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J A Langdale

Publications and source records attributed to J A Langdale.

At least 19 recordsLinked to original sources
PubMed2001

Plastids undifferentiated, a nuclear mutation that disrupts plastid differentiation in Zea mays L.

Photosynthetic development in any plant requires the intracellular co-ordination of chloroplast and nuclear gene expression programs. In this report, we investigate the role of a nuclear gene in photosynthetic development by examining C4 photosynthetic differentiation in a yellow mutant of maize (Zea mays L.). The plastids undifferentiated (pun) mutation disrupts plastid biogenesis in both bundle sheath and mesophyll cells, at an early developmental stage and in a light-independent manner. Chloroplast thylakoids are disrupted in the mutant and both membrane-associated and soluble chloroplast-encoded proteins accumulate at much reduced levels. The observed plastid morphology is consistent with a general defect in chloroplast biogenesis that is most likely exerted at the post-translational level. Despite aberrant chloroplast development, nuclear photosynthetic genes are expressed normally in pun mutants. Thus, neither functional chloroplasts nor the Pun gene product are required to establish nuclear photosynthetic gene expression patterns in maize.

Cell Nucleus↗
PubMed2001

Four mutant alleles elucidate the role of the G2 protein in the development of C(4) and C(3) photosynthesizing maize tissues.

Maize leaf blades differentiate dimorphic photosynthetic cell types, the bundle sheath and mesophyll, between which the reactions of C(4) photosynthesis are partitioned. Leaf-like organs of maize such as husk leaves, however, develop a C(3) pattern of differentiation whereby ribulose bisphosphate carboxylase (RuBPCase) accumulates in all photosynthetic cell types. The Golden2 (G2) gene has previously been shown to play a role in bundle sheath cell differentiation in C(4) leaf blades and to play a less well-defined role in C(3) maize tissues. To further analyze G2 gene function in maize, four g2 mutations have been characterized. Three of these mutations were induced by the transposable element Spm. In g2-bsd1-m1 and g2-bsd1-s1, the element is inserted in the second intron and in g2-pg14 the element is inserted in the promoter. In the fourth case, g2-R, four amino acid changes and premature polyadenylation of the G2 transcript are observed. The phenotypes conditioned by these four mutations demonstrate that the primary role of G2 in C(4) leaf blades is to promote bundle sheath cell chloroplast development. C(4) photosynthetic enzymes can accumulate in both bundle sheath and mesophyll cells in the absence of G2. In C(3) tissue, however, G2 influences both chloroplast differentiation and photosynthetic enzyme accumulation patterns. On the basis of the phenotypic data obtained, a model that postulates how G2 acts to facilitate C(4) and C(3) patterns of tissue development is proposed.

Alleles↗
PubMed2001

The maize golden2 gene defines a novel class of transcriptional regulators in plants.

In the C4 plant maize, three photosynthetic cell types differentiate: C4 bundle sheath, C4 mesophyll, and C3 mesophyll cells. C3 mesophyll cells represent the ground state, whereas C4 bundle sheath and C4 mesophyll cells are specialized cells that differentiate in response to light-induced positional signals. The Golden2 (G2) gene regulates plastid biogenesis in all photosynthetic cells during the C3 stages of development. However, G2 function is specifically committed to the differentiation of bundle sheath cell chloroplasts in C4 leaf blades. In this article, we report the isolation of G2-like (Glk) genes from maize and rice, providing evidence for a family of Glk genes in plants. The expression profiles of the rice Glk genes suggest that these genes may act redundantly to promote photosynthetic development in this C3 species. In maize, G2 and ZmGlk1 transcripts accumulate primarily in C4 bundle sheath and C4 mesophyll cells, respectively, suggesting a specific role for each gene in C4 differentiation. We show that G2 and ZmGLK1 both can transactivate reporter gene transcription and dimerize in yeast, which supports the idea that these proteins act as transcriptional regulators of cell-type differentiation processes.

Amino Acid Sequence↗
PubMed1999

The maize rough sheath2 gene and leaf development programs in monocot and dicot plants.

