Table of Contents

June 2010; 22 (6)

IN BRIEF

IN THIS ISSUE

LETTERS TO THE EDITOR

PERSPECTIVE

RESEARCH ARTICLES

  • Inherited transpositions of the endogenous Ds create stable insertion lines, a resource for targeting gene knockouts and examining mechanisms of transposition. Ds preferentially inserts into genes, at target sites within 16-bpair segments of DNA with specific structural properties. These results suggest approaches to predict insertion sites in transposon mutagenesis experiments.

  • This article describes the molecular analysis of large contiguous sequences produced from the bread wheat genome. It provides novel insights into the number, distribution, and density of genes along chromosome 3B and reveals an unexpectedly high amount of noncollinear genes compared to model grass genomes.

  • This work identifies the putative transcription factor gene VDD as a direct target of MADS box proteins that regulate ovule development. It finds that antipodal and synergid cell identity and/or differentiation are affected in vdd mutant female gametophytes, providing insights into the pathways regulated by the ovule identity factors.

  • This article reports that DWA1 and DWA2 may be the substrate receptors for a CULLIN E3 ligase and that they interact with themselves and each other. Heterodimeric cooperation between DWAs is a previously unknown regulatory mechanism for the action of CULLIN E3 ligases.

  • This work examines the interactions among MOTHER OF FT AND TFL1 (MFT) and the genes of the abscisic acid (ABA) signaling pathways in the initiation of germination, finding that MFT expression is regulated by key ABA- and gibberellin-responsive factors and MFT in turn also regulates ABA signaling, providing a feedback loop.

  • This study describes a newly isolated altered auxin response mutant. It finds that the mutant exhibits a reduction in polar auxin transport caused by a decrease in the levels of members of the PIN family of auxin efflux proteins.

  • Gravitropism of roots depends on a flow of auxin from the root cap to the zone of elongation via the auxin efflux carrier PIN2. While PIN2 in epidermis and lateral root cap is positioned appropriately, PIN2 in the cortex has the opposite polarity. We report that, despite this, PIN2 functions in the root cortex for optimal gravitropism, apparently by limiting the auxin flow.

  • Brassinosteroid (BR) homeostasis is established by the regulatory circuit between receptor BRI1-mediated signaling and BR synthesis. RAVL1 modulates the strength of the circuit by activating expression of both BRI1 and synthetic genes and is necessary for feedback responses to BR levels.

  • Plant development depends on the balance of stem cell renewal and differentiation in several stem cell niches that is achieved by yet unknown regulatory mechanisms. Using inducible RNA interference-mediated downregulation, Arabidopsis RETINOBLASTOMA-RELATED protein is shown to regulate the proliferation, maintenance, and differentiation of stem cells and organ production from stem cell niches.

  • Pharmacological and genetic impairments of phospholipase A2 (PLA2) caused anatomical alterations of the trans-Golgi side and defects in trafficking of auxin-transporting PIN proteins to the plasma membrane in Arabidopsis root epidermal cells. The results implicate PLA2-mediated lipid hydrolysis in PIN trafficking.

  • This study identifies AMSH3 as a major deubiquitinating enzyme in Arabidopsis that hydrolyzes ubiquitin chains in vitro and in vivo. It finds that AMSH3 is essential for proper vacuole biogenesis, trafficking from the Golgi to the vacuole, and the vacuolar trafficking of endocytosed cargo.

  • In yeast and vertebrates, the essential telomere binding protein POT1 protects chromosome ends, but in Arabidopsis, POT1 proteins have evolved to bind telomerase instead. This study examines the function of POT1 in the moss Physcomitrella patens. The findings show that moss POT1 functions in a manner similar to yeast and vertebrate POT1. Thus, POT1 proteins are evolving very rapidly in plants.

