A unique program for cell death in xylem fibers of Populus stem

Maturation of the xylem elements involves extensive deposition of secondary cell-wall material and autolytic processes resulting in cell death. We describe here a unique type of cell-death program in xylem fibers of hybrid aspen (Populus tremula x P. tremuloides) stems, including gradual degradative processes in both the nucleus and cytoplasm concurrently with the phase of active cell-wall deposition. Nuclear DNA integrity, as determined by TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling) and Comet (single-cell gel electrophoresis) assays, was compromised early during fiber maturation. In addition, degradation of the cytoplasmic contents, as detected by electron microscopy of samples fixed by high-pressure freezing/freeze substitution (HPF-FS), was gradual and resulted in complete loss of the cytoplasmic contents well before the loss of vacuolar integrity, which is considered to be the moment of death. This type of cell death differs significantly from that seen in xylem vessels. The loss of vacuolar integrity, which is thought to initiate cell degradative processes in the xylem vessels, is one of the last processes to occur before the final autolysis of the remaining cell contents in xylem fibers. High-resolution microarray analysis in the vascular tissues of Populus stem, combined with in silico analysis of publicly available data repositories, suggests the involvement of several previously uncharacterized transcription factors, ethylene, sphingolipids and light signaling as well as autophagy in the control of fiber cell death.

The maize transcription factor myb-related protein-1 is a key regulator of the differentiation of transfer cells

Transfer cells are highly modified plant cells specialized in the transport of solutes. They differentiate at many plant exchange surfaces, including phloem loading and unloading zones such as those present in the sink organs and seeds. In maize (Zea mays) seeds, transfer cells are located at the base of the endosperm. It is currently unknown how apical-basal polarity is established or why the peripheral cells at the base of the endosperm differentiate into transfer instead of aleurone cells. Here, we show that in epidermal cells committed to develop into aleurone cells, the ectopic expression of the transfer cell-specific transcriptional activator Myb-Related Protein-1 (MRP-1) is sufficient to temporarily transform them into transfer cells. These transformed cells acquire distinct transfer cell features, such as cell wall ingrowths and an elongated shape. In addition, they express a number of MRP-1 target genes presumably involved in defense. We also show that the expression of MRP-1 is needed to maintain the transfer cell phenotype. Later in development, an observed reduction in the ectopic expression of MRP-1 was followed by the reversion of the transformed cells, which then acquire aleurone cell features.

Mapping of QTLs for androgenetic response based on a molecular genetic map of x Triticosecale Wittmack

Quantitative trait loci (QTLs) for androgenetic response were mapped in a doubled haploid (DH) population derived from the F1 hybrid of 2 unrelated varieties of triticale, 'Torote' and 'Presto'. A molecular marker linkage map of this cross was previously constructed using 73 DH lines. This map contains 356 markers (18 random amplified 5 polymorphic DNA, 40 random amplified microsatellite polymorphics, 276 amplified fragment length polymorphisms, and 22 simple sequence repeats) and was used for QTL analysis. The genome was well covered, and of the markers analysed, 336 were located in 21 linkage groups (81.9%) identified using SSR markers. The map covered a total length of 2465.4 cM with an average of 1 marker for each 6.9 cM. The distribution of the markers was not homogeneous across the 3 genomes, with 50.7% detected in the R genome. Several QTLs were found for the following variables related to the androgenetic response: number of embryos/100 anthers; plants regenerated from 100 embryos; number of green plants/total number of plants; and number of green plants/1000 anthers. Two were detected on chromosome 6B and 4R, which together had a 30% total influence on the induction of embryos. Another was found on 6B and on the unidentified LG1; these influenced the production of total plants from haploid embryo cultures. One QTL on chromosome 3R determined the photosynthetic viability of the haploid plantlets regenerated from microspores. Other QTLs were found on chromosomes 1B, 1R, 4R, and 7R, which helped the control of the final androgenetic response (the number of plantlets obtained for every 1000 anthers cultured).

