ANGUSTIFOLIA, a plant homolog of CtBP/BARS, functions outside the nucleus

ANGUSTIFOLIA negatively regulates resistance to Sclerotinia sclerotiorum via modulation of PTI and JA signalling pathways in Arabidopsis thaliana

Sclerotinia sclerotiorum is a devastating pathogen that infects a broad range of host plants. The mechanism underlying plant defence against fungal invasion is still not well characterized. Here, we report that ANGUSTIFOLIA (AN), a CtBP family member, plays a role in the defence against S. sclerotiorum attack. Arabidopsis an mutants exhibited stronger resistance to S. sclerotiorum at the early stage of infection than wild-type plants. Accordingly, an mutants exhibited stronger activation of pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI) responses, including mitogen-activated protein kinase activation, reactive oxygen species accumulation, callose deposition, and the expression of PTI-responsive genes, upon treatment with PAMPs/microbe-associated molecular patterns. Moreover, Arabidopsis lines overexpressing AN were more susceptible to S. sclerotiorum and showed defective PTI responses. Our luminometry, bimolecular fluorescence complementation, coimmunoprecipitation, and in vitro pull-down assays indicate that AN interacts with allene oxide cyclases (AOC), essential enzymes involved in jasmonic acid (JA) biosynthesis, negatively regulating JA biosynthesis in response to S. sclerotiorum infection. This work reveals AN is a negative regulator of the AOC-mediated JA signalling pathway and PTI activation.

BrAN contributes to leafy head formation by regulating leaf width in Chinese cabbage (Brassica rapa L. ssp. pekinensis)

Leafy head is an important agronomic trait that determines the yield and quality of Chinese cabbage. The molecular mechanism underlying heading in Chinese cabbage has been the focus of research, and wide leaves are a prerequisite for leafy head formation. In our study, two allelic leafy heading-deficient mutants (lhd1 and lhd2) with narrow leaf phenotypes were screened in an ethyl methanesulfonate mutagenized population from a heading Chinese cabbage double haploid line 'FT'. Genetic analysis revealed that the mutant trait was controlled by a recessive nuclear gene, which was found to be BraA10g000480.3C by MutMap and Kompetitive allele-specific PCR analyses. As BraA10g000480.3C was the ortholog of ANGUSTIFOLIA in Arabidopsis, which has been found to regulate leaf width by controlling cortical microtubule arrangement and pavement cell shape, we named it BrAN. BrAN in mutant lhd1 carried an SNP (G to A) on intron 2 that co-segregated with the mutant phenotype, and disrupted the exon-intron splice junction generating intron retention and a putative truncated protein. BrAN in mutant lhd2 carried an SNP (G to A) on exon 4 leading to a premature stop codon. The ectopic overexpression of BrAN restored normal leaf phenotype due to abnormal cortical microtubule arrangement and pavement cell shape in the Arabidopsis an-t1 mutant. However, transformation of Bran did not rescue the an-t1 phenotype. These results indicate that BrAN contributes to leafy head formation of Chinese cabbage.

Two atypical ANGUSTIFOLIA without a plant-specific C-terminus regulate gametophore and sporophyte shapes in the moss Physcomitrium (Physcomitrella) patens

