This dissertation presents experimental results to advance our understanding of Nucleoredoxin1 (NRX1) participation in salicylic acid (SA) modulated stress responses of Populus. SA is a well-known mediator of plant response to a variety of stresses. Previous work has implicated NRX1, a relatively minor component in Arabidopsis SA signaling, as a redox partner of SA responses in Populus tremula  Populus alba (INRA 717-1B4). Unlike its single-copy ortholog in Arabidopsis, NRX1 is encoded by seven tandemly arrayed genes (TAGs) with divergent tissue expression profiles. The most abundantly expressed member encodes a unique isoform, PtaNRX1.2, that is structurally and catalytically distinct from the canonical isoform PtaNRX1.3. PtaNRX1.2 and PtaNRX1.3 are both localized to the nucleus but exhibit non-overlapping redox substrates, suggesting their divergent physiological function. Functional characterization of CRISPR/Cas9-mediated NRX1-knockout (KO) plants supports the hypothesis that PtaNRX1 is required to sustain SA homeostasis in poplar. The nrx1 mutant metabolome resembles that of SA-depleted transgenic nahG poplar, including significantly reduced levels of SA-derived conjugates, SA glucoside (SAG) and gentistic glucoside (GAG). RNA-seq analysis showed an attenuated transcriptional response to methyl viologen elicitation in nrx1 leaves relative to wild type, supporting a connection between NRX1, SA homeostasis, and oxidative stress response in poplar. Phylogenomics analysis revealed a strong tendency for NRX1 to be retained as tandem duplicates in perennial or biennial species. In summary, this study lays a foundation for future research on NRX1-mediated SA signaling, defense against oxidative stress, and evolutionary insights in perennial woody plants. In addition, this study also showcases the efficiency of a single consensus guide RNA for CRISPR multiplex editing of TAGs and offers multipronged approaches, including target capture sequencing, to decipher the complex editing outcomes.