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"Pyke, Kevin"
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Divide and shape: an endosymbiont in action
The endosymbiotic evolution of the plastid within the host cell required development of a mechanism for efficient division of the plastid. Whilst a model for the mechanism of chloroplast division has been constructed, little is known of how other types of plastids divide, especially the proplastid, the progenitor of all plastid types in the cell. It has become clear that plastid shape is highly heterogeneous and dynamic, especially stromules. This article considers how such variation in morphology might be controlled and how such plastids might divide efficiently.
Journal Article
Network Inference Analysis Identifies an APRR2-Like Gene Linked to Pigment Accumulation in Tomato and Pepper Fruits
Carotenoids represent some of the most important secondary metabolites in the human diet, and tomato (Solanum lycopersicum) is a rich source of these health-promoting compounds. In this work, a novel and fruit-related regulator of pigment accumulation in tomato has been identified by artificial neural network inference analysis and its function validated in transgenic plants. A tomato fruit gene regulatory network was generated using artificial neural network inference analysis and transcription factor gene expression profiles derived from fruits sampled at various points during development and ripening. One of the transcription factor gene expression profiles with a sequence related to an Arabidopsis (Arabidopsis thaliana) ARABIDOPSIS PSEUDO RESPONSE REGULATOR2-LIKE gene (APRR2-Like) was up-regulated at the breaker stage in wild-type tomato fruits and, when overexpressed in transgenic lines, increased plastid number, area, and pigment content, enhancing the levels of chlorophyll in immature unripe fruits and carotenoids in red ripe fruits. Analysis of the transcriptome of transgenic lines overexpressing the tomato APPR2-Like gene revealed up-regulation of several ripening-related genes in the overexpression lines, providing a link between the expression of this tomato gene and the ripening process. A putative ortholog of the tomato APPR2-Like gene in sweet pepper (Capsicum annuum) was associated with pigment accumulation in fruit tissues. We conclude that the function of this gene is conserved across taxa and that it encodes a protein that has an important role in ripening.
Journal Article
The rice EP3 and OsFBK1 E3 ligases alter plant architecture and flower development, and affect transcript accumulation of microRNA pathway genes and their targets
Summary ERECTA PANICLE 3 (EP3) and ORYZA SATIVA F‐BOX KELCH 1 (OsFBK1) proteins share 57% and 54% sequence identity with the Arabidopsis F‐box protein HAWAIIAN SKIRT (HWS). Previously we showed that EP3 is a functional orthologue of HWS. Here we demonstrate that OsFBK1 is another functional orthologue of HWS and show the complexity of interaction between EP3 and OsFBK1 genes at different developmental stages of the plant. qRT‐PCR expression analyses and studies of EP3‐GFP and OsFBK1‐RFP promoter reporter lines demonstrate that although EP3 and OsFBK1 expression can be detected in the same tissues some cells exclusively express EP3 or OsFBK1 whilst others co‐express both genes. Loss, reduction or gain‐of‐function lines for EP3 and OsFBK1, show that EP3 and OsFBK1 affect plant architecture, organ size, floral organ number and size, floral morphology, pollen viability, grain size and weight. We have identified the putative orthologue genes of the rice microRNA pathway for ORYZA SATIVA DAWDLE (OsDDL) and ORYZA SATIVA SERRATE (OsSE), and demonstrated that EP3 and OsFBK1 affect their transcript levels as well as those of CROWN ROOT DEFECT 1/ORYZA SATIVA Exportin‐5 HASTY (CRD1/OsHST), ORYZA SATIVA DICER‐LIKE 1 (OsDCL) and ORYZA SATIVA WEAVY LEAF1 (OsWAF1). We show that EP3 affects OsPri‐MIR164, OsNAM1 and OsNAC1 transcript levels. OsNAC1 transcripts are modified by OsFBK1, suggesting two independent regulatory pathways, one via EP3 and OsMIR164 and the other via OsFBK1. Our data propose that EP3 and OsFBK1 conjointly play similar roles in rice to how HWS does in Arabidopsis.
Journal Article
Decreased photosynthesis in the erect panicle 3 (ep3) mutant of rice is associated with reduced stomatal conductance and attenuated guard cell development
The ERECT PANICLE 3 gene of rice encodes a peptide that exhibits more than 50% sequence identity with the Arabidopsis F-box protein HAWAIIAN SKIRT (HWS). Ectopic expression of the Os02g15950 coding sequence, driven by the HWS (At3g61950) promoter, rescued the hws-1 flower phenotype in Arabidopsis confirming that EP3 is a functional orthologue of HWS. In addition to displaying an erect inflorescence phenotype, loss-of-function mutants of Os02g15950 exhibited a decrease in leaf photosynthetic capacity and stomatal conductance. Analysis of a range of physiological and anatomical features related to leaf photosynthesis revealed no alteration in Rubisco content and no notable changes in mesophyll size or arrangement. However, both ep3 mutant plants and transgenic lines that have a T-DNA insertion within the Os02g15950 (EP3) gene exhibit smaller stomatal guard cells compared with their wild-type controls. This anatomical characteristic may account for the observed decrease in leaf photosynthesis and provides evidence that EP3 plays a role in regulating stomatal guard cell development.
