Showing papers by "Jitendra P. Khurana published in 2001"

OsIAA1, an Aux/IAA cDNA from rice, and changes in its expression as influenced by auxin and light.

Abstract: The Aux/IAA class of genes are rapidly induced by exogenous auxins and have been characterized extensively from many dicot species like Arabidopsis, Glycine max and Pisum sativum. We report here the isolation and characterization of rice (Oryza sativa L. subsp. Indica) OsIAA1 cDNA as a monocot member of the Aux/IAA gene family. The predicted amino acid sequence of OsIAA1 corresponds to a protein of ca. 26 kDa, which harbors all four characteristic domains known to be conserved in Aux/IAA proteins. The conservation of these Aux/IAA genes indicates that auxins have essentially a similar mode of action in monocots and dicots. Northern blot analysis revealed that the OsIAA1 transcript levels decrease in the excised coleoptile segments on auxin starvation, and the level is restored when auxin is supplemented; the increase in OsIAA1 transcript level was apparent within 15 to 30 min of auxin application. Auxin-induced OsIAA1 expression appears to be correlated with the elongation of excised coleoptile segments. In light-grown rice seedlings, OsIAA1 is preferentially expressed in roots and basal segment of the seedling, whereas in the etiolated rice seedlings, the OsIAA1 transcripts are most abundant in the coleoptile. A comparative analysis in light- and dark-grown seedling tissues indicates that the OsIAA1 transcript levels decrease on illumination.

Isolation and molecular characterization of the COP1 gene homolog from rice, Oryza sativa L. subsp. Indica var. Pusa Basmati 1.

Abstract: The COP1 (CONSTITUTIVE PHOTOMORPHOGENIC 1) gene has been identified earlier from dicot species namely Arabidopsis, tomato and pea. The protein encoded by this gene acts as a molecular switch that negatively regulates the transition from the skotomorphogenic to the photomorphogenic mode of plant development. We have isolated and characterized the COP1 homolog from a monocot species, i.e. rice (var. Pusa Basmati 1). All the functional domains (Zn-binding RING finger motif, coiled-coil region, WD-40 repeats, cytoplasmic/nuclear localization sequences and protein-protein interaction domains) that are known in the COP1 proteins from dicots are conserved in COP1 from rice as well. The transcript levels of COP1 vary in various tissues of the rice plant. These variations were found to be development-dependent and do not solely depend on the light conditions.

Molecular Genetic Analysis of Constitutively Photomorphogenic Mutants of Arabidopsis

Abstract: Light is one of the most important environmental signals that profoundly influence growth and development in plants all through their life cycle. Plants have thus evolved many diverse sensory photoreceptors that scan spectral regions of the solar spectrum essential for regulating photomorphogenic development. The family of red/far-red reversible phytochromes and the blue light-sensing cryptochromes and phototropin principally absorb radiation in the visible range; the latter class also perceives biologically active UV-A radiation (see Quail et al 1995, Cashmore et al 1999, Christie et al 1999, Khurana and Poff 1999). Some morphogenic responses, e.g. cotyledon curling and anthocyanin production, are also elicited by UV-B radiation but the identity of the receptors(s) remains elusive (see Stapleton 1992, Bharti and Khurana 1997). Among these sensory pigment systems, phytochromes are the best studied class primarily because they regulate important plant processes like onset of seed germination, inhibition of stem growth, cotyledon expansion and chloroplast development, and induction of flowering. Moreover, phytochrome was the first photosensory pigment identified in the 1950s (see Sage 1992 for a historical account). The phytochrome apoprotein is encoded by a multigene family in most species examined, but all of them harbor an open-chain tetrapyrrole chromophore towards the N-terminal region.

Genetic and molecular analysis of Arabidopsis thaliana (ecotype ‘Estland’) transformed with Agrobacterium

Abstract: Agrobacterium-mediated transformation of Arabidopsis, ecotype ‘Estland’, was established from root explants using kanamycin selection. Continuous light during callus and shoot induction phases was promotive for shoot regeneration, as compared to light/dark cycles. Use of optimized conditions for transformation led to the formation of kanamycin-resistant calluses (up to 77%) and transformed plantlets at a frequency of up to 45%. Southern analysis showed the presence of 1.2. or more T-DNA inserts in 33%, 50%, and 17% of the primary transformants, respectively. Mendelian, as well as non-Mendelian, inheritance patterns were obtained upon screening the progeny (T1) of various transformants for the expression of gus and nptII genes; the analysis of some of these transformants at the molecular level also corroborated the Mendelian inheritance pattern. Moreover, genotypes of the T1 progeny could be predicted on the basis of T2 progeny analysis.

Mechanism of Regulation of Gene Expression for Chloroplast Proteins

Abstract: Both plastid- and nuclear-encoded proteins are involved in photosynthetic reactions carried out by chloroplasts While the structure of various plastome-encoded photosynthesis-related genes has been worked out, little is known about the mechanism of regulation of gene expression which is responsible for differentiation of chloroplasts At the same time, several signal cascades have been worked out in animals and plants for regulation of nuclear gene expression The aim of the present investigation was to study regulation of plastid and nuclear-encoded photosynthesis-related genes at steady-state mRNA level as influenced by light and development Earlier, we have reported an interaction of light and developmental (temporal and spatial) cues in establishing steady-state transcript levels of photosynthesis-related genes in rice (Grover et al 1998, 1999a, Kapoor et al 1993, 1994) and Arabidopsis (Grover et al 1999b, Jain et al 1998, Kochhar et al 1996) In this article, a summary of these results along with the new information about the signal transduction, the level of gene regulation and promoter analysis, and the progress made towards developing a plastid transformation system for rice has been presented