Trends in Plant Science
Volume 6, Issue 6, 1 June 2001, Pages 262-267
Journal home page for Trends in Plant Science

Review
Abiotic stress signalling pathways: specificity and cross-talk

https://doi.org/10.1016/S1360-1385(01)01946-XGet rights and content

Abstract

Plants exhibit a variety of responses to abiotic stresses that enable them to tolerate and survive adverse conditions. As we learn more about the signalling pathways leading to these responses, it is becoming clear that they constitute a network that is interconnected at many levels. In this article, we discuss the ‘cross-talk’ between different signalling pathways and question whether there are any truly specific abiotic stress signalling responses.

Section snippets

Cross-talk

When stress signalling pathways are examined in the laboratory, they are usually considered in isolation from other stresses to simplify interpretation. In nature, however, the plant encounters stress combinations concurrently or separated temporally and must present an integrated response to them. In the case of phytochrome signalling, the two pathways leading to red-light-induced CHS and CAB gene expression negatively regulate flux through one another1, 2. Seemingly separate abiotic stress

Specificity

In spite of considerable overlap between many abiotic stress signalling pathways, there might, in some instances, be a benefit to producing specific, inducible and appropriate responses that result in a specific change suited to the particular stress conditions encountered. One advantage would be to avoid the high energy cost of producing stress-tolerance proteins, exemplified by the dwarf phenotype of plants constitutively overexpressing the frost tolerance protein DREB1A (Ref. 4). In some

Sensing systems

Specificity might occur at the point of initial stress perception itself. In the case of osmotic stress, the putative osmosensor AtHK1 (Ref. 6), a transmembrane histidine kinase, is thought to be the first component to relay changes in osmotic potential outside the cell to the transduction pathway(s) inside the cell that regulates drought-inducible gene expression. If specific stresses are actually sensed by dedicated receptor molecules, these molecules themselves have the potential to encode

Calcium

The precise kinetics, magnitude and cellular source of stimulus-induced [Ca2+]cyt elevations (the ‘calcium signature’) have been proposed to encode information about the particular stimulus, and to determine the specific end response elicited14. Biphasic elevations, responses lasting from two seconds to tens of minutes and repeated oscillations are among the responses observed after abiotic stress.

Studies using animal cells showed that the Ca2+-induced activation of particular transcription

Calcium-regulated proteins

[Ca2+]cyt elevations achieve control of various processes via Ca2+-regulated effector proteins. Sometimes referred to as ‘calcium sensors’, these include calmodulin, calcium-dependent protein kinases (CDPKs) and calcium-regulated phosphatases. Calmodulin has been implicated in plant responses to cold25, mechanical stimulation25, 26 and oxidative stress27. The use of different isoforms could be involved in control of specificity between these pathways, as has been observed with calmodulin

MAPK cascades

MAPK cascades are activated by numerous abiotic stresses43 but they can introduce specificity into the system. A MAPK kinase kinase (MAPKKK) phosphorylates a MAPK kinase (MAPKK), which in turn phosphorylates a MAPK. Three major types of MAPKKK have been identified in Arabidopsis: CTR1, ANP1-3 and the AtMEKK class. AtMEKK1 (Ref. 44) is expressed in response to abiotic stresses including cold, drought and mechanical stimulation. Of six target MAPKs, only two (AtMPK3 and AtMPK6) showed evidence of

Transcription factors

Low positive temperatures increase the level of freezing tolerance in many plant species through cold acclimation49, but this state can also be achieved in response to drought or by application of the phytohormone ABA (Ref. 50). Many genes that are induced by cold are also induced by drought or ABA (Ref. 51), probably because many cold-inducible genes encode proteins to protect the plant from the consequences of freezing stress, which include dehydration. The gene RD29A (also known as LTI78 or

Perspectives

Studying abiotic stress signalling pathways in isolation is valuable but it can be misleading because they form part of complex networks. In future, the onus will be on taking this fact into account, both intellectually and in terms of technology development. A perfect example of this is the availability of microarray technology. This enables researchers to examine the expression of not only all their particular stress-induced genes of interest but also thousands of others, without prejudice

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