ResearchPad - plant-biology https://www.researchpad.co Default RSS Feed en-us © 2020 Newgen KnowledgeWorks <![CDATA[Chitin perception in plasmodesmata characterizes submembrane immune-signaling specificity in plants]]> https://www.researchpad.co/article/Ned6a2675-e59e-48b1-9bf2-58914df92500 The plasma membrane (PM) is composed of heterogeneous subdomains, characterized by differences in protein and lipid composition. PM receptors can be dynamically sorted into membrane domains to underpin signaling in response to extracellular stimuli. In plants, the plasmodesmal PM is a discrete microdomain that hosts specific receptors and responses. We exploited the independence of this PM domain to investigate how membrane domains can independently integrate a signal that triggers responses across the cell. Focusing on chitin signaling, we found that responses in the plasmodesmal PM require the LysM receptor kinases LYK4 and LYK5 in addition to LYM2. Chitin induces dynamic changes in the localization, association, or mobility of these receptors, but only LYM2 and LYK4 are detected in the plasmodesmal PM. We further uncovered that chitin-induced production of reactive oxygen species and callose depends on specific signaling events that lead to plasmodesmata closure. Our results demonstrate that distinct membrane domains can integrate a common signal with specific machinery that initiates discrete signaling cascades to produce a localized response.

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<![CDATA[Phosphoinositides regulate chloroplast processes]]> https://www.researchpad.co/article/N5fa10e02-9abc-41e9-b9de-ebc5a911aefd <![CDATA[Pathogen manipulation of chloroplast function triggers a light-dependent immune recognition]]> https://www.researchpad.co/article/Nda9be7b8-5caf-4f1d-81e2-2b6bef726e32 In plants and animals, nucleotide-binding leucine-rich repeat (NLR) proteins are intracellular immune sensors that recognize and eliminate a wide range of invading pathogens. NLR-mediated immunity is known to be modulated by environmental factors. However, how pathogen recognition by NLRs is influenced by environmental factors such as light remains unclear. Here, we show that the agronomically important NLR Rpi-vnt1.1 requires light to confer disease resistance against races of the Irish potato famine pathogen Phytophthora infestans that secrete the effector protein AVRvnt1. The activation of Rpi-vnt1.1 requires a nuclear-encoded chloroplast protein, glycerate 3-kinase (GLYK), implicated in energy production. The pathogen effector AVRvnt1 binds the full-length chloroplast-targeted GLYK isoform leading to activation of Rpi-vnt1.1. In the dark, Rpi-vnt1.1–mediated resistance is compromised because plants produce a shorter GLYK—lacking the intact chloroplast transit peptide—that is not bound by AVRvnt1. The transition between full-length and shorter plant GLYK transcripts is controlled by a light-dependent alternative promoter selection mechanism. In plants that lack Rpi-vnt1.1, the presence of AVRvnt1 reduces GLYK accumulation in chloroplasts counteracting GLYK contribution to basal immunity. Our findings revealed that pathogen manipulation of chloroplast functions has resulted in a light-dependent immune response.

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<![CDATA[A roadmap for gene functional characterisation in crops with large genomes: Lessons from polyploid wheat]]> https://www.researchpad.co/article/N561b8197-9853-45cb-bd4a-438988d44d93

Understanding the function of genes within staple crops will accelerate crop improvement by allowing targeted breeding approaches. Despite their importance, a lack of genomic information and resources has hindered the functional characterisation of genes in major crops. The recent release of high-quality reference sequences for these crops underpins a suite of genetic and genomic resources that support basic research and breeding. For wheat, these include gene model annotations, expression atlases and gene networks that provide information about putative function. Sequenced mutant populations, improved transformation protocols and structured natural populations provide rapid methods to study gene function directly. We highlight a case study exemplifying how to integrate these resources. This review provides a helpful guide for plant scientists, especially those expanding into crop research, to capitalise on the discoveries made in Arabidopsis and other plants. This will accelerate the improvement of crops of vital importance for food and nutrition security.

