Boundary domain genes were recruited to suppress bract growth and promote branching in maize

Grass inflorescence development is diverse and complex and involves sophisticated but poorly understood interactions of genes regulating branch determinacy and leaf growth. Here, we use a combination of transcript profiling and genetic and phylogenetic analyses to investigate tasselsheath1 (tsh1) and tsh4, two maize genes that simultaneously suppress inflorescence leaf growth and promote branching. We identify a regulatory network of inflorescence leaf suppression that involves the phase change gene tsh4 upstream of tsh1 and the ligule identity gene liguleless2 (lg2). We also find that a series of duplications in the tsh1 gene lineage facilitated its shift from boundary domain in nongrasses to suppressed inflorescence leaves of grasses. Collectively, these results suggest that the boundary domain genes tsh1 and lg2 were recruited to inflorescence leaves where they suppress growth and regulate a nonautonomous signaling center that promotes inflorescence branching, an important component of yield in cereal grasses.

Recruitment of an ancient branching program to suppress carpel development in maize flowers

Carpels in maize undergo programmed cell death in half of the flowers initiated in ears and in all flowers in tassels. The HD-ZIP I transcription factor gene GRASSY TILLERS1 (GT1) is one of only a few genes known to regulate this process. To identify additional regulators of carpel suppression, we performed a gt1 enhancer screen and found a genetic interaction between gt1 and ramosa3 (ra3). RA3 is a classic inflorescence meristem determinacy gene that encodes a trehalose-6-phosphate (T6P) phosphatase (TPP). Dissection of floral development revealed that ra3 single mutants have partially derepressed carpels, whereas gt1;ra3 double mutants have completely derepressed carpels. Surprisingly, gt1 suppresses ra3 inflorescence branching, revealing a role for gt1 in meristem determinacy. Supporting these genetic interactions, GT1 and RA3 proteins colocalize to carpel nuclei in developing flowers. Global expression profiling revealed common genes misregulated in single and double mutant flowers, as well as in derepressed gt1 axillary meristems. Indeed, we found that ra3 enhances gt1 vegetative branching, similar to the roles for the trehalose pathway and GT1 homologs in the eudicots. This functional conservation over ∼160 million years of evolution reveals ancient roles for GT1-like genes and the trehalose pathway in regulating axillary meristem suppression, later recruited to mediate carpel suppression. Our findings expose hidden pleiotropy of classic maize genes and show how an ancient developmental program was redeployed to sculpt floral form.

The regulatory landscape of a core maize domestication module controlling bud dormancy and growth repression

Many domesticated crop plants have been bred for increased apical dominance, displaying greatly reduced axillary branching compared to their wild ancestors. In maize, this was achieved through selection for a gain-of-function allele of the TCP transcription factor teosinte branched1 (tb1). The mechanism for how a dominant Tb1 allele increased apical dominance, is unknown. Through ChIP seq, RNA seq, hormone and sugar measurements on 1 mm axillary bud tissue, we identify the genetic pathways putatively regulated by TB1. These include pathways regulating phytohormones such as gibberellins, abscisic acid and jasmonic acid, but surprisingly, not auxin. In addition, metabolites involved in sugar sensing such as trehalose 6-phosphate were increased. This suggests that TB1 induces bud suppression through the production of inhibitory phytohormones and by reducing sugar levels and energy balance. Interestingly, TB1 also putatively targets several other domestication loci, including teosinte glume architecture1, prol1.1/grassy tillers1, as well as itself. This places tb1 on top of the domestication hierarchy, demonstrating its critical importance during the domestication of maize from teosinte.

The TB1 transcription factor was selected for the increased apical dominance of maize compared to its ancestor teosinte. A metabolic and genomic analysis of domesticated axillary buds suggest that TB1 achieved this by regulating phytohormone signaling, sugar metabolism and other domestication genes.

microRNA172 plays a crucial role in wheat spike morphogenesis and grain threshability

Wheat domestication from wild species involved mutations in the Q gene. The q allele (wild wheats) is associated with elongated spikes and hulled grains, whereas the mutant Q allele (domesticated wheats) confers subcompact spikes and free-threshing grains. Previous studies showed that Q encodes an AP2-like transcription factor, but the causal polymorphism of the domestication traits remained unclear. Here, we show that the interaction between microRNA172 (miR172) and the Q allele is reduced by a single nucleotide polymorphism in the miRNA binding site. Inhibition of miR172 activity by a miRNA target mimic resulted in compact spikes and transition from glumes to florets in apical spikelets. By contrast, overexpression of miR172 was sufficient to induce elongated spikes and non-free-threshing grains, similar to those observed in three Q loss-of-function mutations. These lines showed transitions from florets to glumes in the basal spikelets. These localized homeotic changes were associated with opposing miR172/Q gradients along the spike. We propose that the selection of a nucleotide change at the miR172 binding site of Q contributed to subcompact spikes and free-threshing grains during wheat domestication.