ANGUSTIFOLIA (AN) is a plant-specific subfamily of the CtBP/BARS/AN family, characterized by a plant-specific C-terminal domain of approximately 200 amino acids. Previously, we revealed that double knockout (DKO) lines of Physcomitrium (Physcomitrella) patens ANGUSTIFOLIA genes (PpAN1-1 and PpAN1-2) show defects in gametophore height and the lengths of the seta and foot region of sporophytes, by reduced cell elongation. In addition to two canonical ANs, the genome of P. patens has two atypical ANs without a coding region for a plant-specific C-terminus (PpAN2-1 and PpAN2-2); these were investigated in this study. Similar to PpAN1s, both promoters of the PpAN2 genes were highly active in the stems of haploid gametophores and in the middle-to-basal region of young diploid sporophytes that develop into the seta and foot. Analyses of PpAN2-1/2-2 DKO and PpAN quadruple knockout (QKO) lines implied that these four AN genes have partially redundant functions to regulate cell elongation in their expression regions. Transgenic strains harboring P. patens α-tubulin fused to green fluorescent protein, which were generated from a QKO line, showed that the orientation of the microtubules in the gametophore tips in the PpAN QKO lines was unchanged from the wild-type and PpAN1-1/1-2 DKO plants. In addition to both PpAN2-1 and PpAN2-2, short Arabidopsis AN without the C-terminus of 200 amino acids could rescue the Arabidopsis thaliana an-1 phenotypes, implying AN activity is dependent on the N-terminal regions.

Arabidopsis C-terminal binding protein ANGUSTIFOLIA modulates transcriptional co-regulation of MYB46 and WRKY33

The apparent antagonism between salicylic acid (SA) and jasmonic acid (JA)/ethylene (ET) signalling resulting in trade-offs between defence against (hemi)biotrophic and necrotrophic pathogens has been widely described across multiple plant species. However, the underlying mechanism remains to be fully established. The molecular and cellular functions of ANGUSTIFOLIA (AN) were characterised, and its role in regulating the pathogenic response was studied in Arabidopsis. We demonstrated that AN, a plant homologue of mammalian C-TERMINAL BINDING PROTEIN (CtBP), antagonistically regulates plant resistance to the hemibiotrophic pathogen Pseudomonas syringae and the necrotrophic pathogen Botrytis cinerea. Consistent with phenotypic observations, transcription of genes involved in SA and JA/ET pathways was antagonistically regulated by AN. By interacting with another nuclear protein TYROSYL-DNA PHOSPHODIESTERASE1 (TDP1), AN imposes transcriptional repression on MYB46, encoding a transcriptional activator of PHENYLALANINE AMMONIA-LYASE (PAL) genes which are required for SA biosynthesis, while releasing TDP1-imposed transcriptional repression on WRKY33, a master regulator of the JA/ET signalling pathway. These findings demonstrate that transcriptional co-regulation of MYB46 and WRKY33 by AN mediates the coordination of SA and JA/ET pathways to optimise defences against (hemi)biotrophic and necrotrophic pathogens.

Two ANGUSTIFOLIA genes regulate gametophore and sporophyte development in Physcomitrella patens

In Arabidopsis thaliana the ANGUSTIFOLIA (AN) gene regulates the width of leaves by controlling the diffuse growth of leaf cells in the medio-lateral direction. In the genome of the moss Physcomitrella patens, we found two normal ANs (PpAN1-1 and 1-2). Both PpAN1 genes complemented the A. thaliana an-1 mutant phenotypes. An analysis of spatiotemporal promoter activity of each PpAN1 gene, using transgenic lines that contained each PpAN1-promoter- uidA (GUS) gene, showed that both promoters are mainly active in the stems of haploid gametophores and in the middle to basal region of the young sporophyte that develops into the seta and foot. Analyses of the knockout lines for PpAN1-1 and PpAN1-2 genes suggested that these genes have partially redundant functions and regulate gametophore height by controlling diffuse cell growth in gametophore stems. In addition, the seta and foot were shorter and thicker in diploid sporophytes, suggesting that cell elongation was reduced in the longitudinal direction, whereas no defects were detected in tip-growing protonemata. These results indicate that both PpAN1 genes in P. patens function in diffuse growth of the haploid and diploid generations but not in tip growth. To visualize microtubule distribution in gametophore cells of P. patens, transformed lines expressing P. patens α-tubulin fused to sGFP were generated. Contrary to expectations, the orientation of microtubules in the tips of gametophores in the PpAN1-1/1-2 double-knockout lines was unchanged. The relationships among diffuse cell growth, cortical microtubules and AN proteins are discussed.

