NONEXPRESSOR OF PR GENES1 (NPR1) is a key regulator of the plant defense response known as systemic acquired resistance. Accumulation of the signal molecule salicylic acid (SA) leads to a change in intracellular redox potential, enabling NPR1 to enter the nucleus and interact with TGACG sequence-specific binding protein (TGA) transcription factors, which in turn bind to SA-responsive elements in the promoters of defense genes. Here, we show that two NPR1-like genes, BLADE-ON-PETIOLE1 (BOP1) and BOP2, function redundantly to control growth asymmetry, an important aspect of patterning in leaves and flowers. Phenotypes in the double mutant include leafy petioles, loss of floral organ abscission, and asymmetric flowers subtended by a bract. We demonstrate that BOP2 is localized to both the nucleus and the cytoplasm, but unlike NPR1, it is highly expressed in young floral meristems and in yeast interacts preferentially with the TGA transcription factor encoded by PERIANTHIA (PAN). In support of a biological relevance for this interaction, we show that bop1 bop2 and pan mutants share a pentamerous arrangement of first whorl floral organs, a patterning defect that is retained in bop1 bop2 pan triple mutants. Our data provide evidence that BOP proteins control patterning via direct interactions with TGA transcription factors and demonstrate that a signaling mechanism similar to that formally associated with plant defense is likely used for the control of developmental patterning.

In some plant species, including Arabidopsis, fertilization induces the epidermal cells of the outer ovule integument to differentiate into a specialized seed coat cell type with a unique morphology and containing large quantities of polysaccharide mucilage (pectin). Such seed coat mucilage cells are necessary for neither viability nor germination under normal laboratory conditions. Thus, the Arabidopsis seed coat offers a unique system with which to use genetics to identify genes controlling cell morphogenesis and complex polysaccharide biosynthesis and secretion. As a first step in the application of this system, we have used microscopy to investigate the structure and differentiation of Arabidopsis seed coat mucilage cells, including cell morphogenesis and the synthesis, secretion, and extrusion of mucilage. During seed coat development in Arabidopsis, the epidermal cells of the outer ovule integument grow and differentiate into cells that produce large quantities of mucilage between the primary cell wall and plasma membrane. Concurrent with mucilage production, the cytoplasm is shaped into a column in the center of the cell. Following mucilage secretion the cytoplasmic column is surrounded by a secondary cell wall to form a structure known as the columella. Thus, differentiation of the seed coat mucilage cells involves a highly regulated series of events including growth, morphogenesis, mucilage biosynthesis and secretion, and secondary cell wall synthesis.The angiosperm seed coat consists of several layers of specialized tissues that provide protection to the embryo and assist in germination and dispersal. Tissues of the seed coat are derived from cells of the ovule integuments that differentiate in response to fertilization. In some species of plants, including members of the Brassicaceae, Solanaceae, Linaceae, and Plantaginaceae, the epidermal cells of the seed coat contain a large quantity of a pectinaceous, complex polysaccharide (mucilage), a property known as myxospermy (Frey-Wyssling, 1976;Grubert, 1981;Van Caeseele et al., 1981, 1987Boesewinkel and Bouman, 1995). When dry myxospermous seeds are placed in an aqueous environment, the mucilage is released (extruded) and completely envelops the seed. Although the role of mucilage is unknown, it is thought to aid in the dispersal and/or protection of the emerging seedling during imbibition and germination. In addition to the seed coat, mucilages are commonly found in the transmitting tract of the pistil and surrounding the root cap (Frey-Wyssling, 1976;Esau, 1977), where they have roles in fertilization and root growth through the soil, respectively.The major component of mucilage is pectin. Pectins are largely acidic polysaccharides that form gels in the extracellular matrix and are present in all cell walls as well as mucilage. The two most common pectins found in dicotyledonous plants are polygalacturonic acid (PGA) and rhamnogalacturonan I (RG I) (Brett and Waldron, 1990;Carpita and Gibeaut, 1993;Cosgrove, 1997). PGA is an unbranched chain of ␣-1,4-l...