Leaves of higher plants develop in a sequential manner from the shoot apical meristem. Previously it was determined that perturbed leaf development in maize rough sheath2 (rs2) mutant plants results from ectopic expression of knotted1-like (knox) homeobox genes. Here, the rs2 gene sequence was found to be similar to the Antirrhinum PHANTASTICA (PHAN) gene sequence, which encodes a Myb-like transcription factor. RS2 and PHAN are both required to prevent the accumulation of knox gene products in maize and Antirrhinum leaves, respectively. However, rs2 and phan mutant phenotypes differ, highlighting fundamental differences in monocot and dicot leaf development programs.

Amino Acid Sequence↗
PubMed1999

BUNDLE SHEATH DEFECTIVE2, a novel protein required for post-translational regulation of the rbcL gene of maize.

The Bundle sheath defective2 (Bsd2) gene is required for ribulose-1, 5-bisphosphate carboxylase/oxygenase (Rubisco) accumulation in maize. Using a Mutator transposable element as a molecular probe, we identified a tightly linked restriction fragment length polymorphism that cosegregated with the bsd2-conferred phenotype. This fragment was cloned, and sequences flanking the Mutator insertion were used to screen a maize leaf cDNA library. Using a full-length cDNA clone isolated in this screen, we show that an abundant 0.6-kb transcript could be detected in wild-type plants but not in bsd2-m1 plants. This 0.6-kb transcript accumulated to low levels in plants carrying an allele derived from bsd2-m1 that conditions a less severe mutant phenotype. Taken together, these data strongly suggest that we have cloned the Bsd2 gene. Sequence analysis of the full-length cDNA clone revealed a chloroplast targeting sequence and a region of homology shared between BSD2 and the DnaJ class of molecular chaperones. This region of homology is limited to a cysteine-rich Zn binding domain in DnaJ believed to play a role in protein-protein interactions. We show that BSD2 is targeted to the chloroplast but is not involved in general photosynthetic complex assembly or protein import. In bsd2 mutants, we could not detect the Rubisco protein, but the chloroplast-encoded Rubisco large subunit transcript (rbcL) was abundant and associated with polysomes in both bundle sheath and mesophyll cells. By characterizing Bsd2 expression patterns and analyzing the bsd2-conferred phenotype, we propose a model for BSD2 in the post-translational regulation of rbcL in maize.

Amino Acid Sequence↗
PubMed1998

Cellular differentiation in the leaf.

The past year has seen significant advances in our understanding of the mechanisms that regulate cellular differentiation in the leaf. It has been suggested that a common developmental pathway involving MYB-like transcription factors is responsible for distinguishing between cellular identities in the epidermis and that nuclear-cytoplasmic partitioning of the GLABRA2 homeodomain protein plays a role in determining trichome cell fate. With respect to the differentiation of subepidermal cell types, molecular links have been made between auxin physiology and vascular development, and between plastid function and photosynthetic cell type development.

Cell Differentiation↗
PubMed1998

The formation of leaves.

The past year has seen major advances in our understanding of the mechanisms through which leaf pattern is elaborated. It has been suggested that developmental subcompartments are delimited within the leaf and that homeobox genes are involved in specifying these domains in compound leaves. Importantly, peptide signaling has emerged as a novel component of leaf developmental pathways.

Cell Division↗
PubMed1998

Transcripts of maize RbcS genes accumulate differentially in C3 and C4 tissues.

RbcS genes exist as multigene families in most plant species examined. In this paper, we report an investigation into the expression patterns of two maize RbcS genes, designated in this report as RbcS1 and RbcS2. We present the sequence of RbcS2 and show that the structure of the gene has several features in common with other monocot RbcS genes. To determine whether RbcS1 and RbcS2 fulfil different functional roles with respect to the C3 and C4 carbon fixation pathways, we have investigated the expression patterns of the two genes in different maize tissue types. Transcripts of both genes are found at high levels specifically in bundle-sheath cells of maize seedling leaves, indicating that both genes are expressed in the C4-type pattern. However, we show that RbcS1 transcripts are relatively more abundant than RbcS2 transcripts in C3 tissues such as husk leaves. These results are discussed with respect to the evolution of C4 carbon fixation and the mechanisms required for the cell-specific expression of RbcS genes.