Excess Pyrophosphate Restrains Pavement Cell Morphogenesis and Alters Organ Flatness in Arabidopsis thaliana

In Arabidopsis thaliana, the vacuolar proton-pumping pyrophosphatase (H⁺-PPase) is highly expressed in young tissues, which consume large amounts of energy in the form of nucleoside triphosphates and produce pyrophosphate (PPi) as a byproduct. We reported that excess PPi in the H⁺-PPase loss-of-function fugu5 mutant severely compromised gluconeogenesis from seed storage lipids, arrested cell division in cotyledonary palisade tissue, and triggered compensated cell enlargement; this phenotype was recovered upon sucrose supply. Thus, we provided evidence that the hydrolysis of inhibitory PPi, rather than vacuolar acidification, is the major contribution of H⁺-PPase during seedling establishment. Here, examination of the epidermis revealed that fugu5 pavement cells exhibited defective puzzle-cell formation. Importantly, removal of PPi from fugu5 background by the yeast cytosolic PPase IPP1, in fugu5-1 AVP1_pro::IPP1 transgenic lines, restored the phenotypic aberrations of fugu5 pavement cells. Surprisingly, pavement cells in mutants with defects in gluconeogenesis (pck1-2) or the glyoxylate cycle (icl-2; mls-2) showed no phenotypic alteration, indicating that reduced sucrose production from seed storage lipids is not the cause of fugu5 epidermal phenotype. fugu5 had oblong cotyledons similar to those of angustifolia-1 (an-1), whose leaf pavement cells display an abnormal arrangement of cortical microtubules (MTs). To gain insight into the genetic interaction between ANGUSTIFOLIA and H⁺-PPase in pavement cell differentiation, an-1 fugu5-1 was analyzed. Surprisingly, epidermis developmental defects were synergistically enhanced in the double mutant. In fact, an-1 fugu5-1 pavement cells showed a striking three-dimensional growth phenotype on both abaxial and adaxial sides of cotyledons, which was recovered by hydrolysis of PPi in an-1 fugu5-1 AVP1_pro::IPP1. Live imaging revealed that cortical MTs exhibited a reduced velocity, were slightly fragmented and sparse in the above lines compared to the WT. Consistently, addition of PPi in vitro led to a dose-dependent delay of tubulin polymerization, thus supporting a link between PPi and MT dynamics. Moreover, mathematical simulation of three-dimensional growth based on cotyledon proximo-distal and medio-lateral phenotypic quantification implicated restricted cotyledon expansion along the medio-lateral axis in the crinkled surface of an-1 fugu5-1. Together, our data suggest that PPi homeostasis is a prerequisite for proper pavement cell morphogenesis, epidermal growth and development, and organ flattening.

Multiple steps of leaf thickening during sun-leaf formation in Arabidopsis

Plant morphological and physiological traits exhibit plasticity in response to light intensity. Leaf thickness is enhanced under high light (HL) conditions compared with low light (LL) conditions through increases in both cell number and size in the dorsoventral direction; however, the regulation of such phenotypic plasticity in leaf thickness (namely, sun- or shade-leaf formation) during the developmental process remains largely unclear. By modifying observation techniques for tiny leaf primordia in Arabidopsis thaliana, we analysed sun- and shade-leaf development in a time-course manner and found that the process of leaf thickening can be divided into early and late phases. In the early phase, anisotropic cell elongation and periclinal cell division on the adaxial side of mesophyll tissue occurred under the HL conditions used, which resulted in the dorsoventral growth of sun leaves. Anisotropic cell elongation in the palisade tissue is triggered by blue-light irradiation. We discovered that anisotropic cell elongation processes before or after periclinal cell division were differentially regulated independent of or dependent upon signalling through blue-light receptors. In contrast, during the late phase, isotropic cell expansion associated with the endocycle, which determined the final leaf thickness, occurred irrespective of the light conditions. Sucrose production was high under HL conditions, and we found that sucrose promoted isotropic cell expansion and the endocycle even under LL conditions. Our analyses based on this method of time-course observation addressed the developmental framework of sun- and shade-leaf formation.

