Volume 24, Issue 10, October 2012

Transcriptomes of iron-limited versus -deficient Chlamydomonas  reinhardtii cells under photoheterotrophic versus photoautotrophic conditions are described. Increased transcript abundance was positively correlated with protein abundance, except for iron-containing proteins where negative correlation was found. Some responses, including upregulation of MDAR1 and CGLD27/At5g67370, are conserved in land plants.

This study identifies regions of noncoding DNA in dicot plants that are likely to facilitate complex regulation of genes by binding multiple transcription factors. Regulatory mechanisms that the model organism Arabidopsis is likely to share with crop plants provide a focus for research that has real-world applications.

This work characterizes the role of cytokinins in lateral root organogenesis, finding that cytokinin activity is likely important to prevent lateral root initiation in close proximity to existing lateral root primordia. The results support the idea that stage-dependent effects of cytokinin are determined by the robustness of the auxin gradient, which might be enhanced in mature primordia.

This study shows that careful coordination of hormonal activities promotes fruit growth after fertilization in Arabidopsis thaliana. It identifies a previously unknown signaling pathway for the hormone gibberellin that may provide fine-tuning opportunities to ensure efficient reproduction. This pathway does not function through DELLA repressor proteins but instead involves the transcription factor SPATULA.

This work identifies of bZIP16 as a transcriptional repressor regulating the expression of PIL5, RGL2, and genes influencing light, GA, and ABA signals. It indicates that bZIP16 is a newly identified G-box binding transcription factor integrating light and hormone pathways to promote seed germination and hypocotyl elongation during the early stages of Arabidopsis seedling development.

This study reveals a mechanism wherein brassinosteroids control the expression level of the microtubule-destabilizing protein MDP40 and regulate cortical microtubule organization to mediate hypocotyl cell elongation in Arabidopsis  thaliana.

Using a combination of genetic and expression analyses, this study reveals a reproductive function of the Armadillo repeat gene ZAK IXIK in promoting early embryo and endosperm development through a distinctive gametophytic maternal effect involving mechanisms for maternal allele-specific expression that are not implicated in the well-established pathways.

A third isoenzyme of Glu dehydrogenase (GDH) is expressed in mitochondria of Arabidopsis root companion cells. A GDH triple mutant differed greatly from the wild type in continuous darkness, suggesting that the main function of the enzyme is to provide 2-oxoglutarate for the tricarboxylic acid cycle, leading to an accumulation of Ala, γ-aminobutyrate, and Asp in both roots and leaves.

Arabidopsis encodes two STIP proteins (SPLICEOSOMAL TIMEKEEPER LOCUS 1/STIPL1 and STIP-LIKE 2/STIPL2) that share homology with human and yeast spliceosomal proteins. One or the other STIPL genes is required for seedling viability. stipl1 mutants have a long period circadian defect and accumulate alternately spliced transcript isoforms, whereas stipl2 plants do not have a circadian defect.

Formative cell divisions produce daughter cells with different identities and are of key importance for the development of multicellular organisms. Here, formative divisions in the root and shoot of Arabidopsis are shown to be modulated by a common mechanism that relies on the activity level of a core cell cycle regulator that integrates cell proliferation with cell differentiation.

This work characterizes factors involved in the predominantly distal location of meiotic crossovers in barley. Recombination initiates first in the distal regions and later in the interstitial regions; manipulating meiotic progression with higher temperatures produced more interstitial crossovers that could improve mapping of agronomical traits and reduce linkage drag.

This work examines the role of a nonhomologous end-joining pathway gene, X-RAY CROSS COMPLEMENTATION GROUP4 (XRCC4), in T-DNA integration, finding that XRCC4 limits T-DNA integration and interacts directly with Agrobacterium VirE2 protein. These results suggest that Agrobacterium may modulate host DNA repair functions to increase T-DNA integration.

This work examines the mechanism by which rye B chromosomes accumulate, finding that a combination of nondisjunction and unequal spindle formation at first pollen mitosis results in the accumulation of Bs in the generative nucleus and therefore ensures their transmission at a higher than expected rate to the next generation.