The function of two type II metacaspases in woody tissues of Populus trees

Metacaspases (MCs) are cysteine proteases that are implicated in programmed cell death of plants. AtMC9 (Arabidopsis thaliana Metacaspase9) is a member of the Arabidopsis MC family that controls the rapid autolysis of the xylem vessel elements, but its downstream targets in xylem remain uncharacterized. PttMC13 and PttMC14 were identified as AtMC9 homologs in hybrid aspen (Populus tremula × tremuloides). A proteomic analysis was conducted in xylem tissues of transgenic hybrid aspen trees which carried either an overexpression or an RNA interference construct for PttMC13 and PttMC14. The proteomic analysis revealed modulation of levels of both previously known targets of metacaspases, such as Tudor staphylococcal nuclease, heat shock proteins and 14-3-3 proteins, as well as novel proteins, such as homologs of the PUTATIVE ASPARTIC PROTEASE3 (PASPA3) and the cysteine protease RD21 by PttMC13 and PttMC14. We identified here the pathways and processes that are modulated by PttMC13 and PttMC14 in xylem tissues. In particular, the results indicate involvement of PttMC13 and/or PttMC14 in downstream proteolytic processes and cell death of xylem elements. This work provides a valuable reference dataset on xylem-specific metacaspase functions for future functional and biochemical analyses.

Protein Profiles of Lipid Droplets during the Hypersensitive Defense Response of Arabidopsis against Pseudomonas Infection

Lipid droplets (LDs) have classically been viewed as seed storage particles, yet they are now emerging as dynamic organelles associated with developmental and stress responses. Nevertheless, their involvement in plant immunity has still been little studied. Here, we found LD accumulation in Arabidopsis thaliana leaves that induced a hypersensitive response (HR) after Pseudomonas infection. We established a protocol to reproducibly isolate LDs and to analyze their protein content. The expression of GFP fusion proteins in Nicotiana benthamiana and in transgenic Arabidopsis lines validated the LD localization of glycerol-3-phosphate acyltransferase 4 (GPAT4) and 8 (GPAT8), required for cutin biosynthesis. Similarly, we showed LD localization of α-dioxygenase1 (α-DOX1) and caleosin3 (CLO3), involved in the synthesis of fatty acid derivatives, and that of phytoalexin-deficient 3 (PAD3), which is involved in camalexin synthesis. We found evidence suggesting the existence of different populations of LDs, with varying protein contents and distributions. GPAT4 and GPAT8 were associated with LDs inside stomata and surrounding cells of untreated leaves, yet they were mainly confined to LDs in guard cells after bacterial inoculation. By contrast, α-DOX1 and PAD3 were associated with LDs in the epidermal cells of HR-responding leaves, with PAD3 mostly restricted to cells near dead tissue, while CLO3 had a more ubiquitous distribution. As such, the nature of the proteins identified, together with the phenotypic examination of selected mutants, suggests that LDs participate in lipid changes and in the production and transport of defense components affecting the interaction of plants with invading pathogens.

Random amplified polymorphic DNA and amplified fragment length polymorphism assessment of genetic variation in Nicaraguan populations of Pinus oocarpa

Pinus oocarpa is the most widely distributed pine species of Mexico and Central America. The natural populations of Nicaragua have been affected by extensive human activities. As a consequence, their size has been reduced, and there is a serious threat to the development of mature woodland. Knowledge of population structures and the genetic diversity of the species is required for the design of sustainable use and conservation strategies. Random amplified polymorphic DNA (RAPD) and amplified fragment length polymorphism (AFLP) markers were used to assess the genetic variation among 10 populations from three geographical regions of Nicaragua. Both markers revealed high levels of diversity in these populations. G(ST) values and analyses of molecular variance (AMOVA) found that most variation was within populations but there is still a significant differentiation between populations indicating that the populations sampled cannot be considered a single panmictic unit. The partitions created by AMOVA also showed that there was little differentiation between populations of different regions, although cluster analyses based on RAPDs and AFLPs indicated a closer relationship among most of the populations from a same geographical region. Management of P. oocarpa in Nicaragua should be aimed to maintain the high degree of genetic variation within individual populations that is still observed even in some of these highly degraded populations.

