Genetic approaches towards overcoming water deficit in plants - special emphasis on LEAs

Abstract

Water deficit arises as a result of low temperature, salinity and dehydration, thereby affecting plant growth adversely and making it imperative for plants to surmount such situations by acclimatizing/adapting at various levels. Water deficit stress results in significant changes in gene expression, mediated by interconnected signal transduction pathways that may be triggered by calcium, and regulated via ABA dependent and/or independent pathways. Hence, adaptation of plants to such stresses involves maintaining cellular homeostasis, detoxification of harmful elements and also growth alterations. Stress in general cause excess production of reactive oxygen species (ROS) and the plants overcome the same by either preventing the accumulation of ROS or by eliminating the ROS formed. Ion homeostasis includes processes such as cellular uptake, sequestration and export in conjunction with long distance transport. Requisite amounts of osmolytes are hence synthesized under stress to maintain turgor along with maintaining the macromolecular structures and also for scavenging ROS. Another noteworthy response is the accumulation of novel proteins, including enzymes involved in the biosynthesis of osmoprotectants, heat-shock proteins (HSPs), late embryogenesis abundant (LEA) proteins, antifreeze proteins, chaperones, detoxification enzymes, transcription factors, kinases and phosphatases. The LEAs belong to a redundant protein family and are highly hydrophilic, boiling-soluble, non-globular and therefore have been defined and classified accordingly. The precise function of LEAs is still unknown, but substantial evidence indicates their involvement in dessication tolerance as the expression of LEAs confers increased resistance to stress in heterologous yeast system and also significantly improves water deficit tolerance in transgenic plants. Genetic manipulation of plants towards conferring abiotic stress tolerance is a daunting task, as the abiotic stress tolerance mechanism is highly complex and various strategies have been exploited to address and evaluate the stress tolerance mechanism, and the molecular responses to water deficit via complex signaling networks. Genomic technologies have recently been useful in integrating the multigenicity of the plant stress responses through, transcriptomics, proteomics and metabolite profilling and their interactions. This review deals with the recent developments on genetic approaches for water stress tolerance in plants, with special emphasis on LEAs.

Overexpression of dehydrin tas14 gene improves the osmotic stress imposed by drought and salinity in tomato

“…Thus, in order to elucidate the role of AtNHX1 antiporter, Leidi et al (2010) carried out a very important study, finally demonstrating that tomato plants overexpressing AtNHX1 had larger K + accumulations in the vacuole in all growth conditions tested, but no consistent enhancement of Na + accumulation, as previously suggested (Pardo et al, 2006). A strategy to increase the level of drought and salinity tolerance is the transfer of genes codifying different types of proteins involved in the molecular responses to abiotic stress, such as osmoprotectants, chaperones, detoxification enzymes, transcription factors, signal transduction proteins (kinases and phosphatases), heatshock proteins (HSPs), and late-embryogenesis-abundant (LEA) proteins (Campalans et al, 1999;Capiati et al, 2006;Khurana et al, 2008;Orsini et al, 2010;Amudha and Balasubramani, 2011).…”

“…This group of very hydrophilic proteins markedly increase during water deficit and/or low temperature stress in vegetative organs, suggesting a protective role during water limitation (Bies-Etheve et al, 2008;Popelka et al, 2010), although their precise functions and mechanisms of action are still hidden even after twenty years of their discovery (Battaglia et al, 2008;Khurana et al, 2008).…”

Transcriptome Profiling of Dehydration Stress in the Chinese Cabbage (Brassica rapa L. ssp. pekinensis) by Tag Sequencing

“…They included enzymes involved in protein degradation, water channel proteins, protease inhibitors, LEA proteins, cytochrome P450, plasma membrane aquaporins, heat shock proteins, lipid transfer proteins, and plant defense-related genes. LEA proteins may function in protecting macromolecules, such as enzymes, protein complexes, and membranes (Wang et al 2003;Khurana et al 2008;George and Parida 2010). Water channel proteins are thought to function in the transport of water through plasma membranes and tonoplasts to adjust the osmotic pressure (Sakurai et al 2005;Zhang et al 2007).…”

Wsi18 promoter from wild rice genotype, Oryza nivara, shows enhanced expression under soil water stress in contrast to elite cultivar, IR20

“…ABRE has been identified as a major cis-acting element in the promoters of several ABA-inducible genes of plants such as the cotton LEA gene D-113 (Luo et al 2008). The bZIP transcription factors AREB/ABF can bind to ABRE and activate the stress responsive gene expression in an ABAdependent manner (Choi et al 2000;Khurana et al 2008). Similarly, the AP2 transcription factors DREB/CBF are reported to specifically bind to another important cis-element DRE and assisted in the regulated expression of the downstream stress-responsive genes during dehydration stress in an ABA-independent manner (Agarwal et al 2006;Mizoi et al 2012).…”