MARIS plays important roles in Arabidopsis pollen tube and root hair growth

In flowering plants, male gametes are delivered to female gametes for double fertilization through pollen tubes.Therefore, pollen tube growth is crucial for double fertilization. Despite its importance to sexual reproduction, genetic mechanisms of pollen tube growth remain poorly understood.In this study, we characterized the receptor-like cytoplasmic protein kinase(RLCK) gene, MARIS(MRI) that plays critical roles in pollen tube growth. MRI is preferentially expressed in pollen grains, pollen tubes and roots. Mutation in MRI by a Ds insertion led to a burst of pollen tubes after pollen germination. Pollen-rescue assay by pollen and pollen tubespecific expression of MRI in the mri-4 mutant showed that loss of MRI function also severely affected root hair elongation. MRI protein interacted with the protein kinase OXIDATIVE SIGNAL INDUCIBLE1(OXI1) in the in vitro and in vivo assays, which functions in plant defence and root hair development, and was phosphorylated by OXI1 in vitro. Our results suggest that MRI plays important roles in pollen tube growth and may function in root hair elongation through interaction with OXI1.     

AtTMEM18 plays important roles in pollen tube and vegetative growth in Arabidopsis

In flowering plants, pollen tube growth is essential for delivery of male gametes into the female gametophyte or embryo sac for double fertilization. Although many genes have been identified as being involved in the process, the molecular mechanisms of pollen tube growth remains poorly understood. In this study, we identified that the Arabidopsis Transmembrane Protein 18 (AtTMEM18) gene played important roles in pollen tube growth. The AtTMEM18 shares a high similarity with the Transmembrane 18 proteins (TMEM18s) that are conserved in most eukaryotes and may play important roles in obesity in humans. Mutation in the AtTMEM18 by a Ds insertion caused abnormal callose deposition in the pollen grains and had a significant impact on pollen germination and pollen tube growth. AtTMEM18 is expressed in pollen grains, pollen tubes, root tips and other vegetative tissues. The pollen‐rescued assays showed that the mutation in AtTMEM18 also caused defects in roots, stems, leaves and transmitting tracts. AtTMEM18‐GFP was located around the nuclei. Genetic assays demonstrated that the localization of AtTMEM18 around the nuclei in the generative cells of pollen grains was essential for the male fertility. Furthermore, expression of the rice TMEM18‐homologous protein (OsTMEM18) driven by LAT52 promoter could recover the fertility of the Arabidopsis attmem18 mutant. These results suggested that the TMEM18 is important for plant growth in Arabidopsis.     

Heat shock protein 101 plays a crucial role in thermotolerance in Arabidopsis

Plants are sessile organisms, and their ability to adapt to stress is crucial for survival in natural environments. Many observations suggest a relationship between stress tolerance and heat shock proteins (HSPs) in plants, but the roles of individual HSPs are poorly characterized. We report that transgenic Arabidopsis plants expressing less than usual amounts of HSP101, a result of either antisense inhibition or cosuppression, grew at normal rates but had a severely diminished capacity to acquire heat tolerance after mild conditioning pretreatments. The naturally high tolerance of germinating seeds, which express HSP101 as a result of developmental regulation, was also profoundly decreased. Conversely, plants constitutively expressing HSP101 tolerated sudden shifts to extreme temperatures better than did vector controls. We conclude that HSP101 plays a pivotal role in heat tolerance in Arabidopsis. Given the high evolutionary conservation of this protein and the fact that altering HSP101 expression had no detrimental effects on normal growth or development, one should be able to manipulate the stress tolerance of other plants by altering the expression of this protein.     

BAK1 plays contrasting roles in regulating abscisic acid-induced stomatal closure and abscisic acid-inhibited primary root growth in Arabidopsis

