Table of Contents

Plants lacking a Ca²⁺-conducting channel do not undergo hypersensitive response to pathogens and have impaired nitric oxide generation in response to application of a pathogen-associated molecular pattern elicitor. Patch clamp analysis demonstrated elicitor activation of inward cation currents; this work provides insights regarding early steps in pathogen response signaling in plants.

Chlorophyll is a central player in photosynthetic light harvesting, but details of chlorophyll catabolism and regulation are unresolved. Here, two different expression systems in two species were used to study the role and regulation of Chlase in chlorophyll catabolism. The results suggest that Chlase is a rate-limiting enzyme in chlorophyll catabolism controlled via posttranslational regulation.

Many floral traits appear to be adapted to particular pollinators. AN2 is a well-defined myb-type transcription factor that is a major determinant of flower color variation between two Petunia species. Transformation of one species with AN2 from the other caused a switch in pollinator preference, suggesting that adaptation to a new pollinator may involve a limited number of genes of large effect.

Mutations in cellulose synthase subunits required for secondary cell wall formation confer resistance to bacterial and fungal pathogens and upregulate ABA-responsive defense genes. Alteration of secondary cell wall integrity by inhibiting cellulose synthesis may lead to activation of novel defense pathways that create antimicrobial-enriched environments hostile to pathogens.

Carotenoids help protect the chloroplast from photoxidative stress. The aba4-1 mutant lacks neoxanthin but retains all other xanthophyll species. This research shows that neoxanthin plays a specific role in protection of Lhc proteins, the PSII reaction center, and thylakoids from photooxidative stress and protects against the damaging effects of reactive oxygen species, particularly superoxide anions.

Plants lacking a Ca²⁺-conducting channel do not undergo hypersensitive response to pathogens and have impaired nitric oxide generation in response to application of a pathogen-associated molecular pattern elicitor. Patch clamp analysis demonstrated elicitor activation of inward cation currents; this work provides insights regarding early steps in pathogen response signaling in plants.

Three Arabidopsis nuclear-encoded T7 phage-type RNA polymerases (RNAPs) localize to mitochondria, plastids, or both. This study finds that two of them can initiate transcription from both mitochondrial and plastid promoters in vitro without auxiliary factors. The ability for promoter recognition appears to have been conserved over a long period of evolution of organellar RNAPs.

TERMINAL FLOWER1 (TFL1) affects the number and identity of aerial organs. TFL1 mRNA is restricted to the inner cells of the meristem, but this work reveals that the protein is a mobile signal that becomes evenly distributed across the meristem and suggests a model for how floral and shoot meristems establish a feedback loop of expression and protein movement to control inflorescence architecture.

Using high-throughput sequencing methods, many transcripts were found to be routed through the RDR6/DCL4-dependent silencing pathway after single or dual targeting events by miRNA or tasiRNA. Several members of a rapidly expanding clade of PPR gene transcripts were targeted, suggesting that this silencing pathway may function to buffer the effects of rapidly expanding gene families.

The importance of oxylipins, such as jasmonic acid, in plant defense and adaptation is well known. This work suggests that other oxylipins, such as 9-hydroxyoctadecatrienoic acid, also function in developmental and defense responses, such as callose and pectin deposition and production of reactive oxygen species. Mutant analyses revealed at least three signaling cascades mediating oxylipin action.

Carotenoids help protect the chloroplast from photoxidative stress. The aba4-1 mutant lacks neoxanthin but retains all other xanthophyll species. This research shows that neoxanthin plays a specific role in protection of Lhc proteins, the PSII reaction center, and thylakoids from photooxidative stress and protects against the damaging effects of reactive oxygen species, particularly superoxide anions.

UDP-glucose pyrophosphorylase functions in carbohydrate metabolism and cell wall biosynthesis. Silencing of rice Ugp1 affects normal callose deposition during pollen mother cell (PMC) meiosis and leads to the degeneration of PMC at the early meiosis stage. This work demonstrates that rice Ugp1 is essential for PMC meiosis and microspore development.