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<![CDATA[Temporal integration of auxin information for the regulation of patterning]]> https://www.researchpad.co/article/N630dfd83-b60b-487d-a7ae-ae424186a4cf

Positional information is essential for coordinating the development of multicellular organisms. In plants, positional information provided by the hormone auxin regulates rhythmic organ production at the shoot apex, but the spatio-temporal dynamics of auxin gradients is unknown. We used quantitative imaging to demonstrate that auxin carries high-definition graded information not only in space but also in time. We show that, during organogenesis, temporal patterns of auxin arise from rhythmic centrifugal waves of high auxin travelling through the tissue faster than growth. We further demonstrate that temporal integration of auxin concentration is required to trigger the auxin-dependent transcription associated with organogenesis. This provides a mechanism to temporally differentiate sites of organ initiation and exemplifies how spatio-temporal positional information can be used to create rhythmicity.

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<![CDATA[Involvement of p53-dependent apoptosis signal in antitumor effect of Colchicine on human papilloma virus (HPV)-positive human cervical cancer cells]]> https://www.researchpad.co/article/Nf252f75d-f123-460d-be01-4a92f19e6b11

Abstract

Colchicine, a plant-derived alkaloid with relatively low toxicity on normal human epidermal keratinocytes (HEKn), has selective inhibitory effect on the growth of CaSki (HPV16-positive) and HeLa (HPV18-positive) human cervical cancer cell lines via the induction of apoptosis. Colchicine (2.5, 5.0 and 10.0 ng/ml) significantly reduced the expression of human papilloma virus (HPV) 16 E6/E7 mRNA and protein in CaSki and HeLa cells. Moreover, reduced expression of E6 and E7 induced by Colchicine resulted in the up-regulation of tumor suppressor proteins, p53 and Rb, as well as down-regulation of phospho Rb (pRb) protein. In addition, Bax, cytosolic cytochrome c and cleaved caspase-3 protein were increased while Bcl-2 protein was decreased significantly by 48 h of Colchicine treatment. These results implied that Colchicine could be explored as a potent candidate agent for the treatment and prevention of HPV-associated cervical cancer without deleterious effects.

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<![CDATA[Molecular mechanisms of Evening Complex activity in Arabidopsis]]> https://www.researchpad.co/article/N2e726ae3-5d30-4e4e-b9e5-a509bc3b6f23

Significance

Circadian gene expression oscillates over a 24-h period and regulates many genes critical for growth and development in plants. A key component of the circadian clock is the Evening Complex (EC), a transcriptional repressor complex that contains the proteins LUX ARRHYTHMO, EARLY FLOWERING 3, and EARLY FLOWERING 4 (ELF4). By repressing the expression of genes such as PHYTOCHROME INTERACTING FACTOR4 (PIF4), the EC reduces elongation growth. At warmer temperatures, EC activity is lost, promoting thermomorphogenesis via PIF4 expression. The molecular mechanisms underlying EC activity are not well understood. Here, we combined structural studies with extensive in vitro assays to determine the molecular mechanisms of the temperature-dependent EC binding to DNA and demonstrate the critical role of ELF4 in this activity.

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<![CDATA[CCR4, a RNA decay factor, is hijacked by a plant cytorhabdovirus phosphoprotein to facilitate virus replication]]> https://www.researchpad.co/article/N6f443eb1-6e21-40aa-8065-dc479414bd12

Carbon catabolite repression 4 (CCR4) is a conserved mRNA deadenylase regulating posttranscriptional gene expression. However, regulation of CCR4 in virus infections is less understood. Here, we characterized a pro-viral role of CCR4 in replication of a plant cytorhabdovirus, Barley yellow striate mosaic virus (BYSMV). The barley (Hordeum vulgare) CCR4 protein (HvCCR4) was identified to interact with the BYSMV phosphoprotein (P). The BYSMV P protein recruited HvCCR4 from processing bodies (PBs) into viroplasm-like bodies. Overexpression of HvCCR4 promoted BYSMV replication in plants. Conversely, knockdown of the small brown planthopper CCR4 inhibited viral accumulation in the insect vector. Biochemistry experiments revealed that HvCCR4 was recruited into N–RNA complexes by the BYSMV P protein and triggered turnover of N-bound cellular mRNAs, thereby releasing RNA-free N protein to bind viral genomic RNA for optimal viral replication. Our results demonstrate that the co-opted CCR4-mediated RNA decay facilitates cytorhabdovirus replication in plants and insects.

