ABI1 and ABI2 encode PP2C-type protein phosphatases and are thought to negatively regulate many aspects of abscisic acid (ABA) signaling, including stomatal closure in Arabidopsis. In contrast, SRK2E/OST1/SnRK2.6 encodes an Arabidopsis SnRK2 protein kinase and acts as a positive regulator in the ABA-induced stomatal closure. SRK2E/OST1 is activated by osmotic stress as well as by ABA, but the independence of the two activation processes has not yet been determined. Additionally, interaction between SRK2E/OST1 and PP2C-type phosphatases (ABI1 and ABI2) is not understood. In the present study, we demonstrated that the abi1-1 mutation, but not the abi2-1 mutation, strongly inhibited ABA-dependent SRK2E/OST1 activation. In contrast, osmotic stress activated SRK2E/OST1 even in abi1-1 and aba2-1 plants. The C-terminal regulatory domain of SRK2E/OST1 was required for its activation by both ABA and osmotic stress in Arabidopsis. The C-terminal domain was functionally divided into Domains I and II. Domain II was required only for the ABA-dependent activation of SRK2E/OST1, whereas Domain I was responsible for the ABA-independent activation. Full-length SRK2E/OST1 completely complemented the wilty phenotype of the srk2e mutant, but SRK2E/OST1 lacking Domain II did not. Domain II interacted with the ABI1 protein in a yeast two-hybrid assay. Our results suggested that the direct interaction between SRK2E/OST1 and ABI1 through Domain II plays a critical role in the control of stomatal closure.

The C10-C18 unsaturated, acyclic, aliphatic compounds that contain an oxygenated functional group (alcohol, aldehyde, or acetate ester) are a major class of sex pheromones produced by female moths. In the biosynthesis of these pheromone components, the key enzyme required to produce the oxygenated functional groups is fatty-acyl reductase (FAR). This enzyme converts fatty-acyl pheromone precursors to their corresponding alcohols, which, depending on the moth species, can then be acetylated or oxidized to the corresponding aldehydes. Despite the significant role this enzyme has in generating the species-specific oxygenated constituents of lepidopteran sex pheromones, the enzyme has yet to be fully characterized and identified. In experiments designed to characterize a pheromone-gland-specific FAR in the silkmoth, Bombyx mori, we have isolated a cDNA clone encoding a protein homologous to a FAR from the desert shrub, Simmondsia chinensis, commonly known as jojoba. The deduced amino acid sequence of this clone predicts a 460-aa protein with a consensus NAD(P)H binding motif within the amino terminus. Northern blot analysis indicated that 2-kb transcripts of this gene were specifically expressed in the pheromone gland at 1 day before adult eclosion. Functional expression of this gene in the yeast Saccharomyces cerevisiae not only confirmed the long-chain FAR activity, but also indicated a distinct substrate specificity. Finally, the transformed yeast cells evoked typical mating behavior in male moths when cultured with the pheromone precursor fatty acid, (E,Z)-10,12-hexadecadienoic acid.

The female parasitic waspCotesia kariyai discriminated between the volatiles of corn leaves infested by younger host larvaePseudaletia separata (first to fourth instar) and uninfested leaves in a Y-tube olfactometer; the wasps were attracted to the infested leaves. In contrast, when corn plants were infested by the later stages (fifth and sixth instar) of the armyworm, the wasps did not distinguish between infested corn leaves and uninfested corn leaves in the olfactometer. Mechanically damaged leaves were no more attractive than undamaged leaves, and host larvae or their feces were not attractive to the parasitoid. Through chemical analysis, the herbivore-induced plant volatiles were identified in the headspace of infested corn leaves. The herbivore-induced volatiles (HIVs) constituted a larger proportion of the headspace of corn leaves infested by early instar armyworms than of corn leaves infested by late instar armyworms. Application of third-instar larval regurgitant onto artificially damaged sites of leaves resulted in emission of parasitoid attractants from the leaf, whereas leaves treated with sixth-instar regurgitant did not. The function of this herbivore-stage related specificity of herbivore-induced synomones is discussed in a tritrophic context.

SummaryPhospholipid metabolism is involved in plant responses to drought and salinity stress. To investigate the role of phospholipase D (PLD) and its product phosphatidic acid (PtdOH) in stress signalling, we isolated a novel PLD cDNA, designated AtPLDd, by screening a cDNA library prepared from dehydrated Arabidopsis thaliana. The AtPLDd protein, of 868 amino acids, has a putative catalytic domain and a C2 domain that is involved in Ca 2+ /phospholipid binding. The AtPLDd mRNA accumulated in response to dehydration and high salt stress. Histochemical analysis showed that the AtPLDd gene is strongly expressed in the vascular tissues of cotyledons and leaves under dehydration stress conditions. Under normal growth conditions, AtPLDd was expressed in roots, leaves, stems and¯owers but not in siliques. We showed that dehydration stimulates the accumulation of PtdOH. The accumulation of PtdOH in response to dehydration was signi®cantly suppressed in AtPLDd antisense transgenic plants. These results suggest that AtPLDd may be involved in PtdOH accumulation in the dehydration stress response.