Genetic analyses of the Arabidopsis 26S proteasome regulatory particle reveal its importance during light stress and a specific role for the N-terminus of RPT2 in development.

The 26S proteasome subunit RPT2 is a component of the hexameric ring of AAA-ATPases that forms the base of the 19S regulatory particle (RP). This subunit has specific roles in the yeast and mammalian proteasomes by helping promote assembly of the RP with the 20S core protease (CP) and gate the CP to prevent indiscriminate degradation of cytosolic and nuclear proteins. In plants, this subunit plays an important role in diverse processes that include shoot and root apical meristem maintenance, cell size regulation, trichome branching, and stress responses. Recently, we reported that mutants in RPT2 and several other RP subunits have reduced histone levels, suggesting that at least some of the pleiotropic phenotypes observed in these plants result from aberrant nucleosome assembly. Here, we expand our genetic analysis of RPT2 in Arabidopsis to shed additional light on the roles of the N- and C-terminal ends. We also present data showing that plants bearing mutations in RP subunit genes have their seedling phenotypes exacerbated by prolonged light exposure.