Biomedical subjects

Linda L Walling

Publications and source records attributed to Linda L Walling.

9 recordsLinked to original sources

PubMed2006

Silverleaf whitefly induces salicylic acid defenses and suppresses effectual jasmonic acid defenses.

The basal defenses important in curtailing the development of the phloem-feeding silverleaf whitefly (Bemisia tabaci type B; SLWF) on Arabidopsis (Arabidopsis thaliana) were investigated. Sentinel defense gene RNAs were monitored in SLWF-infested and control plants. Salicylic acid (SA)-responsive gene transcripts accumulated locally (PR1, BGL2, PR5, SID2, EDS5, PAD4) and systemically (PR1, BGL2, PR5) during SLWF nymph feeding. In contrast, jasmonic acid (JA)- and ethylene-dependent RNAs (PDF1.2, VSP1, HEL, THI2.1, FAD3, ERS1, ERF1) were repressed or not modulated in SLWF-infested leaves. To test for a role of SA and JA pathways in basal defense, SLWF development on mutant and transgenic lines that constitutively activate or impair defense pathways was determined. By monitoring the percentage of SLWF nymphs in each instar, we show that mutants that activate SA defenses (cim10) or impair JA defenses (coi1) accelerated SLWF nymphal development. Reciprocally, mutants that activate JA defenses (cev1) or impair SA defenses (npr1, NahG) slowed SLWF nymphal development. Furthermore, when npr1 plants, which do not activate downstream SA defenses, were treated with methyl jasmonate, a dramatic delay in nymph development was observed. Collectively, these results showed that SLWF-repressed, JA-regulated defenses were associated with basal defense to the SLWF.

Animals↗

PubMed2006

Arabidopsis transcriptome changes in response to phloem-feeding silverleaf whitefly nymphs. Similarities and distinctions in responses to aphids.

Phloem-feeding pests cause extensive crop damage throughout the world, yet little is understood about how plants perceive and defend themselves from these threats. The silverleaf whitefly (SLWF; Bemisia tabaci type B) is a good model for studying phloem-feeding insect-plant interactions, as SLWF nymphs cause little wounding and have a long, continuous interaction with the plant. Using the Affymetrix ATH1 GeneChip to monitor the Arabidopsis (Arabidopsis thaliana) transcriptome, 700 transcripts were found to be up-regulated and 556 down-regulated by SLWF nymphs. Closer examination of the regulation of secondary metabolite (glucosinolate) and defense pathway genes after SLWF-instar feeding shows that responses were qualitatively and quantitatively different from chewing insects and aphids. In addition to the RNA profile distinctions, analysis of SLWF performance on wild-type and phytoalexin-deficient4 (pad4) mutants suggests aphid and SLWF interactions with Arabidopsis were distinct. While pad4-1 mutants were more susceptible to aphids, SLWF development on pad4-1 and wild-type plants was similar. Furthermore, although jasmonic acid genes were repressed and salicylic acid-regulated genes were induced after SLWF feeding, cytological staining of SLWF-infested tissue showed that pathogen defenses, such as localized cell death and hydrogen peroxide accumulation, were not observed. Like aphid and fungal pathogens, callose synthase gene RNAs accumulated and callose deposition was observed in SLWF-infested tissue. These results provide a more comprehensive understanding of phloem-feeding insect-plant interactions and distinguish SLWF global responses.

Animals↗

PubMed2006

Recycling or regulation? The role of amino-terminal modifying enzymes.

Post-translational modifications are essential for a variety of functions, such as the translocation, activation, regulation, and, ultimately, degradation of proteins. The amino-terminal (N-terminal) region is a particularly active area for such alterations. Three types of reactions predominate: limited proteolysis to remove one or more amino acids; modification of the alpha-amino group; and side-chain-specific changes. The N-terminal peptidases expose penultimate residues, providing new substrates for peptidase or transferase action. These enzymes can act sequentially or competitively to influence a protein's longevity, location or activity. N-terminal modifying enzymes (NTMEs) might target a protein for ubiquitination and degradation or protect a protein from rapid turnover. The N-terminal peptidases might also have important roles in processing the peptides that are released from the proteasome. Plant NTMEs have roles in senescence, meiosis and defense, and proposed roles in polar auxin transport.