A New Allele of the SPIKE1 Locus Reveals Distinct Regulation of Trichome and Pavement Cell Development and Plant Growth

The single-celled trichomes of Arabidopsis thaliana have long served as an elegant model for elucidating the mechanisms of cell differentiation and morphogenesis due to their unique growth patterns. To identify new components in the genetic network that governs trichome development, we carried out exhaustive screens for additional Arabidopsis mutants with altered trichome morphology. Here, we report one mutant, aberrantly branched trichome1-1 (abt1-1), with a reduced trichome branching phenotype. After positional cloning, a point mutation in the SPIKE1 (SPK1) gene was identified in abt1-1. Further genetic complementation experiments confirmed that abt1-1 is a new allele of SPK1, so abt1-1 was renamed as spk1-7 according to the literatures. spk1-7 and two other spk1 mutant alleles, covering a spectrum of phenotypic severity, highlighted the distinct responses of developmental programs to different SPK1 mutations. Although null spk1 mutants are lethal and show defects in plant stature, trichome and epidermal pavement cell development, only trichome branching is affected in spk1-7. Surprisingly, we found that SPK1 is involved in the positioning of nuclei in the trichome cells. Lastly, through double mutant analysis, we found the coordinated regulation of trichome branching between SPK1 and two other trichome branching regulators, ANGUSTIFOLIA (AN) and ZWICHEL (ZWI). SPK1 might serve for the precise positioning of trichome nuclei, while AN and ZWI contribute to the formation of branch points through governing the cMTs dynamics. In summary, this study presented a fully viable new mutant allele of SPK1 and shed new light on the regulation of trichome branching and other developmental processes by SPK1.

Reactive oxygen species mediate conical cell shaping in Arabidopsis thaliana petals

Plants have evolved diverse cell types with distinct sizes, shapes, and functions. For example, most flowering plants contain specialized petal conical epidermal cells that are thought to attract pollinators and influence light capture and reflectance, but the molecular mechanisms controlling conical cell shaping remain unclear. Here, through a genetic screen in Arabidopsis thaliana, we demonstrated that loss-of-function mutations in ANGUSTIFOLIA (AN), which encodes for a homolog of mammalian CtBP/BARs, displayed conical cells phenotype with wider tip angles, correlating with increased accumulation of reactive oxygen species (ROS). We further showed that exogenously supplied ROS generated similar conical cell phenotypes as the an mutants. Moreover, reduced endogenous ROS levels resulted in deceased tip sharpening of conical cells. Furthermore, through enhancer screening, we demonstrated that mutations in katanin (KTN1) enhanced conical cell phenotypes of the an-t1 mutants. Genetic analyses showed that AN acted in parallel with KTN1 to control conical cell shaping. Both increased or decreased ROS levels and mutations in AN suppressed microtubule organization into well-ordered circumferential arrays. We demonstrated that the AN-ROS pathway jointly functioned with KTN1 to modulate microtubule ordering, correlating with the tip sharpening of conical cells. Collectively, our findings revealed a mechanistic insight into ROS homeostasis regulation of microtubule organization and conical cell shaping.

ANGUSTIFOLIA contributes to the regulation of three-dimensional morphogenesis in the liverwort Marchantia polymorpha

Arabidopsis thaliana mutants deficient in ANGUSTIFOLIA (AN) exhibit several phenotypes at the sporophyte stage, such as narrow and thicker leaves, trichomes with two branches, and twisted fruits. It is thought that these phenotypes are caused by abnormal arrangement of cortical microtubules (MTs). AN homologs are present in the genomes of diverse land plants, including the basal land plant Marchantia polymorpha, and their molecular functions have been shown to be evolutionarily conserved in terms of the ability to complement the A. thaliana an-1 mutation. However, the roles of ANs in bryophytes, the life cycle of which includes a dominant haploid gametophyte generation, remain unknown. Here, we have examined the roles of AN homologs in the model bryophyte M. polymorpha (MpAN). Mpan knockout mutants showed abnormal twisted thalli and suppressed thallus growth along the growth axis. Under weak blue light conditions, elongated thallus growth was observed in wild-type plants, whereas it was suppressed in the mutants. Moreover, disordered cortical MT orientations were observed. Our findings suggest that MpAN contributes to three-dimensional morphogenesis by regulating cortical MT arrangement in the gametophytes of bryophytes.

