Faculty Member

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Specialization

Biochemistry, Molecular Biology, Genetic Engineering & Biotechnology

Current Research Programme

A. Molecular Biology of Pathogenic Yeast Candida albicans

We are working in the area of molecular biology of pathogenic yeast using Candida albicans as a model system with an aim to understand the nature of virulent factors associated with the medically important yeast. Candida albicans, is the most pathogenic of Candida species. It is a serious agent of infection particularly in immuno compromised patients. The delicate balance between the host and the otherwise normally commensally fungus, turn into a parasitic relationship, resulting in the development of infection is called candidiasis. It is believed that for C. albicans to become invasive, a change from yeast to hypha is important. Yeast to hypha conversion occurs through an intermediate germ tube stage. The germ tube leads to hyphae formation. N-acetylglucosamine (GlcNAc) is utilized by the pathogenic strains of C. albicans. GlcNAc also induces change in cellular morphology in C. albicans. Morphogenetic changes like hyphae and pseudohyphal growth enables to propagate into the host tissue as a preliminary manifestation of invasion and spread of pathogens. To elucidate the role of GlcNAc in pathogen city, NAG1 has been cloned in our laboratory. GlcNAc transcriptionally induces NAG1. Sequence analysis of a 4 kb genomic clone containing NAG1 indicates that this gene is part of a cluster containing two other genes of the GlcNAc catabolic pathway: DAC1 (GlcNAc-6- phosphate deacetylase) and HXK1 (GlcNAc kinase). Clusters of functionally related genes are general features of prokaryotes and are less prevalent in eukaryotes. In E. coli the amino sugar pathway genes are also organized in clusters and possibly have a common regulatory mechanism. This is the first report of a gene cluster in Candida (Proc. Natl. Acad. Sci, USA 97: 14218-14223, 2000). Interestingly, attenuation of virulence occurs by disruption of this pathway (Infection and Immunity, 69 (12), 7898-7903, 2001).

B. Crop Improvement Program.

I. Nutritional improvement of crop plants by expressing a seed albumin gene from Amaranthus hypochondriacus.

In our laboratory, we have been working on crop improvement program for last couple of years (Proc. Natl. Acad. Sci, USA107 (41): 17533-8, 2010). .In order to develop transgenic crop plants with high nutritional value, a seed albumin gene (AmA1) encoding for a protein of high lysine and sulfur containing amino acids from amaranth seeds has been cloned and sequenced. [Raina A and Datta A. Proc. Natl. Acad. Sci. USA 89:11774-11778, 1992]. Very recently, the AmA1 gene has been introduced into potato plants. The expression of AmA1 in transgenic plants, both constitutively and tuber-specifically, resulted in a significant increase in growth and tuber yield besides an increase in most essential amino acids. The transgenic tubers also contained more total protein as compared to control potato tubers (Proc. Natl. Acad. Sci. USA 97: 3724-3729, 2000]. Field trial of India's first GM crop (GM potato) with high nutritional value is now over in collaboration with the Central Potato Research Institute (CPRI). In addition, the technology in the industrial processing of animal feed supplement using yeast cells expressing AmA1 protein, has been transferred to Cadila Pharmaceuticals for commercial production.

II. Expression of oxalate decarboxylase reduces the accumulation of oxalic acid in crop plants and confers fungal resistance.

Some green leafy vegetables (e.g. amaranth, spinach, rhubarb) are rich sources of vitamins and minerals but they contain oxalic acid as a nutritional stress factor because oxalate chelates calcium and precipitation of calcium oxalate in kidney leads to hyperoxaluria and destruction of renal tissues. In addition, the production of oxalic acid is an important attacking mechanism utilized by several phytopathogenic fungi, e.g. Sclerotinia sclerotiorum, Sclerotinia rolfsii, and Sclerotinia ceptivorum. In order to develop transgenic plants with low oxalic content and making them resistant to fungal infection, a DNA (OXDC) encoding oxalate decarboxylase fromCollybia velutipes has been isolated and sequenced [Mehta A and Datta A. J. Biol. Chem.266: 23548-23553, 1991].

Very recently, oxalate-free transgenic tobacco and tomato plants have been developed which are resistant to phytopathogenic fungus Sclerotinia sclerotiorum (J. Biol. Chem.275: 7230-7238, 2000). Oxalate- free GM tomatoes resistant to pathogenic fungus are currently under field trial.

III. Enhanced self life in fruit by using novel genes which are involved in fruit ripening.

In a globalized economy the control of fruit ripening is of strategic importance because excessive softening limits shelf-life. The determining factor in the post-harvest deterioration of fruits and vegetables is the rate of softening, which influence shelf life and limits transportation and storage. Thus, softening and subsequent spoilage in these crops need to be controlled for extension of shelf-life and effective preservation. In this context, two novel genes, namely α-D-mannosidase and β-hexosaminidase have been cloned and sequenced. Silencing these genes in tomato  (climacteric) and capsicum (non-climacteric) has given the desired result [(PNAS, USA 107, 4213-4218 (2010); J. Expt. Botany, 62 (2): 571-82(2011)]

IV. Expression a single gene leads to many benefits.

In recent years, development of transgenic crops with multiple desirable traits such as drought tolerance pathogen resistance and nutritional quality has emerged as an important area in the field of biotechnology. Introduction of several traits in a crop requires manipulation of more than one gene. We reported improved drought tolerance and fungal resistance along with the increased iron and polyunsaturated fatty acid content in tomato by expressing a single gene encoding C-5 sterol desaturase (FvC5SD) from an edible fungus Flammulina velutipes (Scientific Reports (Nature publication) 2: 951 (2012),  Nature Protocols. Protocol Exchange doi:10.103
/protex. 2012.061 (2012)]