Highlighted Article: A nucleotide change in the microRNA172 binding site of the AP2 gene Q played a critical role in wheat domestication and the origin of free-threshing modern wheats. See also Greenwood et al. in this issue.

From organelle to organ: ZRIZI MATE-Type transporter is an organelle transporter that enhances organ initiation

Plant architecture is a predictable but flexible trait. The timing and position of organ initiation from the shoot apical meristem (SAM) contribute to the final plant form. While much progress has been made recently in understanding how the site of leaf initiation is determined, the mechanism underlying the temporal interval between leaf primordia is still largely unknown. The Arabidopsis ZRIZI (ZRZ) gene belongs to a large gene family encoding multidrug and toxic compound extrusion (MATE) transporters. Unique among plant MATE transporters identified so far, ZRZ is localized to the membrane of a small organelle, possibly the mitochondria. Plants overexpressing ZRZ in initiating leaves are short, produce leaves much faster than wild-type plants and show enhanced growth of axillary buds. These results suggest that ZRZ is involved in communicating a leaf-borne signal that determines the rate of organ initiation.

The unique relationship between tsh4 and ra2 in patterning floral phytomers

Phytomers are developmental compartments that display stereotypical patterns dependent on whether they are initiated during the vegetative phase or the floral phases. Differences in appearance result from differential partitioning mechanisms responsible for allocation of cells to different components of the phytomer. The tasselsheath loci of maize control cell partitioning within the phytomer, indirectly influencing growth and development of its individual components. The tasselsheath4 (tsh4) gene accomplishes this through regulation of the ramosa2 (ra2) meristem determinacy gene, whereas tasselsheath1 (tsh1) appears to function differently.

The maize SBP-box transcription factor encoded by tasselsheath4 regulates bract development and the establishment of meristem boundaries

Plant architecture consists of repeating units called phytomers, each containing an internode, leaf and axillary meristem. The formation of boundaries within the phytomer is necessary to differentiate and separate these three components, otherwise some will grow at the expense of others. The microRNA-targeted SBP-box transcription factor tasselsheath4 (tsh4) plays an essential role in establishing these boundaries within the inflorescence. tsh4 mutants display altered phyllotaxy, fewer lateral meristems and ectopic leaves that grow at the expense of the meristem. Double-mutant analyses of tsh4 and several highly branched mutants, such as ramosa1-3 and branched silkless1, demonstrated a requirement for tsh4 in branch meristem initiation and maintenance. TSH4 protein, however, was localized throughout the inflorescence stem and at the base of lateral meristems, but not within the meristem itself. Double labeling of TSH4 with the ramosa2, branched silkless1 and knotted1 meristem markers confirmed that TSH4 forms a boundary adjacent to all lateral meristems. Indeed, double labeling of miR156 showed a meristem-specific pattern complementary to that of TSH4, consistent with tsh4 being negatively regulated by this microRNA. Thus, downregulation of TSH4 by a combination of microRNAs and branching pathway genes allows the establishment of lateral meristems and the repression of leaf initiation, thereby playing a major role in defining meristem versus leaf boundaries.

Small RNAs going the distance during plant development

Small RNAs are 19-27 nucleotide long RNAs that negatively regulate gene expression and function as important regulators of diverse aspects of plant development. Current models for how they function continue to be modified as new research uncovers additional aspects of their biology. Unexpectedly, several previously characterized small RNAs appear to function non-cell autonomously, some moving a few cells away, others moving throughout the plant. This fact may reflect that small RNAs are an essential component of a larger signaling network that orchestrates plant development.

Big impacts by small RNAs in plant development

The identification and study of small RNAs, including microRNAs and trans-acting small interfering RNAs, have added a layer of complexity to the many pathways that regulate plant development. These molecules, which function as negative regulators of gene expression, are now known to have greatly expanded roles in a variety of developmental processes affecting all major plant structures, including meristems, leaves, roots, and inflorescences. Mutants with specific developmental phenotypes have also advanced our knowledge of the biogenesis and mode of action of these diverse small RNAs. In addition, previous models on the cell autonomy of microRNAs may have to be revised as more data accumulate supporting their long distance transport. As many of these small RNAs appear to be conserved across different species, knowledge gained from one species is expected to have general application. However, a few surprising differences in small RNA function seem to exist between monocots and dicots regarding meristem initiation and sex determination. Integrating these unique functions into the overall scheme for plant growth will give a more complete picture of how they have evolved as unique developmental systems.