The mechanisms that balance plant growth and stress responses are poorly understood, but they appear to involve abscisic acid (ABA) signaling mediated by protein kinases. Here, to explore these mechanisms, we examined the responses of Arabidopsis thaliana protein kinase mutants to ABA treatment. We found that mutants of BRASSINOSTEROID INSENSITIVE 1-ASSOCIATED RECEPTOR KINASE 1 (BAK1) were hypersensitive to the effects of ABA on both seed germination and primary root growth. The kinase OPEN STOMATA 1 (OST1) was more highly activated by ABA in bak1 mutant than the wild type. BAK1 was not activated by ABA treatment in the dominant negative mutant abi1-1 or the pyr1 pyl4 pyl5 pyl8 quadruple mutant, but it was more highly activated by this treatment in the abi1-2 abi2-2 hab1-1 loss-of-function triple mutant than the wild type. BAK1 phosphorylates OST1 T146 and inhibits its activity. Genetic analyses suggested that BAK1 acts at or upstream of core components in the ABA signaling pathway, including PYLs, PP2Cs, and SnRK2s, during seed germination and primary root growth. Although the upstream brassinosteroid (BR) signaling components BAK1 and BR INSENSITIVE 1 (BRI1) positively regulate ABA-induced stomatal closure, mutations affecting downstream components of BR signaling, including BRASSINOSTEROID-SIGNALING KINASEs (BSKs) and BRASSINOSTEROID-INSENSITIVE 2 (BIN2), did not affect ABA-mediated stomatal movement. Thus, our study uncovered an important role of BAK1 in negatively regulating ABA signaling during seed germination and primary root growth, but positively modulating ABA-induced stomatal closure, thus optimizing the plant growth under drought stress.     

Guarding the guardian: Mdmx plays important roles in setting p53 basal activity and determining biological responses in vivo

Comment on: Wang YV, et al. Cancer Cell 2009; 16:33-43.     

Humanin-induced autophagy plays important roles in skeletal muscle function and lifespan extension

BackgroundAutophagy, a highly conserved homeostatic mechanism, is essential for cell survival. The decline of autophagy function has been implicated in various diseases as well as aging. Although mitochondria play a key role in the autophagy process, whether mitochondrial-derived peptides are involved in this process has not been explored.MethodsWe developed a high through put screening method to identify potential autophagy inducers among mitochondrial-derived peptides. We used three different cell lines, mice, c.elegans, and a human cohort to validate the observation.ResultsHumanin, a mitochondrial-derived peptide, increases autophagy and maintains autophagy flux in several cell types. Humanin administration increases the expression of autophagy-related genes and lowers accumulation of harmful misfolded proteins in mice skeletal muscle, suggesting that humanin-induced autophagy potentially contributes to the improved skeletal function. Moreover, autophagy is a critical role in humanin-induced lifespan extension in C. elegans.ConclusionsHumanin is an autophagy inducer.General significanceThis paper presents a significant, novel discovery regarding the role of the mitochondrial derived peptide humanin in autophagy regulation and as a possible therapeutic target for autophagy in various age-related diseases.     

Muscle LIM protein plays both structural and functional roles in skeletal muscle

Muscle LIM protein (MLP) has been suggested to be an important mediator of mechanical stress in cardiac tissue, but the role that it plays in skeletal muscle remains unclear. Previous studies have shown that it is dramatically upregulated in fast-to-slow fiber-type transformation and also after eccentric contraction (EC)-induced muscle injury. The functional consequences of this upregulation, if any, are unclear. In the present study, we have examined the skeletal muscle phenotype of MLP-knockout (MLPKO) mice in terms of their response to EC-induced muscle injuries. The data suggest that while the MLPKO mice recover completely after EC-induced injury, their torque production lags behind that of heterozygous littermates in the early stages of the recovery process. This lag is accompanied by decreased expression of the muscle regulatory factor MyoD, suggesting that MLP may influence gene expression. In addition, there is evidence of type I fiber atrophy and a shorter resting sarcomere length in the MLPKO mice, but no significant differences in fiber type distribution. In summary, MLP appears to play a subtle role in the maintenance of normal muscle characteristics and in the early events of the recovery process of skeletal muscle to injury, serving both structural and gene-regulatory roles. eccentric contractions; passive tension     

The Polo-like kinase PLKA in Aspergillus nidulans is not essential but plays important roles during vegetative growth and development

The Polo-like kinases (Plks) are conserved, multifunctional cell cycle regulators that are induced in many forms of cancer and play additional roles in metazoan development. We previously identified plkA in Aspergillus nidulans, the only Plk investigated in filamentous fungi to date, and partially characterized its function through overexpression. Here, we report the plkA null phenotype. Surprisingly, plkA was not essential, unlike Plks in other organisms that contain a single homologue. A subset of cells lacking PLKA contained defects in spindle formation and chromosome organization, supporting some conservation in cell cycle function. However, septa were present, suggesting that PLKA, unlike other Plks, is not a central regulator of septation. Colonies lacking PLKA were compact with multibranched hyphae, implying a role for this factor in aspects of hyphal morphogenesis. These defects were suppressed by high temperature or low concentrations of benomyl, suggesting that PLKA may function during vegetative growth by influencing microtubule dynamics. However, the colonies also showed reduced conidiation and precocious formation of sexual Hülle cells in a benomyl- and temperature-insensitive manner. This result suggests that PLKA may influence reproduction through distinct mechanisms and represents the first example of a link between Plk function and development in fungi. Finally, filamentous fungal Plks have distinct features, and phylogenetic analyses reveal that they may group more closely with metazoan PLK4. In contrast, yeast Plks are more similar to metazoan proteins PLK1 to PLK3. Thus, A. nidulans PLKA shows some conservation in cell cycle function but may also play novel roles during hyphal morphogenesis and development.     

