Aphid wired to the Electrical Penetration Graph. Photo: Cecilia Ström
When a herbivore attacks a host plant, a defence response is initiated, triggered either by the herbivore or by the plant itself. Knowledge about the mechanism behind such responses are used to develop pest management strategies that align with UN-sustainability goals for crop protection. In a new article published in the journal Plant Physiology, a UPSC-team led by Karen Kloth and Benedicte Albrectsen questioned the role of a cell wall modifying enzyme for defence responses to aphid attacks.
In their experiments, the researchers investigated the feeding behaviour of an insect, the so-called green peach aphid, on plant cell walls of thale cress (Arabidopsis thaliana). The aphid manoeuvres its needle-like mouth through the cell wall matrix to reach the phloem, a transport tissue in plants transporting sugars from the leaves to the roots. It feeds on the sugar-rich phloem sap. This penetration through the cell wall damages the cell wall to a certain extent. The researchers wanted to test the hypothesis that plant defence responses are the result of certain cell wall components that break of cell wall carbohydrate pectin, in response to the aphid penetration.
Their study focused on the effect of a special pectin modifying enzyme, called Pectin Acetylesterase 9 (PAE9), which has not been studied in this context up to now. They investigated mutants of the model plant thale cress, which have been modified to shut off PAE9. Their experiments showed that PAE9 is important for general defence reactions. The mutants that did not contain the PAE9 enzyme initially produced less defence hormones and metabolites. These defence compounds seem to make the plant more resistant to aphids. In the mutants, the aphids started phloem feeding earlier than in control plants with normal levels of defence compounds. However, with time, levels of defence compounds recovered to control levels also in the mutants. The researchers concluded therefore that PAE9 act as a front door guard that delays and initially fends off intruding aphid pests.
The article was published in Plant Physiology:
Karen J. Kloth, Ilka N Abreu, Nicolas Delhomme, Ivan Petřík, Cloé Villard, Cecilia Ström, Fariba Amini, Ondřej Novák, Thomas Moritz, Benedicte Riber Albrectsen (2019). PECTIN ACETYLESTERASE9 Affects the Transcriptome and Metabolome and Delays Aphid Feeding. Plant Physiology, Oct 2019: doi.org/10.1104/pp.19.00635
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