The maize transfer cell-specific type-A response regulator ZmTCRR-1 appears to be involved in intercellular signalling

Response regulators are signal-transduction molecules present in bacteria, yeast and plants, acting as relays for environmental challenges. This paper reports the characterization of a Zea mays gene, ZmTCRR-1, that codes for a member of the type-A response regulator class of proteins. The gene was found to be expressed exclusively in the endosperm transfer-cell layer 8-14 days after pollination, when transfer-cell differentiation is most active. The promoter of ZmTCRR-1 was strongly transactivated in heterologous systems by the transfer cell-specific transcription factor ZmMRP-1. The ZmTCRR-1 protein was detected not only in the transfer-cell layer, but also in the conductive tissue deep inside the endosperm, where there is no transcription of the gene. This suggests that two-component systems might be involved in intercellular signal transmission, in contrast to the generally held belief that these systems are involved only in cell-autonomous pathways.

Cell wall invertase activity regulates the expression of the transfer cell-specific transcription factor ZmMRP-1

Studies in cell wall bound invertase mutants indicate that the promoter of the transfer cell-specific transcription factor, ZmMRP - 1 , is modulated by the carbohydrate balance. Transfer cells are highly specialized plant cells located at the surfaces that need to support an intensive exchange of nutrients, such as the entrance of fruits, seeds and nodules or the young branching points along the stem. ZmMRP-1 is a one-domain MYB-related transcription factor specifically expressed at the transfer cell layer of the maize endosperm. Previous studies demonstrated that this factor regulates the expression of a large number of transfer cell-specific genes, and suggested that ZmMRP-1 is a key regulator of the differentiation of this tissue. The expression of this gene is largely dominated by positional cues, but within the ZmMRP-1 expressing cells the promoter appears to be modulated by sugars. Here we have investigated in vivo this modulation. Using maize and Arabidopsis mutants for cell wall invertase genes, we found that the absence of cell wall invertase activity is a major inductive signal of the ZmMRP-1 expression.

Solar recharging system for hearing aid cells

We present a solar recharging system for nickel-cadmium cells of interest in areas where batteries for hearing aids are difficult to obtain. The charger has sun cells at the top. Luminous energy is converted into electrical energy, during the day and also at night if there is moonlight. The cost of the charger and hearing aid is very low at 35 US$. The use of solar recharging for hearing aids would be useful in alleviating the problems of deafness in parts of developing countries where there is no electricity.

Oxylipins From Different Pathways Trigger Mitochondrial Stress Signaling Through Respiratory Complex III

Plant oxylipins are signaling molecules produced from fatty acids by oxidative pathways, mainly initiated by 9- and 13-lipoxygenases (9-LOX and 13-LOX), alpha-dioxygenases or non-enzymatic oxidation. Oxylipins from the 9-LOX pathway induce oxidative stress and control root development and plant defense. These activities have been associated with mitochondrial processes, but precise cellular targets and pathways remain unknown. In order to study oxylipin signaling, we previously generated a collection of Arabidopsis thaliana mutants that were insensitive to the 9-LOX products 9(S)-hydroxy-10,12, 15-octadecatrienoic acid (9-HOT) and its ketone derivative 9-KOT (noxy mutants). Here, we describe noxy1, noxy3, noxy5, noxy23, and noxy54 mutants, all affected in nucleus-encoded mitochondrial proteins, and use them to study the role of mitochondria in oxylipin signaling. Functional and phenotypic analyses showed that noxy plants displayed mitochondrial aggregation, reduced respiration rates and resistance to the complex III inhibitor Antimycin A (AA), thus indicating a close similarity of the oxylipin signaling and mitochondrial stress. Application of 9-HOT and 9-KOT protected plants against subsequent mitochondrial stress, whereas they boosted root growth reduction when applied in combination with complex III inhibitors but did not with inhibitors of other respiratory complexes. A similar effect was caused by linear-chain oxylipins from 13-LOX or non-enzymatic pathways having α,β-unsaturated hydroxyl or keto groups in their structure. Studies to investigate 9-HOT and 9-KOT activity indicated that they do not reduce respiration rates, but their action is primarily associated with enhanced ROS responses. This was supported by the results showing that 9-HOT or 9-KOT combined with AA amplified the expression of oxylipin- and ROS-responding genes but not of the AA marker AOX1a, thus implying the activation of a specific mitochondria retrograde signaling pathway. Our results implicate mitochondrial complex III as a hub in the signaling activity of multiple oxylipin pathways and point at downstream ROS responses as components of oxylipin function.