Floral meristem initiation and meristem cell fate are regulated by the maize AP2 genes ids1 and sid1

Grass flowers are organized on small branches known as spikelets. In maize, the spikelet meristem is determinate, producing one floral meristem and then converting into a second floral meristem. The APETALA2 (AP2)-like gene indeterminate spikelet1 (ids1) is required for the timely conversion of the spikelet meristem into the floral meristem. Ectopic expression of ids1 in the tassel, resulting from a failure of regulation by the tasselseed4 microRNA, causes feminization and the formation of extra floral meristems. Here we show that ids1 and the related gene, sister of indeterminate spikelet1 (sid1), play multiple roles in inflorescence architecture in maize. Both genes are needed for branching of the inflorescence meristem, to initiate floral meristems and to control spikelet meristem determinacy. We show that reducing the levels of ids1 and sid1 fully suppresses the tasselseed4 phenotype, suggesting that these genes are major targets of this microRNA. Finally, sid1 and ids1 repress AGAMOUS-like MADS-box transcription factors within the lateral organs of the spikelet, similar to the function of AP2 in Arabidopsis, where it is required for floral organ fate. Thus, although the targets of the AP2 genes are conserved between maize and Arabidopsis, the genes themselves have adopted novel meristem functions in monocots.

Screening of male patients with autism spectrum disorder for creatine transporter deficiency

Creatine deficiency syndromes (CDS) are newly identified genetic disorders that result in neurological impairment of cognition and communication. The purpose of our study was to screen 100 male subjects with autism spectrum disorder for mutations in the SLC6A8 gene in order to determine the frequency of this genetic disorder in this population. One hundred males ages 3-18 years diagnosed with autism spectrum disorder based on DSM-IV criteria were recruited. DNA sequence analysis was performed on all subjects for creatine transporter gene (SLC6A8) defects. One subject had a novel unclassified variant in the SLC6A8 gene exon 13: c.1890G>C. Given that autistic features are found in a number of patients with CDS, SLC6A8 deficiency as well as the treatable forms of CDS should be included in the differential diagnosis of patients with autism spectrum disorder.

The heterochronic maize mutant Corngrass1 results from overexpression of a tandem microRNA

Retention of juvenile traits in the adult reproductive phase characterizes a process known as neoteny, and speculation exists over whether it has contributed to the evolution of new species. The dominant Corngrass1 (Cg1) mutant of maize is a neotenic mutation that results in phenotypes that may be present in the grass-like ancestors of maize. We cloned Cg1 and found that it encodes two tandem miR156 genes that are overexpressed in the meristem and lateral organs. Furthermore, a target of Cg1 is teosinte glume architecture1 (tga1), a gene known to have had a role in the domestication of maize from teosinte. Cg1 mutant plants overexpressing miR156 have lower levels of mir172, a microRNA that targets genes controlling juvenile development. By altering the relative levels of both microRNAs, it is possible to either prolong or shorten juvenile development in maize, thus providing a mechanism for how species-level heterochronic changes can occur in nature.

ramosa2 encodes a LATERAL ORGAN BOUNDARY domain protein that determines the fate of stem cells in branch meristems of maize

Genetic control of grass inflorescence architecture is critical given that cereal seeds provide most of the world's food. Seeds are borne on axillary branches, which arise from groups of stem cells in axils of leaves and whose branching patterns dictate most of the variation in plant form. Normal maize (Zea mays) ears are unbranched, and tassels have long branches only at their base. The ramosa2 (ra2) mutant of maize has increased branching with short branches replaced by long, indeterminate ones. ra2 was cloned by chromosome walking and shown to encode a LATERAL ORGAN BOUNDARY domain transcription factor. ra2 is transiently expressed in a group of cells that predicts the position of axillary meristem formation in inflorescences. Expression in different mutant backgrounds places ra2 upstream of other genes that regulate branch formation. The early expression of ra2 suggests that it functions in the patterning of stem cells in axillary meristems. Alignment of ra2-like sequences reveals a grass-specific domain in the C terminus that is not found in Arabidopsis thaliana. The ra2-dm allele suggests this domain is required for transcriptional activation of ra1. The ra2 expression pattern is conserved in rice (Oryza sativa), barley (Hordeum vulgare), sorghum (Sorghum bicolor), and maize, suggesting that ra2 is critical for shaping the initial steps of grass inflorescence architecture.

