Development of phloem-mobile xenobiotics with enhanced transport properties

Every year, several thousand chemicals are screened by the agrochemical industry for potential uses as herbicides and pesticides. Very few of these compounds make it to the market place because they do not enter or move in plant tissues effectively. The ability of a given molecule to enter the phloem, the plant's internal conducting system, is a major hurdle to the development of successful systemic herbicides. The worldwide success of Glyphosate (Roundup) is due predominantly to the fact that this chemical moves extremely effectively in the phloem and is therefore able to exert its toxic effects on distant growing tissues. Unlike many other herbicides, Glyphosate appears to use plant membrane carrier proteins for its effective transport. The aim of this project is to develop new-generation chemicals that are designed to move effectively in the phloem.

The run-off that accompanies field applications of chemicals is a matter of considerable environmental concern as several of these potentially toxic chemicals may pollute steams and waterways. It is clear that the development of new chemicals that reach their target sites by more efficient transport would be a major advantage in this field, reducing the amounts that need to be applied to crops and thereby minimizing run-off. This project is therefore aimed directly at improving the movement of agrochemicals in plants by the rational design of new chemicals that show enhanced phloem-mobility properties.

The project takes a novel approach by using fluorescent probes that are designed specifically to move in the phloem of plants. Using fluorescence-based chemicals means that the process of uptake and transport can be studied in fine detail using appropriate fluorescence detection methods (e.g. fluorescence microscopy). A major goal is to 'piggy back' some of these fluorescent compounds into the phloem using existing proteins that function to transport natural compounds in the phloem.

This project aims to develop new-generation xenobiotics that move effectively in the phloem. The approach is to use synthetic chemistry to generate small molecule probes with optimal phloem-transport characteristics. The probes are screened on a simple source-sink system using Arabidopsis seedlings grown on agar. The project also utilises fluorescent, naturally occurring secondary metabolites (e.g. esculin and fraxin) that have been shown to be transported on the phloem sucrose transporter, SUC2. These secondary metabolites are based on the coumarin core, a highly fluorescent bicyclic molecule. In preliminary work, we found that addition of glucose to small fluorophores, including coumarin, NBD and rhodamine, conferred phloem mobility to these compounds, and has generated a new generation of multispectral phloem probes.

This project is aimed at exploring the targeted chemistry of small fluorophores to generate xenobotics that 'piggy back' into the phloem by virtue of their recognition by sucrose carriers. We refer to this highly mobile group of compounds as 'mobilophores'. In addition, we anticipate that some of the compounds we generate will be mobile due to changes in their physico-chemical properties, notably pKa, Log Kow and solubility. In this area, we will work closely with Syngenta who have agreed to measure all these parameters for the probes that we generate. Ultimately, we will generate a range of probes with a wide spectrum of phloem mobilities. The aim is to understand fully the 'rules of engagement' that determine the ability of molecules to enter the translocation stream. We will use this information to alter the chemistry of existing compounds with herbicidal activity (e.g. bleaching herbicides) in an attempt to improve their phloem mobilities.

Finally, we wish to determine the extent to which our phloem mobile probes are able to enter fungal pathogens in an attempt to develop a design for phloem-mobile fungicides.

The proposed project will generate Impact in several key areas:

1. Impact in the agrochemical sector. Income in the xenobiotic (herbicide/pesticide) market amounts to about £60 billion per annum, herbicides accounting for most of this amount. the single herbicide Glyphosate ('Roundup') dominates this market because it moves effectively in the phloem. Fortuitously, this turned out to be because this compound utilises plant membrane transporters for uptake into the phloem. Other features contribute to herbicide movement but it is clear that if xenobiotic compounds could be designed to utilise membrane transporters then phloem transport of these compounds could be maximised. The work proposed here aims to rationally design a new generation of xenobiotics with improved transport features. such features will be invaluable in the design of new and improved herbicides.

2 .Generation of intellectual property (IP). Our project is likely to generate IP in the area of product design. Although many of the probes that we will develop are fluorescent compounds (necessary to trace movement), one of the main aims is to transfer appropriate mobility characteristics to non-fluorescent compounds with biological activity. In the project we will generate new compounds at Edinburgh University and will also access the enormous repository of novel chemicals present in the Syngenta database. Appropriate IP arrangements have been drawn up by Edinburgh (Dr. Adam Irvine) and Syngenta (Dr. Sarah Perfect) to ensure that all potential areas are addressed as they arise, with appropriate freedom to publish when IP arrangements are in place.

3. Addressing environmental concerns. The development of new herbicides with improved movement means that less chemical needs to be applied to crops, with a corresponding reduction in the pollution of waterways. We will engage with environmental groups concerned with pesticides in the environment. Pesticides are a necessary part of modern agriculture. A complete ban on their use would drastically affect yield and pest management. Our approach is to minimize usage by enhancing mobility in the plant extensively. We will seek wherever possible to convey this message to a wide agricultural and environmental community.

4. Scientific and academic Impact. Our work is basic in nature and addresses the key question of how chemicals move in plants. Understanding the 'rules of engagement' by which chemicals interact with the phloem is likely to have enormous scientific impact, as well as leading to the development of a suite of compounds that can be used by the plant-cell biology community to trace systemic movement in plants. We intend tp publish our findings in journals of high scientific impact.

5. Development of new products. We intend to share the compounds that we generate with the scientific community. However, it is unlikely that we will be able to synthesize sufficient amounts for widespread use by the plant community. In such cases, we will consider approaching named companies (e.g Sigma, Life Technologies) who will be able to produce the compounds on a larger scale for distribution. Here, also, we will be guided by Dr Adam Irvine (ERI) who will draw up appropriate licensing arrangements on a case-by-case basis.