Date of Award

8-2014

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Botany and Plant Pathology

Advisor

Benildo G. de los Reyes

Second Committee Member

Andrei Alyokhin

Third Committee Member

David DeKoeyer

Abstract

Vacuolar processing enzymes (VPE) have been implicated in plant defensive strategies against abiotic and biotic stresses including insect herbivores. Interspecific introgression studies in Solanum for example have a significant upregulation of specific VPE isoforms in aphid-resistance donor parent and aphid-resistant progenies, but not in susceptible sibling lines. To clarify the direct involvement of VPEs in plant defenses against the phloem-feeding green peach aphid (Myzus persicae), a subset of T-DNA insertion mutants of Arabidopsis thaliana was examined. Two VPE isoforms (β-VPE, δ- VPE) were found to be induced within 48 hours after aphid feeding in wild-type Arabidopsis, while their T-DNA insertion mutants exhibited a knock-out expression. Because Arabidopsis is susceptible, it was hypothesized that the knock-out mutants have impaired basal defenses leading to super-susceptibility. The early onset of leaf curling and tissue necrosis, increased mean aphid population, and increased tissue injury (electrolyte leakage assay) relative to the wild-type , indicate that basal defense to aphids were compromised among the various β-VPE and δ-VPE mutant lines. VPE co- expression networks are comprised of genes involved in sucrose metabolism and transport (AtSUC5, AtSUS3, invertases), efflux and detoxification-related proteins, and known modulators of gene-for-gene-type disease response linked to sucrose metabolism (AtSWEET13, AtSWEET15). These results suggest that VPEs are important components of basal defense to phloem-feeders, perhaps by mediating mechanisms directly involved in detoxification, while also ensuring metabolite availability to the host tissues to counteract a potentially depleting condition caused by insect feeding. These processes might be important as a coping mechanism that slows down the progression of perturbations caused by herbivory.

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