Glycine decarboxylase mutations: a distinctive phenotype of nonketotic hyperglycinemia in adults

Three unrelated adult patients with mild hyperglycinemia, infantile hypotonia, mental retardation, behavioral hyperirritability, and aggressive outbursts were screened for glycine decarboxylase (GLDC) mutations; two novel missense mutations (A389V and R739H) were found. Both mutations had a 6 to 8% of normal GLDC activities when expressed in COS7 cells.

Regulation of developmental transitions

Plants undergo a series of profound developmental changes throughout their lifetimes in response to both external environmental factors and internal intrinsic ones. When these changes are abrupt and dramatic, the process is referred to as phase change. Recently, several genes have been discovered that play a role in these developmental transitions. Their sequence and expression patterns shed new light on the mechanisms of phase change, and provide a link between the external and internal factors that control them. Examples of these transitions include changes from juvenile to adult leaf formation, vegetative to inflorescence meristem development, and inflorescence to floral meristem initiation.

The control of spikelet meristem identity by the branched silkless1 gene in maize

Most of the world's food supply is derived from cereal grains that are borne in a unique structure called the spikelet, the fundamental unit of inflorescence architecture in all grasses. branched silkless1 (bd1) is a maize mutation that alters the identity of the spikelet meristem, causing indeterminate branches to form in place of spikelets. We show that bd1 encodes a putative ERF transcription factor that is conserved in different grasses and is expressed in a distinct domain of the spikelet meristem. Its expression pattern suggests that signaling pathways regulate meristem identity from lateral domains of the spikelet meristem.

Congenital creatine transporter deficiency

BACKGROUND

Two inborn errors of metabolism of creatine synthesis as well as the X-linked creatine transporter (SLC6A8) deficiency have been recognized. This report describes the features of five identified male patients and their female relatives who are carriers of the X-linked creatine transporter deficiency syndrome.

METHODS

Proton MR spectroscopy was used to recognize creatine deficiency in the patients. Molecular analysis of the SLC6A8 gene was performed, confirming the diagnosis of homozygous males and heterozygous females.

RESULTS

We describe four families from a metropolitan area in the U. S. with X-linked creatine transporter deficiency. All affected males present with developmental delay and severe developmental language impairment. Proton MR spectroscopy shows significantly depressed to essentially absent creatine and phosphocreatine in the male patients. Nonsense mutations and amino acid deletions were found in the SLC6A8 gene in the affected families.

CONCLUSION

Creatine transporter deficiency may be a more common X-linked genetic disorder than originally presumed. The affected males exhibit mental retardation with severe expressive language impairment.

KNAT1 and ERECTA regulate inflorescence architecture in Arabidopsis

Plant architecture is dictated by morphogenetic factors that specify the number and symmetry of lateral organs as well as their positions relative to the primary axis. Mutants defective in the patterning of leaves and floral organs have provided new insights on the signaling pathways involved, but there is comparatively little information regarding aspects of the patterning of stems, which play a dominant role in architecture. To this end, we have characterized five alleles of the brevipedicellus mutant of Arabidopsis, which exhibits reduced internode and pedicel lengths, bends at nodes, and downward-oriented flowers and siliques. Bends in stems correlate with a loss of chlorenchyma tissue at the node adjacent to lateral organs and in the abaxial regions of pedicels. A stripe of achlorophyllous tissue extends basipetally from each node and is positioned over the vasculature that services the corresponding lateral organ. Map-based cloning and complementation studies revealed that a null mutation in the KNAT1 homeobox gene is responsible for these pleiotropic phenotypes. Our observation that wild-type Arabidopsis plants also downregulate chlorenchyma development adjacent to lateral organs leads us to propose that KNAT1 and ERECTA are required to restrict the action of an asymmetrically localized, vasculature-associated chlorenchyma repressor at the nodes. Our data indicate that it is feasible to alter the architecture of ornamental and crop plants by manipulating these genetically defined pathways.

