Honors College

Document Type

Honors Thesis

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A recent study in Solanum bulbocastanum (a wild relative of the cultivated potato) aiming to identify potential genes involved in aphid and pathogen resistance mechanisms found that a homolog of the Arabidopsis thaliana cysteine protease gene RD19a is upregulated during aphid infestation. RD19a is upregulated in response to abiotic stresses such as drought and high salinity, and rd19a mutants show increased susceptibility to bacterial infection. In this study, Arabidopsis rd19a mutants and wild-type plants were subjected to aphid feeding to observe and compare the molecular, physiological and phenotypic responses. The aim was to further establish the proof of concept regarding the direct role of this gene in resistance mechanisms. Gene expression analysis was conducted to determine if RD19a is inducible by insect herbivory. Mutants showed an increased susceptibility to aphids, demonstrated by earlier appearance of tissue necrosis, higher percentages of electrolyte leakage and greater levels of aphid reproduction on these plants. Gene expression analysis showed that RD19a is aphid-inducible, implicating it in biotic as well as abiotic stress resistance. Furthermore, mutation of RD19a appeared to compromise specific herbivory response mechanisms as demonstrated by an impaired induction of chitinase, a known insect defense-related gene, in rd19a mutants. This study confirmed that RD19a is an important component of the basal defense against aphid herbivory in Arabidopsis; perhaps its role is more important in plant species exhibiting greater resistance to aphids than Arabidopsis (e.g. S. bulbocastanum). RD19a appears to be highly conserved in plants and animals, although the biological functions may have diverged.