When plant tissues are detached or wounded, they can regenerate new roots, shoots or become a new plant. De novo root regeneration (DNRR) is one type of such process in which adventitious roots are regenerated from a detached leaf. Unlike tissue culture procedure where exogenous plant hormones, such as auxin and cytokinin are added to induce regeneration, DNRR completely relies on endogenous hormones. Almost all published studies on DNRR are done in sterile conditions. The precise roles and pathways that pathogen signals or stress hormones may impact root regeneration are unclear. Here we show that salicylic acid (SA), a phytohormone involved for activating plant defenses, affects overall root regeneration in Arabidopsis thaliana. My results show that SA has a negative impact on root regeneration. Mutants with low of SA have increased number and rate of adventitious roots production. Interestingly, NPR1, a central regulator of SA-mediated defense response, is not required for SA-mediated suppression of DNRR. SA suppresses the expression of WOX11, a key gene required for cell fate transition during DNRR. This shows that pathogenic signals and activation of plant defenses can decrease the root regeneration ability. SA may engage in crosstalk with auxin during the root regeneration process. I have also developed a system to study DNRR in the presence of microbes. Arabidopsis explants sown in sand with the liquid microbial mixture had significantly less roots compared to explants that were treated with only liquid ½ MS. In addition, I have also shown how the addition of flg22, a peptide that contains the 22 amino acids that make up the bacterial flagellin, can affect root regeneration in sterile conditions. The average number of roots was significantly lower from explants treated with flg22 compared to those that were not. These findings indicate that pathogen-induced signals and activation of plant defenses can decrease the root regeneration ability.