Mutational and radiographic analysis of pulmonary disease consistent with lymphangioleiomyomatosis and micronodular pneumocyte hyperplasia in women with tuberous sclerosis

Lymphangioleiomyomatosis (LAM) and multifocal micronodular pneumocyte hyperplasia (MMPH) produce cystic and nodular disease, respectively, in the lungs of patients with tuberous sclerosis. The objective of this study was to prospectively characterize the prevalence, clinical presentation, and genetic basis of lung disease in TSC. We performed genotyping and computerized tomographic (CT) scanning of the chest on 23 asymptomatic women with tuberous sclerosis complex (TSC). Cystic pulmonary parenchymal changes consistent with LAM were found in nine patients (39%). These patients tended to be older than cyst-negative patients (31.9 +/- 7.6 yr versus 24.8 +/- 11.6 yr, p = 0.09). There was no correlation between presence of cysts and tobacco use, age at menarche, history of pregnancy, or estrogen-containing medications. Three of the cyst-positive patients had a prior history of pneumothorax. Pulmonary function studies revealed evidence of gas trapping but normal spirometric indices in the cyst-positive group. All nine cyst-positive patients had angiomyolipomas (AML), which were larger (p < 0.05) and more frequently required intervention (p = 0.08) than cyst-negative patients (8 of 14 with AMLs, p < 0.05). Ten patients (43%) had pulmonary parenchymal nodules. Pulmonary nodules were more common in women with cysts (78% versus 21%, p < 0.05), and 52% of all patients had either cystic or nodular changes. TSC2 mutations were identified in all cyst-positive patients who were tested (n = 8), whereas both TSC1 and TSC2 mutations were found in patients with nodular disease. Correlation of the mutational and radiographic data revealed one pair of sisters who were discordant for cystic disease, two mother- daughter pairs who were discordant for nodular disease, and no clear association between cyst development and a specific mutational type. This prospective analysis demonstrates that cystic and nodular pulmonary changes consistent with LAM and MMPH are common in women with TSC.

Irreversible brain creatine deficiency with elevated serum and urine creatine: a creatine transporter defect?

Recent reports highlight the utility of in vivo magnetic resonance spectroscopy (MRS) techniques to recognize creatine deficiency syndromes affecting the central nervous system (CNS). Reported cases demonstrate partial reversibility of neurologic symptoms upon restoration of CNS creatine levels with the administration of oral creatine. We describe a patient with a brain creatine deficiency syndrome detected by proton MRS that differs from published reports. Metabolic screening revealed elevated creatine in the serum and urine, with normal levels of guanidino acetic acid. Unlike the case with other reported creatine deficiency syndromes, treatment with oral creatine monohydrate demonstrated no observable increase in brain creatine with proton MRS and no improvement in clinical symptoms. In this study, we report a novel brain creatine deficiency syndrome most likely representing a creatine transporter defect.

Mechanisms that control knox gene expression in the Arabidopsis shoot

Knotted1-like homeobox (knox) genes are expressed in specific patterns within shoot meristems and play an important role in meristem maintenance. Misexpression of the knox genes, KNAT1 or KNAT2, in Arabidopsis produces a variety of phenotypes, including lobed leaves and ectopic stipules and meristems in the sinus, the region between lobes. We sought to determine the mechanisms that control knox gene expression in the shoot by examining recessive mutants that share phenotypic characteristics with 35S::KNAT1 plants. Double mutants of serrate (se) with either asymmetric1 (as1) or asymmetric2 (as2) showed lobed leaves, ectopic stipules in the sinuses and defects in the timely elongation of sepals, petals and stamens, similar to 35S::KNAT1 plants. Ectopic stipules and in rare cases, ectopic meristems, were detected in the sinuses on plants that were mutant for pickle and either as1 or as2. KNAT1 and KNAT2 were misexpressed in the leaves and flowers of single as1 and as2 mutants and in the sinuses of leaves of the different double mutants, but not in se or pickle single mutants. These results suggest that AS1 and AS2 promote leaf differentiation through repression of knox expression in leaves, and that SE and PKL globally restrict the competence to respond to genes that promote morphogenesis.

The control of maize spikelet meristem fate by the APETALA2-like gene indeterminate spikelet1

The orderly production of meristems with specific fates is crucial for the proper elaboration of plant architecture. The maize inflorescence meristem branches several times to produce lateral meristems with determinate fates. The first meristem formed, the spikelet pair meristem, produces two spikelet meristems, each of which produces two floral meristems. We have identified a gene called indeterminate spikelet1 (ids1) that specifies a determinate spikelet meristem fate and thereby limits the number of floral meristems produced. In the absence of ids1 gene function, the spikelet meristem becomes indeterminate and produces additional florets. Members of the grass family vary in the number of florets within their spikelets, suggesting that ids1 may play a role in inflorescence architecture in other grass species. ids1 is a member of the APETALA2 (AP2) gene family of transcription factors that has been implicated in a wide range of plant development roles. Expression of ids1 was detected in many types of lateral organ primordia as well as spikelet meristems. Our analysis of the ids1 mutant phenotype and expression pattern indicates that ids1 specifies determinate fates by suppressing indeterminate growth within the spikelet meristem.