zmsbt1 and zmsbt2, two new subtilisin-like serine proteases genes expressed in early maize kernel development

Two subtilisin-like proteases show highly specific and complementary expression patterns in developing grains. These genes label the complete surface of the filial-maternal interface, suggesting a role in filial epithelial differentiation. The cereal endosperm is the most important source of nutrition and raw materials for mankind, as well as the storage compartment enabling initial growth of the germinating plantlets. The development of the different cell types in this tissue is regulated environmentally, genetically and epigenetically, resulting in the formation of top-bottom, adaxial-abaxial and surface-central axes. However, the mechanisms governing the interactions among the different inputs are mostly unknown. We have screened a kernel cDNA library for tissue-specific transcripts as initial step to identify genes relevant in cell differentiation. We report here on the isolation of two maize subtilisin-related genes that show grain-specific, surficial expression. zmsbt1 (Zea mays Subtilisin1) is expressed at the developing aleurone in a time-regulated manner, while zmsbt2 concentrates at the pedicel in front of the endosperm basal transfer layer. We have shown that their presence, early in the maize caryopsis development, is dependent on proper initial tissue determination, and have isolated their promoters to produce transgenic reporter lines that assist in the study of their regulation.

Robust and efficient genotyping of factor V and prothrombin alleles using amplicon high-resolution melting and synthetic DNA controls: validation of the test with three different commercial chemistries

OBJECTIVES

Developing robust HRM (amplicon High Resolution Melting) analysis valid for different commercial reaction mixes, using synthetic control DNA samples and the RotorGeneQ (Qiagen) instrument.

DESIGN AND METHODS

126 samples were analyzed for the presence of the factor Leiden and the 20210G>A prothrombin alleles. The four alleles were cloned and used to prepare synthetic controls.

RESULTS

All mutant alleles present in the sample were successfully detected. Genotyping confidence mean was higher than 95%.

CONCLUSIONS

Cost effective HRM genotyping is very reliable using synthetic control DNAs and the RotorGenQ instrument.

ZmLrk-1, a receptor-like kinase induced by fungal infection in germinating seeds

We report here on the identification and characterization of ZmLrk-1, a member of the Lrk class of receptor-like kinases in Zea mays. This gene was found to be located at the bin21.40 region on the short arm of maize chromosome 8, closely linked to the previously reported pseudogene of the same class psiZmLrk (originally called Zm2Lrk). Transient expression experiments in onion epithelium cells, using a ZmLrk-1:GFP fusion protein, indicate that ZmLrk-1 is a membrane protein. ZmLrk-1 is ubiquitously expressed in the maize plant, including roots and aerial parts. In seeds, ZmLrk-1 transcripts can be detected by in situ hybridization exclusively at the basal endosperm transfer cell layer during the first stages of development. However, from 14 days after pollination its transcripts are preferentially detected at the upper half of the kernel, including both the aleurone and the starchy endosperm. ZmLrk-1 expression is not induced after treatment with salicylic acid, jasmonic acid or wounding, but it clearly increases after infection of germinating seeds with Fusarium oxysporum. This suggests that ZmLrk-1 could be involved in a sensing system to activate plant defence mechanisms against fungal attacks during endosperm development and seed germination.

A PCR-based forward genetics screening, using expression domain-specific markers, identifies mutants in endosperm transfer cell development

Mutant collections are an invaluable source of material on which forward genetic approaches allow the identification of genes affecting a wide variety of biological processes. However, some particular developmental stages and morphological structures may resist analysis due to their physical inaccessibility or to deleterious effects associated to their modification. Furthermore, lethal mutations acting early in development may escape detection. We have approached the characterization of 101 maize seed mutants, selected from a collection of 27,500 visually screened Mu-insertion lines, using a molecular marker approach based on a set of genes previously ascribed to different tissue compartments within the early developing kernel. A streamlined combination of qRT-PCR assays has allowed us to preliminary pinpoint the affected compartment, establish developmental comparisons to WT siblings and select mutant lines with alterations in the different compartments. Furthermore, clusters of markers co-affected by the underlying mutation were identified. We have analyzed more extensively a set of lines presenting significant variation in transfer cell-associated expression markers, and have performed morphological observations, and immunolocalization experiments to confirm the results, validating this approach as an efficient mutant description tool.