Amino Acid Sequence↗
PubMed1998

GOLDEN 2: a novel transcriptional regulator of cellular differentiation in the maize leaf.

The differentiation of distinct cell types within the leaf is essential for normal plant development. We characterized previously a transposon-induced mutant of maize (bundle sheath defective1) that disrupts the differentiation of a single photosynthetic cell type in the leaf. In this study, we show that this mutation is allelic to golden2 (g2), a lesion first reported 70 years ago. We cloned G2 by using Suppressor-mutator as a molecular tag. The gene encodes a 2. 2-kb transcript that is present throughout the wild-type leaf but is most abundant in C4 leaf blade tissue. Gene sequence data showed the existence of a bipartite nuclear localization signal encoded by the first exon, and we determined that G2 reporter gene fusions are targeted to the nucleus in onion epidermal cells. Further sequence analysis indicated the presence of a novel motif within the deduced protein sequence that shares features with TEA DNA binding domains. Therefore, we propose that G2 acts as a novel transcriptional regulator of cellular differentiation in the maize leaf.

Amino Acid Sequence↗
PubMed1998

The rough sheath2 gene negatively regulates homeobox gene expression during maize leaf development.

Leaves of higher plants are produced in a sequential manner through the differentiation of cells that are derived from the shoot apical meristem. Current evidence suggests that this transition from meristematic to leaf cell fate requires the down-regulation of knotted1-like homeobox (knox) gene expression. If knox gene expression is not repressed, overall leaf shape and cellular differentiation within the leaf are perturbed. In order to identify genes that are required for the aquisition of leaf cell fates, we have genetically screened for recessive mutations that confer phenotypes similar to dominant mutations (e.g. Knotted1 and Rough sheath1) that result in the ectopic expression of class I knox genes. Independently derived mutations at the rough sheath2 (rs2) locus condition a range of pleiotropic leaf, node and internode phenotypes that are sensitive to genetic background and environment. Phenotypes include dwarfism, leaf twisting, disorganized differentiation of the blade-sheath boundary, aberrant vascular patterning and the generation of semi-bladeless leaves. knox genes are initially repressed in rs2 mutants as leaf founder cells are recruited in the meristem. However, this repression is often incomplete and is not maintained as the leaf progresses through developement. Expression studies indicate that three knox genes are ectopically or over-expressed in developing primordia and in mature leaves. We therefore propose that the rs2 gene product acts to repress knox gene expression (either directly or indirectly) and that rs2 gene action is essential for the elaboration of normal leaf morphology.

Cell Differentiation↗
PubMed1998

Cellular differentiation in the maize leaf is disrupted by bundle sheath defective mutations.

The mature maize leaf is characterised by a series of parallel veins that are surrounded by concentric rings of bundle sheath (BS) and mesophyll (M) cells. To identify genes that control cellular differentiation patterns in the leaf, we have isolated a group of mutations that specifically disrupt the differentiation of a single cell type. In maize bundle sheath defective (bsd) mutants, C4 photosynthetic development is perturbed in BS cells while M cells appear to develop normally. Two mutants, bsd1 and bsd2, have been characterised in detail. Analysis of these mutants, and the corresponding Bsd1 and Bsd2 genes is providing an insight into cellular processes regulating photosynthetic cell type differentiation in maize.

Cell Differentiation↗
PubMed1994

Plant morphogenesis. More knots untied.

Knox genes are expressed within restricted domains of the maize shoot apical meristem. The patterns observed suggest that this homeobox gene family plays a pivotal role in the control of plant morphogenesis.

Genes, Homeobox↗
PubMed1991

Cell-specific accumulation of maize phosphoenolpyruvate carboxylase is correlated with demethylation at a specific site greater than 3 kb upstream of the gene.

