Transgenic manipulation of glutamine synthetase: A target with untapped potential in various aspects of crop improvement

Abstract

Glutamine synthetase (GS) plays a key role in the nitrogen (N) metabolism in higher plants. N is a major limiting nutrient in crop production, and most of it is lost due to volatilization or leaching which has deleterious effects on the environment. Hence, GS is considered a prime target for transgenic approaches to increase nitrogen use efficiency (NUE) which is paramount for sustainable agriculture. The current status of such attempts at increasing NUE utilizing GS, their outcomes, constraints, and future prospects have been discussed in detail. GS is also modulated by various abiotic stresses including salt and drought which have adverse effects on crop production. Modulation of GS by various abiotic stresses and transgenic approaches utilizing GS for tolerance, their results, limitations, and possibilities of further advancement have been reviewed. GS is also the target of the commonly used herbicide glufosinate (Basta). Herbicide-tolerant transgenic crops have become a necessity for modern agriculture, given the labor and expenditure involved in traditional weed control practices. In the light of public resentment and biosafety concerns of utilizing bacterial genes for herbicide tolerance in food crops, the overexpression of mutant GS enzymes as an alternative strategy for developing glufosinate-resistant crops has been discussed. This chapter also examines the inconsistent results of overexpression of GS genes for various applications in view of intricate regulation of GS due to its critical role in metabolism.