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<![CDATA[Evolutionarily unique mechanistic framework of clathrin-mediated endocytosis in plants]]> https://www.researchpad.co/article/N2549fc31-7fa8-4f19-ac40-ec0599f5fff4

In plants, clathrin mediated endocytosis (CME) represents the major route for cargo internalisation from the cell surface. It has been assumed to operate in an evolutionary conserved manner as in yeast and animals. Here we report characterisation of ultrastructure, dynamics and mechanisms of plant CME as allowed by our advancement in electron microscopy and quantitative live imaging techniques. Arabidopsis CME appears to follow the constant curvature model and the bona fide CME population generates vesicles of a predominantly hexagonal-basket type; larger and with faster kinetics than in other models. Contrary to the existing paradigm, actin is dispensable for CME events at the plasma membrane but plays a unique role in collecting endocytic vesicles, sorting of internalised cargos and directional endosome movement that itself actively promote CME events. Internalized vesicles display a strongly delayed and sequential uncoating. These unique features highlight the independent evolution of the plant CME mechanism during the autonomous rise of multicellularity in eukaryotes.

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<![CDATA[Shaping the genome of plants]]> https://www.researchpad.co/article/N242446ca-b9d4-4ad5-9a55-f360cb5be552

Fertilization of an egg cell by more than one sperm cell can produce viable progeny in a flowering plant.

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<![CDATA[Selective egg cell polyspermy bypasses the triploid block]]> https://www.researchpad.co/article/Nc7253530-bb7a-46bd-a222-01b63849d8a5

Polyploidization, the increase in genome copies, is considered a major driving force for speciation. We have recently provided the first direct in planta evidence for polyspermy induced polyploidization. Capitalizing on a novel sco1-based polyspermy assay, we here show that polyspermy can selectively polyploidize the egg cell, while rendering the genome size of the ploidy-sensitive central cell unaffected. This unprecedented result indicates that polyspermy can bypass the triploid block, which is an established postzygotic polyploidization barrier. In fact, we here show that most polyspermy-derived seeds are insensitive to the triploid block suppressor admetos. The robustness of polyspermy-derived plants is evidenced by the first transcript profiling of triparental plants and our observation that these idiosyncratic organisms segregate tetraploid offspring within a single generation. Polyspermy-derived triparental plants are thus comparable to triploids recovered from interploidy crosses. Our results expand current polyploidization concepts and have important implications for plant breeding.

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<![CDATA[Insect herbivory antagonizes leaf cooling responses to elevated temperature in tomato]]> https://www.researchpad.co/article/N7b9e9a99-9152-4825-848a-bc294e4d1376

Significance

Crop damage by insect pests is predicted to increase as rising surface temperatures accelerate insect metabolism, population size, and range expansion. The plant defense hormone jasmonate promotes resistance to diverse herbivores, but how this wound signal impacts the plant’s ability to cope with a combination of herbivory and elevated temperature remains unknown. Here, we show that heat shock proteins contribute to enhanced jasmonate responses in tomato plants subjected to simulated heat waves. Herbivore-induced jasmonate signaling at elevated temperature, however, blocked stomatal opening and leaf hyponasty, leading to leaf overheating, reduced photosynthesis, and growth inhibition. Our results show how signal conflict between biotic and abiotic stress may exaggerate crop losses under warming conditions that accelerate herbivory, potentially jeopardizing food security.

