Plant development: the flowers that bloom in the spring.
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Arabidopsis↗
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Flavonoids: signal molecules in plant development.
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Arabidopsis↗
AKRP and EMB506 are two ankyrin repeat proteins essential for plastid differentiation and plant development in Arabidopsis.
EMB506 is a chloroplast protein essential for embryo development, the function of which is unknown. A two-hybrid interaction screen was performed to provide insight into the role of EMB506. A single interacting partner, AKRP, was identified among a cDNA library from immature siliques. The AKR gene (Zhang et al., 1992, Plant Cell 4, 1575-1588) encodes a protein containing five ankyrin repeats, very similar to EMB506. Protein truncation series demonstrated that both proteins interact through their ankyrin domains. Using reverse genetics, we showed that loss of akr function resulted in an embryo-defective (emb) phenotype indistinguishable from the emb506 phenotype. Transient expression of the signal peptide of AKRP fused to green fluorescent protein demonstrated the chloroplast localization of AKRP. The ABI3 promoter was used to express AKR in a seed-specific manner in order to analyse the post-embryonic effect of AKR loss of function in akr/akr seedlings. Homozygous fertile and viable akr/akr plants were obtained. These plants exhibited mild to severe defects in chloroplast and leaf cellular organization. We conclude that EMB506 and AKRP are involved in crucial and tightly controlled events in plastid differentiation linked to cell differentiation, morphogenesis and organogenesis during the plant life cycle.
Amino Acid Sequence↗
Enhancement of Wheat Root Colonization and Plant Development by Azospirillum brasilense Cd. Following Temporary Depression of Rhizosphere Microflora.
Inoculation of wheat with Azospirillum brasilense, combined with the application of four fungal and bacterium-inhibiting substances to which A. brasilense is resistant in the soil, decreased the rhizosphere population, while it increased wheat root colonization by A. brasilense, even in cases of poor inoculation. The inoculation significantly increased the following wheat plant parameters as well: plant dry weight, number of tillers per plant, spikelet fertility, harvest index, and grain yield. This model may provide a new approach to improve control of root colonization by beneficial bacteria.
Journal Article↗
Emerging role for transcript elongation in plant development.
Transcript elongation by RNA polymerase II (RNAPII), once regarded as the simple extension of the initiated mRNA, is a complex and highly regulated phase of the transcription cycle. Many factors have been identified that contribute to the dynamic control of the elongation stage of transcription. There are elongation factors that modulate the activity of RNAPII and other factors that facilitate the transcription through chromatin. Recent studies of mutants defective in elongation factors have revealed the importance of proper transcript elongation for the development of higher eukaryotes. Here, the essentials of transcript elongation are briefly summarized to discuss its role in developmental processes.
Animals↗
An S18 ribosomal protein gene copy at the Arabidopsis PFL locus affects plant development by its specific expression in meristems.
In Arabidopsis, mutation at PFL causes pointed first leaves, reduced fresh weight and growth retardation. We have cloned the wild-type PFL gene by T-DNA tagging, and demonstrate that it complements the mutant phenotype. PFL codes for ribosomal protein S18, based on the high homology with rat S18 and on purification of S18-equivalent peptides from plant ribosomes. pfl represents the first mutation in eukaryotic S18 proteins or their S13 prokaryotic counterparts, involved in translation initiation. Arabidopsis contains three S18 gene copies dispersed in the genetic map; they are all transcribed and code for completely identical proteins. No transcript is detected from the mutated gene, S18A. The activity of the S18A promoter is restricted to meristems, with a markedly high expression at the embryonic heart stage, and to wounding sites. This means that plants activate an extra copy of this ribosomal protein gene in tissues with cell division activity. We postulate that in meristematic tissues plants use transcriptional control to synthesize extra ribosomes to increase translational efficiency. In analogy with this, an additional, developmentally regulated gene copy might be expected for all ribosomal proteins.
Amino Acid Sequence↗
Cullin-containing E3 ubiquitin ligases in plant development.
In eukaryotes, the ubiquitin-proteasome system participates in the control of signal transduction events by selectively eliminating regulatory proteins. E3 ubiquitin ligases specifically bind degradation substrates and mediate their poly-ubiquitylation, a prerequisite for their degradation by the 26S proteasome. On the basis of the analysis of the Arabidopsis genome sequence, it is predicted that there are more than 1000 E3 ubiquitin ligases in plants. Several types of E3 ubiquitin ligases have already been characterized in eukaryotes. Recently, some of these E3 enzymes have been implicated in specific plant signaling pathways.
Arabidopsis↗
LRR-containing receptors regulating plant development and defense.
