Table of Contents

This work contributes to our understanding of plasmodesmal (Pd) structure and function through the identification of a novel Pd protein. This protein shows binding to callose, a component important in Pd regulation, and accordingly the protein appears to influence molecular flux through these cell-to-cell communication channels.

This work shows that the proteasome Regulatory Particle 5 (RPT5) subunits are essential for male and female gametophyte development. Analysis of mutants for both genes encoding these subunits in two different Arabidopsis accessions also highlights that redundancy between the two RPT5 genes is accession dependent and in particular that the rpt5a mutant phenotype depends on its background.

RNA editing in plant mitochondria changes 400 to 500 Cs to Us, mostly in mRNAs. This article identifies a trans-factor involved in RNA editing in plant mitochondria and reports that single-nucleotide mutations in this pentatricopeptide repeat protein differentially influence editing at the three sites addressed in different mRNAs.

Glutaredoxins are ubiquitous glutathione-dependent oxidoreductases that are associated mainly with redox-regulated processes participating in stress responses. This work shows that ROXY1, a CC-type glutaredoxin, acts in the nucleus to influence petal primordia initiation and later petal morphogenesis, likely by modifying TGA transcription factors posttranslationally.

This study explores the function of two highly conserved isoforms of the Arabidopsis 26S proteasome subunit RPN5. The data point to a specific role for RPN5 in the plant 26S proteasome and suggest that its two isoforms in Arabidopsis have both redundant and unique roles in development.

The PIN auxin efflux transporters, which are themselves regulated by auxin, determine the direction and rate of intercellular auxin flow. This work shows that the auxin regulation of endocytosis, recycling, and plasma membrane accumulation of specific plasma membrane–resident proteins, including some PIN proteins, is dependent on a ubiquitin ligase and on membrane sterols.

Magnaporthe oryzae LHS1 is an ER protein that functions in the unfolded protein response, as shown in yeast and plant systems. Disruption of the LHS1 gene causes improper processing and secretion of proteins. This disproportionately impacts early plant colonization steps in the compatible interaction and induction of plant defenses in the incompatible interaction.

PIL5 is a phytochrome-interacting bHLH transcription factor that regulates seed germination. This work identifies genes directly targeted by PIL5 through comparison of microarray and ChIP-chip data. The analysis of the target genes shows that PIL5 regulates seed germination by coordinating various hormone signaling pathways and by modifying cell wall properties in imbibed seeds.

Annexins are soluble proteins capable of binding to membranes. Annexins purified from maize were found to increase cytosolic free calcium in Arabidopsis protoplasts and form a transport route for calcium, possibly by interacting with an unidentified membrane binding protein. These results implicate annexins in the regulation of cell calcium and hence cell signaling and development.

Annexins are soluble proteins capable of binding to membranes. Annexins purified from maize were found to increase cytosolic free calcium in Arabidopsis protoplasts and form a transport route for calcium, possibly by interacting with an unidentified membrane binding protein. These results implicate annexins in the regulation of cell calcium and hence cell signaling and development.

This work examines a leucine-rich repeat-like kinase (RLK) induced in response to salt stress in the model legume Medicago truncatula. Mutants in this gene showed an impaired physiological and molecular response to high salt and accumulate less salt in their tissues. This RLK plays a key role in the adaptation of M. truncatula to salt stress.

This work analyzes the protein–protein interactions between phytochrome A (phyA) and two far-red light signaling proteins (FHY1 and FHL). In addition, it finds that phyA exhibits kinase activity toward FHY1 in vitro and that FHY1 undergoes phyA-dependent phosphorylation during dark to red light transition, revealing a role of phyA in regulating this low fluence response.

Two GRAS domain Nodulation Signaling Pathway proteins, NSP1 and NSP2, from Medicago truncatula form a complex on the promoters of Nod factor–inducible genes. This complex is enhanced upon Nod factor elicitation, and the interaction between NSP1 and NSP2 is necessary for efficient nodulation.

This work contributes to our understanding of plasmodesmal (Pd) structure and function through the identification of a novel Pd protein. This protein shows binding to callose, a component important in Pd regulation, and accordingly the protein appears to influence molecular flux through these cell-to-cell communication channels.

This work shows that the proteasome Regulatory Particle 5 (RPT5) subunits are essential for male and female gametophyte development. Analysis of mutants for both genes encoding these subunits in two different Arabidopsis accessions also highlights that redundancy between the two RPT5 genes is accession dependent and in particular that the rpt5a mutant phenotype depends on its background.

This work shows that the proteasome Regulatory Particle 5 (RPT5) subunits are essential for male and female gametophyte development. Analysis of mutants for both genes encoding these subunits in two different Arabidopsis accessions also highlights that redundancy between the two RPT5 genes is accession dependent and in particular that the rpt5a mutant phenotype depends on its background.