Non‐marine turtle plays important functional roles in Indonesian ecosystems

The Southeast Asian box turtle (Cuora amboinensis) is numerically the most important turtle exported from Indonesia. Listed as Vulnerable by the IUCN, this turtle is heavily harvested and exported for food and traditional medicine in China and for the pet trade primarily in the United States, Europe, and Japan. Despite its significance in global markets, relatively little is known about the species’ ecology or importance to ecosystems. We conducted our research in a national park in Sulawesi, Indonesia, and our objectives were to quantify trophic breadth, capacity for seed dispersal between aquatic and terrestrial ecosystems, and whether ingestion of seeds by C. amboinensis enhances germination. We obtained diet samples from 200 individual turtles and found that the species is omnivorous, exhibiting an ontogenetic shift from more carnivorous to more omnivorous. Both subadults and adults scavenged on other vertebrates. In a seed passage experiment, turtles passed seeds for 2?9 days after ingestion. Radio‐tracked turtles moved, on average, about 35 m per day, indicating that seeds from ingested fruits, given seed passage durations, could be dispersed 70?313 m from the parent tree and potentially between wetland and upland ecosystems. In a seed germination experiment, we found that ingestion of seeds by turtles enhanced germination, as compared with control seeds, for four of six plant species tested. Of these, two are common in the national park, making up a significant proportion of plant biomass in lowland swamp forest and around ephemeral pools in savanna, and are highly valued outside of the park for their lumber for construction of houses, furniture, and boats. Protection of C. amboinensis populations may be important for maintaining trophic linkages that benefit biodiversity, communities, and local economies.     

A soybean 101-kD heat shock protein complements a yeast HSP104 deletion mutant in acquiring thermotolerance.

A cDNA clone encoding a 101-kD heat shock protein (HSP101) of soybean was isolated and sequenced. Genomic DNA gel blot analysis indicated that the corresponding gene is a member of a multigene family. The mRNA for HSP101 was not detected in 2-day-old etiolated soybean seedlings grown at 28 degrees C but was induced by elevated temperatures. DNA sequence comparison has shown that the corresponding gene belongs to the Clp (caseinolytic protease) (or Hsp100) gene family, which is evolutionarily conserved and found in both prokaryotes and eukaryotes. On the basis of the spacer length between the two conserved ATP binding regions, this gene has been identified as a member of the ClpB subfamily. Unlike other Clp genes previously isolated from higher plants, the expression of this soybean Hsp101 gene is heat inducible, and it does not have an N-terminal signal peptide for targeting to chloroplasts. Transformation of the soybean Hsp101 gene into a yeast HSP104 deletion mutant complemented restoration of acquired thermotolerance, a process in which cells survive an otherwise lethal heat stress after they are given a permissive heat treatment.     

A nonclassically secreted effector of Magnaporthe oryzae targets host nuclei and plays important roles in fungal growth and plant infection

Rice blast caused by Magnaporthe oryzae is one of the most destructive diseases and poses a growing threat to food security worldwide. Like many other filamentous pathogens, rice blast fungus releases multiple types of effector proteins to facilitate fungal infection and modulate host defence responses. However, most of the characterized effectors contain an N-terminal signal peptide. Here, we report the results of the functional characterization of a nonclassically secreted nuclear targeting effector in M. oryzae (MoNte1). MoNte1 has no signal peptide, but can be secreted and translocated into plant nuclei driven by a nuclear targeting peptide. It could also induce hypersensitive cell death when transiently expressed in Nicotiana benthamiana. Deletion of the MoNTE1 gene caused a significant reduction of fungal growth and conidiogenesis, partially impaired appressorium formation and host colonization, and also dramatically attenuated the pathogenicity. Taken together, these findings reveal a novel effector secretion pathway and deepen our understanding of rice–M. oryzae interactions.     