Despite the presence of more than 400 genes that encode receptor-like kinases (RLKs) in the Arabidopsis thaliana genome, very little is known about the range of biological processes that they control, or the mechanisms by which they function. This review focuses on the most recent findings from studies of several leucine-rich-repeat (LRR) class RLKs in A. thaliana, and their implications for our understanding of plant receptor function and signaling. We compare the biological functions of plant and animal LRR-containing receptors, and the potential commonalities in the signaling mechanisms employed.
Animals↗
A putative FAD-binding domain in a distinct group of oxidases including a protein involved in plant development.
Using methods for database screening with individual protein sequences and alignment blocks, a conserved domain is delineated in a group of proteins including several FAD-dependent oxidases. Two motifs within this domain resemble phosphate-binding loops and may be directly involved in FAD binding. These motifs can be readily distinguished from previously described nucleotide-binding sites using a method for database screening with position-dependent weight matrices derived from alignment blocks. Unexpectedly, this group of known and predicted FAD-dependent oxidases includes the product of the DIMINUTO gene, which is involved in Arabidopsis development, and its homologues from man and Mycobacterium leprae.
Amino Acid Sequence↗
Plant development: Genetic clues to petal evolution.
A recent study of the expression of floral organ identity genes in buttercups, poppies and their relatives has shed light on the evolutionary origin of petals.
Evolution, Molecular↗
Stress responses in alfalfa (Medicago sativa L.) 12. Sequence analysis of phenylalanine ammonia-lyase (PAL) cDNA clones and appearance of PAL transcripts in elicitor-treated cell cultures and developing plants.
An expression library containing cDNAs derived from transcripts from fungal elicitor-treated alfalfa cell suspension cultures was screened with an antiserum raised against phenylalanine ammonia-lyase (PAL) from alfalfa. A single immunoreactive clone was isolated which encoded a full-length PAL cDNA (APAL1) consisting of a 2175 bp open reading frame, 96 bp 5'-untranslated leader and 128 bp 3'-non-coding region. The deduced amino acid sequence was 86.5% similar to that of the PAL2 gene of bean, and encoded a polypeptide of Mr 78,865. A second PAL cDNA species was isolated, whose 3'-untranslated region was 86% identical to that of APAL1. Southern blot analysis indicated that PAL is encoded by a small multigene family in alfalfa. PAL transcript levels were rapidly and massively induced, and preceded increased PAL extractable activity, on exposure of alfalfa suspension cells to elicitor from baker's yeast. PAL transcripts were most abundant in roots, stems and petioles during growth and development of alfalfa seedlings. These studies provide the basis for an examination of the developmental and environmental control of a key enzyme of phenylpropanoid synthesis in a plant species which is readily amenable to stable genetic transformation.
Amino Acid Sequence↗
Differential activation of two ACC oxidase gene promoters from melon during plant development and in response to pathogen attack.
ACC (1-aminocyclopropane-1-carboxylate) oxidase genes are differentially expressed in melon during development and in response to various stresses. We investigated the molecular basis of their transcription by analyzing the 5' untranslated regions of the ACC oxidase genes CM-ACO1 and CM-ACO3. In order to determine how their temporal and spatial expression patterns were established, we fused the promoter regions of CM-ACO1 (726 bp) and CM-ACO3 (2260 bp) to the beta-glucuronidase (GUS) reporter gene and examined their regulation in transgenic tobacco plants. The CM-ACO1 promoter was able to drive GUS expression in response to wounding, and to treatment with ethylene or copper sulfate. It was also rapidly induced (8-12 h postinoculation) in tobacco leaves inoculated with the hypersensitive response (HR)-inducing bacterium Ralstonia solanacearum. Expression was also observed during compatible interactions but was delayed. In contrast, the CM-ACO3 promoter was not expressed in response to infection, but was up-regulated during flower development. Both promoters were regulated during leaf senescence but in different patterns. The CM-ACO1-driven GUS activity increased sharply concomitantly with the onset of chlorophyll breakdown, while the CM-ACO3 promoter drove strong GUS expression in green, fully expanded leaves and this declined at the onset of senescence. This result is consistent with the expression patterns of these two genes in senescent melon leaves. These data suggest that the regulation of expression of CM-ACO1 is related preferentially to stress responses, whereas CM-ACO3 seems to be associated with developmental processes. The possible role of ethylene is discussed, particularly in the regulation of the CM-ACO1 gene in response to stress and during senescence.
Amino Acid Oxidoreductases↗
Plant development: timing when to flower.
The time to flowering in Arabidopsis is controlled by many genes; recently, progress has been made in the cloning of a number of such genes. One of them, the FCA gene, turns out to encode an RNA binding protein.
Animals↗
Reversible histone acetylation and deacetylation mediate genome-wide, promoter-dependent and locus-specific changes in gene expression during plant development.
