FIERY1 encoding an inositol polyphosphate 1-phosphatase is a negative regulator of abscisic acid and stress signaling in Arabidopsis

Salt and drought stress signal transduction in plants

Salt and drought stress signal transduction consists of ionic and osmotic homeostasis signaling pathways, detoxification (i.e., damage control and repair) response pathways, and pathways for growth regulation. The ionic aspect of salt stress is signaled via the SOS pathway where a calcium-responsive SOS3-SOS2 protein kinase complex controls the expression and activity of ion transporters such as SOS1. Osmotic stress activates several protein kinases including mitogen-activated kinases, which may mediate osmotic homeostasis and/or detoxification responses. A number of phospholipid systems are activated by osmotic stress, generating a diverse array of messenger molecules, some of which may function upstream of the osmotic stress-activated protein kinases. Abscisic acid biosynthesis is regulated by osmotic stress at multiple steps. Both ABA-dependent and -independent osmotic stress signaling first modify constitutively expressed transcription factors, leading to the expression of early response transcriptional activators, which then activate downstream stress tolerance effector genes.

Plant hormone signaling: getting the message out

Molecular genetic analysis has identified a variety of molecules that are required for correct signaling of the plant hormone abscisic acid (ABA). It now appears that proteins involved in RNA metabolism also modulate the ABA response in Arabidopsis.

Modulation of abscisic acid signal transduction and biosynthesis by an Sm-like protein in Arabidopsis

The phytohormone abscisic acid (ABA) regulates plant growth and development as well as stress tolerance. The Arabidopsis sad1 (supersensitive to ABA and drought) mutation increases plant sensitivity to drought stress and ABA in seed germination, root growth, and the expression of some stress-responsive genes. sad1 plants are also defective in the positive feedback regulation of ABA biosynthesis genes by ABA and are impaired in drought stress induction of ABA biosynthesis. SAD1 encodes a polypeptide similar to multifunctional Sm-like snRNP proteins that are required for mRNA splicing, export, and degradation. These results suggest a critical role for mRNA metabolism in the control of ABA signaling as well as in the regulation of ABA homeostasis.

ABA signalling: a messenger's FIERY fate

There is considerable circumstantial evidence that the Ca(2+)-mobilizing second messenger IP(3) is involved in plant responses to the drought hormone abscisic acid. More direct evidence for this has now come from studies in which endogenous IP(3) levels have been manipulated in plants.