Aminopeptidases↗

PubMed2006

Constitutive and jasmonate-inducible traits of Datura wrightii.

Plants in the family Solanaceae possess numerous traits that are induced from damage from herbivores. Many of these also can be induced by exposing plants to the plant hormone jasmonic acid or its volatile ester methyl jasmonate. Datura wrightii (Solanaceae) is dimorphic for leaf trichome morphology in most southern California populations. Trichome phenotype is governed by a single gene, and the glandular trichome condition is dominant and under developmental control. This study addressed two major objectives. The first was to determine if mature plants with glandular or nonglandular trichomes responded differentially to methyl jasmonate. The second objective was to determine if exposure of seedlings to methyl jasmonate during the period of trichome differentiation altered either the phenotype or the density of trichomes that mature plants expressed. Methyl jasmonate induced from 200 to 800 microg/ml of proteinase inhibitor activity and increased the activity of polyphenol oxidase by more than threefold depending on the experiment. These increases did not differ significantly between plants expressing glandular or nonglandular trichomes. Methyl jasmonate exposure did not increase the activity of peroxidase or the concentration of scopolamine or hyoscyamine, the two major alkaloids of Datura. Exposure to methyl jasmonate during trichome differentiation did not affect either the final trichome phenotype or the density of either type of trichome, but did increase the production of acylsugars in glandular trichomes by 44%. Because trichome phenotype was not inducible, and because both trichome phenotypes showed similar increases in proteinase inhibitors and polyphenol oxidase activity, the methyl-jasmonate-inducible responses of D. wrightii are independent of trichome phenotype in D. wrightii.

Acetates↗

PubMed2006

Leucine aminopeptidases: diversity in structure and function.

Leucine aminopeptidases (LAPs) are metallopeptidases that cleave N-terminal residues from proteins and peptides. While hydrolyzing Leu substrates, LAPs often have a broader specificity. LAPs are members of the M1 or M17 peptidase families, and therefore the LAP nomenclature is complex. LAPs are often viewed as cell maintenance enzymes with critical roles in turnover of peptides. In mammals, the M17 and M1 enzymes with LAP activity contribute to processing peptides for MHC I antigen presentation, processing of bioactive peptides (oxytocin, vasopressin, enkephalins), and vesicle trafficking to the plasma membrane. In microbes, the M17 LAPs have a role in proteolysis and have also acquired the ability to bind DNA. This property enables LAPs to serve as transcriptional repressors to control pyrimidine, alginate and cholera toxin biosynthesis, as well as mediate site-specific recombination events in plasmids and phages. In plants the roles of the M17 LAPs and the peptidases related to M1 LAPs are being elucidated. Roles in defense, membrane transport of auxin receptors, and meiosis have been implicated.

Animals↗

PubMed2005

Hemipterans as plant pathogens.

Integration of the tools of genetics, genomics, and biochemistry has provided new approaches for identifying genes responding to herbivory. As a result, a picture of the complexity of plant-defense signaling to different herbivore feeding guilds is emerging. Plant responses to hemipteran insects have substantial overlap with responses mounted against microbial pathogens, as seen in changes in RNA profiles and emission of volatiles. Responses to known defense signals and characterization of the signaling pathways controlled by the first cloned insect R gene (Mi-1) indicate that perception and signal transduction leading to resistance may be similar to plant-pathogen interactions. Additionally, novel signaling pathways are emerging as important components of plant defense to insects. The availability of new tools and approaches will further enhance our understanding of the nature of defense in plant-hemipteran interactions.

Animals↗

PubMed2004

Isolation and characterization of a TERMINAL FLOWER homolog and its correlation with juvenility in citrus.

