Gregory R. Heck

Bio: Gregory R. Heck is an academic researcher from Monsanto. The author has contributed to research in topics: Genetically modified maize & RNA silencing. The author has an hindex of 21, co-authored 56 publications receiving 3359 citations.

Control of coleopteran insect pests through RNA interference

Abstract: Commercial biotechnology solutions for controlling lepidopteran and coleopteran insect pests on crops depend on the expression of Bacillus thuringiensis insecticidal proteins1,2, most of which permeabilize the membranes of gut epithelial cells of susceptible insects3 However, insect control strategies involving a different mode of action would be valuable for managing the emergence of insect resistance Toward this end, we demonstrate that ingestion of double-stranded (ds)RNAs supplied in an artificial diet triggers RNA interference in several coleopteran species, most notably the western corn rootworm (WCR) Diabrotica virgifera virgifera LeConte This may result in larval stunting and mortality Transgenic corn plants engineered to express WCR dsRNAs show a significant reduction in WCR feeding damage in a growth chamber assay, suggesting that the RNAi pathway can be exploited to control insect pests via in planta expression of a dsRNA

Characterizing the mechanism of action of double-stranded RNA activity against western corn rootworm (Diabrotica virgifera virgifera LeConte).

Abstract: RNA interference (RNAi) has previously been shown to be effective in western corn rootworm (WCR, Diabrotica virgifera virgifera LeConte) larvae via oral delivery of synthetic double-stranded RNA (dsRNA) in an artificial diet bioassay, as well as by ingestion of transgenic corn plant tissues engineered to express dsRNA. Although the RNAi machinery components appear to be conserved in Coleopteran insects, the key steps in this process have not been reported for WCR. Here we characterized the sequence of events that result in mortality after ingestion of a dsRNA designed against WCR larvae. We selected the Snf7 ortholog (DvSnf7) as the target mRNA, which encodes an essential protein involved in intracellular trafficking. Our results showed that dsRNAs greater than or equal to approximately 60 base-pairs (bp) are required for biological activity in artificial diet bioassays. Additionally, 240 bp dsRNAs containing a single 21 bp match to the target sequence were also efficacious, whereas 21 bp short interfering (si) RNAs matching the target sequence were not. This result was further investigated in WCR midgut tissues: uptake of 240 bp dsRNA was evident in WCR midgut cells while a 21 bp siRNA was not, supporting the size-activity relationship established in diet bioassays. DvSnf7 suppression was observed in a time-dependent manner with suppression at the mRNA level preceding suppression at the protein level when a 240 bp dsRNA was fed to WCR larvae. DvSnf7 suppression was shown to spread to tissues beyond the midgut within 24 h after dsRNA ingestion. These events (dsRNA uptake, target mRNA and protein suppression, systemic spreading, growth inhibition and eventual mortality) comprise the overall mechanism of action by which DvSnf7 dsRNA affects WCR via oral delivery and provides insights as to how targeted dsRNAs in general are active against insects.

Investigations into glyphosate-resistant horseweed (Conyza canadensis): retention, uptake, translocation, and metabolism

Abstract: The mechanism of glyphosate resistance in horseweed was investigated. Eleven biotypes of putative sensitive (S) and resistant (R) horseweed were obtained from regions across the United States and examined for foliar retention, absorption, translocation, and metabolism of glyphosate. Initial studies used spray application of 14C-glyphosate to simulate field application. When S and R biotypes were compared in the absence of toxicity at a sublethal dose, we observed comparable retention and absorption but reduced root translocation in the R biotypes. S and R biotypes from Delaware were further examined at field use rates and results confirmed similar retention and absorption but reduced root translocation in the R biotypes. Application of 14C-glyphosate to a single leaf demonstrated reduced export out of the treated leaf and lower glyphosate import into other leaves, the roots, and the crown in R relative to S biotypes. Examination of the treated leaf by autoradiography showed that glyphosate loadin...