At least nine different bacterial proteins belong to the LysR family. The gene sequence for one of these proteins is presented here. Six others (Escherichia cofi LysR, IlvY, CysB; Salmonela typhimunium MetR; Rhizobium NodD; and Enterobacter cloacae AmpR) are known to activate other genes. Based on sequence alignments, each member of this family is predicted to have a helix-turn-helix DNA binding motif near its amino terminus. The combined evidence indicates that all nine proteins are related by common ancestry, are similarly folded, and are not detectably related to other known bacterial regulatory proteins. The DNA database searching procedure and other methods used in this study should be useful in detecting other groups of related proteins.A full understanding of gene expression will require the elucidation of mechanisms whereby different regulatory proteins interact with specific DNA sequences. This task has been simplified in recent years by the discovery of short peptide motifs within diverse proteins that interact with DNA. One is the helix-turn-helix motif originally seen in A Cro protein and later recognized in many other DNA-binding proteins (1,2). A second is the zinc finger domain, originally hypothesized for Xenopus transcription factor IIIA and later recognized by sequence comparisons to be in several other zinc-dependent DNA-binding proteins (3). These short motifs are found in regulatory proteins that might not be similar overall. However, in some cases, DNA-binding proteins resemble one another more extensively, implying common ancestry and a similar mechanism of action (4-8).Here we report extensive similarities between the sequences for nine bacterial proteins, six of which are known to activate other genes. These relationships were found initially by searching DNA databases for amino acid sequence homologies. The relationships were confirmed by completion of the sequence of one family member$ and by pairwise and consensus comparisons. Each protein was scored for the likelihood that it contains a helix-turn-helix motif. Evidence for a helix-turn-helix motif in each case at an aligned position argues that all members of the family are helix-turn-helix DNA-binding proteins. METHODSDatabase searches, dot matrices, and alignments were done with GENEPRO version 4.1 software and EMBL 14, GenBank 52, and NBRF:PIR 15 databases obtained from Riverside Scientific Enterprises (Seattle). Searches were done on a BIOS AT personal computer obtained from Lang Systems (Arlington, MA).The DNA database searching procedure involved comparing a "query sequence" to every possible translated reading frame of every database sequence (9). The software that we used performed these operations by fetching an individual nucleotide sequence, translating each reading frame into protein, comparing that reading frame with the query, repeating the comparison for the next reading frame, and then repeating the entire operation for the next nucleotide sequence.The comparison strategy was to align 90 amino acids of the que...

Summary. Chlorsulfuron-resistant mutants of Arabidopsis thaliana were isolated by screening for growth of seedlings in the presence of the herbicide. Both whole plants and derived tissue cultures were resistant to concentrations of the herbicide approximately 300-fold higher than that required to prevent growth of the wild-type. The resistance is due to a single dominant nuclear mutation at a locus designated csr which has been genetically mapped to chromosome-3. Acetohydroxy acid synthase activity in extracts from chlorsulfuron-resistant plants was much less-susceptible to inhibition by chlorsulfuron and a structurally related inhibitor than the activity in wild-type extracts. This suggests that the csr locus is the structural gene for acetohydroxy acid synthase.

No abstract

RESULTSLoss of abscission in bop1 bop2 mutants is independent of senescence Loss of floral organ abscission is a striking phenotype of bop1 bop2 plants (Fig. 1A). In wild type, sepals, petals and stamens normally abscise shortly after anthesis (flower opening). The convention used Development 135 (8) RESEARCH ARTICLE

Variation in plant shoot structure may be described as occurring through changes within a basic unit, the metamer. Using this terminology, the apical meristem of Arabidopsis produces three metameric types sequentially: type 1, rosette; type 2, coflorescence-bearing with bract; and type 3, flower-bearing without bract. We describe a mutant of Arabidopsis, Leafy, homozygous for a recessive allele of a nuclear gene LEAFY (LFY), that has an inflorescence composed only of type 2-like metamers. These data suggest that the LFY gene is required for the development of type 3 metamers and that the transition from type 2 to type 3 metamers is a developmental step distinct from that between vegetative and reproductive growth (type 1 to type 2 metamers). Results from double mutant analysis, showing that /fy-7 is epistatic to the floral organ homeotic gene ap2-6, are consistent with the hypothesis that a functional LFY gene is necessary for the expression of downstream genes controlling floral organ identity.

Acyl-CoA Synthetase (ACOS) genes are related to 4-coumarate:CoA ligase (4CL) but have distinct functions. The Arabidopsis thaliana ACOS5 protein is in clade A of Arabidopsis ACOS proteins, the clade most closely related to 4CL proteins. This clade contains putative nonperoxisomal ACOS enzymes conserved in several angiosperm lineages and in the moss Physcomitrella patens. Although its function is unknown, ACOS5 is preferentially expressed in the flowers of all angiosperms examined. Here, we show that an acos5 mutant produced no pollen in mature anthers and no seeds by selffertilization and was severely compromised in pollen wall formation apparently lacking sporopollenin or exine. The phenotype was first evident at stage 8 of anther development and correlated with maximum ACOS5 mRNA accumulation in tapetal cells at stages 7 to 8. Green fluorescent protein-ACOS5 fusions showed that ACOS5 is located in the cytoplasm. Recombinant ACOS5 enzyme was active against oleic acid, allowing kinetic constants for ACOS5 substrates to be established. Substrate competition assays indicated broad in vitro preference of the enzyme for medium-chain fatty acids. We propose that ACOS5 encodes an enzyme that participates in a conserved and ancient biochemical pathway required for sporopollenin monomer biosynthesis that may also include the Arabidopsis CYP703A2 and MS2 enzymes.