Genetic Engineering for Enhancing Abiotic Stress Tolerance

Abstract

A major factor, which reduces the potential yield of legume crops very significantly, is their sensitivity to abiotic stresses, e.g. drought, flooding, heavy metals, high and low temperature, salinity, alkalinity and acidity of the soil, ozone and UV-irradiations, etc. Stress signals are perceived by the plants and their transduction within the cellular compartments can modulate the gene expression leading to the synthesis and build up of the strategic biomolecules which help the plants to develop stress tolerance. The signal perception involves membrane receptors. The perceived signal is further transduced into the cells by a change in the levels of intracellular signaling molecules known as secondary messengers. Certain protein-modifiers, scaffolds and adapters, etc. are also known to be involved in regulating the abiotic stress signals in plants as the signaling partners, which provide physical supports for the certain signaling events. Many stress responsive genes, promoters and transcription factors have been identified in the plants including the legumes. The transcription factors modulate the expression of a cascade of stress inducible genes to impart tolerance to the stressed plants. Several stress related proteins have been characterized in plants, which are involved in conferring the stress tolerance by various ways. Compatible solutes provide osmoprotection and scavenge free radicals generated during the stress. Anti-oxidative defense system is also induced during the various abiotic stresses, which provide a quick and efficient removal of toxic free radicals, e.g. reactive oxygen species (ROI). Recent studies indicate that the manipulation of specific key regulatory steps, singly or in combinations or by a cascade of genes using transcription factors through genetic engineering, can confer the stress tolerance in transgenic plants. Most of the studies, however, are related to model plants like Arabidopsis and Nicotiana which have many differences with legumes. Direct studies with legumes or a leguminous model plant like Lotus japonicus or Medicago truncatula can provide better insight to understand the complex interactions of abiotic stress signaling and tolerance mechanisms and strategic target points can be characterized to achieve stable stress tolerance to the abiotic stresses in legumes.