The tissue specific expression and sub-cellular localization of PCB1, a putative calcium-binding protein in Arabidopsis thaliana, was analyzed in this work. It was predicted that PCB1 function is essential in the phloem to defend against Green Peach Aphid (GPA; Myzus periscae) infestation. Additionally, a transmembrane topology predictor indicated that PCB1 was highly likely to be localized in the plasma membrane. In order to test this hypothesis, a mutant plant was developed in which PCB1 was not expressed. A phloem-specific promoter known as SUC2 was used to express PCB1 in this plant. Thus, based on the hypothesis, this plant should confer a degree of aphid resistance consistent with the wild-type plant. A GPA fecundity assay was conducted to assess this hypothesis by placing 2 one-day-old GPA nymphs per plant on wild-type plants, pcb1 mutant plants, and pcb1 mutant plants complemented with SUC2 promoter expressing pcb1. After 12 days, the number of aphids on each plant was counted. Upon performing this assay, the results indicated that the number of aphids was, in fact, lower on the plants complemented with pcb1 expressed by SUC2. However, upon performing a hypothesis test, it was shown that the data was not significant at the 0.05 significance level. This indicated that the necessity of PCB1 in the phloem for defense against GPA could not be proven through this experiment. In a separate experiment to determine the localization of PCB1, Green fluorescent protein (GFP) was fused to PCB1 in order to visually indicate the sub-cellular locations of PCB1 expression. The results of this experiment showed that PCB1 was localized in the plasma membrane and not in the chloroplasts nor nucleus, confirming the hypothesized localization of PCB1.