27 October 2010 Weed invasions and fungal protein battles targeted by Lincoln University Marsden-funded researchers

Two “war zones” in nature provide the setting for a pair of Lincoln University research projects backed by more than a million dollars from the Government-initiated Marsden Fund, administered through the Royal Society of New Zealand.

The projects concern the way weeds become winners when migrating to new environments free from traditional enemies, and the mechanism by which the microscopic fungus Trichoderma, used in plant inoculants, defends itself against attack by the immune system of host organisms.

The invasive weed work will be carried out by Lincoln University ecologist Professor Richard Duncan in collaboration with the University’s Professor of Plant Biosecurity Philip Hulme, and the fungus project will be conducted by Post-Doctoral Fellow Dr Artemio Mendoza Mendoza, in collaboration with the Director of the Bio-Protection Research Centre, Professor Alison Stewart. Their work will contribute to the theoretical understanding of weed invasion success and fungal immune mechanisms.

Both scientists are members of the Lincoln University-based Bio-Protection Research Centre, a Centre of Research Excellence.

Professor Duncan’s project “Testing the dynamic enemy release hypothesis for invasive species”, assessed by the Marsden Fund’s Ecology, Evolution and Behaviour Panel, has received a three-year grant totalling $785,000.

Dr Mendoza’s project “Overcoming plant immune responses  -  the key to fungal symbiosis”, assessed by the Cellular, Molecular and Physiological Biology Panel, has received a Fast-Start grant valued at $300,000 also over three years. Marsden Fast-Start grants are designed to support outstanding researchers early in their careers.

Professor Duncan says the phenomenon of weeds flourishing when moved to new environments free from their usual natural enemies is well known. It is termed the  “enemy release hypothesis”. Less understood is the way in which the initial benefits of escaping their enemies can be followed by attack from a new range of antagonists which the invasive species has not previously encountered.

“The survival process of invasive species in new environments is very fluid and dynamic,” says Professor Duncan. “Some species benefit a lot through release from their traditional enemies, while others do not. We want to gain an appreciation of the circumstances under which they do well and identify the situations in which it is less of an issue. We’re looking to develop a body of theoretical knowledge about how the process works.”

Professor Duncan will use clover species and antagonistic soil microbes for his investigation.

Most of the work will be done in greenhouse experiments at Lincoln University with comparative studies conducted in Europe where the clover species originate.

Dr Mendoza’s project is focused on proteins in the tiny, soil borne fungus Trichoderma, a micro-organism with  beneficial pathogen-killing properties used in inoculants against a number of diseases of commercial vegetable crops.

Using cutting edge technology and working at the single cell level, Dr Mendoza wants to establish how Trichoderma defends itself against attack during the process of plant root colonisation,  in other words, how it defeats the host plant’s immune system and establishes itself to carry out its protective task.

“Our attention is on all the proteins and genes expressed during the interaction of Trichoderma with the targeted plant,” he says.

“Most plants are infested by fungi without any outward signs of disease. These fungi are called endophytes and they can improve plant growth, provide resistance to disease and tolerance to environmental stress. The fungi themselves derive nutrients from the plants they colonise, so the relationship is a symbiotic one.

“Despite benefitting from the relationship, plants still react to endophytes by activating their immune systems.

“How endophytes evade or suppress a plant’s immune system is largely unknown. We are hypothesizing that a molecular-level ‘dialogue’ between the endophyte and the plant takes place which eventually provides predisposing conditions for successful fungal colonisation.

“The key seems likely to be protein-mediated cross-communication between plants and fungi at the initial contact stage.

“Our research will address two questions  -  how do plants and endophytes establish a friendly relationship and what are the signals involved in the successful dialogue when the encounter takes place.

“We know that when Trichoderma interacts with the host plant it secretes proteins to avert attack by the plant. The host plant in turn recognises these proteins and secretes proteins of its own in response  and a ‘battle’ ensues.

“We want to identify the proteins secreted and record the morphological changes that take place and the genetic profiles of Trichoderma during the interaction.

“The study will contribute significantly to understanding how endophytic fungi modulate or evade plant defences and will provide fundamental new insights to processes required for the establishment of plant colonisation by endophytic fungi. Not all Trichoderma are able to colonise the root systems of other plants. We need to determine which proteins of Trichoderma are capable of reducing the host plant’s defence system.” Dr Mendoza will use maize as the host plant for the Trichoderma in his investigation.

• The Marsden Fund is regarded as a hallmark of excellence for research, allowing New Zealand’s best researchers to explore their ideas. Projects are initiated by the investigator and are not subject to the Government’s socio-economic priorities. The fund was established by the Government in 1994 to support excellence in fundamental research. This year a record 1089 applications were received with 102 ultimately successful.