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Transcriptional and biochemical responses of monoacylglycerol acyltransferase-mediated oil synthesis and associated senescence-like responses in Nicotiana benthamiana.

ABSTRACT: Triacylglycerol (TAG) accumulates in plant seeds as a major renewable source of carbon for food, fuel and industrial feedstock. Approaches to enhance TAG content by altering lipid pathways and genes in vegetative parts have gained significant attention for biofuel and other applications. However, consequences of these modifications are not always studied in detail. In an attempt to increase TAG levels in leaves we previously demonstrated that a novel substrate, monoacylglycerol (MAG), can be used for the biosynthesis of diacylglycerol (DAG) and TAG. Transient expression of the Mus musculus monoacylglycerol acyltransferases MGAT1 and 2 in the model plant Nicotiana benthamiana increased TAG levels at 5 days post-infiltration (dpi). Here we show that increased TAG and DAG levels can be achieved as early as 2 dpi. In addition, the MGAT1 infiltrated areas showed senescence-like symptoms from 3 dpi onwards. To unravel underlying molecular mechanisms, Illumina deep sequencing was carried out (a) for de-novo assembling and annotation of N. benthamiana leaf transcripts and (b) to characterize MGAT1-responsive transcriptome. We found that MGAT1-responsive genes are involved in several processes including TAG biosynthesis, photosynthesis, cell-wall, cutin, suberin, wax and mucilage biosynthesis, lipid and hormone metabolism. Comparative analysis with transcript profiles from other senescence studies identified characteristic gene expression changes involved in senescence induction. We confirmed that increased TAG and observed senescence-symptoms are due to the MAG depletion caused by MGAT1 activity and suggest a mechanism for MGAT1 induced TAG increase and senescence-like symptoms. The data generated will serve as a valuable resource for oil and senescence related studies and for future N. benthamiana transcriptome studies.

SUBMITTER: Divi UK

PROVIDER: S-EPMC4033622 | biostudies-literature | 2014

REPOSITORIES: biostudies-literature

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Transcriptional and biochemical responses of monoacylglycerol acyltransferase-mediated oil synthesis and associated senescence-like responses in Nicotiana benthamiana.

Divi Uday K UK El Tahchy Anna A Vanhercke Thomas T Petrie James R JR Robles-Martinez Jose A JA Singh Surinder P SP

Frontiers in plant science 20140526

Triacylglycerol (TAG) accumulates in plant seeds as a major renewable source of carbon for food, fuel and industrial feedstock. Approaches to enhance TAG content by altering lipid pathways and genes in vegetative parts have gained significant attention for biofuel and other applications. However, consequences of these modifications are not always studied in detail. In an attempt to increase TAG levels in leaves we previously demonstrated that a novel substrate, monoacylglycerol (MAG), can be use ...[more]

PMID: 24904604

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Project description:Carbon accumulation and remobilization are essential mechanisms in plants to ensure energy transfer between plant tissues with different functions or metabolic needs and to support new generations. Knowledge about the regulation of carbon allocation into oil (triacylglycerol) in plant storage tissue can be of great economic and environmental importance for developing new high-yielding oil crops. Here, the effect on global gene expression as well as on physiological changes in leaves transiently expressing five homologs of the transcription factor WRINKLED1 (WRI1) originating from diverse species and tissues; Arabidopsis thaliana and potato (Solanum tuberosum) seed embryo, poplar (Populus trichocarpa) stem cambium, oat (Avena sativa) grain endosperm, and nutsedge (Cyperus esculentus) tuber parenchyma, were studied by agroinfiltration in Nicotiana benthamiana.All WRI1 homologs induced oil accumulation when expressed in leaf tissue. Transcriptome sequencing revealed that all homologs induced the same general patterns with a drastic shift in gene expression profiles of leaves from that of a typical source tissue to a source-limited sink-like tissue: Transcripts encoding enzymes for plastid uptake and metabolism of phosphoenolpyruvate, fatty acid and oil biosynthesis were up-regulated, as were also transcripts encoding starch degradation. Transcripts encoding enzymes in photosynthesis and starch synthesis were instead down-regulated. Moreover, transcripts representing fatty acid degradation were up-regulated indicating that fatty acids might be degraded to feed the increased need to channel carbons into fatty acid synthesis creating a futile cycle. RT-qPCR analysis of leaves expressing Arabidopsis WRI1 showed the temporal trends of transcripts selected as 'markers' for key metabolic pathways one to five days after agroinfiltration. Chlorophyll fluorescence measurements of leaves expressing Arabidopsis WRI1 showed a significant decrease in photosynthesis, even though effect on starch content could not be observed.This data gives for the first time a general view on the transcriptional transitions in leaf tissue upon induction of oil synthesis by WRI1. This yields important information about what effects WRI1 may exert on global gene expression during seed and embryo development. The results suggest why high oil content in leaf tissue cannot be achieved by solely transcriptional activation by WRI1, which can be essential knowledge in the development of new high-yielding oil crops.

Project description:Objectives: Our work focuses on the responses of Solanaceous plants to viruses that cause economically important diseases in tree fruits. Using mock inoculated leaf tissue as a reference, we plan to compare the gene expression profiles of Nicotiana Benthamiana plants infected with one of three viruses; Plum Pox Potyvirus (PPV), Tomato Ringspot Nepovirus (ToRSV), and Prunus Nectrotic Ringspot Nepovirus (PNRSV). Our goals are as follows: (1) Identify genes that are induced/repressed in response to individual viruses. (2) Identify genes that are induced/repressed in response to all 3 viruses. (3) Compare results to existing potato array data to look for similarities in responses to other pathogens. Experimental Design: Nicotiana benthamiana plants were inoculated with one of three viruses: PPV, ToRSV, or PNRSV. 3 week old plants were inoculated by rubbing virus infected plant sap onto leaves dusted with carborundum. Control plants were mock inoculated using sap from healthy plants. All plants were maintained in a growth chamber at 22C for 18 days. 8 plants were inoculated with each virus or mock inoculated. This experiment was repeated twice. 4 biological replicates derived from 2 virus infected plants from each replica experiment (4 plants) are to be used for hybridizations. RNA from all mock inoculated plants was similarly pooled to create 4 biological replicates. Each replicate control will serve as a universal reference sample that is to be hybridized pair wise with each of the three virus infected samples. RNA extraction: After 18 days, un-inoculated leaves displaying clear symptoms were harvested and immediately frozen in liquid N2. Total RNA was purified using Trizol according to TIGRs listed protocol. RNA was subsequently treated with Turbo DNA-free RNase (Ambion cat#1907). Finally, total RNA was further purified on RNeasy columns (Qiagen) according to manufacturer’s instructions and quantified using a Nanodrop spectrophotometer. Keywords: Reference design

Dataset Information

Transcriptional and biochemical responses of monoacylglycerol acyltransferase-mediated oil synthesis and associated senescence-like responses in Nicotiana benthamiana.

Publications

Transcriptional and biochemical responses of monoacylglycerol acyltransferase-mediated oil synthesis and associated senescence-like responses in Nicotiana benthamiana.

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