Molecular dissection of the interaction between the transcriptional activator ZmMRP-1 and the promoter of BETL-1

The interaction between the transfer cell specific transcriptional activator ZmMRP-1 and the promoter of the transfer cell specific gene BETL-1 constitutes an exceptionally robust system. Reporter constructs containing the BETL-1 promoter are virtually silent in a variety of cell types, from maize leaves to yeast. The introduction of ZmMRP-1 in co-transformation assays leads to the transactivation of the reporter construct by up to two orders of magnitude. In this work we have investigated the molecular basis of this interaction. We found that the BETL-1 promoter includes four potential targets for ZmMRP-1 binding, consisting of a 12 bp motif containing two repeats. Co-transformation assays and electrophoretic mobility shift experiments identified the sequence TATCTCTATCTC as the preferred one for the interaction with the transcription factor. Identification of similar sequences in other transfer cell specific promoters lead us to propose as a transfer cell box a sequence related to those identified in the BETL-1 promoter, positioned 50-100 bp upstream the TATA box.

The detection, cloning, and characterisation of WIS 2-1A retrotransposon-like sequences in Triticum aestivum L. and xTriticosecale Wittmack and an examination of their evolution in related Triticeae

Retrotransposons and other mobile elements are major components of the repeated DNA fraction in higher-plant genomes. They have undoubtedly played an important role in higher plant genome evolution. The present work details the detection and characterisation of a WIS 2-1A related sequence in direct wheat relatives, and discusses the prevalence and evolution of its copy number in their genomes. An increase in copy number is detected when following the natural hybridisation processes that gave rise to bread and durum wheats. However, the opposite is observed in the development of triticale, a synthetic hybrid.

[Importance of Mycoplasma pneumoniae and Chlamydia pneumoniae in children with community-acquired pneumonia]

OBJECTIVES

To determine the importance of Mycoplasma pneumoniae and Chlamydia pneumoniae in community-acquired pneumonia (CAP) of children from different latitudes and to compare clinical outcome using azithromycin (AZM) versus either amoxicillin-clavulanate (A-C) or erythromycin estolate (EE).

METHODS

Ambulatory patients with CAP were identified at either the Children's Medical Center of Dallas, Texas or the Hospital del Niño of Panama City, Panama. Children 6 months to 15 years of age were enrolled and randomized to receive either AZM for 5 days or a 10 day course of either A-C or EE, for those younger or older than 5 years of age, respectively. Mycoplasma pneumoniae and C. pneumoniae were identified by measuring acute and convalescent serum antibody titers and by performing nasopharyngeal (NP) and oropharyngeal (OP) swabs for culture and polymerase chain reaction (PCR) testing.

RESULTS

Overall 335 patients (168 in Dallas and 167 in Panama) were evaluated from February 1996 through December 1997. Acute M. pneumoniae infection was detected in 12 (7%) patients each in Dallas and Panama. Acute C. pneumoniae infection was observed in 10 (6%) children at each site. Infection caused by these "atypical" microorganisms occurred more frequently in children older than 5 years of age (23% vs 9%, P = 0.001, RR 2.5, 95% CI 1.4-4.3). No distinctive pattern of clinical or radiologic abnormalities was seen in relation to etiology. Clinical cure was achieved in 43 of 44 children infected by these bacteria regardless of treatment assignment.

CONCLUSION

Mycoplasma pneumoniae and C. pneumoniae are common etiologic agents of CAP in older children from different latitudes. Children with CAP present with similar clinical and radiologic findings to those caused by other etiologic agents. Outcome was excellent for the three treatment regimens studied.