  • This work examines the repair of DNA double-strand breaks in the mitochondria and plastids of Arabidopsis. The crystal structures of a Whirly protein bound to single-stranded DNA suggest a role for these proteins in DNA damage tolerance in the organelles.

  • Class XI myosins are unique to plants and known to function in cytoplasmic streaming. This study demonstrates that the two myosin XI genes present in the moss Physcomitrella patens are functionally redundant, localize to the apical region of actively growing protonemal cells, and play a key role in tip growth.

  • The molecular motors termed myosins are involved in transport of subcellular particles in diverse organisms from fungi to animals to plants. Here, we show that myosin-dependent transport is critical for the growth of plant cells and entire plants as well as for proper organization of the cell interior.

  • The target of rapamycin (TOR) pathway, which is known to regulate cell growth in eukaryotes, is shown to affect cell wall structure in plants. ROL5 (REPRESSOR of LRX1) is identified as a possible mitochondrial component of the TOR pathway.

  • This work identifies a group of WRKY transcription factors that function as negative abscisic acid (ABA) signaling regulators acting as transcription repressors directly downstream of a previously identified ABA receptor ABAR, describing an ABA signaling pathway from primary events to downstream gene expression.

  • The Arabidopsisgene ABI3 shows developmentally regulated alternative splicing. ABI3-α and ABI3-β splice variants encode full-length and truncated ABI3 proteins, respectively. The conserved splicing factor SUA reduces splicing of a cryptic ABI3 intron, which leads to the accumulation of ABI3-α. Mutations in sua suppress the frameshift mutant abi3-5 by restoring its reading frame.

  • This work investigates the structural determinants for receptor and pathway specificity in chloroplast protein targeting. It provides evidence that the A-domains of the Toc159 family of import receptors are major determinants of distinct pathways for protein import into plastids.

  • Floral scent and color play major roles in the plant's life cycle. Using petunia as a model system, a MYB-like factor was identified that transcriptionally regulates floral scent but not pigmentation. The multilayered regulation allows efficient control of metabolic flux in the phenylpropanoid pathway.

  • In this study, the characterization of OrrDs, a dominant transposon-tagged tomato mutant deficient in the NDH-M subunit, provided evidence that the plastid NAD(P)H dehydrogenase (NDH) complex is essential for the fruit ripening process and related metabolism.

  • This report describes the effect that protein modifications by isoforms of the small ubiquitin-like modifier (SUMO) have on plant development and innate immunity. SUM1 and SUM2 were found to be essential for suppressing defense responses in noninfected plants by preventing accumulation of the defense hormone salicylic acid, whereas SUM3 enhances these defense responses in infected plants.

  • This work examines translocation of the flax rust effector protein AvrM, showing that it accumulates in the haustorial wall and extracellular matrix and is delivered into the host cytoplasm. Protein fusions expressed in the plant showed that AvrM can be secreted by the plant and subsequently internalized in the absence of pathogen.

  • This study demonstrates that the HopF2 effector of Pseudomonas syringae can interact with MAP KINASE KINASE5 to weaken pathogen-associated molecular pattern–triggered immunity in Arabidopsis and identifies key residues required for this interaction.

  • Gametophytes of the fern Pteris vittata can accumulate and tolerate more than 1% of their dry weight as arsenic. The authors provide evidence that the ACR3 arsenic transporter protein plays an important role in tolerance to high levels of arsenic by transporting arsenic into the vacuole.

  • Sulfur deprivation of the unicellular alga Chlamydomonas reinhardtii triggers massive changes in the levels of transcripts associated with sulfate assimilation, the synthesis and turnover of sulfur-containing metabolites, and the remodeling of the photosynthetic apparatus and cell wall. These responses are critical for survival of the organism under sulfur deprivation conditions.

  • A crucial step for diseases caused by phytopathogenic fungi is the penetration of the plant cuticle. Here, we highlight that two conserved plasma membrane proteins are required for plant surface sensing and regulate the penetration process via MAP kinase signaling.