Biochemical and molecular analysis in a patient with the severe form of Hunter syndrome after bone marrow transplantation

Hunter syndrome (mucopolysaccharidosis type II, or MPS II) results from a deficiency of iduronate-2-sulfatase (IDS) activity due to a primary genetic defect in the X-chromosomal iduronate-2-sulfatase gene. We have studied a 10-year-old male, diagnosed with Hunter syndrome at age 2 years, who underwent bone marrow transplantation (BMT) at age 5 years. To evaluate the metabolic effect of BMT, biochemical and enzymatic studies were performed. Urinary glycosaminoglycans (GAGs) were quantitated, and iduronate-2-sulfatase activity was measured in serum, leukocytes, and liver homogenates. Decreased urinary glycosaminoglycan excretion and increased iduronate-2-sulfatase activity in serum and leukocytes were observed. Furthermore, molecular analysis was performed using reverse transcriptional polymerase chain reaction (RT-PCR) sequencing and restriction enzyme assay. The patient was found to have a novel nonsense mutation, L279X (TTA to TGA) in exon 6 of the IDS gene, inherited from his mother. A comparison of the DNA contents of cultured skin fibroblasts prior to BMT with leukocyte DNA after BMT showed coexisting host mutant and donor normal alleles in post-BMT leukocyte DNA. We postulate that the L279X mutation is a severe disease-causing mutation for Hunter syndrome.

KNAT1 induces lobed leaves with ectopic meristems when overexpressed in Arabidopsis

Plant development depends on the activity of apical meristems, which are groups of indeterminate cells whose derivatives elaborate the organs of the mature plant. Studies of knotted1 (kn1) and related gene family members have determined potential roles for homeobox genes in the function of shoot meristems. The Arabidopsis kn1-like gene, KNAT1, is expressed in the shoot apical meristem and not in determinate organs. Here, we show that ectopic expression of KNAT1 in Arabidopsis transforms simple leaves into lobed leaves. The lobes initiate in the position of serrations yet have features of leaves, such as stipules, which form in the sinus, the region at the base of two lobes. Ectopic meristems also arise in the sinus region close to veins. Identity of the meristem, that is, vegetative or floral, depends on whether the meristem develops on a rosette or cauline leaf, respectively. Using in situ hybridization, we analyzed the expression of KNAT1 and another kn1-like homeobox gene, SHOOT MERISTEMLESS, in cauliflower mosaic virus 35S::KNAT1 transformants. KNAT1 expression is strong in vasculature, possibly explaining the proximity of the ectopic meristems to veins. After leaf cells have formed a layered meristem, SHOOT MERISTEMLESS expression begins in only a subset of these cells, demonstrating that KNAT1 is sufficient to induce meristems in the leaf. The shootlike features of the lobed leaves are consistent with the normal domain of KNAT1's expression and further suggest that kn1-related genes may have played a role in the evolution of leaf diversity.

Homeobox genes in the functioning of plant meristems

The maize homebox gene knotted1 (kn1) is expressed in vegetative and floral meristems and is down-regulated at the site of primordia formation. kn1-related genes from maize and other species also show meristem-specific expression and offer additional tools for studying the activities of shoot meristems. Members of this gene family are expressed early in embryogenesis, providing molecular markers for meristem initiation. Ectopic expression of either kn1 or a related Arabidopsis gene, KNAT1, causes dramatic alterations in Arabidopsis and tobacco leaf morphology. Most significantly, meristems form on the leaf, producing small shoots. We discuss whether the phenotypes can be interpreted as changes in positional information or timing of determination.

Weanling and adult rats differ in fatty acid and carnitine metabolism during sepsis

Increased oxidation of fat is an important host response to sepsis, and carnitine is essential for long-chain fatty acid oxidation. Because neonates have low levels of carnitine, their ability to respond to a septic insult may be impaired. The purpose of this study was to compare fatty acid and carnitine metabolism in septic weanling (60 to 85 g) and septic adult (285 to 310 g) rats. Sepsis was induced in weanling and adult male Sprague-Dawley rats by cecal ligation and puncture (CLP). The rats were killed 16 hours after CLP or sham operation, and serum glucose, lactate, beta-hydroxybutyrate, fatty acid, carnitine, liver fatty acid, and tissue carnitine levels were measured. The data suggest that during sepsis weanling rats may be more dependent on fatty acid oxidation than adult rats are, as evidenced by their elevated serum fatty acid and acylcarnitine levels, and relative hypoglycemia and hyperketonemia. In addition, although total serum carnitine levels were increased in both adult and weanling septic rats, tissue carnitine levels of weanling rats became significantly depleted during sepsis, unlike in adult rats. This study supports further investigation regarding the role of exogenous carnitine in newborn sepsis.

