High hopes for parasite-resistant plant

DODDER, the parasitic plant that causes major

crop damage world-wide, has given up some of the secrets of its success – a development that could see the creation of parasite-resistant plants.

An American research team has found that dodder silences the expression of genes in the host plants from which it obtains water and nutrients.

This cross-species gene regulation, which includes genes that contribute to the host plant’s defence against parasites, has never before been seen from a parasitic plant.

Understanding this could allow researchers to engineer plants to resist the parasite.

The researchers sequenced all the microRNAs in tissue from the parasite alone, the host plant alone, and a combination of two.

By comparing the sequencing data from each source, they were able to identify microRNAs from dodder that had entered the plant tissue. They then measured the amount of messenger RNA of genes that were targeted by the dodder microRNAs and found the level of messenger RNA from the host was reduced when the dodder microRNAs were present.

“With this knowledge, the dream is that we could eventually use gene editing technology to edit the microRNA target sites in the host plants, preventing the microRNAs from binding and silencing these genes,” Penn State University biology professor Michael Axtell says in a statement.

Axtell says dodder is an obligate parasite, meaning it can’t live on its own.

“Unlike most plants that get energy through photosynthesis, dodder siphons off water and nutrients from other plants by connecting itself to the host vascular system.

“We were able to show that, in addition to the nutrients that flow into dodder from the host plant across the haustoria, dodder passes microRNAs into its host plant that regulate the expression of host genes in a very direct way.”

When a plant is attacked by a parasite it initiates defence mechanisms. In one of these mechanisms, the plants produce a protein that clots the flow of nutrients to the site of the parasite. MicroRNA from dodder targets the messenger RNA that codes for this protein, which then helps to maintain a free flow of nutrients to the parasite.

Professor of plant pathology James Westwood of Virginia Tech says dodder seems to turn on the expression of the microRNAs when it comes into contact with the host plant.

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