Cross-talk between abscisic acid-dependent and abscisic acid-independent pathways during abiotic stress

Abstract

Salinity, drought and low temperature are the common forms of abiotic stress encountered by land plants. To cope with these adverse environmental factors, plants execute several physiological and metabolic responses. Both osmotic stress (elicited by water deficit or high salt) and cold stress increase the endogenous level of the phytohormone abscisic acid (ABA). ABA-dependent stomatal closure to reduce water loss is associated with small signaling molecules like nitric oxide, reactive oxygen species and cytosolic free calcium, and mediated by rapidly altering ion fluxes in guard cells. ABA also triggers the expression of osmotic stress-responsive (OR) genes, which usually contain single/multiple copies of cis-acting sequence called abscisic acid-responsive element (ABRE) in their upstream regions, mostly recognized by the basic leucine zipper-transcription factors (TFs), namely, ABA-responsive element-binding protein/ABA-binding factor. Another conserved sequence called the dehydration-responsive element (DRE)/C-repeat, responding to cold or osmotic stress, but not to ABA, occurs in some OR promoters, to which the DRE-binding protein/C-repeat-binding factor binds. In contrast, there are genes or TFs containing both DRE/CRT and ABRE, which can integrate input stimuli from salinity, drought, cold and ABA signaling pathways, thereby enabling cross-tolerance to multiple stresses. A strong candidate that mediates such cross-talk is calcium, which serves as a common second messenger for abiotic stress conditions and ABA. The present review highlights the involvement of both ABA-dependent and ABA-independent signaling components and their interaction or convergence in activating the stress genes. We restrict our discussion to salinity, drought and cold stress.

ABA Regulation of Plant Responses to Drought and Salt Stresses

“…Green characters represent the transcription regulatory circuit in response to stress conditions through an ABA-independent pathway. (Figure is modified from the following sources: Miyakawa et al 2013;Nakashima et al 2009;Roychoudhury et al 2013;Umezawa et al 2010). …”

“…The expression of stress-responsive genes will finally determine whether plants adapt and survive or succumb to the stressor. Both drought and high salinity induce the expression of osmotic stressresponsive (OR) genes, which are activated under stressful conditions but silent under normal conditions (Kawasaki et al 2001;Roychoudhury et al 2013;Seki et al 2001Seki et al , 2002. The ABA-responsive genes increased by drought and high salinity can be classified into two general groups.…”

“…More than 10 % of the arable land has suffered from drought and salinity, resulting in more than 50 % crop losses worldwide (Bray et al 2000;Roychoudhury et al 2013). Dry soil during a drought causes photosynthetic decline, which affects nutrient availability.…”

“…Salinity can result in physiological drought and ion toxicity (Zhu 2002). Most of the high salinity-inducible genes are also induced by drought, indicating extensive overlapping mechanisms between drought and salt stresses (Roychoudhury et al 2013). Both stresses can induce cellular dehydration, causing osmotic stress that triggers the biosynthesis and increases the endogenous levels of the phytohormone abscisic acid (ABA).…”

Hsp transcript induction is correlated with physiological changes under drought stress in Indian mustard

“…Drought-induced crop losses have a significant economic impact and are predicted to increase with global climate change (Roychoudhury et al 2013). As most of the abiotic stresses result in desiccation of the cell and osmotic imbalance, there is an overlap in the expression pattern of stress genes after cold, drought, high temperature, high salt and ABA treatment (Mahajan and Tuteja 2005).…”