Nicotiana tabacum Kunitz Peptidase Inhibitor-like Protein Regulates Intercellular Transport

A coordinated and generalized plant response to adverse environmental factors largely depends on the proper and finely-tuned regulation of intercellular transport via plasmodesmata (PD). However, the knowledge of the whole network of PD-controlling mechanisms is far from complete. Earlier, a cellular factor, Kunitz peptidase inhibitor-like protein (KPILP), that affects PD gating and plays a proviral role, was identified in <i>Nicotiana benthamiana</i> plants. Here we characterized its homolog from <i>N. tabacum</i>, <i>NtKPILP</i>, which is hardly detectable in leaves of intact plants, in contrast to roots, flowers and seeds where <i>NtKPILP</i> is highly expressed. However, its mRNA accumulation in leaves increases in response to various stresses, including viral infection. <i>NtKPILP</i> was demonstrated to affect chloroplast functioning. Using the virus-induced gene silencing approach, we have shown that <i>NtKPILP</i> downregulation negatively affects intercellular transport of macromolecules, inducing callose deposition at PD and suppressing beta-1,3-glucanase mRNA accumulation. Together, the obtained results indicate that NtKPILP is a viral infection-responsive cellular factor that is involved in PD permeability regulation, sharing thus the features of KPILPs from other <i>Nicotiana</i> species.