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<![CDATA[Multifeature analyses of vascular cambial cells reveal longevity mechanisms in old Ginkgo biloba trees]]> https://www.researchpad.co/article/Nfb9add52-72ae-4a91-ae11-d28f7d7f5d68

Significance

There is considerable interest in how ancient trees maintain their longevity. Ginkgo biloba is the only living species in the division Ginkgophyta, and specimens can live for over 1,000 y. Here, we show that trees up to 600 y of age display similar leaf areas, leaf photosynthetic efficiencies, and seed germination rates. Transcriptomic analysis indicates that the vascular cambium of the oldest trees, although undergoing less xylem generation, exhibits no evidence of senescence; rather, extensive expression of genes associated with preformed and inducible defenses likely contributes to the remarkable longevity of this species.

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<![CDATA[A cis-carotene derived apocarotenoid regulates etioplast and chloroplast development]]> https://www.researchpad.co/article/N4cae6bc7-975c-4670-b50a-219e6e48d482

Carotenoids are a core plastid component and yet their regulatory function during plastid biogenesis remains enigmatic. A unique carotenoid biosynthesis mutant, carotenoid chloroplast regulation 2 (ccr2), that has no prolamellar body (PLB) and normal PROTOCHLOROPHYLLIDE OXIDOREDUCTASE (POR) levels, was used to demonstrate a regulatory function for carotenoids and their derivatives under varied dark-light regimes. A forward genetics approach revealed how an epistatic interaction between a ζ-carotene isomerase mutant (ziso-155) and ccr2 blocked the biosynthesis of specific cis-carotenes and restored PLB formation in etioplasts. We attributed this to a novel apocarotenoid retrograde signal, as chemical inhibition of carotenoid cleavage dioxygenase activity restored PLB formation in ccr2 etioplasts during skotomorphogenesis. The apocarotenoid acted in parallel to the repressor of photomorphogenesis, DEETIOLATED1 (DET1), to transcriptionally regulate PROTOCHLOROPHYLLIDE OXIDOREDUCTASE (POR), PHYTOCHROME INTERACTING FACTOR3 (PIF3) and ELONGATED HYPOCOTYL5 (HY5). The unknown apocarotenoid signal restored POR protein levels and PLB formation in det1, thereby controlling plastid development.

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<![CDATA[From plasmodesma geometry to effective symplasmic permeability through biophysical modelling]]> https://www.researchpad.co/article/N2dcfd14d-aa9a-4f95-946f-b3938af27e3e

Regulation of molecular transport via intercellular channels called plasmodesmata (PDs) is important for both coordinating developmental and environmental responses among neighbouring cells, and isolating (groups of) cells to execute distinct programs. Cell-to-cell mobility of fluorescent molecules and PD dimensions (measured from electron micrographs) are both used as methods to predict PD transport capacity (i.e., effective symplasmic permeability), but often yield very different values. Here, we build a theoretical bridge between both experimental approaches by calculating the effective symplasmic permeability from a geometrical description of individual PDs and considering the flow towards them. We find that a dilated central region has the strongest impact in thick cell walls and that clustering of PDs into pit fields strongly reduces predicted permeabilities. Moreover, our open source multi-level model allows to predict PD dimensions matching measured permeabilities and add a functional interpretation to structural differences observed between PDs in different cell walls.

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<![CDATA[Coordination of tissue cell polarity by auxin transport and signaling]]> https://www.researchpad.co/article/N3a1cf0c9-c84c-4ce1-af60-c9f30c399f67

Plants coordinate the polarity of hundreds of cells during vein formation, but how they do so is unclear. The prevailing hypothesis proposes that GNOM, a regulator of membrane trafficking, positions PIN-FORMED auxin transporters to the correct side of the plasma membrane; the resulting cell-to-cell, polar transport of auxin would coordinate tissue cell polarity and induce vein formation. Contrary to predictions of the hypothesis, we find that vein formation occurs in the absence of PIN-FORMED or any other intercellular auxin-transporter; that the residual auxin-transport-independent vein-patterning activity relies on auxin signaling; and that a GNOM-dependent signal acts upstream of both auxin transport and signaling to coordinate tissue cell polarity and induce vein formation. Our results reveal synergism between auxin transport and signaling, and their unsuspected control by GNOM in the coordination of tissue cell polarity during vein patterning, one of the most informative expressions of tissue cell polarization in plants.