A Variable Polyglutamine Repeat Affects Subcellular Localization and Regulatory Activity of a Populus ANGUSTIFOLIA Protein

Polyglutamine (polyQ) stretches have been reported to occur in proteins across many organisms including animals, fungi and plants. Expansion of these repeats has attracted much attention due their associations with numerous human diseases including Huntington’s and other neurological maladies. This suggests that the relative length of polyQ stretches is an important modulator of their function. Here, we report the identification of a Populus C-terminus binding protein (CtBP) ANGUSTIFOLIA (PtAN1) which contains a polyQ stretch whose functional relevance had not been established. Analysis of 917 resequenced Populus trichocarpa genotypes revealed three allelic variants at this locus encoding 11-, 13- and 15-glutamine residues. Transient expression assays using Populus leaf mesophyll protoplasts revealed that the 11Q variant exhibited strong nuclear localization whereas the 15Q variant was only found in the cytosol, with the 13Q variant exhibiting localization in both subcellular compartments. We assessed functional implications by evaluating expression changes of putative PtAN1 targets in response to overexpression of the three allelic variants and observed allele-specific differences in expression levels of putative targets. Our results provide evidence that variation in polyQ length modulates PtAN1 function by altering subcellular localization.

Palisade cell shape affects the light-induced chloroplast movements and leaf photosynthesis

Leaf photosynthesis is regulated by multiple factors that help the plant to adapt to fluctuating light conditions. Leaves of sun-light-grown plants are thicker and contain more columnar palisade cells than those of shade-grown plants. Light-induced chloroplast movements are also essential for efficient leaf photosynthesis and facilitate efficient light utilization in leaf cells. Previous studies have demonstrated that leaves of most of the sun-grown plants exhibited no or very weak chloroplast movements and could accomplish efficient photosynthesis under strong light. To examine the relationship between palisade cell shape, chloroplast movement and distribution, and leaf photosynthesis, we used an Arabidopsis thaliana mutant, angustifolia (an), which has thick leaves that contain columnar palisade cells similar to those in the sun-grown plants. In the highly columnar cells of an mutant leaves, chloroplast movements were restricted. Nevertheless, under white light condition (at 120 µmol m⁻² s⁻¹), the an mutant plants showed higher chlorophyll content per unit leaf area and, thus, higher light absorption by the leaves than the wild type, which resulted in enhanced photosynthesis per unit leaf area. Our findings indicate that coordinated regulation of leaf cell shape and chloroplast movement according to the light conditions is pivotal for efficient leaf photosynthesis.

ANGUSTIFOLIA, a Plant Homolog of CtBP/BARS Localizes to Stress Granules and Regulates Their Formation

The ANGUSTIFOLIA (AN) gene in Arabidopsis is important for a plethora of morphological phenotypes. Recently, AN was also reported to be involved in responses to biotic and abiotic stresses. It encodes a homolog of the animal C-terminal binding proteins (CtBPs). In contrast to animal CtBPs, AN does not appear to function as a transcriptional co-repressor and instead functions outside nucleus where it might be involved in Golgi-associated membrane trafficking. In this study, we report a novel and unexplored role of AN as a component of stress granules (SGs). Interaction studies identified several RNA binding proteins that are associated with AN. AN co-localizes with several messenger ribonucleoprotein granule markers to SGs in a stress dependent manner. an mutants exhibit an altered SG formation. We provide evidence that the NAD(H) binding domain of AN is relevant in this context as proteins carrying mutations in this domain localize to a much higher degree to SGs and strongly reduce AN dimerization and its interaction with one interactor but not the others. Finally, we show that AN is a negative regulator of salt and osmotic stress responses in Arabidopsis suggesting a functional relevance in SGs.

