Interaction Between Phloem Sap Feeding Insects and Plant Phloem Sieve Element Defense Response

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Several large groups of plant-feeding insects such as aphids (3000 species) and whiteflies (1500 species) are specialized feeders on phloem sap. Nutrients are transported throughout the plant in phloem sap, and because of its critical importance, plants protect themselves from loss of sap by redundant systems that seal off damaged sieve elements (the specific phloem cells that transport the sap). In order to successfully feed on phloem sap, these insects must circumvent these sealing mechanisms. This project's goal is to determine how they accomplish this. Phloem responses to insect feeding will be observed by various microscopy techniques. The effect of the phloem response on the insect and the insect's counter-responses will be monitored by an electrophysiological technique, somewhat similar to an EKG, that reveals in real time what plant tissues and cells the insects have penetrated with their mouthparts and their behaviors (such as salivation, ingestion, mouthpart movement) within those tissues and cells. The responses and counter-responses and their effects on both the insects and plants will be determined during normal (natural) feeding and in experiments where the phloem sealing mechanism will be manipulated. The goal of the project is to determine mechanistically how insects circumvent the phloem sealing response. These results will be important not only for understanding the co-evolution between plants and these highly successful specialized herbivores, but also because these insects include some of the world's worst agricultural pests. The results might thus be valuable for revealing mechanisms that could be exploited for developing crop resistance to these pests. This project also will provide a research experience for a postdoctoral student in this field which bridges the gap between plant physiology and entomology. Results also will be incorporated into coursework in the PI's department.