Tagging and Cloning of a Petunia Flower Color Gene with the Maize Transposable Element Activator

We report here the use of the maize transposable element Activator (Ac) to isolate a dicot gene. Ac was introduced into petunia, where it transposed into Ph6, one of several genes that modify anthocyanin pigmentation in flowers by affecting the pH of the corolla. Like other Ac-mutable alleles, the new mutation is unstable and reverts to a functional form in somatic and germinal tissues. The mutant gene was cloned using Ac as a probe, demonstrating the feasibility of heterologous transposon tagging in higher plants. Confirmation that the cloned DNA fragment corresponded to the mutated gene was obtained from an analysis of revertants. In every case examined, reversion to the wild-type phenotype was correlated with restoration of a wild-type-sized DNA fragment. New transposed Acs were detected in many of the revertants. As in maize, the frequency of somatic and germinal excision of Ac from the mutable allele appears to be dependent on genetic background.

Antenatal diagnosis of mucopolysaccharidosis type I (Hurler's disease) is not possible by electron microscopy of uncultured amniotic fluid cells

Mucopolysaccharidosis type I (MPS I) is a lysosomal storage disorder characterised by the deficient activity of iduronidase and by the presence of MPS vacuoles in many tissues of affected patients. We studied whether these characteristics could be used for the antenatal diagnosis of the disease. We obtained amniotic fluid cells from two pregnancies at risk for MPS I, one pregnancy at risk for GSD II (another lysosomal disease), and eight normal control pregnancies. Measurements of iduronidase activity in cultured amniotic fluid cells indicated the presence of a MPS I fetus in one high risk pregnancy and an unaffected fetus in the other. This diagnosis was confirmed at delivery. On electron microscopy the uncultured amniotic fluid cells exhibited MPS-like vacuoles in the pregnancy with a GSD II fetus, in three of eight normal pregnancies, and in the pregnancy at risk for MPS I that had a normal fetus. No such vacuoles were seen in the pregnancy with the MPS I fetus. These false positive and false negative findings indicate that antenatal diagnosis of MPS I cannot be based on the electron microscopic presence or absence of MPS I vacuoles in uncultured amniotic fluid cells.

Rapid prenatal diagnosis of glycogen-storage disease type II by electron microscopy of uncultured amniotic-fluid cells

Glycogen-storage disease Type IIa is a fatal, genetically determined disease of infancy or early childhood that is characterized by deficient activity of acid alpha-glucosidase and by the presence of intracellular vacuoles full of glycogen, which are found in most tissues, including skin and liver. On electron microscopy these specific vacuoles are tightly packed accumulations of glycogen particles surrounded by a single membrane. We did electron-microscopical examinations on uncultured amniotic-fluid cells from 26 women whose fetuses were at risk for glycogen-storage disease Type IIa and from 8 normal control pregnant women. We found specific vacuoles in cells from 6 of the 26 high-risk patients. At delivery, glycogen-storage disease Type IIa was present in the infants of these 6 women and absent in those of the other 20 according to results of clinical, biochemical, and electron-microscopical studies of gestational products. After amniocentesis at 15 to 18 weeks of gestation, the prenatal diagnosis made by electron microscopy of uncultured amniotic-fluid cells was available in three to six days, whereas it took from three to six weeks to make the diagnosis by enzymatic analysis of the cultured amniotic-fluid cells. We conclude that the electron-microscopical prenatal diagnosis of glycogen-storage disease Type IIa is rapid, safe, and reliable. It should facilitate earlier diagnosis and thereby help to preserve parental options.

Membranoproliferative glomerulonephritis and alpha 1-antitrypsin deficiency in children

Two white girls had reduced serum concentration of alpha 1-antitrypsin (alpha-AT), phenotype ZZ, and liver disease. Hepatocytes exhibited the microscopic criteria of alpha-AT deficiency. Hypocomplementemia, elevated circulating immune complexes (patient 1), clinical signs of renal disease, and the histologic findings of membranoproliferative glomerulonephritis (MPGN) type I developed. Immunoglobulin A (but not alpha-AT) was demonstrable immunologically as a component of glomerular deposits in patient 1. Among 53 patients with MPGN but without clinical signs of liver disease, none had Pi type Z. Among 23 patients with phenotype ZZ but without clinical signs of kidney disease, six had abnormal complement protein levels, but the pattern did not resemble that of idiopathic MPGN type I. These results are consistent with the conclusion that MPGN in the two patients reported here is a consequence of their chronic liver disease and is not directly related to the presence of the allelic alpha-AT variant PiZ.