Orchestration of microtubules and the actin cytoskeleton in trichome cell shape determination by a plant-unique kinesin

Microtubules (MTs) and actin filaments (F-actin) function cooperatively to regulate plant cell morphogenesis. However, the mechanisms underlying the crosstalk between these two cytoskeletal systems, particularly in cell shape control, remain largely unknown. In this study, we show that introduction of the MyTH4-FERM tandem into KCBP (kinesin-like calmodulin-binding protein) during evolution conferred novel functions. The MyTH4 domain and the FERM domain in the N-terminal tail of KCBP physically bind to MTs and F-actin, respectively. During trichome morphogenesis, KCBP distributes in a specific cortical gradient and concentrates at the branching sites and the apexes of elongating branches, which lack MTs but have cortical F-actin. Further, live-cell imaging and genetic analyses revealed that KCBP acts as a hub integrating MTs and actin filaments to assemble the required cytoskeletal configuration for the unique, polarized diffuse growth pattern during trichome cell morphogenesis. Our findings provide significant insights into the mechanisms underlying cytoskeletal regulation of cell shape determination.

ANGUSTIFOLIA mediates one of the multiple SCRAMBLED signaling pathways regulating cell growth pattern in Arabidopsis thaliana

In Arabidopsis thaliana, an atypical leucine-rich repeat receptor-like kinase, SCRAMBLED (SCM), is required for multiple developmental processes including root epidermal cell fate determination, silique dehiscence, inflorescence growth, ovule morphogenesis, and tissue morphology. Previous work suggested that SCM regulates these multiple pathways using distinct mechanisms via interactions with specific downstream factors. ANGUSTIFOLIA (AN) is known to regulate cell and tissue morphogenesis by influencing cortical microtubule arrangement, and recently, the AN protein was reported to interact with the SCM protein. Therefore, we examined whether AN might be responsible for mediating some of the SCM-dependent phenotypes. We discovered that both scm and an mutant lines cause an abnormal spiral or twisting growth of roots, but only the scm mutant affected root epidermal patterning. The siliques of the an and scm mutants also exhibited spiral growth, as previously reported, but only the scm mutant altered silique dehiscence. Interestingly, we discovered that the spiral growth of roots and siliques of the scm mutant is rescued by a truncated SCM protein that lacks its kinase domain, and that a juxtamembrane domain of SCM was sufficient for AN binding in the yeast two-hybrid analysis. These results suggest that the AN protein is one of the critical downstream factors of SCM pathways specifically responsible for mediating its effects on cell/tissue morphogenesis through cortical microtubule arrangement.

Atkinesin-13A modulates cell-wall synthesis and cell expansion in Arabidopsis thaliana via the THESEUS1 pathway

Growth of plant organs relies on cell proliferation and expansion. While an increasingly detailed picture about the control of cell proliferation is emerging, our knowledge about the control of cell expansion remains more limited. We demonstrate here that the internal-motor kinesin AtKINESIN-13A (AtKIN13A) limits cell expansion and cell size in Arabidopsis thaliana, with loss-of-function atkin13a mutants forming larger petals with larger cells. The homolog, AtKINESIN-13B, also affects cell expansion and double mutants display growth, gametophytic and early embryonic defects, indicating a redundant role of the two genes. AtKIN13A is known to depolymerize microtubules and influence Golgi motility and distribution. Consistent with this function, AtKIN13A interacts genetically with ANGUSTIFOLIA, encoding a regulator of Golgi dynamics. Reduced AtKIN13A activity alters cell wall structure as assessed by Fourier-transformed infrared-spectroscopy and triggers signalling via the THESEUS1-dependent cell-wall integrity pathway, which in turn promotes the excess cell expansion in the atkin13a mutant. Thus, our results indicate that the intracellular activity of AtKIN13A regulates cell expansion and wall architecture via THESEUS1, providing a compelling case of interplay between cell wall integrity sensing and expansion.