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<![CDATA[Comprehensive mapping of abiotic stress inputs into the soybean circadian clock]]> https://www.researchpad.co/article/N6c6edbfa-bd86-4197-be81-a17705683485

Significance

The effects of diverse environmental factors on the crop circadian clock have not been systemically studied. We devised a reliable and cost-effective discovery pipeline and demonstrated its feasibility by mapping the abiotic stress “inputome” of the soybean clock. We found that the interfaces between the soybean clock and abiotic stress signals were quite different from those in Arabidopsis. Furthermore, alkaline stress was identified as a circadian clock modulator. These findings highlight the complexity of the soybean clock, which cannot be simply extrapolated from knowledge obtained from Arabidopsis. Our discovery pipeline thus offers a broadly applicable and affordable tool for similar large-scale circadian clock studies in diverse species since it does not rely on transgenic circadian reporters or expensive imaging systems.

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<![CDATA[Overexpression of zmm28 increases maize grain yield in the field]]> https://www.researchpad.co/article/N0da4ca32-4363-44a8-8562-5d6f47039fea

Significance

In the approaching decades, food security will likely be more of an issue as there will be an increased demand for grain which will need to be met in an environmentally sustainable manner. To date, commercial transgenic maize has primarily targeted resistance to insects and herbicides. Here we describe a transgenic approach to improve the yield and yield stability of maize. We have demonstrated that increasing and extending the expression of a maize gene, zmm28, alters vegetative and reproductive growth parameters and significantly enhances yield in large-scale field trials conducted over multiple years. We conclude that alteration in expression of a native maize gene in maize can create a substantially positive change in a complex trait like grain yield.

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<![CDATA[Transgressive segregation reveals mechanisms of Arabidopsis immunity to Brassica-infecting races of white rust (Albugo candida)]]> https://www.researchpad.co/article/5c8015bbd5eed0c484a9fa29

Significance

Most plants resist most plant pathogens. Barley resists wheat-infecting powdery mildew races (and vice versa), and both barley and wheat resist potato late blight. Such “nonhost” resistance could result because the pathogen fails to suppress defense or triggers innate immunity due to failure to evade detection. Albugo candida causes white rust on most Brassicaceae, and we investigated Arabidopsis NHR to Brassica-infecting races. Transgressive segregation for resistance in Arabidopsis recombinant inbred lines revealed genes encoding nucleotide-binding, leucine-rich repeat (NLR) immune receptors. Some of these NLR-encoding genes confer resistance to white rust in Brassica sp. This genetic method thus provides a route to reveal resistance genes for crops, widening the pool from which such genes might be obtained.

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<![CDATA[TOR and RPS6 transmit light signals to enhance protein translation in deetiolating Arabidopsis seedlings]]> https://www.researchpad.co/article/5c26b3afd5eed0c484760c9d

Significance

Light enhances the translation efficiency of thousands of mRNAs during photomorphogenic development in Arabidopsis, but the underlying molecular mechanism remains elusive. Here we show that light activates the auxin-target of rapamycin (TOR)-ribosome protein S6 (RPS6) pathway to enhance translation in deetiolating Arabidopsis. We discovered that CONSTITUTIVE PHOTOMORPHOGENIC 1 (COP1) represses TOR activity in dark-grown seedlings. The perception of far-red and blue light by photoreceptors inactivates COP1, which leads to the derepression of the auxin-TOR-RPS6 pathway and enhanced de novo protein synthesis. Our study revealed a light-triggered signaling pathway for translational regulation. This sophisticated regulation also functions to ensure that young seedlings have strict skotomorphogenic development in the dark and a timely switch to photomorphogenic development.

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