Lack of detectable oral bioavailability of plant microRNAs after feeding in mice

Abstract: 965 chow preparation where we observed the expected distribution and abundance of rice miRNAs. Oryza sativa (rice) osa-miR168a was among the most abundant miRNAs (Supplementary Table 1) in both ricecontaining chow and rice grain, consistent with previous reports9,12. Diet composition had no impact on food consumption (Supplementary Fig. 1). Following completion of the feeding regimen, small RNAs were sequenced from mouse liver and plasma samples using the Illumina (San Diego) HiSeq system. Details of the experimental protocols can be found in Supplementary Methods. We observed the expected endogenous miRNA profile and miRNA length distribution in mouse plasma and liver and rice samples, indicating consistent quality of the small RNA sequencing procedure (Supplementary Fig. 2a,b). Analysis of small RNAs from plasma and liver of mice fed on balanced rice chow and rice chow did not reveal measurable uptake of any rice grain miRNAs, including osa-miR168a. Of >10 million total sequence reads per library, fewer than ten reads identical to known rice miRNAs per library were noted in five out of eight samples from mice fed on rice-containing chow and four out of five samples from mice fed on synthetic chow (Table 1). Synthetic chow did not contain any grain or forage from plants (all plant-derived ingredients were highly purified isolates, for example, cornstarch and soybean oil); therefore, these low number of rice miRNAmappable reads could be explained by sequence errors or by cross-contamination. Mapping of mouse small RNA data to all annotated rice miRNAs in miRBase v19 identified a low number of mouse small RNA reads identical to several rice miRNA sequences (Table 1). Even so, most of the rice-like sequences were identical to the miR414 sequence (Supplementary Table 1), which is not detectable in rice grain12. In addition, these plant-like sequences were present in similar quantities in all mouse To the Editor: Human therapeutics based on nucleic acid targeting rely on sequence-specific interactions between effector and target molecules to achieve beneficial effects through specific modification to the expression of targeted genes. A variety of such compounds are being tested in laboratories and in clinical trials to treat a range of genetic and acquired diseases. Efficient, safe and cost-effective delivery of nucleic acid–based drug candidates is required to enable therapeutic levels of targeted gene regulation and overall success of this exciting new class of therapeutics. For several types of compounds in this class, effective drug delivery relies on injection of formulated nucleic acids at the site of action or into the bloodstream. Oral delivery would excel as a treatment strategy as it could offer convenient and patient-friendly features, however, progress in this approach has been hampered by substantial challenges associated with biological barriers that limit oral activity of nucleic acid therapeutics (e.g., stability within and uptake of nucleic acids from the mammalian gastrointestinal tract, nucleases and membrane barriers)1. Considerable effort has been applied to improve the stability and uptake efficiency of orally administered nucleic acids by introducing chemical modifications and formulating with excipients; however, limited success has been reported thus far2,3. The naturally occurring RNA interference (RNAi) response has been extensively reported after feeding double-stranded RNA (dsRNA) in some invertebrates, such as the model organism Caenorhabditis elegans4 and some agricultural pests5,6 (e.g., corn rootworm and cotton bollworm). Yet, despite responsiveness to ingested dsRNA, a recent survey revealed substantial variation in sensitivity to dsRNA in other Caenorhabditis nematodes7 and other invertebrate species8. In addition, despite major efforts in academic and pharmaceutical laboratories to activate the RNA silencing pathway in response to ingested RNA, the phenomenon had not been reported in mammals until a recent publication by Zhang et al.9 in Cell Research. This report described the uptake of plant-derived microRNAs (miRNA) into the serum, liver and a few other tissues in mice following consumption of rice, as well as apparent gene regulatory activity in the liver. The observation provided a potentially groundbreaking new possibility that RNAbased therapies could be delivered to mammals through oral administration and at the same time opened a discussion on the evolutionary impact of environmental dietary nucleic acid effects across broad phylogenies. A recently reported survey of a large number of animal small RNA datasets from public sources has not revealed evidence for any major plant-derived miRNA accumulation in animal samples10. Given the number of questions evoked by these analyses, the limited success with oral RNA delivery for pharmaceutical development, the history of safe consumption for dietary small RNAs11 and lack of evidence for uptake of plant-derived dietary small RNAs, we felt further evaluation of miRNA uptake and the potential for cross-kingdom gene regulation in animals was warranted to assess the prevalence, impact and robustness of the phenomenon. To address this question, we conducted a well-controlled mouse feeding study with rice-containing chow diets or with a purified synthetic chow devoid of plant grain or forage. After a two-week acclimation on synthetic chow (modified AIN93-G), animals were fasted for 12 h and then placed on synthetic chow; a nutritionally balanced, rice-containing chow (modified AIN93-G with 40.8% rice); or rice-based chow (75% rice), for 1, 3 and 7 days (Supplementary Methods). These groups are referred to herein as synthetic chow, balanced rice chow and rice chow, respectively. To confirm rice miRNA availability in feeding material, we first sequenced rice small RNAs from ricecontaining chow and rice grains used for Lack of detectable oral bioavailability of plant microRNAs after feeding in mice correspondence