Induction of cotton ovule culture fibre branching by co-expression of cotton BTL, cotton SIM, and Arabidopsis STI genes

The highly elongated single-celled cotton fibre consists of lint and fuzz, similar to the Arabidopsis trichome. Endoreduplication is an important determinant in Arabidopsis trichome initiation and morphogenesis. Fibre development is also controlled by functional homologues of Arabidopsis trichome patterning genes, although fibre cells do not have a branched shape like trichomes. The identification and characterization of the homologues of 10 key Arabidopsis trichome branching genes in Gossypium arboreum are reported here. Nuclear ploidy of fibres was determined, and gene function in cotton callus and fibre cells was investigated. The results revealed that the nuclear DNA content was constant in fuzz, whereas a limited and reversible change occurred in lint after initiation. Gossypeum arboreum branchless trichomes (GaBLT) was not transcribed in fibres. The homologue of STICHEL (STI), which is essential for trichome branching, was a pseudogene in Gossypium. Targeted expression of GaBLT, Arabidopsis STI, and the cytokinesis-repressing GaSIAMESE in G. hirsutum fibre cells cultured in vitro resulted in branching. The findings suggest that the distinctive developmental mechanism of cotton fibres does not depend on endoreduplication. This important component may be a relic function that can be activated in fibre cells.

Components of the CtBP1/BARS-dependent fission machinery

The brefeldin A ADP-ribosylated substrate, a member of the C-terminal-binding protein family that is referred to as CtBP1/BARS, is a dual-function protein that acts as a transcriptional co-repressor in the nucleus and as an inducer of membrane fission in the cytoplasm. In this review, we first discuss the mechanisms that enable CtBP1/BARS to shift between the nuclear transcriptional co-repressor and the cytosolic fission-inducing activities. Then, we focus on the role of CtBP1/BARS in membrane fission. CtBP1/BARS controls several fission events including macropinocytosis, fluid-phase endocytosis, COPI-coated vesicle formation, basolaterally directed post-Golgi carrier formation, and Golgi partitioning in mitosis. We report on recent advances in our understanding of the CtBP1/BARS membrane fission machineries that operate at the trans-side and at the cis-side of the Golgi complex. Specifically, we discuss how these machineries are assembled and regulated, and how they operate in the formation of the basolaterally directed post-Golgi carriers.

C-Terminal Binding Protein: A Molecular Link between Metabolic Imbalance and Epigenetic Regulation in Breast Cancer

The prevalence of obesity has given rise to significant global concerns as numerous population-based studies demonstrate an incontrovertible association between obesity and breast cancer. Mechanisms proposed to account for this linkage include exaggerated levels of carbohydrate substrates, elevated levels of circulating mitogenic hormones, and inflammatory cytokines that impinge on epithelial programming in many tissues. Moreover, recently many scientists have rediscovered the observation, first described by Otto Warburg nearly a century ago, that most cancer cells undergo a dramatic metabolic shift in energy utilization and expenditure that fuels and supports the cellular expansion associated with malignant proliferation. This shift in substrate oxidation comes at the cost of sharp changes in the levels of the high energy intermediate, nicotinamide adenine dinucleotide (NADH). In this review, we discuss a novel example of how shifts in the concentration and flux of substrates metabolized and generated during carbohydrate metabolism represent components of a signaling network that can influence epigenetic regulatory events in the nucleus. We refer to this regulatory process as "metabolic transduction" and describe how the C-terminal binding protein (CtBP) family of NADH-dependent nuclear regulators represents a primary example of how cellular metabolic status can influence epigenetic control of cellular function and fate.