This work shows that the evolutionarily conserved DUF59 family gene AE7 encodes a central member of the cytosolic iron-sulfur cluster assembly pathway and demonstrates that this pathway is required for maintaining nuclear genome integrity and, thus, normal mitotic cell cycle in Arabidopsis thaliana. The results link plant mitochondria to nuclear genome integrity through assembly of Fe-S proteins.

When they move, transposons can cause mutations not only of host genes but also of themselves. This article reports that the maize (Zea mays) element Ac can mutate at a surprisingly high frequency on transposition and documents the several types of self-inflicted changes that it can undergo.

This article shows that regulation of the ovule identity gene STK is dependent on the binding of a MADS domain protein containing repressor complex to its promoter and that BPC binding sites are essential for the recruitment of this complex. It provides evidence that this is probably a general mechanism by which BPCs regulate gene expression in plants.

This work investigates the residues of plastocyanin in close proximity to photosystem I and cytochrome b  ₆  f, in both the thylakoid vesicle–embedded and solubilized states. It demonstrates that electrostatic interactions are used to form a transient and loose contact of plastocyanin with photosystem I and cytochrome b  ₆  f, and then hydrophobic interactions are used to form electron transfer complexes of plastocyanin with photosystem I and cytochrome b  ₆  f.

This study shows that Arabidopsis  thaliana TAAC is a plant PAPS transporter (PAPST1). Its functional characterization and the analysis of corresponding mutants demonstrate that TAAC/PAPST1 connects plastidic PAPS synthesis and cytosolic sulfation reactions. In contrast with the known animal PAPS antiporters that are members of the nucleotide-sugar transporter family, TAAC/PAPST1 belongs to the mitochondrial carrier family.

The immune receptor FLAGELLIN SENSING2 (FLS2) plays important roles in plant resistance to bacterial pathogens and is internalized from the plasma membrane via the endocytic pathway. Ligand-activated FLS2 traffics into late endosomal compartments, and this process requires the function of components distinct from nonactivated FLS2 that recycles between early endosomes and the plasma membrane.

This work identifies NONRECOGNITION OF BTH4 (NRB4), which acts in SA signaling in defense and development, finding that NRB4 encodes a predicted subunit of the Mediator complex, which connects specific transcription factors to the general transcription machinery. NRB4 functions downstream of NONEXPRESSER OF PATHOGENESIS-RELATED1in SA signaling.

The arbuscule-specific expression of two rice PHOSPHATE TRANSPORTER1 (PHT1) genes, PT11 and PT13, suggests that both of these genes play a role in symbiotic phosphate acquisition. Indeed, they are both important for the development of arbuscular mycorrhizal symbioses in rice; however, PT11 is the key player in fungus-delivered phosphate uptake.

This work reveals that in addition to storing mono- and sesquiterpene compounds or emitting them into the headspace, trichomes can also secrete products into the intercellular space of sub-epidermal tissues. This secretion allows roles in tissues unable to produce such compounds themselves, for instance ultimately immunizing seedlings of the following generation against fungi and insects,

This work examines the chloroplast ribonucleoproteins CP31A and CP29A by plastome-wide analysis of chloroplast RNA metabolism, finding that these proteins associate with a large set of chloroplast transcripts and are required for cold stress resistance, targeting multiple chloroplast mRNA processing steps.

Mutations generating constitutively active (CA) mitogen-activated protein kinases (MAPKs) were identified and used to investigate the role of Arabidopsis MPK4 in plant immunity, revealing functions of MPK4 activity in PTI and ETI, establishing that the generation of CA-MAPKs offers a powerful tool to analyze MAPK functions in plants.

This article identifies a role for the Arabidopsis  thaliana Mediator complex subunit MED16 in bridging between specific transcription activators and the transcriptional machinery in the activation of salicylic acid–responsive defenses, including defense gene transcription, pathogen resistance, and systemic acquired resistance. MED16 also participates in ethylene- and jasmonic acid–induced defenses.