Jasmonic acid and its methyl ester, methyl jasmonate (MeJA), are plant signaling molecules that affect plant growth and gene expression. Primary root growth of wild-type Arabidopsis thaliana seedlings was inhibited 50% when seedlings were grown on agar medium containing 0.1 IAMMeJA. An ethyl methanesulfonate mutant (jarn) with decreased sensitivity to MeJA inhibition of root elongation was isolated and characterized. Genetic data indicated the trait was recessive and controlled by a single Mendelian factor. MeJAinduced polypeptides were detected in Arabidopsis leaves by antiserum to a MeJA-inducible vegetative storage protein from soybean. The induction of these proteins by MeJA in the mutant was at least 4-fold less in jar] compared to wild type. In contrast, seeds ofjarl plants were more sensitive than wild type to inhibition of germination by abscisic acid. These results suggest that the defect in jar) affects a general jasmonate response pathway, which may regulate multiple genes in different plant organs.Jasmonate is an endogenous plant compound that affects growth and was recently recognized for its ability to induce the expression of specific plant genes. Methyl jasmonate (MeJA), the methyl ester ofjasmonic acid (JA), is one of the few plant compounds that is effective as a vapor at low concentrations, inducing tomato leaf proteinase inhibitors (1) and soybean leaf vegetative storage proteins (VSPs) (2). These two protein classes are also wound-inducible and recent results indicate that MeJA induces the phytoalexin plant defense pathway in several species (3). This evidence suggests that jasmonate may be an important stress-signaling molecule in plants.Jasmonate is derived from the lipoxygenase-dependent oxidation of linolenic acid (4). By analogy with the production of various eicosanoids involved in animal stress signaling (e.g., prostaglandins), it has been suggested that JA arises from the release of cell membrane fatty acids through the action of lipase in response to wounding or autolytic events (5, 6). MeJA also has pheromone activity in at least one insect (7) and is found in certain fungi. Thus, jasmonate is of general biological interest.Evidence that de novo synthesis ofjasmonate plays a role in regulating soybean VSP genes in response to wounding was recently reported (8). However, little is known about the signal-transduction mechanism for jasmonate action in plants. Mutants in phytohormone synthesis and response have received increased attention in recent years. Such mutants not only provide a better understanding of plant growth regulator function but, with emerging technology, may provide a strategy for the isolation of genes involved in plant hormone signaling pathways (9, 10). The purpose of this study was to find and characterize Arabidopsis mutants with an altered response to MeJA. METHODS 6837The publication costs of this article were defrayed in part by page charge payment. This article must therefore be hereby marked "advertisement" in accordance with 18 U.S.C. §1734 solely...

SummaryCereal grains accumulate carbohydrates, storage proteins and fatty acids via different pathways during their development. Many genes that participate in nutrient partitioning during grain filling and that affect starch quality have been identified. To understand how the expression of these genes is coordinated during grain development, a genomic approach to surveying the participation and interactions of all the pathways is necessary.Using recently published rice genome information, we designed a rice GeneChip microarray that covers half the rice genome. By monitoring the expression of 21 000 genes in parallel, we identified genes involved in the grain filling process and found that the expression of genes involved in different pathways is coordinately controlled in a synchronized fashion during grain filling. Interestingly, a known promoter element in genes encoding seed storage proteins, AACA, is statistically over-represented among the 269 genes in different pathways with diverse functions that are significantly up-regulated during grain filling. By expression pattern matching, a group of transcription factors that have the potential to interact with this element was identified. We also found that most genes in the starch biosynthetic pathway show multiple distinct spatial and temporal expression patterns, suggesting that different isoforms of a given enzyme are expressed in different tissues and at different developmental stages. Our results reveal key regulatory machinery and provide an opportunity for modifying multiple pathways by manipulating key regulatory elements for improving grain quality and quantity.

Nitrate reductase (NR) is rapidly inactivated by phosphorylation of serine residues in response to loss of light or reduction in COz levels. To identify sites within NR protein that play a role in this post-translational regulation, a heterologous expression system and an in vitro inactivation assay for Arabidopsis NR were developed. Protein extracts containing NR kinases and inhibitor proteins were prepared from an NR-defective mutant that had lesions in both the NIAí and NIA2 NR genes of Arabidopsis. Active NR protein was produced in a Pichia pastoris expression system. lncubation of these two preparations resulted in a Mg-ATP-dependent inactivation of NR that was reversed with EDTA. Mutant forms of NR were constructed, produced in F! pastoris, and tested in the in vitro inactivation assay. Six conserved serine residues in the hinge 1 region of NR, which separates the molybdenum cofactor and heme domains, were specifically targeted for mutagenesis because they are located in a potential regulatory region identified as a target for NR kinases in spinach.A change in Ser-534 to aspartate was found to block NR inactivation; changes in the other five serines had no effect.The aspartate that replaced Ser-534 did not appear to mimic a phosphorylated serine but simply prevented the NR from being inactivated. These results identify Ser-534, located in the hinge 1 of NR and conserved among higher plant NRs, as an essential site for post-translational regulation in vitro.

Arabidopsis mutants resistant to cytokinin (benzyladenine [BA]) have been isolated with the intent to find plants defective in cytokinin perception or response. At low concentrations, BA produces a "cytokinin root syndrome" in which primary root elongation is inhibited, but root hair elongation is stimulated. Five independent mutants that did not express this syndrome in the presence of BA were selected. All five mutants were recessive, and crosses between them indicated that they were in the same complementation group. The genetic locus represented by these mutations has been designated ckrl and mapped to chromosome 5.The analysis of mutants with altered responses to hormones is an important approach to understanding hormonesignaling mechanisms in plants. Because to ABA and to an inhibitor of GA3 biosynthesis, paclobutrazol. The authors suggested that the cross-resistance was a result of the interaction of the hormones in promoting normal growth. Recently, new N. plumbaginifolia mutants have been isolated that are not resistant but are more sensitive to auxin (5).Less progress has been made in isolating mutant plants with altered responses to cytokinin. There is only one report of a higher plant mutant selected on the basis of its resistance to cytokinin. The defect in the mutant does not appear to be specific to cytokinin. Instead, the mutant seems to be less growth inhibited in response to general stresses produced by high cytokinin concentrations (2).In this report, we describe the isolation and characterization of cytokinin-resistant mutants in Arabidopsis. To avoid mutants with defects not specifically related to cytokinin responses, we selected mutants at relatively low concentrations of cytokinin. Five independent mutants were identified and found to be mutations in the same complementation group, defining a locus called ckrl in Arabidopsis. MATERIALS AND METHODS Plant Materials and Growth ConditionsAll mutant lines described in this report were derived from the Arabidopsis thaliana Columbia ecotype (Col-0). For growing sterile plants, seeds were sterilized and grown on 0.8% agar medium as described by Estelle and Somerville (6)