Journal Article
ARC6 Is a J-Domain Plastid Division Protein and an Evolutionary Descendant of the Cyanobacterial Cell Division Protein Ftn2
Replication of chloroplasts is essential for achieving and maintaining optimal plastid numbers in plant cells. The plastid division machinery contains components of both endosymbiotic and host cell origin, but little is known about the regulation and molecular mechanisms that govern the division process. The Arabidopsis mutant arc6 is defective in plastid division, and its leaf mesophyll cells contain only one or two grossly enlarged chloroplasts. We show here that arc6 chloroplasts also exhibit abnormal localization of the key plastid division proteins FtsZ1 and FtsZ2. Whereas in wild-type plants, the FtsZ proteins assemble into a ring at the plastid division site, chloroplasts in the arc6 mutant contain numerous short, disorganized FtsZ filament fragments. We identified the mutation in arc6 and show that the ARC6 gene encodes a chloroplast-targeted DnaJ-like protein localized to the plastid envelope membrane. An ARC6-green fluorescent protein fusion protein was localized to a ring at the center of the chloroplasts and rescued the chloroplast division defect in the arc6 mutant. The ARC6 gene product is related closely to Ftn2, a prokaryotic cell division protein unique to cyanobacteria. Based on the FtsZ filament morphology observed in the arc6 mutant and in plants that overexpress ARC6, we hypothesize that ARC6 functions in the assembly and/or stabilization of the plastid-dividing FtsZ ring. We also analyzed FtsZ localization patterns in transgenic plants in which plastid division was blocked by altered expression of the division site-determining factor AtMinD. Our results indicate that MinD and ARC6 act in opposite directions: ARC6 promotes and MinD inhibits FtsZ filament formation in the chloroplast.
Journal Article
The suffulta mutation in tomato reveals a novel method of plastid replication during fruit ripening
Mutant alleles at the suffulta locus of tomato dramatically affect the pattern of plastid division throughout the plant, resulting in few, greatly enlarged chloroplasts in leaf and stem cells. suffulta plants are compromised in growth and have distinctly pale stems. The green developing tomato fruit are generally paler compared with the wild type, but ripe red fruit are much more similar in colour and pigment content. By using plastid-targeted green fluorescent protein, the underlying plastid phenotypes in the ripening suffulta fruit reveal that enlarged chlorophyll-containing chloroplasts degenerate and give rise to a wild type-like population of chromoplasts in ripe fruit by a process of plastid budding and fragmentation, resulting in a heterogeneous population of plastid-derived structures which eventually become chromoplasts. In stomatal guard cells, plastid-derived structures lacking chlorophyll, but containing GFP, are also observed, especially in guard cells which completely lack normal chloroplasts. How this novel 'replication' process in suffulta relates to conventional plastid division and stromule formation is discussed.
Journal Article
comparison of the Thlaspi caerulescens and Thlaspi arvense shoot transcriptomes
• Whole-genome transcriptome profiling is revealing how biological systems are regulated at the transcriptional level. This study reports the development of a robust method to profile and compare the transcriptomes of two nonmodel plant species, Thlaspi caerulescens, a zinc (Zn) hyperaccumulator, and Thlaspi arvense, a nonhyperaccumulator, using Affymetrix Arabidopsis thaliana ATH1-121501 GeneChip® arrays (Affymetrix, Santa Clara, CA, USA). • Transcript abundance was quantified in the shoots of agar- and compost-grown plants of both species. Analyses were optimized using a genomic DNA (gDNA)-based probe-selection strategy based on the hybridization efficiency of Thlaspi gDNA with corresponding A. thaliana probes. In siIico alignments of GeneChip® probes with Thlaspi gene sequences, and quantitative real-time PCR, confirmed the validity of this approach. • Approximately 5000 genes were differentially expressed in the shoots of T. caerulescens compared with T. arvense, including genes involved in Zn transport and compartmentalization. • Future functional analyses of genes identified as differentially expressed in the shoots of these closely related species will improve our understanding of the molecular mechanisms of Zn hyperaccumulation.
Journal Article
phosphoenolpyruvate/phosphate translocator is required for phenolic metabolism, palisade cell development, and plastid-dependent nuclear gene expression
The Arabidopsis chlorophyll a/b binding protein (CAB) gene underexpressed 1 (cue1) mutant underexpresses light-regulated nuclear genes encoding chloroplast-localized proteins. cue1 also exhibits mesophyll-specific chloroplast and cellular defects, resulting in reticulate leaves. Both the gene underexpression and the leaf cell morphology phenotypes are dependent on light intensity. In this study, we determine that CUE1 encodes the plastid inner envelope phosphoenolpyruvate/phosphate translocator (PPT) and define amino acid residues that are critical for translocator function. The biosynthesis of aromatics is compromised in cue1, and the reticulate phenotype can be rescued by feeding aromatic amino acids. Determining that CUE1 encodes PPT indicates the in vivo role of the translocator in metabolic partitioning and reveals a mesophyll cell-specific requirement for the translocator in Arabidopsis leaves. The nuclear gene expression defects in cue1 suggest that a light intensity-dependent interorganellar signal is modulated through metabolites dependent on a plastid supply of phosphoenolpyruvate.
Journal Article