The cell morphogenesis ANGUSTIFOLIA (AN) gene, a plant homolog of CtBP/BARS, is involved in abiotic and biotic stress response in higher plants

BACKGROUND

ANGUSTIFOLIA (AN), one of the CtBP family proteins, plays a major role in microtubule-dependent cell morphogenesis. Microarray analysis of mammalian AN homologs suggests that AN might function as a transcriptional activator and regulator of a wide range of genes. Genetic characterization of AN mutants suggests that AN might be involved in multiple biological processes beyond cell morphology regulation.

RESULTS

Using a reverse genetic approach, we provide in this paper the genetic, biochemical, and physiological evidence for ANGUSTIFOLIA's role in other new biological functions such as abiotic and biotic stress response in higher plants. The T-DNA knockout an-t1 mutant exhibits not only all the phenotypes of previously described angustifolia null mutants, but also copes better than wild type under dehydration and pathogen attack. The stress tolerance is accompanied by a steady-state modulation of cellular H(2)O(2) content, malondialdehyde (MDA) derived from cellular lipid peroxidation, and over-expression of stress responsive genes. Our results indicate that ANGUSTIFOLIA functions beyond cell morphology control through direct or indirect functional protein interaction networks mediating other biological processes such as drought and pathogen attacks.

CONCLUSIONS

Our results indicate that the ANGUSTIFOLIA gene participates in several biochemical pathways controlling cell morphogenesis, abiotic, and biotic stress responses in higher plants. Our results suggest that the in vivo function of plant ANGUSTIFOLIA has been overlooked and it needs to be further studied beyond microtubule-dependent cell morphogenesis.

ANGUSTIFOLIA is a central component of tissue morphogenesis mediated by the atypical receptor-like kinase STRUBBELIG

BACKGROUND

During plant tissue morphogenesis cells have to coordinate their behavior to allow the generation of the size, shape and cellular patterns that distinguish an organ. Despite impressive progress the underlying signaling pathways remain largely unexplored. In Arabidopsis thaliana, the atypical leucine-rich repeat receptor-like kinase STRUBBELIG (SUB) is involved in signal transduction in several developmental processes including the formation of carpels, petals, ovules and root hair patterning. The three STRUBBELIG-LIKE MUTANT (SLM) genes DETORQUEO (DOQ), QUIRKY (QKY) and ZERZAUST (ZET) are considered central elements of SUB-mediated signal transduction pathways as corresponding mutants share most phenotypic aspects with sub mutants.

RESULTS

Here we show that DOQ corresponds to the previously identified ANGUSTIFOLIA gene. The genetic analysis revealed that the doq-1 mutant exhibits all additional mutant phenotypes and conversely that other an alleles show the slm phenotypes. We further provide evidence that SUB and AN physically interact and that AN is not required for subcellular localization of SUB.

CONCLUSIONS

Our data suggest that AN is involved in SUB signal transduction pathways. In addition, they reveal previously unreported functions of AN in several biological processes, such as ovule development, cell morphogenesis in floral meristems, and root hair patterning. Finally, SUB and AN may directly interact at the plasma membrane to mediate SUB-dependent signaling.

Leaf development

Leaves are the most important organs for plants. Without leaves, plants cannot capture light energy or synthesize organic compounds via photosynthesis. Without leaves, plants would be unable perceive diverse environmental conditions, particularly those relating to light quality/quantity. Without leaves, plants would not be able to flower because all floral organs are modified leaves. Arabidopsis thaliana is a good model system for analyzing mechanisms of eudicotyledonous, simple-leaf development. The first section of this review provides a brief history of studies on development in Arabidopsis leaves. This history largely coincides with a general history of advancement in understanding of the genetic mechanisms operating during simple-leaf development in angiosperms. In the second section, I outline events in Arabidopsis leaf development, with emphasis on genetic controls. Current knowledge of six important components in these developmental events is summarized in detail, followed by concluding remarks and perspectives.