Closing the backdoor
Fusarium is a major threat to agriculture. With resistance giving only temporary relieve. Now Dutch researchers report in Plant Biotechnology Journal that they have found a way for plants to lose susceptibility.
The soil fungus Fusarium infects lots of crops, like tomato, cucumber, and banana. Frustratingly, once infected there is nothing a farmer can do to save its crop. And making it even worse, the fungus invisible spores travel easily with us wherever we go.
There are only two ways a crop can deal with Fusarium. That is either to be resistant or not susceptible. For the first the crop relies on the presence of resistance genes that activate its defence response as soon as they spot the Fusarium. While the second relies on the absence of susceptibility genes, which create a backdoor through which the fungus can get in. Although resistance is good, it is easily overcome by the fungus. Making lacking susceptibility genes a better option.
To find the susceptibility genes that make a plant susceptible to Fusarium the researchers went fishing. Using a Fusarium protein, SIX8 that likely functions a key to the plants backdoor. The researchers baited a protein called TOPLESS. A protein that the plant uses to regulate gene expression.
By closing the backdoor the plants lose their susceptibility
To make sure TOPLESS was indeed interacting with SIX8 the researchers added half a fluorescent tag to both proteins. When the proteins are interacting, the tags combine into a fluorescent proteins and light up. When they then looked under the microscope the researchers saw fluorescent signals light up when both proteins were present. What’s more an interaction in yeast also showed that they interacted.
Following the researchers inactivated two TOPLESS proteins in tomato plants, and subsequently infected these plants with Fusarium. When the plant contained one inactivated protein, they got less infected with fusarium, but they did not as well as an resistant tomato variety. Had the plant two inactivated TOPLESS proteins, then they did as well as the resistant tomato variety. They did not get infected.
As TOPLESS is involved in gene regulation, the researchers were worried that the development of the tomato plants might be affected. However, observing the plants while they grew, flowered, and fruited showed only an increase in flower size and an reduction in seed number.
TOPLESS genes are wide spread throughout the plant kingdom. To test if they could make other species also none-susceptible to fusarium, they repeated this analysis for Arabidopsis. Showing that inactivation of two SIX8 interacting TOPLESS proteins in Arabidopsis also make them none-susceptible.
Through closing the TOPLESS backdoor plants lose their susceptibility to Fusarium. This study gives plant breeders a new weapon in their arms race against Fusarium.
Literature
Aalders, T.R., de Sain, M., Gawehns, F., Oudejans, N., Jak, Y.D., Dekker, H.L., Rep, M., van den Burg, H.A. and Takken, F.L.W. (2023), Specific members of the TOPLESS family are susceptibility genes for Fusarium wilt in tomato and Arabidopsis. Plant Biotechnol. J. https://doi.org/10.1111/pbi.14183
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