This work examines an abscisic acid (ABA)–sensitive mutant, which is caused by mutation of DNA polymerase ϵ. This hypomorphic mutation caused increased somatic homologous recombination, sensitivity to DNA-damaging agents, activation of silenced loci, and early flowering, indicating a role for DNA replication enzymes in maintenance of epigenetic states and in ABA signaling.

Two GRAS domain Nodulation Signaling Pathway proteins, NSP1 and NSP2, from Medicago truncatula form a complex on the promoters of Nod factor–inducible genes. This complex is enhanced upon Nod factor elicitation, and the interaction between NSP1 and NSP2 is necessary for efficient nodulation.

Annexins are soluble proteins capable of binding to membranes. Annexins purified from maize were found to increase cytosolic free calcium in Arabidopsis protoplasts and form a transport route for calcium, possibly by interacting with an unidentified membrane binding protein. These results implicate annexins in the regulation of cell calcium and hence cell signaling and development.

This study explores the function of two highly conserved isoforms of the Arabidopsis 26S proteasome subunit RPN5. The data point to a specific role for RPN5 in the plant 26S proteasome and suggest that its two isoforms in Arabidopsis have both redundant and unique roles in development.

Aluminum toxicity is a major factor limiting crop production in acidic soil. This work identifies two genes (STAR1 and STAR2) involved in aluminum tolerance in rice. STAR1 encodes a nucleotide binding domain of a putative ABC transporter. It interacts with STAR2, which encodes a transmembrane domain protein, to form an ABC transporter complex that transports UDP-glucose.

Precise control of chromosome recombination is vital for conferring genome and meiotic stability and, thus, fitness of sexually reproductive polyploids. This work provides new insights on the genetic system that regulates the number of associations between nonhomologous chromosomes during meiosis of Brassica napus haploids.

PIL5 is a phytochrome-interacting bHLH transcription factor that regulates seed germination. This work identifies genes directly targeted by PIL5 through comparison of microarray and ChIP-chip data. The analysis of the target genes shows that PIL5 regulates seed germination by coordinating various hormone signaling pathways and by modifying cell wall properties in imbibed seeds.

Magnaporthe oryzae LHS1 is an ER protein that functions in the unfolded protein response, as shown in yeast and plant systems. Disruption of the LHS1 gene causes improper processing and secretion of proteins. This disproportionately impacts early plant colonization steps in the compatible interaction and induction of plant defenses in the incompatible interaction.

Two GRAS domain Nodulation Signaling Pathway proteins, NSP1 and NSP2, from Medicago truncatula form a complex on the promoters of Nod factor–inducible genes. This complex is enhanced upon Nod factor elicitation, and the interaction between NSP1 and NSP2 is necessary for efficient nodulation.

The role of ubiquitination in responses to abiotic stresses is not clearly understood. This work shows that overexpression of a hot pepper homolog of a human ubiquitin ligase results in markedly increased tolerance to severe drought stress in transgenic Arabidopsis plants by ubiquitinating the water channel protein aquaporin.

This work examines a leucine-rich repeat-like kinase (RLK) induced in response to salt stress in the model legume Medicago truncatula. Mutants in this gene showed an impaired physiological and molecular response to high salt and accumulate less salt in their tissues. This RLK plays a key role in the adaptation of M. truncatula to salt stress.

This work shows that the proteasome Regulatory Particle 5 (RPT5) subunits are essential for male and female gametophyte development. Analysis of mutants for both genes encoding these subunits in two different Arabidopsis accessions also highlights that redundancy between the two RPT5 genes is accession dependent and in particular that the rpt5a mutant phenotype depends on its background.

The role of ubiquitination in responses to abiotic stresses is not clearly understood. This work shows that overexpression of a hot pepper homolog of a human ubiquitin ligase results in markedly increased tolerance to severe drought stress in transgenic Arabidopsis plants by ubiquitinating the water channel protein aquaporin.

Magnaporthe oryzae LHS1 is an ER protein that functions in the unfolded protein response, as shown in yeast and plant systems. Disruption of the LHS1 gene causes improper processing and secretion of proteins. This disproportionately impacts early plant colonization steps in the compatible interaction and induction of plant defenses in the incompatible interaction.

The gene that determines the formation of tendrils, novel filamentous leaf organs present in peas and their allies, has been identified as Tendril-less, encoding a Class I homeodomain leucine zipper transcription factor. Characterization of mutants shows that these tendrils are modified leaflets, inhibited from laminar development by the action of the Tendril-less gene.

This work analyzes the protein–protein interactions between phytochrome A (phyA) and two far-red light signaling proteins (FHY1 and FHL). In addition, it finds that phyA exhibits kinase activity toward FHY1 in vitro and that FHY1 undergoes phyA-dependent phosphorylation during dark to red light transition, revealing a role of phyA in regulating this low fluence response.

Annexins are soluble proteins capable of binding to membranes. Annexins purified from maize were found to increase cytosolic free calcium in Arabidopsis protoplasts and form a transport route for calcium, possibly by interacting with an unidentified membrane binding protein. These results implicate annexins in the regulation of cell calcium and hence cell signaling and development.

