mango, an important climacteric fruit crop with low shelf life, requires technologies to increase shelf life to reduce post harvest losses. During ripening of mango, the authors isolated five ripening related cDNAs from two mango varieties, Alphonso and Totapuri, using RT-PCR technique. The predicted polypeptides of five of these clones exhibit similarity to database protein sequences of PRL-1 protein, transcription initiation factor, CCR-4 protein, 18S ribosomal RNA gene and 23S ribosomal RNA gene. None of these proteins appear to be directly related to events generally associated with ripening such as cell wall metabolism or the accumulation of sugars and pigments or ethylene biosynthetic pathway. They are the regulatory elements/signals known to be involved during fruit ripening and may, therefore, be involved in regulating the expression of other genes directly associated with fruit ripening. The probable role of these proteins in mango fruit ripening needs to be elucidated further

Development of <i>Trichoderma harzianum</i> endochitinase gene construct conferring antifungal activity in transgenic tobacco

199-206Trichoderma harzianum is a popular biocontrol agent used extensively against phytopathogenic fungi. The mode of action of this fungus is through secretion of cell wall degrading enzymes including chitinases. Thus, the chitinase genes isolated from T. harzianum have been successfully utilized in the production of transgenic plants with enhanced resistance to several fungi. The stringent rules of IPR necessitates that genes are cloned and constructs are developed from the local isolates of this fungus. In view of which full length chitinase gene was isolated and a construct was developed under the expression of constitutive promoter CaMV 35S for use in plant transformation. Expression of chitinase gene in transgenic tobacco plants was found to be higher as revealed by the endochitinase assay and relative quantitative RT-PCR. Its efficacy in inhibiting the fungal growth was also reported in vitro as well as in vivo in the detached leaves of tobacco transformants containing the gene. Thus, the development of T. harzianum chitinase gene construct (pIIHR-Th-Chit) would facilitate the exchange of the construct amongst researchers in the country for the development of fungus resistant transgenic plants