TERMINAL FLOWER1 (TFL1) affects the number and identity of aerial organs. TFL1 mRNA is restricted to the inner cells of the meristem, but this work reveals that the protein is a mobile signal that becomes evenly distributed across the meristem and suggests a model for how floral and shoot meristems establish a feedback loop of expression and protein movement to control inflorescence architecture.

Many floral traits appear to be adapted to particular pollinators. AN2 is a well-defined myb-type transcription factor that is a major determinant of flower color variation between two Petunia species. Transformation of one species with AN2 from the other caused a switch in pollinator preference, suggesting that adaptation to a new pollinator may involve a limited number of genes of large effect.

Mutations in cellulose synthase subunits required for secondary cell wall formation confer resistance to bacterial and fungal pathogens and upregulate ABA-responsive defense genes. Alteration of secondary cell wall integrity by inhibiting cellulose synthesis may lead to activation of novel defense pathways that create antimicrobial-enriched environments hostile to pathogens.

The NADPH oxidase RBOH and calcium-dependent protein kinases (CDPKs) are implicated in rapid production of reactive oxygen species, or oxidative burst, early in plant–pathogen interactions, but the regulatory mechanisms are unknown. The results of this work suggest that Ca²⁺-dependent phosphorylation of potato RBOHB by CDPK5 plays a central role in oxidative burst during pathogen infection.

Mutations in cellulose synthase subunits required for secondary cell wall formation confer resistance to bacterial and fungal pathogens and upregulate ABA-responsive defense genes. Alteration of secondary cell wall integrity by inhibiting cellulose synthesis may lead to activation of novel defense pathways that create antimicrobial-enriched environments hostile to pathogens.

Arsenate [As(V)], the most abundant chemical form of the toxic element arsenic, is very similar to phosphate (Pi), which enables its uptake from the soil through the high-affinity Pi transport system. This work identifies a Pi transporter mutant with enhanced ability to accumulate arsenic but with a reduced Pi and As(V) uptake rate, suggesting a protective mechanism operating in arsenic-tolerant plants.

Light signals induce complex developmental programs in plants. The transcription factor HY5 acts downstream of multiple photoreceptors, but its target genes are not well known. Putative HY5 binding sites were mapped to 3894 genes with diverse developmental functions, including early light-responsive genes. HY5 appears to be an early regulator of the transcriptional cascades for photomorphogenesis.

Chlorophyll is a central player in photosynthetic light harvesting, but details of chlorophyll catabolism and regulation are unresolved. Here, two different expression systems in two species were used to study the role and regulation of Chlase in chlorophyll catabolism. The results suggest that Chlase is a rate-limiting enzyme in chlorophyll catabolism controlled via posttranslational regulation.

Chlorophyll is a central player in photosynthetic light harvesting, but details of chlorophyll catabolism and regulation are unresolved. Here, two different expression systems in two species were used to study the role and regulation of Chlase in chlorophyll catabolism. The results suggest that Chlase is a rate-limiting enzyme in chlorophyll catabolism controlled via posttranslational regulation.

To divide or not is one of the most crucial choices made by cells. As in other eukaryotes, progression through the cell cycle in plants is governed by cyclin-dependent kinases (CDKs), and one of the major regulatory inputs to CDK function is phosphorylation. Here, it is shown that Arabidopsis CDKA;1 is phosphorylated in the T-loop region and that phosphorylation is essential for kinase function.

Chlorophyll is a central player in photosynthetic light harvesting, but details of chlorophyll catabolism and regulation are unresolved. Here, two different expression systems in two species were used to study the role and regulation of Chlase in chlorophyll catabolism. The results suggest that Chlase is a rate-limiting enzyme in chlorophyll catabolism controlled via posttranslational regulation.