Alpha 1-antitrypsin phenotype: transient cathodal shift in serum of infant girl with urinary cytomegalovirus and fatty liver

A 2-month-old white girl had severe liver disease (but without signs of hepatic necrosis, infection or cirrhosis), urinary cytomegalovirus, transient reduction of alpha 1-antitrypsin concentration and transient abnormal alpha 1-antitrypsin phenotype that were not present in her parents. Five serum specimens that were obtained during the 11/2 months of acute phase liver disease indicated, by polyacrylamide gel isoelectric focusing (PAG-IEF), acid starch gel and agarose electrophoresis as well as immunofixation, an unusual alpha 1-antitrypsin phenotype that we labeled delta (delta). It migrated adjacent to Z, i.e., cathodal of Z and Zpratt on PAG-IEF; anodal of Z but cathodal of X, S, Zpratt on starch gel. We labeled the girl's complete phenotype M delta. After clinical recovery, her phenotype was MM and identical to that of her parents. Hepatic electronmicroscopy of the acute phase specimen showed dilated bile canaliculi. We observed the following in hepatocytes: clusters of globular inclusions surrounded by myelin sheets that, to a lesser extent, also appeared in the liver of CMV-infected children with phenotype MM; dilated endoplasmic reticulum cisternae that contained floccular material; and marked steatosis. These changes were less severe in the convalescent liver specimen.

PiPclifton: a new alpha 1-antitrypsin allele in an American Negro family

Serum specimens from eight females and two males representing three generations of an American Negro family exhibited an α₁-antitrypsin phenotype that we labelled MPclifton because of its electrophoretic mobility. The family study and examination of multiple specimens from the same subject indicated that the phenotype represented an α₁-antitrypsin allele, labelled Pi^Pclifton. The new genetic variant is not associated with deficiency of α₁-antitrypsin or of trypsin inhibitory capacity in the serum.

PiZpratt: a new alpha 1-antitrypsin allele in an American Negro family

A rare alpha 1-antitrypsin phenotype was detected in serum of individuals belonging to three generations of an American Negro family. Following the recommended guidelines of nomenclature, we labeled the new Pi type Zpratt; the corresponding allele is PiZpratt. Alpha 1-antitrypsin concentration and trypsin inhibitory capacity are normal in MZpratt serum.

Pi Ecincinnati: a new alpha 1-antitrypsin allele in three Negro families

Serum specimens of three unrelated black males had an unusual alpha-1-antitrypsin phenotype, designated pi Ecincinnati because of its electrophoretic mobility. Family studies indicated that the new phenotype was the expression of an alpha-1-antitrypsin allele, labeled pi Ecincinnati.

Deficient activity of dephosphophosphorylase kinase and accumulation of glycogen in the liver

Low activity of phosphorylase and increased concentration of glycogen were found in liver tissue from five children with asymptomatic hepatomegaly. In vitro activation of liver phosphorylase in these patients occurred at the rate of 10% or less of normal. Elimination of the defect by the addition of kinase that activates phosphorylase demonstrated the integrity of the phosphorylase enzyme and the deficient activity of dephophophosphorylase kinase. On the average, 60% of the phosphorylase enzyme of normal human liver was in the active form. Phosphorylase kinase of rabbit muscle activated phosphorylase of normal human liver to a final value that was significantly higher than the one obtained in the absence of muscle phosphorylase kinase. The ultrastructural examination of hepatic tissue from the five patients revealed increased amounts of glycogen. There was scarcity of endoplasmic reticulum. There was intercellular glycogen in continuity with the glycogen of the hepatocytes through breaks in their circumference. Lipid droplets with lucid areas in the form of needles and plates contained aggregates of glycogen. There were numerous lysosomes, some containing glycogen. Large vacuoles filled with glycogen and surrounded by a membrane were seen occasionally. The vacuoles might reflect the lysosomal pathway of glycogen degradation, since there was apparent fusion of such autophagic vacuoles with small vesicles resembling primary lysosomes.

Phosphorylase kinase of the liver: deficiency in a girl with increased hepatic glycogen

Studies of a child with glycogenosis revealed an increased concentration of glycogen and low phosphorylase activity in her liver. Using mixtures of homogenates of the patient's liver and of normal liver, we found the low phosphorylase activity to be caused by a deficiency of phosphorylase kinase and not of hepatic phosphorylase. The fact that phosphorylase activity was restored to normal values by the addition of phosphorylase b kinase from rabbit muscle substantiates this conclusion.