Abscisic acid-induced elevation of guard cell cytosolic Ca2+ precedes stomatal closure.

STOMATTA allow the diffusion of CO2 into the leaf for photosynthesis and the diffusion of H2O out of the leaf during transpiration1,2. This gaseous exchange is regulated by pairs of guard cells that surround each stomatal pore. During water stress the loss of water through transpiration is reduced in response to abscisic acid3, a naturally occurring plant growth regulator which is also present in certain mammals4, algae5 and fungi6, by the promotion of stomatal closure and inhibition of opening7. This involves alterations to guard cell turgor, causing the cells to shrink and thereby reducing the size of the stomatal pore. These changes are driven by cation and anion effluxes8. It has been proposed that an abscisic acid-dependent increase in the concentration of guard cell cytosolic free calcium triggers the intracellular machinery responsible for stomatal closure9(for a review, see ref. 10), but attempts to test this hypothesis by measuring [45Ca] fluxes have produced equivocal results11. Using the fluorescent calcium indicator fura-2, we report that abscisic acid induces a rapid increase in guard cell cytosolic free Ca2+ in Commelina communisL., and that this increase precedes stomatal closure. These results strongly support the suggestion that Ca2+ is an intracellular second messenger in this response

mRNA cap binding proteins: effects on abscisic acid signal transduction, mRNA processing, and microarray analyses.

International audienceThe plant hormone abscisic acid (ABA) intricately regulates a multitude of processes during plant growth and development. Recent studies have established a connection between genes participating in various steps of cellular RNA metabolism and the ABA signal transduction machinery. In this chapter we focus on the plant nuclear mRNA cap binding proteins, CBP20 and CBP80. We summarize and report recent findings on their effects on cellular signal transduction networks and mRNA processing events. ABA hypersensitive 1 (abh1) harbors a gene disruption in the Arabidopsis CBP80 gene. Loss-of-function mutation of ABH1 can also result in an early flowering phenotype in the Arabidopsis accession C24. abh1 revealed noncoding cis-natural antisense transcripts (cis-NATs) at the CONSTANS locus in wild-type plants with elevated cis-NAT expression in the mutant. abh1 also revealed an influence on the splicing of the MADS box transcription factor Flowering Locus C pre-mRNA, which may result in the regulation of flowering time. Furthermore, new experiments analyzing complementation of cpb20 with site-directed cpb20 mutants provide evidence that the CAP binding activity of CBP20 is essential for the observed cbp-associated phenotypes. In conclusion, mutants in genes participating in RNA processing provide excellent tools to uncover novel molecular mechanisms for the regulation of RNA metabolism and of signal transduction networks in wild-type plants