Light signals induce complex developmental programs in plants. The transcription factor HY5 acts downstream of multiple photoreceptors, but its target genes are not well known. Putative HY5 binding sites were mapped to 3894 genes with diverse developmental functions, including early light-responsive genes. HY5 appears to be an early regulator of the transcriptional cascades for photomorphogenesis.

Some double-stranded RNA binding proteins participate in miRNA biogenesis. A series of deletion mutants demonstrated that the N-terminal region of HYPONASTIC LEAVES1 with two double-stranded RNA binding domains is sufficient for miRNA biogenesis and capable of rescuing the hyl1 phenotype. This study also showed that the putative NLS is a true nuclear localization signal.

Mitogen-activated protein kinase (MAPK) signaling mediates plant responses to herbivore attack, but the transduction of these signals is poorly understood. This work examines how plants deploy defense reactions and demonstrates that herbivore oral secretions (OS) dramatically amplify wound-induced MAPK activity and that fatty acid–amino acid conjugates in herbivore OS are the elicitors.

Many floral traits appear to be adapted to particular pollinators. AN2 is a well-defined myb-type transcription factor that is a major determinant of flower color variation between two Petunia species. Transformation of one species with AN2 from the other caused a switch in pollinator preference, suggesting that adaptation to a new pollinator may involve a limited number of genes of large effect.

The cuticle, an extracellular matrix of cutin polyester and waxes, covers and protects plant aerial organs, but little is known about the regulation of cuticular wax deposition. Mutant analysis and gene isolation and characterization demonstrate that wax production is controlled, at least in part, by the mRNA stability of a repressor that is recognized and degraded by the CER7 ribonuclease.

Using high-throughput sequencing methods, many transcripts were found to be routed through the RDR6/DCL4-dependent silencing pathway after single or dual targeting events by miRNA or tasiRNA. Several members of a rapidly expanding clade of PPR gene transcripts were targeted, suggesting that this silencing pathway may function to buffer the effects of rapidly expanding gene families.

Using high-throughput sequencing methods, many transcripts were found to be routed through the RDR6/DCL4-dependent silencing pathway after single or dual targeting events by miRNA or tasiRNA. Several members of a rapidly expanding clade of PPR gene transcripts were targeted, suggesting that this silencing pathway may function to buffer the effects of rapidly expanding gene families.

Mutations in cellulose synthase subunits required for secondary cell wall formation confer resistance to bacterial and fungal pathogens and upregulate ABA-responsive defense genes. Alteration of secondary cell wall integrity by inhibiting cellulose synthesis may lead to activation of novel defense pathways that create antimicrobial-enriched environments hostile to pathogens.

The role of the chloroplast as a phosphorus (P) reservoir in acclimation to P limitation is not well known. Polynucleotide phosphorylase consumes P through RNA decay, and while P deprivation usually stimulates RNA decay, in Chlamydomonas chloroplasts RNA levels rise but DNA levels fall during acclimation, suggesting that chloroplast polyploidy may be adaptive as a repository for P.

Many floral traits appear to be adapted to particular pollinators. AN2 is a well-defined myb-type transcription factor that is a major determinant of flower color variation between two Petunia species. Transformation of one species with AN2 from the other caused a switch in pollinator preference, suggesting that adaptation to a new pollinator may involve a limited number of genes of large effect.

Arsenate [As(V)], the most abundant chemical form of the toxic element arsenic, is very similar to phosphate (Pi), which enables its uptake from the soil through the high-affinity Pi transport system. This work identifies a Pi transporter mutant with enhanced ability to accumulate arsenic but with a reduced Pi and As(V) uptake rate, suggesting a protective mechanism operating in arsenic-tolerant plants.

Light signals induce complex developmental programs in plants. The transcription factor HY5 acts downstream of multiple photoreceptors, but its target genes are not well known. Putative HY5 binding sites were mapped to 3894 genes with diverse developmental functions, including early light-responsive genes. HY5 appears to be an early regulator of the transcriptional cascades for photomorphogenesis.

