Faba bean forisomes can function in defence against generalist aphids.

Area of Science:

• Plant Biology
• Entomology
• Biochemistry

Background:

• Phloem sieve elements possess protective mechanisms to prevent nutrient loss upon damage.
• Phloem proteins, like legume forisomes, form occlusions to seal damaged sieve elements.
• A hypothesized function of phloem proteins is defense against phloem-feeding insects, such as aphids.

Purpose of the Study:

• To provide the first experimental evidence that aphid feeding induces phloem protein occlusion.
• To demonstrate that aphid-induced occlusions inhibit phloem sap ingestion.
• To elucidate the role of forisome occlusion in preventing aphid feeding.

Main Methods:

• Investigated aphid feeding behavior on Vicia faba (faba bean).
• Observed forisome occlusion in response to aphid stylet penetrations using generalist aphids (Myzus persicae, Macrosiphum euphorbiae).
• Utilized lanthanum (a calcium channel blocker) to inhibit forisome occlusion and assess its impact on aphid feeding.

Main Results:

• The majority of phloem penetrations by generalist aphids triggered forisome occlusion.
• Aphids frequently withdrew their stylets without ingesting phloem sap due to induced occlusions.
• Inhibition of forisome occlusion with lanthanum enabled aphids to readily ingest phloem sap.
• Specialist aphids (Acyrthosiphon pisum) did not trigger forisome occlusion and readily ingested sap in a previous study, highlighting specificity.

Conclusions:

• Aphid feeding can actively induce phloem protein (forisome) occlusion as a defense mechanism.
• Forisome occlusion is a key factor inhibiting phloem sap ingestion by aphids.
• Plant defense responses involving phloem proteins are crucial in plant-insect interactions.