Histone acetylation and deacetylation activate or repress transcription, yet the physiological relevance of reversible changes in chromatin structure and gene expression is poorly understood. We have shown that disrupting the expression of AtHD1 that encodes a putative Arabidopsis thaliana histone deacetylase induces a variety of developmental abnormalities. However, causal effects of the AtHD1 disruption on chromatin structure and gene expression are unknown. Using Arabidopsis spotted oligo-gene microarray analysis, here we report that >7% of the transcriptome was up- or downregulated in A. thaliana plants containing a T-DNA insertion in AtHD1 (athd1-t1), indicating that AtHD1 provides positive and negative control of transcriptional regulation. Remarkably, genes involved in ionic homeostasis and protein synthesis were ectopically expressed, whereas genes in ionic homeostasis, protein transport, and plant hormonal regulation were repressed in athd1-t1 leaves or flowers, suggesting a role of AtHD1 in developmental and environmental regulation of gene expression. Moreover, defective AtHD1 induced site-specific and reversible acetylation changes in H3-Lys9, H4-Lys12, and H4 tetra-lysines (residues 5, 8, 12, and 16) in homozygous recessive and heterozygous plants. Transcriptional activation was locus specific and often associated with specific acetylation sites in the vicinity of promoters, whereas gene repression did not correlate with changes in histone acetylation or correlated directly with H3-Lys9 methylation but not with DNA methylation. The data suggest that histone acetylation and deacetylation are promoter dependent, locus specific, and genetically reversible, which provides a general mechanism for reversible gene regulation responsive to developmental and environmental changes.
Acetylation↗
Simultaneous down-regulation of caffeic/5-hydroxy ferulic acid-O-methyltransferase I and cinnamoyl-coenzyme A reductase in the progeny from a cross between tobacco lines homozygous for each transgene. Consequences for plant development and lignin synthesis.
Inhibition of specific lignin biosynthetic steps by antisense strategy has previously been shown to alter lignin content and/or structure. In this work, homozygous tobacco (Nicotiana tabacum) lines transformed with cinnamoyl-coenzyme A reductase (CCR) or caffeic acid/5-hydroxy ferulic acid-O-methyltransferase I (COMT I) antisense sequences have been crossed and enzyme activities, lignin synthesis, and cell wall structure of the progeny have been analyzed. In single transformed parents, CCR inhibition did not affect COMT I expression, whereas marked increases in CCR activity were observed in COMT I antisense plants, suggesting potential cross talk between some genes of the pathway. In the progeny, both CCR and COMT I activities were shown to be markedly decreased due to the simultaneous repression of the two genes. In these double transformants, the lignin profiles were dependent on the relative extent of down-regulation of each individual enzyme. For the siblings issued from a strongly repressed antisense CCR parent, the lignin patterns mimicked the patterns obtained in single transformants with a reduced CCR activity. In contrast, the specific lignin profile of COMT I repression could not be detected in double transformed siblings. By transmission electron microscopy some cell wall loosening was detected in the antisense CCR parent but not in the antisense COMT I parent. In double transformants, immunolabeling of non-condensed guaiacyl-syringyl units was weaker and revealed changes in epitope distribution that specifically affected vessels. Our results more widely highlight the impact of culture conditions on phenotypes and gene expression of transformed plants.
Aldehyde Oxidoreductases↗
Plant development: YABBYs claw to the fore.
The YABBY gene family was identified recently by homology to CRABS CLAW, a gene involved in carpel and nectary development in Arabidopsis. Several of the transcription factors encoded by the YABBY genes appear to have conserved roles in specifying abaxial cell fate in leaves, floral organs and ovules.
Arabidopsis↗
Characterization of a cDNA encoding a rice mitochondrial voltage-dependent anion channel and its gene expression studied upon plant development and osmotic stress.
The voltage-dependent anion channel (VDAC) of mitochondria forms a large pore in the outer envelope membrane. Here, the full Oryza sativa OSVDAC1 cDNA was sequenced and is shown to belong to a small multigene family in the rice genome. This cDNA is 1093 bp long and codes for a protein of 274 amino acids. Expression studies of the osvdac1 gene show a regulation of its level in function of the plantlets maturation and organs. In contrast with several bacterial porins, osmotic stress does not have any effect on the plant osvdac1 gene expression.
Amino Acid Sequence↗
Plant development: Medea's maternal instinct.
The Arabidopsis MEDEA gene is required in maternal tissues to restrict cell proliferation in embryos. Molecular characterisation indicates that MEDEA encodes a Polycomb-group protein, particularly intriguing as MEDEA's maternal effects may be a consequence of genomic imprinting.
Arabidopsis↗