Development of the C4 photosynthetic pathway relies upon the cell-specific accumulation of photosynthetic enzymes. Although the molecular basis of this cell-specific gene expression is not known, regulation appears to be exerted at the level of transcript accumulation. We have investigated the relationship between gene expression patterns and DNA methylation for genes of two of the C4 photosynthetic enzymes, ribulose bisphosphate carboxylase (RuBPCase) and phosphoenolpyruvate carboxylase (PEPCase). We found no correlation between methylation state and gene expression for either the large subunit or a small subunit gene of RuBPCase. In contrast, demethylation of a specific site 5' to the PEPCase gene was correlated with the light-induced, cell-specific accumulation of PEPCase mRNA. This differentially methylated site is positioned at great distance (greater than 3 kb) from the start of transcription. This observation is made more interesting by the fact that the immediate 5' region of the gene, and some of the coding region, represents an unmethylated CpG island. Such islands are normally associated with constitutively expressed genes.

DNA↗
PubMed1991

Spatial regulation of photosynthetic development in C4 plants.

Leaf development in C4 plants requires the morphological and functional differentiation of two photosynthetic cell types (bundle sheath and mesophyll). Photosynthetic reactions are split between bundle sheath and mesophyll cells, with each cell type accumulating a specific complement of photosynthetic enzymes. Current evidence suggests that in order to activate this cell-specific expression of photosynthetic genes, bundle sheath and mesophyll cells must interpret positional information distributed locally around each vein.

Carbon Dioxide↗
PubMed1990

Expression of a maize cell wall hydroxyproline-rich glycoprotein gene in early leaf and root vascular differentiation.

The spatial pattern of expression for a maize gene encoding a hydroxyproline-rich glycoprotein (HRGP) was determined by in situ hybridization. During normal development of roots and leaves, the expression of the gene was transient and particularly high in regions initiating vascular elements and associated sclerenchyma. Its expression was also associated with the differentiation of vascular elements in a variety of other tissues. The gene encoded an HRGP that had been extracted from the cell walls of maize suspension culture cells and several other embryonic and post-embryonic tissues. The gene was present in one or two copies in different varieties of maize and in the related monocots teosinte and sorghum. A single gene was cloned from maize using a previously characterized HRGP cDNA clone [Stiefel et al. (1988). Plant Mol. Biol. 11, 483-493]. In addition to the coding sequences for the HRGP and an N-terminal signal sequence, the gene contained a single intron in the nontranslated 3' end.

Amino Acid Sequence↗
PubMed1989

Cell lineage analysis of maize bundle sheath and mesophyll cells.

Maize leaves are divided into repeated longitudinal units consisting of vascular tissue, bundle sheath (BS), and mesophyll (M) cells. We have carried out a cell lineage analysis of these cell types using six spontaneous striping mutants of maize. We show that certain cell division patterns are preferentially utilized, but not required, to form the characteristic arrangement of cell types. Our data suggest that early in development a central cell layer is formed, most frequently by periclinal divisions in the adaxial subepidermal layer of the leaf primordium. Lateral and intermediate veins are initiated in this central layer, most often by divisions which contribute daughter cells to both the procambium and the ground meristem. These divisions generate "half vein" units which comprise half of the bundle sheath cells around a vein and a single adjacent M cell. We show that intermediate veins are multiclonal both in this transverse direction and along their lengths. BS cells are more closely related to M cells in the middle layer of the leaf than to those in the upper and lower subepidermal layers. An examination of sector boundaries has shown that photosynthetic differentiation in M cells is affected by the phenotype of neighboring BS cells.

Cell Differentiation↗
PubMed1988

Cell position and light influence C4 versus C3 patterns of photosynthetic gene expression in maize.

C4 plants such as maize partition photosynthetic activities in two morphologically distinct cell types, bundle sheath (BS) and mesophyll (M), which lie as concentric layers around veins. We show that both light and cell position relative to veins influence C4 photosynthetic gene expression. A pattern of gene expression characteristic of C3 plants [ribulose bisphosphate carboxylase (RuBPCase) and light-harvesting chlorophyll a/b binding protein in all photosynthetic cells] is observed in leaf-like organs such as husk leaves, which are sparsely vascularized. This pattern of gene expression reflects direct fixation of CO2 in the C3 photosynthetic pathway, as determined by O2 inhibition assays. Light induces a switch from C3-type to C4-type gene expression patterns in all leaves, primarily in cells that are close to a vein. We propose that light causes repression of RuBPCase expression in M cells, by a mechanism associated with the vascular system, and that this is an essential step in the induction of C4 photosynthesis.

Cell Compartmentation↗