Role of the Putative Osmosensor Arabidopsis Histidine Kinase1 in Dehydration Avoidance and Low-Water-Potential Response    

Abstract

The molecular basis of plant osmosensing remains unknown. Arabidopsis (Arabidopsis thaliana) Histidine Kinase1 (AHK1) can complement the osmosensitivity of yeast (Saccharomyces cerevisiae) osmosensor mutants lacking Synthetic Lethal of N-end rule1 and SH3-containing Osmosensor and has been proposed to act as a plant osmosensor. We found that ahk1 mutants in either the Arabidopsis Nossen-0 or Columbia-0 background had increased stomatal density and stomatal index consistent with greater transpirational water loss. However, the growth of ahk1 mutants was not more sensitive to controlled moderate low water potential (c w ) or to salt stress. Also, ahk1 mutants had increased, rather than reduced, solute accumulation across a range of low c w severities. ahk1 mutants had reduced low c w induction of D 1 -Pyrroline-5-Carboxylate Synthetase1 (P5CS1) and 9-cisEpoxycarotenoid Dioxygenase3, which encode rate-limiting enzymes in proline and abscisic acid (ABA) synthesis, respectively. However, neither Pro nor ABA accumulation was reduced in ahk1 mutants at low c w . P5CS1 protein level was not reduced in ahk1 mutants. This indicated that proline accumulation was regulated in part by posttranscriptional control of P5CS1 that was not affected by AHK1. Expression of AHK1 itself was reduced by low c w , in contrast to previous reports. These results define a role of AHK1 in controlling stomatal density and the transcription of stress-responsive genes. These phenotypes may be mediated in part by reduced ABA sensitivity. More rapid transpiration and water depletion can also explain the previously reported sensitivity of ahk1 to uncontrolled soil drying. The unimpaired growth, ABA, proline, and solute accumulation of ahk1 mutants at low c w suggest that AHK1 may not be the main plant osmosensor required for low c w tolerance.

The natural and social history of the indigenous lands and protected areas corridor of the Xingu River basin

“…Declining cell volume may trigger signals via sensors within the cytoskeleton, or the cell membrane (i.e. sensors of membrane tension, of membrane protein distances, of the increase of specific ions or metabolites), or at the interface of cell membrane and cell wall (Christmann et al, 2013;Kumar et al, 2013;Haswell and Verslues, 2015;Pandey, 2017). These proteins may directly sense negative effects on processes or structures threatened by cell volume shrinkage, such as the cytoskeleton, membrane-cell wall contacts, or ion transport, even before detrimental biochemical effects arise (Oliver, 1996;Zhang et al, 2001;Pandey 2017).…”

ABA Regulation of the Cold Stress Response in Plants

“…In Arabidopsis, the cytokinin receptor histidine kinases AHK2, AHK3, and CRE1 have been shown to play important roles in the regulation of plant abiotic responses in both ABA-dependent and ABA-independent signalling pathways (Tran et al 2007); on the other hand, the homologous gene AHK1 was identified as an osmotic stress sensor that positively regulates abiotic stress (Wohlbach et al 2008;Kumar et al 2013;Tran et al 2007). Increasing evidence suggests a negative role for cytokinin signalling in cold-and ABA-mediated abiotic stress.…”

Phosphoproteomic Analyses Reveal Early Signaling Events in the Osmotic Stress Response

“…The osmotic stress response is initiated by two yeast transmembrane osmosensors that act upstream of a mitogen-activated protein kinase (MAPK) signaling cascade to control gene expression in the Hog1 (for high-osmolality glycerol response1) signaling pathway (Hohmann, 2002). There is evidence to suggest that a similar pathway may be present in plants (Urao et al, 1999;Tran et al, 2007;Wohlbach et al, 2008;Kumar et al, 2013), and MAPK phosphorylation likely plays an important role in the osmotic stress response, as MAPK cascades are known to regulate several abiotic and biotic stress response pathways (Rodriguez et al, 2010).…”