Identification of residues important both for primary receptor binding and specificity in fibroblast growth factor-7

Fibroblast growth factors (FGFs) mediate a multitude of physiological and pathological processes by activating a family of tyrosine kinase receptors (FGFRs). Each FGFR binds to a unique subset of FGFs and ligand binding specificity is essential in regulating FGF activity. FGF-7 recognizes one FGFR isoform known as the FGFR2 IIIb isoform or keratinocyte growth factor receptor (KGFR), whereas FGF-2 binds well to FGFR1, FGFR2, and FGFR4 but interacts poorly with KGFR. Previously, mutations in FGF-2 identified a set of residues that are important for high affinity receptor binding, known as the primary receptor-binding site. FGF-7 contains this primary site as well as a region that restricts interaction with FGFR1. The sequences that confer on FGF-7 its specific binding to KGFR have not been identified. By utilizing domain swapping and site-directed mutagenesis we have found that the loop connecting the beta4-beta5 strands of FGF-7 contributes to high affinity receptor binding and is critical for KGFR recognition. Replacement of this loop with the homologous loop from FGF-2 dramatically reduced both the affinity of FGF-7 for KGFR and its biological potency but did not result in the ability to bind FGFR1. Point mutations in residues comprising this loop of FGF-7 reduced both binding affinity and biological potency. The reciprocal loop replacement mutant (FGF2-L4/7) retained FGF-2 like affinity for FGFR1 and for KGFR. Our results show that topologically similar regions in these two FGFs have different roles in regulating receptor binding specificity and suggest that specificity may require the concerted action of distinct regions of an FGF.     

CD43 plays both antiadhesive and proadhesive roles in neutrophil rolling in a context-dependent manner

As the first step in the recruitment of neutrophils into tissues, the cells become tethered to and roll on the vessel wall. These processes are mediated by interactions between the P- and E-selectins, expressed on the endothelial cells of the vessel wall, and their ligands, expressed on the neutrophils. Recently, we reported that CD43 on activated T cells functions as an E-selectin ligand and thereby mediates T cell migration to inflamed sites, in collaboration with P-selectin glycoprotein ligand-1 (PSGL-1), a major P- and E-selectin ligand. Here, we examined whether CD43 on neutrophils also functions as an E-selectin ligand. CD43 was precipitated with an E-selectin-IgG chimera from mouse bone marrow neutrophils. A CD43 deficiency diminished the E-selectin-binding activity of neutrophils when PSGL-1 was also deficient. Intravital microscopy showed that the CD43 deficiency significantly increased leukocyte rolling velocities in TNF-alpha-stimulated venules blocked with an anti-P-selectin mAb, where the rolling was mostly E-selectin dependent, when PSGL-1 was also absent. In contrast, in venules with trauma-induced inflammation, where the rolling was largely P-selectin dependent, the CD43 deficiency reduced leukocyte rolling velocities. Collectively, these observations suggest that CD43 generally serves as an antiadhesive molecule to attenuate neutrophil-endothelial interactions, but when E-selectin is expressed on endothelial cells, it also plays a proadhesive role as an E-selectin ligand.     

The pH sensing receptor AopalH plays important roles in the nematophagous fungus Arthrobotrys oligospora

There is well-conserved PacC/Rim101 signaling among ascomycete fungi to mediate environmental pH sensing. For pathogenic fungi, this pathway not only enables fungi to grow over a wide pH range, but it also determines whether these fungi can successfully colonize and invade the targeted host. Within the pal/PacC pathway, palH is a putative ambient pH sensor with a seven-transmembrane domain. To characterize the function of a palH homolog, AopalH, in the nematophagous fungus Arthrobotrys oligospora, we knocked out the encoding gene of AopalH through homologous recombination, and the transformants exhibited slower growth rates, greater sensitivities to cationic and hyperoxidation stresses, as well as reduced conidiation and reduced trap formation, suggesting that the pH regulatory system has critical functions in nematophagous fungi. Our results provide novel insights into the mechanisms of pH response and regulation in fungi.     

Ce-wts-1 plays important roles in Caenorhabditis elegans development

The Hippo-Warts pathway defines a novel signaling cascade involved in organ size control and tumor suppression. However, the developmental function of this pathway is less understood. Here we report that the Caenorhabditis elegans homolog of Warts, Ce-wts-1, plays important roles during worm development. The null allele of Ce-wts-1 causes L1 lethality. Partial loss of Ce-wts-1 function by RNAi reveals that Ce-wts-1 is involved in many developmental processes such as larval development, growth rate regulation, gut granule formation, pharynx development, dauer formation, lifespan and body length control. Genetic analyses show that Ce-wts-1 functions synergistically with the TGF-β Sma/Mab pathway to regulate body length. In addition, CE-WTS-1::GFP is enriched near the inner cell membrane, implying its possible membrane-related function.