TERMINAL FLOWER is a key regulator of floral timing in Arabidopsis and other herbaceous species. A homolog of this gene, CsTFL, was isolated from the hybrid perennial tree crop Washington navel orange (Citrus sinensis L. Osbeck). The deduced amino acid sequence of CsTFL was 65% identical to the Arabidopsis TFL1 protein. Wild-type Arabidopsis plants ectopically expressing CsTFL showed late-flowering phenotypes similar to those described for overexpression of Arabidopsis TFL1. In addition, the 35S:CsTFL transgene complemented the tfl1-2 mutant. The severity of the overexpression phenotypes correlated with the amount of CsTFL transcript that accumulated. Unlike many model systems that have been studied, C. sinensis maintains two distinguishable CsTFL alleles. CsTFL transcripts from either allele were not detected in adult vegetative tissues using reverse transcription-PCR, but CsTFL RNAs were detected in all floral organs. In addition, real-time PCR determined that juvenility in citrus was positively correlated with CsTFL transcript accumulation and negatively correlated with the floral-regulatory genes, LEAFY and APETALA1, RNA levels.

Amino Acid Sequence↗

PubMed2003

Isolation and characterization of the neutral leucine aminopeptidase (LapN) of tomato.

Tomatoes (Lycopersicon esculentum) express two forms of leucine aminopeptidase (LAP-A and LAP-N) and two LAP-like proteins. The relatedness of LAP-N and LAP-A was determined using affinity-purified antibodies to four LAP-A protein domains. Antibodies to epitopes in the most N-terminal region were able to discriminate between LAP-A and LAP-N, whereas antibodies recognizing central and COOH-terminal regions recognized both LAP polypeptides. Two-dimensional immunoblots showed that LAP-N and the LAP-like proteins were detected in all vegetative (leaves, stems, roots, and cotyledons) and reproductive (pistils, sepals, petals, stamens, and floral buds) organs examined, whereas LAP-A exhibited a distinct expression program. LapN was a single-copy gene encoding a rare-class transcript. A full-length LapN cDNA clone was isolated, and the deduced sequence had 77% peptide sequence identity with the wound-induced LAP-A. Comparison of LAP-N with other plant LAPs identified 28 signature residues that classified LAP proteins as LAP-N or LAP-A like. Overexpression of a His(6)-LAP-N fusion protein in Escherichia coli demonstrated distinct differences in His(6)-LAP-N and His(6)-LAP-A activities. Similar to LapA, the LapN RNA encoded a precursor protein with a molecular mass of 60 kD. The 5-kD presequence had features similar to plastid transit peptides, and processing of the LAP-N presequence could generate the mature 55-kD LAP-N. Unlike LapA, the LapN transcript contained a second in-frame ATG, and utilization of this potential initiation codon would yield a 55-kD LAP-N protein. The localization of LAP-N could be controlled by the balance of translational initiation site utilization and LAP-N preprotein processing.

Amino Acid Sequence↗

PubMed2002

Identification of residues critical for activity of the wound-induced leucine aminopeptidase (LAP-A) of tomato.

The importance of two putative Zn2+-binding (Asp347, Glu429) and two catalytic (Arg431, Lys354) residues in the tomato leucine aminopeptidase (LAP-A) function was tested. The impact of substitutions at these positions, corresponding to the bovine LAP residues Asp255, Glu334, Arg336, and Lys262, was evaluated in His6-LAP-A fusion proteins expressed in Escherichia coli. Sixty-five percent of the mutant His6-LAP-A proteins were unstable or had complete or partial defects in hexamer assembly or stability. The activity of hexameric His6-LAP-As on Xaa-Leu and Leu-Xaa dipeptides was tested. Most substitutions of Lys354 (a catalytic residue) resulted in His6-LAP-As that cleaved dipeptides at slower rates. The Glu429 mutants (a Zn2+-binding residue) had more diverse phenotypes. Some mutations abolished activity and others retained partial or complete activity. The E429D His6-LAP-A enzyme had Km and kcat values similar to the wild-type His6-LAP-A. One catalytic (Arg431) and one Zn-binding (Asp347) residue were essential for His6-LAP-A activity, as most R431 and D347 mutant His6-LAP-As did not hydrolyze dipeptides. The R431K His6-LAP-A that retained the positive charge had partial activity as reflected in the 4.8-fold decrease in kcat. Surprisingly, while the D347E mutant (that retained a negative charge at position 347) was inactive, the D347R mutant that introduced a positive charge retained partial activity. A model to explain these data is proposed.

Amino Acid Sequence↗