Characterization of contrasting rice (Oryza sativa L.) genotypes reveals the Pi-efficient schema for phosphate starvation tolerance.

BACKGROUND: Phosphorus (P), being one of the essential components of nucleic acids, cell membranes and enzymes, indispensable for diverse cellular processes like photosynthesis/carbohydrate metabolism, energy production, redox homeostasis and signaling. Crop yield is severely affected due to Phosphate (Pi) deficiency; and to cope with Pi-deficiency, plants have evolved several strategies. Some rice genotypes are compatible with low Pi availability, whereas others are sensitive to Pi deficiency. However, the underlying molecular mechanism for low Pi tolerance remains largely unexplored. RESULT: Several studies were carried out to understand Pi-deficiency responses in rice at seedling stage, but few of them targeted molecular aspects/responses of Pi-starvation at the advanced stage of growth. To delineate the molecular mechanisms for low Pi tolerance, a pair of contrasting rice (Oryza sativa L.) genotypes [viz. Pusa-44 (Pi-deficiency sensitive) and its near isogenic line (NIL-23, Pi-deficiency tolerant) harboring Phosphorus uptake 1 (Pup1) QTL from an aus landrace Kasalath] were used. Comparative morphological, physiological, and biochemical analyses confirmed some of the well-known findings. Transcriptome analysis of shoot and root tissues from 45-day-old rice plants grown hydroponically under P-sufficient (16 ppm Pi) or P-starved (0 ppm Pi) medium revealed that Pi-starvation stress causes global transcriptional reprogramming affecting several transcription factors, signaling pathways and other regulatory genes. We could identify several significantly up-regulated genes in roots of NIL-23 under Pi-starvation which might be responsible for the Pi starvation tolerance. Pathway enrichment analysis indicated significant role of certain phosphatases, transporters, transcription factors, carbohydrate metabolism, hormone-signaling, and epigenetic processes in improving P-starvation stress tolerance in NIL-23. CONCLUSION: We report the important candidate mechanisms for Pi acquisition/solubilization, recycling, remobilization/transport, sensing/signalling, genetic/epigenetic regulation, and cell wall structural changes to be responsible for P-starvation tolerance in NIL-23. The study provides some of the novel information useful for improving phosphorus-use efficiency in rice cultivars.

Morphological and molecular changes on cytoplasmic male sterility (CMS) introgression in Asiatic carrot (Daucus carota L.).

MAIN CONCLUSION: 'Petaloid' cytoplasmic male sterility is commonly used as a stable genetic mechanism in carrot hybrid breeding. Its introgression in tropical carrot showed morphometric changes and molecular markers were identified for detection at early stage. Cytoplasmic male sterility (CMS) is the only genetic mechanism in carrot for commercial exploitation of heterosis and production of low cost affordable hybrid seeds. The 'petaloid' CMS system is stable and commonly used in hybrid breeding in temperate carrot but there is no information available on existence of natural CMS system in tropical Asiatic carrot. Therefore, the present study was aimed to investigate morphometric traits and organizational features of cytoplasmic atp9 gene sequences in newly converted CMS lines (BC4-7) of tropical carrot. The CMS lines had root traits at par with fertile counterparts while floral traits had variation. Petal colour and length, petaloids colour and shape and style length showed differences among the CMS lines and with their maintainers. Molecular markers are effective to establish male sterility at genetic level, for this, six fixed and stable CMS lines were screened with seven novel primer combinations. Out of which five pairs produced clearly distinguishable bands in CMS lines and their fertile counterparts. The study confirmed that the region between 3' end of atp9-1/atp9-3 gene and 5' end of region of homology to Arabidopsis thaliana mtDNA is ideal for developing the trait specific markers. These new CMS lines have potential to use in hybrid development and molecular markers will be useful to confirm male sterility to rogue out fertile plants.

Molecular cloning, overexpression, purification, crystallization and preliminary X-ray diffraction studies of histidinol phosphate aminotransferase (HisC2) from Mycobacterium tuberculosis.

HisC2 from Mycobacterium tuberculosis was overexpressed in M. smegmatis and purified to homogeneity using nickel-nitrilotriacetic acid metal-affinity and gel-filtration chromatography. Diffraction-quality crystals were grown using the hanging-drop vapour-diffusion technique from a condition consisting of 7 mg ml(-1) HisC2 (in 20 mM Tris pH 8.8, 50 mM NaCl and 5% glycerol), 1 M succinic acid pH 7.0, 0.1 M HEPES pH 7.0 and 1%(w/v) polyethylene glycol monomethyl ether 2000. The crystals belonged to the orthorhombic space group P2(1)2(1)2, with unit-cell parameters a = 255.98, b=77.09, c = 117.97 Å. X-ray diffraction data were recorded to 2.45 Å resolution from a single crystal using the in-house X-ray facility.