Plants lacking a Ca²⁺-conducting channel do not undergo hypersensitive response to pathogens and have impaired nitric oxide generation in response to application of a pathogen-associated molecular pattern elicitor. Patch clamp analysis demonstrated elicitor activation of inward cation currents; this work provides insights regarding early steps in pathogen response signaling in plants.

Arsenate [As(V)], the most abundant chemical form of the toxic element arsenic, is very similar to phosphate (Pi), which enables its uptake from the soil through the high-affinity Pi transport system. This work identifies a Pi transporter mutant with enhanced ability to accumulate arsenic but with a reduced Pi and As(V) uptake rate, suggesting a protective mechanism operating in arsenic-tolerant plants.

Three Arabidopsis nuclear-encoded T7 phage-type RNA polymerases (RNAPs) localize to mitochondria, plastids, or both. This study finds that two of them can initiate transcription from both mitochondrial and plastid promoters in vitro without auxiliary factors. The ability for promoter recognition appears to have been conserved over a long period of evolution of organellar RNAPs.

Some double-stranded RNA binding proteins participate in miRNA biogenesis. A series of deletion mutants demonstrated that the N-terminal region of HYPONASTIC LEAVES1 with two double-stranded RNA binding domains is sufficient for miRNA biogenesis and capable of rescuing the hyl1 phenotype. This study also showed that the putative NLS is a true nuclear localization signal.

The importance of oxylipins, such as jasmonic acid, in plant defense and adaptation is well known. This work suggests that other oxylipins, such as 9-hydroxyoctadecatrienoic acid, also function in developmental and defense responses, such as callose and pectin deposition and production of reactive oxygen species. Mutant analyses revealed at least three signaling cascades mediating oxylipin action.

Many floral traits appear to be adapted to particular pollinators. AN2 is a well-defined myb-type transcription factor that is a major determinant of flower color variation between two Petunia species. Transformation of one species with AN2 from the other caused a switch in pollinator preference, suggesting that adaptation to a new pollinator may involve a limited number of genes of large effect.

Mutations in cellulose synthase subunits required for secondary cell wall formation confer resistance to bacterial and fungal pathogens and upregulate ABA-responsive defense genes. Alteration of secondary cell wall integrity by inhibiting cellulose synthesis may lead to activation of novel defense pathways that create antimicrobial-enriched environments hostile to pathogens.

The importance of oxylipins, such as jasmonic acid, in plant defense and adaptation is well known. This work suggests that other oxylipins, such as 9-hydroxyoctadecatrienoic acid, also function in developmental and defense responses, such as callose and pectin deposition and production of reactive oxygen species. Mutant analyses revealed at least three signaling cascades mediating oxylipin action.

Chloroplasts are a major sink for metal ions like iron and copper, which play essential roles in photosynthetic electron transport. However, very little is known about iron uptake by the chloroplast. This study characterized PIC1 from Arabidopsis, which is a transmembrane protein of cyanobacterial origin that most likely functions as a metal ion permease in the chloroplast envelope.

Chlorophyll is a central player in photosynthetic light harvesting, but details of chlorophyll catabolism and regulation are unresolved. Here, two different expression systems in two species were used to study the role and regulation of Chlase in chlorophyll catabolism. The results suggest that Chlase is a rate-limiting enzyme in chlorophyll catabolism controlled via posttranslational regulation.

The hormone jasmonic acid (JA) functions in stress responses and plant development. This work identified the mitogen-activated protein kinase cascade, MKK3–MPK6, which is activated by JA, and indicates key roles for this kinase unit in the JA signaling pathway in processes such as root growth and negative regulation of the transcriptional activator ATMYC2.

Carotenoids help protect the chloroplast from photoxidative stress. The aba4-1 mutant lacks neoxanthin but retains all other xanthophyll species. This research shows that neoxanthin plays a specific role in protection of Lhc proteins, the PSII reaction center, and thylakoids from photooxidative stress and protects against the damaging effects of reactive oxygen species, particularly superoxide anions.

