One of the approaches for understanding the functions of the genes predicted in the rice genome requires use of mutants. Mutations induced in a given genetic background provide opportunities to assign function to a given gene with a minimum of background genetic noise. This paper describes generation and initial characterization of a large set of Ethyl Methane Sulphonate (EMS) induced mutants in the upland rice variety Nagina22, through a National Initiative involving six Research Institutes namely National Research Centre on Plant Biotechnology, New Delhi; Indian Agricultural Research Institute, New Delhi; Tamil Nadu Agricultural University, Coimbatore; Directorate of Rice Research, Hyderabad; University of Agricultural Sciences, Bangalore and Punjab Agricultural University, Ludhiana, funded by the Department of Biotechnology (DBT), Government of India. The uniqueness of this collaborative effort is phenotyping for a range of traits that has led to identification of mutants for plant growth and architecture, flowering, maturity, grain number, shape and size, yield, phosphorus use efficiency, resistance to blast and bacterial leaf blight diseases, and tolerance to drought, salinity and herbicide. A set of 22, 292 mutagenised lines generated under this initiative and phenotyped for the traits enlisted above has resulted in the isolation of a few promising mutants which are being characterized. Shortly, these mutants will be registered and made available to the researchers in the country for use in studies in rice genetics, breeding and functional genomics. The mutant stock is expected to serve as a national resource for understanding rice biology as well as for use in genetic improvement of the crop.

The mammalian heme peroxidases are distinguished from their plant and fungal counterparts by the fact that the heme group is covalently bound to the protein through ester links from glutamate and aspartate residues to the heme 1- and 5-methyl groups and, in the case of myeloperoxidase, through an additional sulfonium link from the Cbeta of the 2-vinyl group to a methionine residue. To duplicate the sulfonium link in myeloperoxidase and to obtain information on its mechanism of formation, we have engineered a methionine residue close to the 2-vinyl group in recombinant pea cytosolic ascorbate peroxidase (rpAPX) by replacement of Ser160 by Met (S160M variant). The S160M variant is isolated from Escherichia coli as apo-protein. Reconstitution of apo-S160M with exogenous heme gives a red protein (S160M(R)) which has UV-visible (lambda(max)/nm = 407, 511, 633) and steady-state kinetic (kcat = 156 +/- 7 s(-1), KM = 102 +/- 15 microM) properties that are analogous to those of rpAPX. The reaction of S160M(R) with H2O2 gives a green protein (S160M(G)). Electronic spectroscopy, mass spectrometry, and HPLC analyses are consistent with the formation of a covalent linkage between the methionine residue and the heme vinyl group in S160M(G). Single-wavelength and photodiode array stopped-flow kinetic analyses identify a transient Compound I species as a reaction intermediate. The results provide the first direct evidence that covalent heme linkage formation occurs as an H2O2-dependent process that involves Compound I formation. A mechanism that is consistent with the data is presented.

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Water stress is a serious challenge to rice production. Understanding water stress tolerance is essential for precise trait modification. We identified an EMS induced mutant showing enhanced tolerance to water deficit stress at the vegetative stage. Multiple alterations in physiological behaviour, root morphological and anatomical structure, stomatal response and gene expression in various signalling pathways were found to be responsible for increased tolerance in the mutant. The mutant will be useful for dissecting the water stress tolerance mechanism in rice.

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Dwarf plant height and tillering ability are two of the most important agronomic traits that determine the plant architecture, and have profound influence on grain yield in rice. To understand the molecular mechanism controlling these two traits, an EMS-induced recessive dwarf and increased tillering1 (dit1) mutant was characterized. The mutant showed proportionate reduction in each internode as compared to wild type revealing that it belonged to the category of dn-type of dwarf mutants. Besides, exogenous application of GA3 and 24-epibrassinolide, did not have any effect on the phenotype of the mutant. The gene was mapped on the long arm of chromosome 4, identified through positional candidate approach and verified by cosegregation analysis. It was found to encode carotenoid cleavage dioxygenase7 (CCD7) and identified as an allele of htd1. The mutant carried substitution of two nucleotides CC to AA in the sixth exon of the gene that resulted in substitution of serine by a stop codon in the mutant, and thus formation of a truncated protein, unlike amino acid substitution event in htd1. The new allele will facilitate further functional characterization of this gene, which may lead to unfolding of newer signalling pathways involving plant development and architecture.

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