Methods for genetic control of insect infestations in plants and compositions thereof

Abstract: The present invention relates to control of pest infestation by inhibiting one or more biological functions. The invention provides methods and compositions for such control, By feeding one or more recombinant double stranded RNA molecules provided by the invention to the pest, a reduction in pest infestation is obtained through suppression of gene expression. The invention is also directed to methods for making transgenic plants that express the double stranded RNA molecules, and to particular combinations of transgenic pesticidal agents for use in protecting plants from pest infestation.

Soybean event MON89788 and methods for detection thereof

Abstract: The present invention provides for soybean plant and seed comprising transformation event MON89788 and DNA molecules unique to these events. The invention also provides methods for detecting the presence of these DNA molecules in a sample.

MicroRNAs and their targets: recognition, regulation and an emerging reciprocal relationship

Abstract: MicroRNAs (miRNAs) have emerged as key gene regulators in diverse biological pathways. These small non-coding RNAs bind to target sequences in mRNAs, typically resulting in repressed gene expression. Several methods are now available for identifying miRNA target sites, but the mere presence of an miRNA-binding site is insufficient for predicting target regulation. Regulation of targets by miRNAs is subject to various levels of control, and recent developments have presented a new twist; targets can reciprocally control the level and function of miRNAs. This mutual regulation of miRNAs and target genes is challenging our understanding of the gene-regulatory role of miRNAs in vivo and has important implications for the use of these RNAs in therapeutic settings.

Evolution in Action: Plants Resistant to Herbicides

Abstract: Modern herbicides make major contributions to global food production by easily removing weeds and substituting for destructive soil cultivation. However, persistent herbicide selection of huge weed numbers across vast areas can result in the rapid evolution of herbicide resistance. Herbicides target specific enzymes, and mutations are selected that confer resistance-endowing amino acid substitutions, decreasing herbicide binding. Where herbicides bind within an enzyme catalytic site very few mutations give resistance while conserving enzyme functionality. Where herbicides bind away from a catalytic site many resistance-endowing mutations may evolve. Increasingly, resistance evolves due to mechanisms limiting herbicide reaching target sites. Especially threatening are herbicide-degrading cytochrome P450 enzymes able to detoxify existing, new, and even herbicides yet to be discovered. Global weed species are accumulating resistance mechanisms, displaying multiple resistance across many herbicides and posing a great challenge to herbicide sustainability in world agriculture. Fascinating genetic issues associated with resistance evolution remain to be investigated, especially the possibility of herbicide stress unleashing epigenetic gene expression. Understanding resistance and building sustainable solutions to herbicide resistance evolution are necessary and worthy challenges.

Molecular Plant Breeding as the Foundation for 21st Century Crop Improvement

Abstract: The fundamental discoveries of Darwin and Mendel established the scientific basis for plant breeding and genetics at the turn of the 20th century. Similarly, the recent integration of advances in biotechnology, genomic research, and molecular marker applications with conventional plant breeding