Chloroplasts are a major sink for metal ions like iron and copper, which play essential roles in photosynthetic electron transport. However, very little is known about iron uptake by the chloroplast. This study characterized PIC1 from Arabidopsis, which is a transmembrane protein of cyanobacterial origin that most likely functions as a metal ion permease in the chloroplast envelope.

Mutations in cellulose synthase subunits required for secondary cell wall formation confer resistance to bacterial and fungal pathogens and upregulate ABA-responsive defense genes. Alteration of secondary cell wall integrity by inhibiting cellulose synthesis may lead to activation of novel defense pathways that create antimicrobial-enriched environments hostile to pathogens.

To divide or not is one of the most crucial choices made by cells. As in other eukaryotes, progression through the cell cycle in plants is governed by cyclin-dependent kinases (CDKs), and one of the major regulatory inputs to CDK function is phosphorylation. Here, it is shown that Arabidopsis CDKA;1 is phosphorylated in the T-loop region and that phosphorylation is essential for kinase function.

The hormone jasmonic acid (JA) functions in stress responses and plant development. This work identified the mitogen-activated protein kinase cascade, MKK3–MPK6, which is activated by JA, and indicates key roles for this kinase unit in the JA signaling pathway in processes such as root growth and negative regulation of the transcriptional activator ATMYC2.

UDP-glucose pyrophosphorylase functions in carbohydrate metabolism and cell wall biosynthesis. Silencing of rice Ugp1 affects normal callose deposition during pollen mother cell (PMC) meiosis and leads to the degeneration of PMC at the early meiosis stage. This work demonstrates that rice Ugp1 is essential for PMC meiosis and microspore development.

The NADPH oxidase RBOH and calcium-dependent protein kinases (CDPKs) are implicated in rapid production of reactive oxygen species, or oxidative burst, early in plant–pathogen interactions, but the regulatory mechanisms are unknown. The results of this work suggest that Ca²⁺-dependent phosphorylation of potato RBOHB by CDPK5 plays a central role in oxidative burst during pathogen infection.

Arsenate [As(V)], the most abundant chemical form of the toxic element arsenic, is very similar to phosphate (Pi), which enables its uptake from the soil through the high-affinity Pi transport system. This work identifies a Pi transporter mutant with enhanced ability to accumulate arsenic but with a reduced Pi and As(V) uptake rate, suggesting a protective mechanism operating in arsenic-tolerant plants.

Mutations in cellulose synthase subunits required for secondary cell wall formation confer resistance to bacterial and fungal pathogens and upregulate ABA-responsive defense genes. Alteration of secondary cell wall integrity by inhibiting cellulose synthesis may lead to activation of novel defense pathways that create antimicrobial-enriched environments hostile to pathogens.

Proper regulation of seed dormancy and germination is critical to plant survival. It was thought that disappearance of the negative regulator RGA-LIKE2 (RGL2) protein is required for seed germination. This report finds instead that RGL2 accumulates in germinating sleepy1 (sly1) mutants, suggesting that protein disappearance is not the only mechanism that relieves RGL2 repression of seed germination.

Light signals induce complex developmental programs in plants. The transcription factor HY5 acts downstream of multiple photoreceptors, but its target genes are not well known. Putative HY5 binding sites were mapped to 3894 genes with diverse developmental functions, including early light-responsive genes. HY5 appears to be an early regulator of the transcriptional cascades for photomorphogenesis.

Using high-throughput sequencing methods, many transcripts were found to be routed through the RDR6/DCL4-dependent silencing pathway after single or dual targeting events by miRNA or tasiRNA. Several members of a rapidly expanding clade of PPR gene transcripts were targeted, suggesting that this silencing pathway may function to buffer the effects of rapidly expanding gene families.