Photorespiration is the light-stimulated consumption of oxygen and evolution of carbon dioxide that occurs at ambient levels of carbon dioxide. Ferredoxin-dependent Glutamate Synthase, a key enzyme in the photorespiratory cycle previously known to localize in chloroplasts, is shown to occur also in mitochondria, where it interacts with serine hydroxymethyltransferase.

This work examines a leucine-rich repeat-like kinase (RLK) induced in response to salt stress in the model legume Medicago truncatula. Mutants in this gene showed an impaired physiological and molecular response to high salt and accumulate less salt in their tissues. This RLK plays a key role in the adaptation of M. truncatula to salt stress.

Aluminum toxicity is a major factor limiting crop production in acidic soil. This work identifies two genes (STAR1 and STAR2) involved in aluminum tolerance in rice. STAR1 encodes a nucleotide binding domain of a putative ABC transporter. It interacts with STAR2, which encodes a transmembrane domain protein, to form an ABC transporter complex that transports UDP-glucose.

The gene that determines the formation of tendrils, novel filamentous leaf organs present in peas and their allies, has been identified as Tendril-less, encoding a Class I homeodomain leucine zipper transcription factor. Characterization of mutants shows that these tendrils are modified leaflets, inhibited from laminar development by the action of the Tendril-less gene.

Precise control of chromosome recombination is vital for conferring genome and meiotic stability and, thus, fitness of sexually reproductive polyploids. This work provides new insights on the genetic system that regulates the number of associations between nonhomologous chromosomes during meiosis of Brassica napus haploids.

PIL5 is a phytochrome-interacting bHLH transcription factor that regulates seed germination. This work identifies genes directly targeted by PIL5 through comparison of microarray and ChIP-chip data. The analysis of the target genes shows that PIL5 regulates seed germination by coordinating various hormone signaling pathways and by modifying cell wall properties in imbibed seeds.

Plant response to low nutrients is vital for growth and survival. This study shows that the ethylene signaling pathway is induced by potassium deprivation and positively regulates reactive oxygen species production and K⁺ transporter expression (HAK5) in Arabidopsis roots. Ethylene also enhances plant tolerance to low potassium and modulates root hair elongation and primary root growth.

This study implicates an acyl-CoA synthetase that is preferentially expressed in flowers in the sporopollenin biosynthesis pathway in Arabidopsis. ACOS5 was found to localize to the cytoplasm of tapetal cells, to act on medium-chain fatty acids, and to be required for pollen formation.

Plant response to low nutrients is vital for growth and survival. This study shows that the ethylene signaling pathway is induced by potassium deprivation and positively regulates reactive oxygen species production and K⁺ transporter expression (HAK5) in Arabidopsis roots. Ethylene also enhances plant tolerance to low potassium and modulates root hair elongation and primary root growth.

This study explores the function of two highly conserved isoforms of the Arabidopsis 26S proteasome subunit RPN5. The data point to a specific role for RPN5 in the plant 26S proteasome and suggest that its two isoforms in Arabidopsis have both redundant and unique roles in development.

This work examines a leucine-rich repeat-like kinase (RLK) induced in response to salt stress in the model legume Medicago truncatula. Mutants in this gene showed an impaired physiological and molecular response to high salt and accumulate less salt in their tissues. This RLK plays a key role in the adaptation of M. truncatula to salt stress.

Accumulation of misfolded protein in the cytosol of Arabidopsis, for example following heat shock, activates a stress response that includes a range of specific transcriptional events. This response was found to be partly regulated by the transcription factor HsfA2.

This work analyzes the protein–protein interactions between phytochrome A (phyA) and two far-red light signaling proteins (FHY1 and FHL). In addition, it finds that phyA exhibits kinase activity toward FHY1 in vitro and that FHY1 undergoes phyA-dependent phosphorylation during dark to red light transition, revealing a role of phyA in regulating this low fluence response.

This work examines a leucine-rich repeat-like kinase (RLK) induced in response to salt stress in the model legume Medicago truncatula. Mutants in this gene showed an impaired physiological and molecular response to high salt and accumulate less salt in their tissues. This RLK plays a key role in the adaptation of M. truncatula to salt stress.

RNA editing in plant mitochondria changes 400 to 500 Cs to Us, mostly in mRNAs. This article identifies a trans-factor involved in RNA editing in plant mitochondria and reports that single-nucleotide mutations in this pentatricopeptide repeat protein differentially influence editing at the three sites addressed in different mRNAs.

This work shows that the proteasome Regulatory Particle 5 (RPT5) subunits are essential for male and female gametophyte development. Analysis of mutants for both genes encoding these subunits in two different Arabidopsis accessions also highlights that redundancy between the two RPT5 genes is accession dependent and in particular that the rpt5a mutant phenotype depends on its background.